Help me diagnose this vibration/noise problem

[Killercanary]

I bent three mainshafts in my T5 and recently upgraded to a TKO. The day I put it in I didn't make it 1/4 mile from my house and the new front universal joint let go at about 45mph, just as I starting into the throttle in 3rd gear. Well the DS loop ate my aluminum DS and its now junk and the loop was severly bent. I put my dad's stock DS that too was setup for a TKO to get it home. I noticed it vibrated badly at speeds over 75mph. I put mine on and the vibrations weren't as bad, but were still there. I also installed a set of GW LCA's. Before the LCA install, my car would bottom out all the time. Well, now the vibration is worse. Here's what it does... as soon as I hit 75mph, the car vibrates baddly, when the clutch is in its worse at that high speed, when I hit bumps and the suspension collapses I hear a grinding sound.

So here's what I did tonight. I put the rear up on jack stands and fired the car up. I put it in first and let the clutch out... it would make a LOUD grinding sound every few seconds as the car "loped". I then put it in 5th and took it to 75mph, the car shook badly. Both times in looking from the rear of the car I could see the front of the rear where the DS mounts to go down and back to normal. The DS looked to be spinning fine. My dad crawled under the car and stuck his ear on the diff. cover and said it sounded like the noise cam from the rear. We then removed the DS and started the car. I put it in second and got it toabout 3000rpms before the fluid started to come out, but there was NO noise, and my dad took a small screw driver and whlie the tailshaft was spinning he touched it with the screw driver to feel it is was "wobbling"... it wasn't. So I think the tranny is fine. I then started to spin the back tires and I could see the place where the DS bolts to has a slight wobble. Would this be the pinion that is bent? Any ideas, sorry this is long but I had to list everything. BTW- the DS is NOT hitting the loop, and the exhaust is NOT hitting the DS. Thanks!

[shadowblue89]

I know this doesn't help you out but Thanks. My car does the same at 75mph and that is one thing I did not look at yet. Also though the output shaft on my tranny wobbles a little and I think that is part of the problem.

[PKRWUD]

That sounds exactly like a bent pinion gear, but there was another problem first that caused the pinion to bend. That's what you need to figure out.

Take care,
-Chris

[7DMACH1]

Check the pinion nut. Mine came loose and I had a vibration over 75 mph not matter what gear or neutral. Push up on the rear flange and if it move the nut has come loose. This is a common problem when people change ring and pinions and don't use a new nut. I heard this happening to at least 20 people. RAY

[Killercanary]

Thanks everyone for the replys. How can I determine if it is the pinion that is bent? I know its not the pinion nut as I had to remove it to replace the seal there, and the guy that just looked at the rear end rechecked it for me as I thought maybe I didn't put it on right. Plus the guy that puts all of my gears in center punches the threads on the pinion so that the nut can not come off... its good insurance! But thanks for the idea.


PKRWUD - Well, I think I have that figured out, I'm thinking the sudden jolt from the universal failing may have done it since it was still connected back there. Or... from running it so long with the bent mainshafts in the tranny maybe that worked on it too???

What may be causing the grinding sound when the suspension collapses... the bent pinion shaft???