[LILCBRA]

Alright, I have a problem. I am 75 miles from home for a show, and about 3/4 of the way up, the minor vibration I had doing 60-75 mph just suddenly stops. There was no noise associated with it stopping. When I get into town with stop and go driving, it vibrates a hell of alot more than before, but only between lets say 20-45 mph. At cruising speed it seems to be fine without vibrations at all. I had the driveshaft shortened of course for the t5 swap, and it was balanced at that time. Could it be something with the balance of the driveshaft, maybe a u-joint, or was there something going on with the tranny. It seems to shift and drive fine except for this vibration. I haven't been able to get under the car to check anything, and it sits too low to the ground to do it without a jack available. So, I guess, my main question is with the tranny. Has anyone run into anything like this, and if so what was the problem?

[Wart]

From the number of times I've seen your situation posted I'm guessing it happens allot.

My first guess is you may have a drive line angle issue.

Quite a while ago I worked out how much difference drive line angles were changed by shortening the drive shaft a couple of inches, shortening the shaft increased the angle of incidence 1~2 degrees at the rear yoke, IIRC.

I would degree the drive line/power train.

As to why the pattern of vibration changed? I could speculate all day and still not get the answer. And it may not be any one thing.

[StangIIttop]

Did you get the U-joints from Sadler? They installed mine but the caps for the yoke were a bit too big and the needle bearings started to come out the seal which caused about the same type of vibrations you have.

[LILCBRA]

I am not sure if the angle is too far off, but it could be. It seems to be a pretty straight line, but I could be wrong-never actually measured, just more of an eyeball look. I will try to measure it at least up and down to the floor.

As for the U-joints, it should be the same joints that were in it to begin with, When I got it back, to the best of my recollection anyways, they seemed fine. Now that I got it home, that was the first thing I was going to look at with it. Problem in Waterloo was I couldn't get underneath it to find anything out. It will probably be a couple days now before I can get under it, but I am hoping it is as simple as that.

[Wart]

Originally Posted by StangIIttop

Did you get the U-joints from Sadler? They installed mine but the caps for the yoke were a bit too big and the needle bearings started to come out the seal which caused about the same type of vibrations you have.

A 'change' in the U-Joints (by being driven) would be one of my speculations. Heat, wear, binding, etc.

How the hell do they get the wrong caps on a new set of joints? They come as a set. More than likely they lost needles during install?

Originally Posted by LILCBRA

I am not sure if the angle is too far off, but it could be. It seems to be a pretty straight line, but I could be wrong-never actually measured, just more of an eyeball look. I will try to measure it at least up and down to the floor.

You'll need a machinist protractor or inclinometer/angle finder.



Problem with inexpensive inclinometers is they can give different readings when measuring from different directions or the other surface on the gage.

[LILCBRA]

I was just having a thought, and I don't remember ever seeing anyone checking, changing or mentioning it. Is the II yoke OD the same as the T5 yoke OD? I guess where I am going with it is if there is a difference, couldn't the original vibration have been from the difference in the bushing ID and my yoke's OD? Then the sudden change could be from maybe the bushing and/or tailshaft housing cracked? Like I said, it is going to be a couple of days before I can get underneath it, so I am just speculating, but it seems to make some sense in my mind right now.

As far as measuring the angle, what I was going to do with it was get the car off the ground as level as I can, then with the driveshaft out, I was going to measure the centers of the tailshaft and axle to the ground. Trick is with either way you go, with either the angle finder or just measuring, the car has to be level. Where do you check for level-the rocker panel? That seems to make the most sense to me, but I just don't know.

[Wart]

Originally Posted by LILCBRA

As far as measuring the angle, what I was going to do with it was get the car off the ground as level as I can, then with the driveshaft out, I was going to measure the centers of the tailshaft and axle to the ground. Trick is with either way you go, with either the angle finder or just measuring, the car has to be level. Where do you check for level-the rocker panel? That seems to make the most sense to me, but I just don't know.

Only way I know of that works is using a protractor head or inclinometer.

