Vibration

[351 Pinto]

Hi folks. Thanks in advance for any suggestions. I have a 63 1/2 with a vibration problem (most noticeable in the shifter). It is not too bad at low RPM, bad in the mid-range, and calms back down at higher RPMs. It goes away if I push the clutch pedal down. Now for the weird part. The car did this when I got in 2016. Since then, I replaced the 260 with a 331. I replaced the entire exhaust system. I replaced the 4 speed with a T5. I had a new driveshaft made. The motor mounts are like new and do not touch the headers. The clutch, PP, and TOB are new. I replaced all 4 wheels and tires. The vibration is the same as before. I didn't do those things to battle the vibration issue. I just mention them because a lot of possible vibration causes "should" have been addressed by those things. The transmission mount seems sturdy enough, but has clearly been cobbled together and modified numerous times over the years. Same for the transmission tunnel. I am starting to think maybe the floor is just weak. Is that even a possibility? Any other suggestions?

[poboyjo65]

Use an angle finder gauge to check pinion angle. easiest way is to check the front of the motor & pinion they should be the same .

[A/FX]

I agree that you should check the driveline angle. Here is an app that works well for checking for misalignment. https://www.tremec.com/menu/tremec-toolbox-app/
I have used it and it seems to be able to determine if there is something out of alignment.
Jim
Here is a diagram that might help you understand what is correct:

[351 Pinto]

Thanks guys! I will give it a try.

[351 Pinto]

I got the app from Tremec. The readings are a little sketchy because my phone has buttons on both sides, but after countless measurements, I believe the trans output shaft is at ~2.5 degrees, the driveshaft is pretty much 0, and the diff is ~6.5. I read that the diff should be pointing down because the pinion tries to climb the ring gear when power is applied. My diff is already pointing up, so when I am on the power, the 6.5 probably goes much higher.

Because the diff is so far out, I think I will take a big swing at it and use 8 degree shims on the leafs and see how it does. If needed, I can also shim trans mount to improve the ~2.5 reading.

Basic info on the car- 63.5, 331, T5, stock suspension all around, 195/70/14 tires. In other words, good power, crappy handling, and no traction, just the way an old (street only) car should be!

[poboyjo65]

I got the app from Tremec. The readings are a little sketchy because my phone has buttons on both sides, but after countless measurements, I believe the trans output shaft is at ~2.5 degrees, the driveshaft is pretty much 0, and the diff is ~6.5.

I read that the diff should be pointing down because the pinion tries to climb the ring gear when power is applied.

If you go too far it will vibrate when you let off the gas. If I understand you right I would think 8 degrees is too much .4 degree shims would put your diff & the trans on the same angle of 2.5 if I understand you right.

If you look at Jim diagram above look at center line A & center line C. they should be the same or near it.

as for the ring climbing the gear yes but not a crazy amount on a street car. & only on hard take offs & wot. A half of a degree to maybe a whole one would be plenty. You want it at its happiest when driving normal.

[351 Pinto]

Thanks again. I went back and ordered 4 degree shims as well. The set I don't use will make expensive door stops.

So I should not be concerned about the diff pointing up? I was thinking 4 degrees originally, but several sites I checked made a big deal out of having the diff pointed up.

[poboyjo65]

There are lots of these types of videos,heres a quicky that will help make it clear what you need. it talks about angles & phasing which both need to be right .
https://www.youtube.com/watch?v=Idk3BVDVHq4

[351 Pinto]

I found the source of my trouble when I crawled under to install the shims. A previous owner made elongated shackles, presumably to compensate for sagging leaf springs. I ordered new leaf springs, shackles, and bushings. I got the 6 leaf version as my car was an original V8 car. I suspect restoring everything to new and original spec will cure the issue with the pinion angle. At the very least, it will change the angle of the diff (for the better), meaning I have to re-measure.

[351 Pinto]

OK, to close this one out, I got the new leaf springs and shackles installed. Vibration is gone, car sits level, the ride is better, the handling is better, and the wheel hop is gone.

If I was any happier, I could poop a Twinkie!