Another vibration thread
11-29-2010, 05:34 PM
#1
Another vibration thread I am currently deployed to Iraq so I cant do anything about it right now but im trying to get some ideas of what it might be so when I get home in a couple months I can get this fixed.
I had my GF take my camaro (1999 Z28 A4) to a shop to get the gears changed out. The origional rearend (10 bolt) had a bad axle bearing so I decided on a complete rebuild. I had them put new gears in it, all new bearings and a new axle in it because it was messed up from the bad bearing. After the install she noticed a vibration. Her dad found that it had a broken trans mount so he put a poly trans mount in it and that didnt cure it. The symptoms are.....
When accelerating there is no vibration. When she lets her foot off of the gas at 45 mph or more it vibrates. I had her accelerate to 35 mph and let off the gas and she felt nothing. I had her accelerate to 55 mph and let her foot off the gas and she said it was worse than it was at 45 mph. The vibration only occurs when she is at 45 mph or more and her foot is not on the gas. The higher the mph the worse the vibration gets but only when the car is coasting.
The vibration is not a small one. She said it rattled change in the cup holder. I could hear it over the phone. The shop isnt helping us out. They are saying its the poly trans mount but I have had poly trans mounts on all of my 4th gen cars and she is describing a completely different vibration that what those cause. Im thinking maybe they dropped the DS and knocked a weight off of it but wouldnt that cause the vibration all the time? What do you think it is?
Thanks for the help guys and im sorry for the long post. I was trying to be complete.
I had my GF take my camaro (1999 Z28 A4) to a shop to get the gears changed out. The origional rearend (10 bolt) had a bad axle bearing so I decided on a complete rebuild. I had them put new gears in it, all new bearings and a new axle in it because it was messed up from the bad bearing. After the install she noticed a vibration. Her dad found that it had a broken trans mount so he put a poly trans mount in it and that didnt cure it. The symptoms are.....
When accelerating there is no vibration. When she lets her foot off of the gas at 45 mph or more it vibrates. I had her accelerate to 35 mph and let off the gas and she felt nothing. I had her accelerate to 55 mph and let her foot off the gas and she said it was worse than it was at 45 mph. The vibration only occurs when she is at 45 mph or more and her foot is not on the gas. The higher the mph the worse the vibration gets but only when the car is coasting.
The vibration is not a small one. She said it rattled change in the cup holder. I could hear it over the phone. The shop isnt helping us out. They are saying its the poly trans mount but I have had poly trans mounts on all of my 4th gen cars and she is describing a completely different vibration that what those cause. Im thinking maybe they dropped the DS and knocked a weight off of it but wouldnt that cause the vibration all the time? What do you think it is?
Thanks for the help guys and im sorry for the long post. I was trying to be complete.
11-29-2010, 09:20 PM
#2
Replace the transmission mount with a stock one rather than the poly one.
There are a lot of threads verifying that poly mounts do not isolate the vibration as well as the stock rubber mount.
Or the poly mount is the wrong size causing the front of the drive shaft to be lower than it should be causing the front u-joint to be out of line. Just a 1/2 inch difference in height can case severe vibrations at the front u joint.
You wouldn't think a 1/2" would make it difference but it does.
On my car the 1/2" difference was caused by an aftermarket transmission mount and the wrong poly mount which lowered the transmission tailshaft by a 1/2 inch.
I doubt they removed the rear end when they fixed it - but if they did - then the rear u joint might be out of alignment also (pinion angle) after reinstalling the rearend and driveshaft. There are also tons of posts with pics showing how to set the alignment of the rear u joint.
There are a lot of threads verifying that poly mounts do not isolate the vibration as well as the stock rubber mount.
Or the poly mount is the wrong size causing the front of the drive shaft to be lower than it should be causing the front u-joint to be out of line. Just a 1/2 inch difference in height can case severe vibrations at the front u joint.
You wouldn't think a 1/2" would make it difference but it does.
On my car the 1/2" difference was caused by an aftermarket transmission mount and the wrong poly mount which lowered the transmission tailshaft by a 1/2 inch.
I doubt they removed the rear end when they fixed it - but if they did - then the rear u joint might be out of alignment also (pinion angle) after reinstalling the rearend and driveshaft. There are also tons of posts with pics showing how to set the alignment of the rear u joint.
Last edited by dlandsvZ28; 11-30-2010 at 10:09 AM.
11-30-2010, 09:59 AM
#3
the car will need the driveline angles checked. the poly trans mounted can be shaved some if needed. how to do it is in another thread on here somewhere. also, make sure the rear u-joint is all the way seated properly. it'll contribute to vibration if it wasn't seated correctly after the gear swap. fwiw, a broken tranny mount isn't going to cause that serious a vibration. so if it started after the gear swap, i'd be looking in the area of driveline angles. other than that, you'll have to deal with it when you get home. i wouldnt recommend anyone to continue driving it until then.