Level is irrelevant, and the suspension should be normally loaded (IE: Over a pit, on an alignment rack (or similar lifting device), rear wheels on blocks with stands under the front cross member, and so on).

Years ago I chased this s**t around, lots of stories there, some even funny.

I pulled the last "factory installed" engine from the last car with a factory 8", and as the engine and trans cleared the engine bay I realized I forgot to measure the angles before pulling the engine ... Kick myself in the ass! Now I have to stick the frigging engine/trans back into the frigging car to measure the frigging angles before the rear is swapped because it's going to be my last frigging chance to personally acquire that frigging data.

[Dano78]

Originally Posted by LILCBRA

I was just having a thought, and I don't remember ever seeing anyone checking, changing or mentioning it. Is the II yoke OD the same as the T5 yoke OD? I guess where I am going with it is if there is a difference, couldn't the original vibration have been from the difference in the bushing ID and my yoke's OD? Then the sudden change could be from maybe the bushing and/or tailshaft housing cracked? Like I said, it is going to be a couple of days before I can get underneath it, so I am just speculating, but it seems to make some sense in my mind right now.

As far as measuring the angle, what I was going to do with it was get the car off the ground as level as I can, then with the driveshaft out, I was going to measure the centers of the tailshaft and axle to the ground. Trick is with either way you go, with either the angle finder or just measuring, the car has to be level. Where do you check for level-the rocker panel? That seems to make the most sense to me, but I just don't know.

You don't need to do anything fancy. You don't even have to remove the driveline and car should be on the ground or positioned as such. Just put a magnetic degree (finder)scale (easily found at home depot) on the yoke in the tranny with the yoke's u-joint ear 'down' and then place another scale on the rear axle's yoke (should also be down as the ears on the driveshaft should be clocked the same) now compare the angles in degrees. Also seen adapters or round magnets that are designed to 'sit' right on the u-joint caps themselves at each end... in cases where the yoke is not square with the face of the u-joint cap. Compare the readings on both scales and make your adjustments.

Here's a couple links to a good articles explaining it all.
DRIVE LINE PHASING

Inland Empire Driveline Service, Inc. - Driveshafts, Pinion and Transmission Yokes, Center Support Bearings

[Dano78]

Also wanted to add-

Check the torque on the pinion nut on your 3rd member (rear axle pinion @ the yoke)
I've been finding 9" fords fromt he late 60s and 70s have been working the nuts loose causing the pinion yoke to slide forward and become loose causing occasional vibrations and quick destruction of the rear u-joints. I have yet to run into a case with the 8" rear but have found at least 4 different cases with the 9" rear, mostly in trucks.

[Wart]

Originally Posted by Dano78

You don't need to do anything fancy. You don't even have to remove the driveline and car should be on the ground or positioned as such.

Fact is the shaft can't be measured with it out of the car.

Here's a couple links to a good articles explaining it all.

With all due respect, Not really.

DRIVE LINE PHASING[/quote]

I've worked with drivelines and drive shafts on my cars, fleet trucks and installed equipment and the above artical left me scratching my head. The author was going back and forth between cars and trucks which are the same but different, and doesn't explain relationships, etc.

Take the following illustration:




Wrong is Right for a leaf sprung vehicle in motion at "speed", speed being ? 30-40-50-60 mph? and above ?

THe author does write this: Normally the pinion gear angle is a negative angle and the nose of the rear end is pointed down. This allows for the upward movement of the rear end when torque is applied. Those who follow racing will know the term spring wrap. Setting up a drive line for racing situations or high torque off-roading is different and much more complicated than for street vehicles, as many more variables enter into the formula.

A Story:

When I was a kid I had the rear axle of the '71 on stands and spun up the drive line like we do when we're kids. I noticed there was a vibration ~ 40? (this was a long, long time ago). So I watched under the car while playing with the throttle. (Speeds are for purpose of illustration only)

At low speed there was no vibration, then as I gradually increased speed there started a vibration. In looking at the chunk I saw it was getting a little blurry. Continuing to gradually increase speed the rear yoke would pop up - no vibration- drop down - vibration - pop up - no vibration - and so on. Increasing speed a bit more the rear yoke popped up and stayed up and didn't vibrate.

