1966 T5 Vibration Issue

[phutch11]

Hey guys,

I've got the T5 vibration issue that so common on 1964-1966 stangs that occurs at highway speeds.

I've been through damn near everything to try and fix it and thus far nothing has worked. To be specific:

- Custom length driveshaft (balanced and re-balanced) - u-joint location same as stock 5.0 T5
- New clutch, pilot bearing
- New axles, bearings, gears
- New wheels, tires
- New u-joints, slip joint, rear tranny bearing and seals
- Tranny/Pinion angles equal but opposite to within 1/4 degree of each other
- Engine/tranny/pinoin all dead center of car

Anyway, I'm trying to hunt down someone that has successfuly swapped a T5 into a 1964-66 mustang with a 8" rear that does NOT have any vibration issues at highway speeds (70-80 mph).

Do you have an AL driveshaft? Did you have this issue and somehow conquer it?

Please help...

Thanks.

 

[Rapid]

Is it a shudder or more of a buzz? I m working on a buzz at 70 plus in my 65 with a T5. I can fell it best when I get up to 80 and push in the clutch. It vibrates coming down to about 70 and then stops.

You have already verified the pinion angles which was my next step.

 

[phutch11]

Yes it is definitely a buzz - a very loud annoying buzz that starts rythmically and builds in intensity as you pick up speed.

What RPM are you in in 5th when it starts? It seems like the problem begins at about 2500 rpm and gets much worse from there up.

Rapid - what slip yoke and driveshaft do you have?

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[red65]

- Tranny/Pinion angles equal but opposite to within 1/4 degree of each other

My '65 has a T-5 with a 9" rear ('59 Ford), but the choice of rear axle shouldn't make much difference in this discussion. Drivetrain is relatively smooth - no perceptible vibration through 140mph (just lots of noise and wind buffeting!). I do have an aluminum driveshaft.

I'm curious about your statement about "equal but opposite" angles. The pinion and trans angle should really just be equal, not opposite. For instance, if your trans is on a 3-degree slope, your pinion should be on the same 3-degree slope.

It might just be your choice of words, but if your trans is on an angle that slopes down toward the back, and your pinion is on the same angle, but it slopes down toward the front, then that's your problem. You'd have had to go to some misguided trouble to accomplish this, but I thought it was worth pointing out.

It sounds like you've already checked all the most common trouble spots, so maybe it's time to get creative...

 

[phutch11]

Thanks for the excellent input - choice of words. Equal but opposite meaning that a down slope of 1 deg from the tranny and a 1 deg upslope on the pinion.

The thought on the rear end issue is to eliminate all the possible variables. True the 9 vs 8 shouldn't matter but the rear ends have differnet pinion offsets, total weight, and rotational mass. All of those things could affect vibration.

Red - what slip yoke did you use?

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[red65]

Red - what slip yoke did you use?

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Been too long - I don't remember. Sorry! I assume it's a stock T-5 slip yoke, but I had the driveshaft fabbed / assembled by a local shop, and don't know with much certainty what they used.

Are you positive you're dealing with drivetrain vibration? You mention an RPM range - does the vibration dissipate at a constant road speed if you downshift (changing the engine RPM, but not the driveshaft speed)?

 

[phutch11]

I think there may again be confusion on the terminology - from everything I have read, the tranny should slope down (front to rear) and the pinion should slope down as well (front to rear). In other words the tranny shaft points down and the pinion shaft points up.

Looking at each from front to rear.

Trans Shaft - -.5
Driveshaft - 0
Pinon - -.5

To be clear the front of the pinon is HIGHER than the rear and is sloped from front to rear at .5 degrees.

As you can see my driveline is damn near completely aligned. That is why I don't think this issue has anything to do with driveline angles.

As an FYI..with stock motor 66 mounts and a RonMorris swap mount, I was able to easily get the angle of the tranny shaft to it's current location with any surgery at all.

Blkfrd - do you have an AL driveshaft? What rear are you running?

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[phutch11]

They are a little different, but should be okay from what I've seen everyone post. They were different, but I shimmed both the tranny and the diff to get them as close as possible.

Stock 66 engine mounts with prob 5k on them and a RM tranny mount with the same mileage.

From the research I've done, the stock 3 degrees was done to increase space in the passenger compartment, not for any technical reason.

Yes, you are correct, the DS is dead flat to the ground.

Blkfrd- where did your pinion yoke come from?

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[phutch11]

Not pinion yoke, slip yoke...my bad.

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[Rapid]

Yes it is definitely a buzz - a very loud annoying buzz that starts rythmically and builds in intensity as you pick up speed.

What RPM are you in in 5th when it starts? It seems like the problem begins at about 2500 rpm and gets much worse from there up.

