t5 issues

[Wart]

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]

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.