Apparently the physics of the spinning drive shaft created forces about the rear yoke resulting in the rotation of axle to a point the physics of the drive shaft locked the axle in position, apparently where the system was going through a minimum change in velocity. The minimum change of velocity is when the system is in as straight of line it can get.

In my observation it was only the physics of the drive shaft causing the change of angle of the pinion. In operation there is hte "torquing" of the axle and climb of hte pinion from "pushing" the car.

So in the above illustration wrong is right for a vehicle in motion, the physics involved "lifting" the pinion till the system in in a straight line.

At least this is the way it is suppose to work in a leaf sprung automobile!!!!

Also, in the above illustration, both pictures are the same. In both pictures the driver (engine and trans) and driven (pinion) lie in the same plane so rotating the axle will take both systems out of phase.

Phase, I forgot to address that, sorry. In a U-Joint system there are two acceleration and decelerations per rotation (unless both driver and driven are in a straight line). So now you have a joint on each end of a shaft and when the driver is accelerating the shaft the driven is decelerating the shaft keeping a constant velocity.

I didn't want to get into any of this .....

Inland Empire Driveline Service, Inc. - Driveshafts, Pinion and Transmission Yokes, Center Support Bearings

When I forst looked at the illustration on this site I thought Madness , shear MADNESS!!! The shaft will rotate into knuckle city.

Then I realized it was a toy car site. And their using heims. Heim joints don't allow the axle to rotate so the driver and driven have to be set in the same plane.

Then tere is factory 4 link (sic) and the bushings allow a little play.

Leaf springs? Axle wrap is our nightmare.

I'll re read this and see where I forgot this or that, where something could have been written better ... it's not a term paper.


Conclusion ...

Leaf sprung automobile drivelines are designed so the rear axle rotates into a straight line thus everything is in phase and everything is spinning at a constant velocity resulting in a nice cushy ride.

Truck drivelines, otoh, such as my Toyota 4x4, will never be in a straight line, the system is designed for the axle to rotate (sort of,) into phase. The truck will always have some vibration because the drive shaft will always have two accel/decel cycles per revolution.

Continued later .....

Originally Posted by Dano78

Also wanted to add-

Check the torque on the pinion nut on your 3rd member (rear axle pinion @ the yoke)
I've been finding 9" fords fromt he late 60s and 70s have been working the nuts loose causing the pinion yoke to slide forward and become loose causing occasional vibrations and quick destruction of the rear u-joints. I have yet to run into a case with the 8" rear but have found at least 4 different cases with the 9" rear, mostly in trucks.

And heres a funny thing.

Shortly after buying the Toyots the rear pinion seal started leaking. I had it fixed (Warranty) and when I got the truck back it had a vibration. WTF? Of course the dealer couldn't feel it ... WTF?

As time went on, a couple 10k miles or so, the vibration got worse and locking in the front hubs would turn the truck into a vibrator.

They traced the initial vibration to the Tech having over-torqued the rear pinion nut (which took out the bearings making the vibration worse).

Wow, an overtorqued pinion nut causing vibration... learned something new.

[Wart]

Something needs addressed.

I have an AOD I want to install in one II. The transmission cross member is the hang up as I believe I'm going to run into the same problems as those installing the T5, that being relocation of hte cross member or other mods needed to support the transmission mount.

In one car it wouldn't be a problem, I only need to attach the cross member to the sub frame connectors (actually a frame). The car I want to install the AOD in needs to remain stock, or able to be returned to stock, so welding and hole punching is well out of the question.

I mention this to let you know I feel your pain. .....

I have seen only ONE person relocate the cross member in an acceptable manner.

From what I have seen most have handled the relocation of hte cross member by simply getting a couple of pieces of pipe and long bolts.

While it may work it is a solution that is far from sound engineering. It creates a bouncy flexy mount which could create or aggravate vibration. It is most certainly weak.