Rapid - what slip yoke and driveshaft do you have?

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I have the T5Z and 3:55 gears. The buzz starts at about 2200 and builds. Thats 75 to 80 mph. I have the original shaft shortened one inch by a local shop. I can't remember who the yolk came from.

 

[STSFCTN67]

I agree...

It is important that the driveline angles be close to one another and phased. The phasing is created by the trans shaft being pointed down and the pinion shaft being pointed down. This makes the angles opposite as you call it.

I can tell you that most is not all T5 trans crossmembers for classic stangs and '65/'66 cars in particular do NOT restore the original 3 degree driveline angle. It's more like 4 degrees. Getting close to 3 degrees can only be accomplished by notching the upper trans crossmember in the tunnel and raising the trans with a shim. I shimmed mine 1/2" which got the driveline angle to about 3.4 degrees.

Tell us what each angle is:

Trans shaft angle (should be down)
driveshaft angle (should slope down)
pinion angle (should be down)

I was getting the same vibration and needed to put a few shims (washers) between the mount and the crossmemeber to raise the tranny. No More Vibrations.

 

[gjz30075]

What about suspecting the T5 itself? Is there any way to swap in another T5 just to eliminate that variable? If not, if could be the bushing in the tailshaft. If your T5 was rebuilt, not new, maybe it wasn't changed out and could be worn.

I must be in the minority as my '66, with a new T5Z, 8" diff, new steel driveshaft, stock motor mounts and a T5 mount from Modern Driveline, using the stock (new) trans mount, does not have a vibration anywhere. I honestly don't know my driveline angles but can check if needed.

 

[zm830101]

i am on a lot of fox body forums, and many of them complain about a natural harmonic that the t5 has. you can feel it in the shifter handle on most foxes but not the chassis. maybe it is something about the older chassis that transfers that harmonic to the chassis more than hte foxes?

 

[phutch11]

My thoughts exactly...specifically b/c Foxes have a "dogbone" dampener on the pinion.

Giz - if you don't mind checking that would help.

I have thought it might be an issue with this particular tranny, but it seems too odd that others with the same issue have exaclty the same symptoms.

Anyone know if the dogbone could be adapted to a 8"?

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[Shakin66]

While I have a T56 I am a bit confussed as to what angle your engine is at? It needs 3 degrees or close to it. I set mine up this way and have had no vibration issues so I would make certain you are very close to that.
View attachment 260964

 

[mdjay]

vibration

Did you address the counter balance of the motor?

In other words:

Do you have an early sbf engine (ie pre 79) in the car with a 28oz crank counterbalance?

If so what flywheel counterbalance did you use?

If you used the t5 one from the year of the t5 trans, it would be a 50oz counterbalance and cause a bad vibration and serious damage to the motor bearings.

 

[phutch11]

So as it turns out the simplest solution is usually the right now....and it turns out that my springs settle a tremendous, and important amount.

B/c my car is lowered, I have always jacked the car up, put concrete blocks under the tires and then lowered the car so that the car would be at ride height, but so that I could get under it. Well, I would jack it up and then immediately crawl under and measure the angles - they would always come back as I reported earlier in the postings.

This time I let the car settle for several days b/c I had other fish to fry, then crawled under the car to re-measure - turns out that car does settle and the driveline angles change. Measuring now, they look much closer to what everyone else reported.

Tranny: -4
Pinion: 0

Doh!

Just ordered some wedges from Summit.

Thanks guys - AND LET THE CAR SETTLE!!

 

[Rapid]

So as it turns out the simplest solution is usually the right now....and it turns out that my springs settle a tremendous, and important amount.

B/c my car is lowered, I have always jacked the car up, put concrete blocks under the tires and then lowered the car so that the car would be at ride height, but so that I could get under it. Well, I would jack it up and then immediately crawl under and measure the angles - they would always come back as I reported earlier in the postings.

This time I let the car settle for several days b/c I had other fish to fry, then crawled under the car to re-measure - turns out that car does settle and the driveline angles change. Measuring now, they look much closer to what everyone else reported.

Tranny: -4
Pinion: 0

Doh!

Just ordered some wedges from Summit.

Thanks guys - AND LET THE CAR SETTLE!!

Please let us know if the change solves the problem.

 

[phutch11]

I was actually able to get the wedges locally and they did not solve the problem.

Still have the vibration, it's just much more muted now.

I need to get the car back up on blocks, let it settle and see where the angles are.

Thanks again.

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[gjz30075]

Sorry for being late with my measurements and I'm sure I'll muddy the waters here but, as best as I can tell my trans points downward 4 degrees, the driveshaft is at 0 degrees and the diff is at 0 degrees. The numbers don't seem to add up but with the car on the ground, using the angle tool, as shown in a previous post, these are my numbers.