[prostreet64]

Had a new gear set installed several weeks ago in the Trans Am, and now have a vibration I am trying to track down. I plan on taking the car back to the shop for their diagnosis but first wanted to run it by you experts. Under steady acceleration up to 50 or 55 everything seems normal but when I hold the speed a vibration sets in until I either let off the gas completely or let off and put the trans in neutral and coast. There is still some vibration but not near as much. I went through the exhaust system carefully to make sure no components were touching the body or frame; all was good. So, could the ring and pinion cause this or am I more likely looking at u-joints or bearings?

[hurryinhoosier62]

How do your universal joints look? Has your driveshaft been balanced?

[prostreet64]

Driveshaft is an aftermarket unit that I installed about 4 years ago. It was balanced when I got it and has not given any trouble; u-joints were new at the same time; probably need to have a look at them.

[Brian Baker]

From your statement, the vibration is always there at speeds of 50-55 MPH, it's just more pronounced under load than it is when coasting or "maintaining speed under a light load".

I'm leaning towards it being a driveshaft issue, They had to remove it to install the ring & pinion. It's possible the shop may have damaged the shaft, even unintentionally. For instance, leaning it against the shop wall, and have it tip over, slide down the wall and strike the concrete floor could damage it ever so slightly which could effect its balance.

[Elarson]

My suspicion would be the rear u-joint....either got damaged or isn't seated properly in the pinion flange.

Eric

[FrankieT/A]

Try 180ing your drive shaft. Cheap quick and sometimes works...

[prostreet64]

Thanks guys for the suggestions; I will be taking a closer look at the driveshaft and u-joints, especially the rear one. Will give an update when I can.

[455firebird1969]

If you do remove the driveshaft to troubleshoot, you should assess the pinion while the shaft is disconnected.

1. Grasp the pinion yoke and try to move it up & down, side to side and in and out, it should be solid with no movement.

If the pinion nut broke torque and has lost bearing preload, you will be able to feel slop, which is a problem.

2. Rotate the pinion, if you do so very slowly & carefully, you should be able to feel the .006”-010” of backlash that should be there.

Having set up many gear sets, I can feel (just barely) .010” of pinion movement. If it moves more, it will be easier to feel, and that would indicate a problem. A properly set up gear set should have about .010” backlash (rotational slop). This is barely detectable when the differential assembly is assembled, as in your case, because there is rotational slop in the axle splines too, and discerning the difference is not easy.

I would suggest you drive the car to warm the gear lube before performing the pinion checks I have suggested, since warm gear lube is thinner. It will help you feel the tolerance easier.

[Bill Eveland]

As long as the ring and pinion are set up correctly, the only other issue i've seen is too much backlash variance to get a vibration. Usually once you get over .005 it can cause a vibration. It needs to be measured in at least 6 spots around the ring and pinion.

[wrench]

I have seen the seal spring pop out undetected during installation. Then gets caught between the pinion yoke and bearing inner race. Always causes a vibration.

[Mark G]

U-joint or driveshaft.. make sure the shop never knock off the balancing weight.

Sometimes the driveshaft will cause vibrations after a rear gear change, either by not being reinstalled in the same positions it was originally.

[prostreet64]

Just dropped the driveshaft on the Trans Am. The pinion yoke has no movement side to side or up/down. If I turn it back and forth it appears to have maybe 2 or 3 degrees of slop; don't know what that translates into as far as backlash is concerned but it seems 'loose' to me. The u-joints appear to be in good shape; no bearings missing and they are well lubed and move freely. At the other end, the output shaft can be wiggled back and forth about 1/16 of an inch. There are no dings in the driveshaft and the balance weight is in place.

[Gary H]

Originally Posted by prostreet64

Just dropped the driveshaft on the Trans Am. The pinion yoke has no movement side to side or up/down. If I turn it back and forth it appears to have maybe 2 or 3 degrees of slop; don't know what that translates into as far as backlash is concerned but it seems 'loose' to me. The u-joints appear to be in good shape; no bearings missing and they are well lubed and move freely. At the other end, the output shaft can be wiggled back and forth about 1/16 of an inch. There are no dings in the driveshaft and the balance weight is in place.

Install the driveshaft 180 degrees from where it was and see if it helps

[prostreet64]

Gary, I did that but won't have a chance to test drive it until tomorrow. Will post up results.

[prostreet64]

And the winner is...................... Just got back from a test drive and it would appear that relocating the driveshaft 180* has done the trick. No more vibration. Woohoo!

[ta man]

Originally Posted by prostreet64

And the winner is...................... Just got back from a test drive and it would appear that relocating the driveshaft 180* has done the trick. No more vibration. Woohoo!

I'm always amazed why this works? If a driveshaft is balanced what is the difference?

[hurryinhoosier62]

Originally Posted by prostreet64

And the winner is...................... Just got back from a test drive and it would appear that relocating the driveshaft 180* has done the trick. No more vibration. Woohoo!

Good deal. Anytime you drop a balanced driveshaft you need to index its position so it is reinstalled in the same position.

[hurryinhoosier62]

Originally Posted by ta man

I'm always amazed why this works? If a driveshaft is balanced what is the difference?

It’s 180 degrees out of balance. This is why balanced driveshafts need to be indexed before removal and reinstallation.