More later.

[LILCBRA]

alright, alot of personal s**t has happened that wouldn't allow me to get under the car until last night....
what i found after checking the u-joints and finding them to appear fine was the output shaft bushing was outside the tailshaft housing and wrapped around my driveshaft yoke. i guess my thoughts about that were pretty much right on. i am still going to check the angles, but didn't take the time to get that done yet. the one question i have for anyone is this: i have been doing the internet search for a new bushing/rear seal to replace them with and have had minimal success. i found a thread or two that state the same bushing and seal are used for the aod-is this true? haven't had a chance to go to the parts store yet to see if they know which it is.

Originally Posted by Wart

I have seen only ONE person relocate the cross member in an acceptable manner.

From what I have seen most have handled the relocation of hte cross member by simply getting a couple of pieces of pipe and long bolts.

While it may work it is a solution that is far from sound engineering. It creates a bouncy flexy mount which could create or aggravate vibration. It is most certainly weak.

More later.

agreed. what i did was modify the crossmember. i basically cut it into 3 pieces and welded it back together using 1/4 flat stock, relocating the mounting holes back where they needed to be for the t5. i am still not too crazy about that, but i felt it was better than using the pipe and mile long bolt idea. i really like what cobraii351 did with his aod swap and am seriously considering doing this with mine over the winter if i can get my personal life back on track.

[54deuce]

My car has a vibration also. It starts at 75 and at 80 its bad. I will have to measure the drive line angles. One thing is my car has lifted leaf springs in the back they are not stock I think it is raised about 2 or 3 inches. I also have the southside machine bars and those change the pinion angle. They maybe for stock springs only. I will have to drive it with the fronts loose and see if that has any effect. I have gone 120+ with the car and it was fine the only things I changed since then were the rear gear 3.40 to 3.80 and installed the lift bars. I will have to measure the angles in the next couple days.

[LILCBRA]

To answer my own question about the bushing, it is pretty much the same as the AOD. The AOD bushing is a little longer than the T5, but the OD and ID work fine, and it fits in the T5 housing just fine. My driveshaft yoke is pretty worn down from having to drive it back home the 75 or so miles, so that is going to be replaced also.

I checked the angles also. If I did it right, the tailshaft of the tranny is pretty much straight on 90 degrees. The pinion is a little out of whack though. I used the 2 radii where the u-joint is attached, and it read about 82 degrees. The car seemed to be fine until the T5 swap, so the angles have me a little confused... I also checked the mounting location of the tranny mount compared to my old SROD. They appear to be the same height wise. I am guessing that the weight that is usually attached to the tailshaft housing on the Fox Mustangs needs to stay with the tranny-probably something to do with harmonics? When I got this tranny, it didn't have the weight. So, my next question is this: does anyone still have the weight and are or are not using it on their car? And, what does it weigh? I figure if the tailshaft bushing and new yoke don't fix the whole problem, I would try that next to see if it does any good.

[54deuce]

I measured mine yesterday and I got on the back of trans 4 degrees down, and the pinion was 7 degrees up. What the hell does this mean? I am going to try to get the trans down 1 degree to 3 and I am going to install 4 degree shims in the back to point the pinion down to 3 degrees. Then that would be 3 down 3 up so then I guess that would be the ideal situation.

[LILCBRA]

I am getting back underneath my car this morning/afternoon and I am going to double check my measurements now that I have the tranny back together. I also have the SSM bars, but I am at a loss as to why, if I checked everything right, why it wasn't a problem with the SROD, but it is with the T5? Also, if the angles are off, I am going to attempt to fix them-it can only do good things I would think-I just hope I can get ahold of some axle shims today if that is the case.

[Wart]

Wow.

1) When measuring this the cars rear suspension needs loaded as though it's sitting on the ground. The rear axle needs set on blocks or stands or the tires on blocks, the front wheels need to be on blocks or the front held by stands on the cross member (on a line between the spindles). I've had the back on blocks and the front frame rails on stands in the header area and notised when lifting from the cross member the rear pops up or down when coming off or going on the front stands.

