Driveshaft thump with new carrier bearings?

[Ryan H]

I recently replaced the carrier bearings and u-joints and just yesterday while logging the car I decided to launch the car and for the first time ever the driveshaft smacked the bottom of the car and the exhaust. I did another launch to make sure it wasn't the way I had launhced the car and boom, it did it again. Now just some history here, over a year ago I filled the old carrier bearings with silicone thinking that would help stop that driveline noise, ya know the whum, whum, whum when on the decel, ya well I was obviously wrong. Having done that I never did have a problem with the thump once the car was modded more. The thing is now with brand new carrier bearings I shouldn't be getting this thumping on the launch. I'll end up filling these ones with silicone, but why would new bearings do this?

 

[ecstasytsi]

Fill the carrier bearings with 3M Window Weld®. I found the shit at a local autobody paint supply shop. Just call around. It's supposed to be for repairing the seal on your windshield. It's liquid and when cured it hardens into a hard polyurethane. You probably have too much horsepower for the stock bearings. What turbo do you have? Is your car full-weight, you might want to put it on a diet.

 

[wastefuldreamer]

Did u put the driveshaft back together the right way? Because it is balanced.

 

[Ryan H]

yes i marked everything and put it back the way it was before. It must be balanced cause there is no vibration at all. I asked my friend who has more power than me, about 400whp+ and he has never had this problem and his bearings are untouched, no silicone, nothing.
As for power I'm running an 18g @ 20psi, about 300whp now, maybe a bit more.
I have no problem filling them again with silicone, but what gets me is that one my friend with more power and original bearings doesn;t have this problem and 2 the bearings are brand friggin new?? I'm just surprised.

 

[Ryan H]

I went to go pull the driveshaft off to fill the bearings with silicone, but I noticed that the rubber bushings that hold the bearings onto the car were not installed right, so I reversed them and that tighten things up since there was too much play before. So I took it for a test drive, lauched it 3 times and the thump is minimal now, just a little smack smack thats barely noticeable, but still not good enough for me so I'm filling them with silicone.

 

[pneumo]

Maybe check your motor mounts, too. If the engine rocks back too far under power that could put the first U-joint at a hard angle.

 

[Ryan H]

I just filled the front and driver side mounts with urethane, they're rock hard.