2) as has been stated, the inexpensive inclinometers arent to be trusted, Their repeatability needs verified. IE: Mine will read 1 ~ 1 1/2+ degree different depending. IE #2, If I measure from the tail shaft of the trans and the measurement is 1 degree off true, then rotate/spin the gage 180 deg and measure the rear and it reads 1 degree off in the other direction it's actually reading 2 degrees off.

3) Unless measuring from the machined surfaces of the yoke your probably not getting a good reading. I don't remember seeing a factory yoke with other than the cap surfaces that could be considered measure worthy. So you need to seat a set of caps in the yoke, or figure another way to measure from the machined surfaces.

I get the tail shaft angle from the front belt pulley/dampener. Luckily I have a 2' steel rule so I can drop a parallel measuring surface about 14~16" under the pulley. Any straight and parallel item of sufficient length will work.

Doing it this way I can measure from the "right" in the front and from the "right" in the back and inaccuracies in the inclinometer matter little if any.

4) Then that would be 3 down 3 up so then I guess that would be the ideal situation.

Um, Yeah, that is called 'in phace' and is the ideal situation with a car in motion. Not at rest.

The force needed to move the car rotates the axle causing the pinion to climb.

When you start in phase the pinion rotates/climbs out of phase. I did this ... once. At 55 the rear end banged/slammed so badly it sounded like it was going to come up through the bottom of the car.

So you want to set the pinion "low" so the axle rotates and the pinion comes into phase.

In an ideal world when the pinion comes into phase the trans shaft, drive shaft and pinion would be in a perfectly straight line*.

How low to set the pinion ... I believe the figures are ~ 3 1/2 degrees for a 'street driven' car, and up to 7 degrees for a purpose built straight line car. Of course this only applies to leaf springs.

* One of the things that make the "straight Line" a laugh is the IIs drive shaft isn't "straight'. The 'shaft' doesn't leave the trans at 180 degrees nor enter the rear at 90 degrees. Thus there will always be a measure of vibration. The best you can hope for is to minimize vibration.

I believe that's why the II came with soft engine and trans mounts and rubber freaking mounted rear ends.

[LILCBRA]

Alright-I got everything back together and the vibration is gone. I did recheck the angles and this is how I did it: I used the "new yoke" inserted into the tailshaft until it was engaged into the new bushing. I then used a 1-2-3 block to take the reading from the inclinometer. It read 0. I then checked the pinion in the same manner-I used a 1-2-3 block against the flat portions of the pinion yoke and got a measurement of about 2-3 degrees. I double checked it in the way that I did it the first time to the best I could get it, using the machined u joint area, and it read the same, about 2-3 degrees. I had done some research, and as wart mentioned, if the pinion is angled a couple degrees, it should come back into phase under load. I called mine good, and put the driveshaft in. I took it out for a test drive, and everything works as it should-no more vibration anywhere in the rpm range.

[54deuce]

I am still working on mine. I will get to it this week end maybe. Now I noticed my ssm bars pointed the pinion way up when the fronts were bolted to spring. I do have differant springs in back taller. That was probably throwing it all off.

[54deuce]

Originally Posted by Wart

Wow.

1) When measuring this the cars rear suspension needs loaded as though it's sitting on the ground. The rear axle needs set on blocks or stands or the tires on blocks, the front wheels need to be on blocks or the front held by stands on the cross member (on a line between the spindles). I've had the back on blocks and the front frame rails on stands in the header area and notised when lifting from the cross member the rear pops up or down when coming off or going on the front stands.

2) as has been stated, the inexpensive inclinometers arent to be trusted, Their repeatability needs verified. IE: Mine will read 1 ~ 1 1/2+ degree different depending. IE #2, If I measure from the tail shaft of the trans and the measurement is 1 degree off true, then rotate/spin the gage 180 deg and measure the rear and it reads 1 degree off in the other direction it's actually reading 2 degrees off.

3) Unless measuring from the machined surfaces of the yoke your probably not getting a good reading. I don't remember seeing a factory yoke with other than the cap surfaces that could be considered measure worthy. So you need to seat a set of caps in the yoke, or figure another way to measure from the machined surfaces.

I get the tail shaft angle from the front belt pulley/dampener. Luckily I have a 2' steel rule so I can drop a parallel measuring surface about 14~16" under the pulley. Any straight and parallel item of sufficient length will work.

Doing it this way I can measure from the "right" in the front and from the "right" in the back and inaccuracies in the inclinometer matter little if any.

4) Then that would be 3 down 3 up so then I guess that would be the ideal situation.

Um, Yeah, that is called 'in phace' and is the ideal situation with a car in motion. Not at rest.

The force needed to move the car rotates the axle causing the pinion to climb.

When you start in phase the pinion rotates/climbs out of phase. I did this ... once. At 55 the rear end banged/slammed so badly it sounded like it was going to come up through the bottom of the car.

So you want to set the pinion "low" so the axle rotates and the pinion comes into phase.

In an ideal world when the pinion comes into phase the trans shaft, drive shaft and pinion would be in a perfectly straight line*.

How low to set the pinion ... I believe the figures are ~ 3 1/2 degrees for a 'street driven' car, and up to 7 degrees for a purpose built straight line car. Of course this only applies to leaf springs.

* One of the things that make the "straight Line" a laugh is the IIs drive shaft isn't "straight'. The 'shaft' doesn't leave the trans at 180 degrees nor enter the rear at 90 degrees. Thus there will always be a measure of vibration. The best you can hope for is to minimize vibration.

I believe that's why the II came with soft engine and trans mounts and rubber freaking mounted rear ends.

So then my 4 degrees down and 7 degrees up will change to say ten up under load. I thought the numbers have to be within 1 degree to be vibration free. I plan on drag racing this car. So 3 down and 1 or 2 up? And then under load it will maybe go to 4 or more?

[Wart]

Originally Posted by 54deuce

So then my 4 degrees down and 7 degrees up will change to say ten up under load.

You mean the trans 'points down' 4 degrees and the pinion 'points up' 7 degrees? If this is correct your already 3 degrees 'above phase', under acceleration and while driving (aka: torguing the axle) the shaft will want to climb more out of 'phase', I can't see it ever being vibration free (unless accelerating or at speed in reverse), and I suspect your U-Joints will not last long.



Also, I believe this was the situation I had in my car ("above phase) when it sounded like the rear end was beating it's way through the floor.

I thought the numbers have to be within 1 degree to be vibration free.

1) Well, in theory 1 degree isn't cutting it, but I'm guessing 1 degree is just enough so the average persons butt doesn't feel it. Once again:

2) You'll have to be more specific with that 1 degree. 1 degree when? Under load? 1 degree which direction? Pinion Up? No. Pinion down at rest? Not enough but it might work, providing the gyroscopic effect of the drive shaft is enough to keep the pinion from climbing above 'phase'. THen there is the thing about the mass of the vehicle acting through the pinion yoke and trying to make the yoke rotate at a constant velocity (It's a Newton thing). It's these last two I think of when I look at my '95 Toy 4x4, back shaft runs through crazy angles (compared to a car) and not much vibration. It has a body vibration at 20. 40 and 80 mph (roughly), harmonics and sympathetic vibrations ... but wouldn't that be another subject?

I plan on drag racing this car. So 3 down and 1 or 2 up? And then under load it will maybe go to 4 or more?

In a way this is reminding me of carburetors in that with EFI the Old School of Jets and Power Valves seemed to become forgotten. With IRS and 4-Link on most vehicles Old School Leaf Spring Tech seems to have been forgotten.

I went looking for a site to cite.

MADNESS!!!

On THIS SITE (which is half clueless) I found the following reference from another site:

quote from Mark William's web site

"There is a general misunderstanding bout "dropping the pinion down" several degrees. This is a practice that could be applied only to leaf spring cars without any traction control devices where springs can “wrap” and change pinion angle. This practice would not apply to 4-link, ladder bar or torque arm equipped cars. Failure to maintain matched and minimum operating angles increase erratic non-uniform output velocity from the drive shaft to the differential."

So I go to the Mark WIlliams site and don't find the article but I do find this: ({LINK} to page)



THEN I find this page at Car Craft {LINK}

How To Set Pinion Angle

Cliff Notes:

Pinion angle simply refers to the angle of the differential’s pinion in relation to the driveshaft. But ask 10 guys about optimal pinion angle and a lively debate will ensue. ....

... Furthermore, we live in the real world where time takes its toll on our automobiles. Engines may not sit squarely in their motor mounts, motor mounts may not sit properly between the framerails, crossmembers may not sit straight, and who knows where the rearend is positioned

Pro Stock chassis builder Jerry Bickel ... there is no mystery to pinion angle ... The goal is to create a straight line from the back of the crankshaft through the transmission, driveshaft, and the pinion of the differential—under load. ... According to Bickel, a ladder-bar suspension normally requires ½ degree of pinion angle, a four-link requires 1-2½ degrees, and a leaf-spring suspension requires up to 6 to 7 degrees.

Ray Currie ... explains that a universal joint is designed to handle between 1 and 3 degrees of pinion angle. This is a safe operating range ...always strives for 2 degrees of pinion angle on a street car regardless of the type of rear suspension being used. ...With a leaf spring–equipped car, the differential movement isn’t nearly as controlled as that of a four-link suspension, so more angle may be needed to prevent the U-joint from hyperextending beyond zero degrees under load.

Suspension specialist Dick Miller bases pinion angle settings on horsepower. Miller likes to see 2 degrees of negative pinion angle (relative to the driveshaft) on applications in the 400hp range, 3½ to 4½ degrees in the 500hp to 650hp range, and up to 7 degrees with 700 horses or more. ...Miller notes that these angles are merely guidelines, and each individual combination should be fine-tuned.

Then there is a cursory section on how to measure the angles and set up, very minimal info, and it's from Currie (I've seen a few things from Currie to wonder about them), there is a lack of explicitness that could lead to confusion.

I know, we all want cut and dried answers, twiddle the nipple this way and crank the nut that way and life will be Puppy Dogs and Rainbows.



Not this time.
.

[54deuce]

Ok this week end I adjust the pinion down so instead of 7 degrees up its now 3 degrees up not under load car just sitting there. The trans is 4 degrees down not under load. As for the one degree I thought they just have to be at least one degree from each other up or down not under load. I did drive the car and its hard say it did seem better but still there. You hit it right on the head sounds like its beating its way though the rear floor. Thats how mine sounds. I did read these articles and the car craft one was saying to be negative 2 degrees on the pinion for drag racing. Thats fine but I still have a vibration and it is now within spec. I could lower the trans that one degree but I dont think the one degree will matter or will it? I also kept the front of my ssm bars loose for the test drive I didnt want them pulling the pinion angle back up. Maybe I am looking at the wrong thing, spacers and tires but it sounds like it is coming from the center back like you were saying.

[Wart]

Originally Posted by 54deuce

Ok this week end I adjust the pinion down so instead of 7 degrees up its now 3 degrees up not under load car just sitting there. The trans is 4 degrees down not under load. As for the one degree I thought they just have to be at least one degree from each other up or down not under load.

I've noticed there is an ambiguity in stating which way and angles, I attribute the lack of specificity to the ubiquity of the 4 link. Even a marshmallow soft bushed 4 link will not twist as much as a leaf thus 'under load' isn't near the issue as with a leaf.

I did drive the car and its hard say it did seem better but still there. You hit it right on the head sounds like its beating its way though the rear floor. Thats how mine sounds.

You **** your pants? I almost did.

I did read these articles and the car craft one was saying to be negative 2 degrees on the pinion for drag racing. Thats fine but I still have a vibration and it is now within spec.

Sort of.

It would be "within spec" if it were under load.

This is what you do, set your parking brake. Rhythmically push/pull on the back bumper and get the car rocking .... the rocking is hte spring(s) wrapping and unwrapping and re-wrapping and unwrapping ... you get the idea. Watching the tires will give you an idea how much the pinions changing angle. And that's just with hand pressure.

How much force you figure it takes to roll a car up the road? How much you figure the springs are wrapping?

I could lower the trans that one degree but I dont think the one degree will matter or will it?

From the Car Craft Article:

... Jerry Bickel (says) The goal is to create a straight line from the back of the crankshaft through the transmission, driveshaft, and the pinion of the differential under load.

And this graphic:




In the above picture the driver and driven are parallel but not in the same plane ("straight" in the parlance of Bickle) thus the shaft will go through two acceleration/deceleration cycles per revolution and since the shaft isn't massless the acc/dec cycles will create a vibration.

THe above illustration resembles my 4x4 truck, it has a skinny drive shaft t6o minimize rotational moment of inertia, the truck has perceptible vibration, it's a fact of life.

What I'm getting at is it's now time to measure the angles relative to the driveshaft.

I also kept the front of my ssm bars loose for the test drive I didnt want them pulling the pinion angle back up.

The bumper contacting the spring (at rest) pulls the pinion down.

Maybe I am looking at the wrong thing, spacers and tires but it sounds like it is coming from the center back like you were saying.

Well you know if it's the spacers thats making sounds like a sledge hammer on the floor ....

In the time I've psent writing in this thread I could have had this diagnosed, maybe even fixed.

I'm wondering how your changing the angle on the rear? Wedges? Hope your not using rubber mounts with wedges, that isn't the safest set up.

And the rubber doesn't do much for keeping the housing under control.

First non II rear I installed I let someone else weld the perches on the axle, they said it was 'right' , that's the one that sounded like it was coming up through the floor.

And the first time I installed a 9" in a II I sat down and did all this math, and set the perches, then chased vibration around with wedges, then said to hell with it, I set the perches to the same angle relative to the pinion as on the II 8" housing ... Problem solved.

What you need to do is see this holistically, that everything from the engine mounts to the rear spring eye plays a part in this. Some more of a part than others.

[LILCBRA]

Alright, I guess I lied-I do still have a vibration-comes in play at higher speeds still, say around 50+. I jacked up the car and ran it in 4th and 5th gear and it is knocking and shaking the car pretty bad. I think there are 2 things I am going to try to investigate. First, I am going to buy some axle shims and play with it from that perspective. The other is I am going to see about taking my laser level or a piece of string or some other means of creating a straight line from the front of the crank back to the pinion and see if everything lines up that way. I guess I just don't know where else to look other than that. The funny thing I noticed the other day-when it was vibrating, it would only do it with no load (clutch engaged, rpm level just right-not accelerating/decelerating) and if I downshifted to 3rd, when it is just about to engage 3rd gear the vibration almost disappeared. When it gets into 3rd, it comes back-and this is all with the clutch engaged. I thought that might be worth mentioning.

[Wart]

I really can't write much more than I've written.

Laterally II engines and pinions are not in a straight line so there will always be a vibration.

Link suspension theories don't have much to do with leaf sprung drive axles.

Leaf sprung drive axles are set 'pinion low' so the pinion rotates 'into phase' under load.

In theory, and in a perfect world, when the pinion in a leaf sprung suspension climbs into phase the entire drive line from the trans output, through the shaft, and through the pinion, should be in a straight line.

All measurements have to be made with the drive axle wheels on the ground/ weight loaded.

Newtonian Physics need considered.

Way back when .... When I got tired of blowing up RAD transmissions I swapped to a C4. The drive shaft was an inch and something short. I drove the car this way for quite a while. Eventually I got vibration which over time got worse. I found that while 'freeway cruising' (55~60) I could go to a neutral or slightly trailing throttle and the physics of the spinning shaft would make the shaft 'straight' and vibration would go away, then the physics would hold the shaft straight and vibration free to ... much higher speeds. I know , I'm lucky something didn't fracture and I'm not dead.

Point being theres more at play than simple axle rotation and climbing pinions.