Well I've been trying to figure this problem out from sometime now. We have in narrowed down some. First I'll explain the problem.

When driving and you let off the gas with the clutch out you get a horrable vibration, it shakes the car pretty good. It only does it when there is back pressure on the drivetrain. I knows its nothing in the engine...its for sure drivetrain. The vibration is like driving on some rumble stripes almost. Sometimes its worse than others. When it does it I can make it stop by one of two ways. One, step on the gas just alittle and it doesn't do it as long as I'm have the pedal down just a hair. Two, clutch in/out of gear, I can make it stop by pressing the clutch in and/or taking it out of gear (clutch in or out)...when I do that it also will stop the problem.

Its mostly likely a bearing in the drivetrain somewhere. It could be in the tranny too...I'm not totally sure where it is yet...otherwise I wouldn't be posting. It might be in the driveshaft; maybe the carrier bearing? Maybe a joint somewhere. When I put the driveshaft on the u-joint(s) had some detent in them...could this be the problem? Do most DS' have detent in them on the u-joint? I've already replaced the diff. (open diff.) with a Kaaz LSD thinking that it was the diff. making the noise but it didn't fix the problem. But I wanted one anyways. But I dont want to start throwing money like crazy at every drivetrain part trying to fix it. That would cost alittle lol. If anyone can help me out that would be so awesome.

Again this only happens when there is back pressure on the drivetrain...back pressure would be when you have you foot off the gas and clutch out and in gear and your car is slowing down but your engine/drivetain is still wanting to move foward. This causing a "twist"/backpressure on the drivetrain.

If you need anyone info I would be more than happy to help...anything to figure this out. Thanks, Nate

To me, it sounds like a u-joint or driveshaft alignment problem. I'm not sure about the detent issue, but it sounds by this that you've had the driveshaft off the vehicle. If you did, did you mark it properly to ensure the shaft mated with the tranny yoke and differential the way it came off?

If the u-joints or center bearing are loose enough to cause this vibration, you should be able to feel this if you're under the vehicle and you yank around on the drive shaft.

Let us know what you find.

I am having a similar problem right now. When I run a 2piece driveshaft I get smooth accelleration and decelleration and coast.

When I switched to a 1 piece driveshaft I get vibration on accleeration and decelleration (and I am on my 3rd 1 piece driveshaft right now, so its safe to say that isnt the problem).

Before I put a NISMO LSD in the stock differential that came with my car, the differential/driveshaft did vibrate a bit on accelleration decelleration but when I switched the differential I realized that the pinion gear in the differential had a bit more play than spec.

I didnt think anything of it with a 2 piece because it didnt have any vibration after I rebuilt the differential, but when I switched to a 1 piece it was vibration city.

So what I am planning on doing now is; crack open the differential once again, and put in some new pinion gears. Hopefully this will fix it, Ill let you know.

The car was bought as a shell (90) and I put a DOHC engine in it. Also at the same time I did a 5-spd swap. So everything was bought used or new. Including the driveshaft from the auto to 5-spd swap.

Thanks for all the help this far. I'll try some of that stuff.

Anymore help?

I just jack up rear and spinned tires and I could hear the sound I heard when I'm drive. I didn't try disconnecting my DS. I had my dad get under as I spun the wheels and the sound was NOT coming from the tranny or the DS. It was coming from the diff. Most likely the pinion gear but some where in the diff. I'm pretty sure the noise is the same noise that I hear when driving.

So with that I think its the pinion gear possably. With the rear end of the car jack up and turning the wheels by hand, It appears to be some slack in the pinion gear. In other words there is slack between the driveshaft and the wheels or another way to explain it is you can hold the driveshaft still and turn the wheels a little bit/rock the car back and forth without the driveshaft moving. But I can do the samething to other cars also like my vr-4 or my dads f-350 ect. But the noise I hear when turning the wheels is same noise I hear when I'm driving as explained before. So how much slack is to much slack? Could this be the problem? How should I go about checking it further and/or fixing it?
Modified by youngmanvr4 at 7:47 PM 4/22/2006

Looks like you're narrowing it down. I know that a certain amount of "lash" (play) in the gears is normal, but how much, I couldn't say. But since sound can "travel" through steel, I would maybe suggest that you do the same test again but this time remove the driveshaft from the differential to completely eliminate the u-joint from the equation. Just make sure you mark the yokes to ensure you get them back together the same way, and not 180 degrees around.

If the sound is still there, then you know for sure it's from the diff - - maybe even your pinion bearing.

Maybe open the diff up and look for wear on the pinion and ring gears. Also try and get a Factory Service Manual for your vehicle. It would probably explain the set-up procedure and tolerances for the gears. Personally, I have never set up a rear end (onlt replaced pinion seals), but I know that getting the offsets and the amount of lash in the gears to spec is critical.

Keep in touch.

The only problem with removing the driveshaft is since the driveshaft is connected to the pinion gear so when you remove the driveshaft from the pinion gear it could lessen the pressure/tension on the pinion gear making it so it wont make the sound. I'm not saying that it wont but it may not make the noise when I take the DS off and it could still be the diff.

Will I'm back to thinking its the tranny. Reasoning is we jacked up the back car again but this time I started (yes, I had wheel blocks on the front and two jackstands in the rear) and I had my dad and our business parter there (he is into cars also) and as I rev'ed it up to 65 in 5th; which is the gear and speed it does it most; and it wasn't as bad but there was a noise from the tranny when I let up on the gas. So I think I'm going to replace the tranny...I need to but a new clutch in anyways because its making a noise when I slip the clutch also. So I'm hoping to kill 2 birds with 1 stone. I mean trannys are cheap enough, I would spend just that much on replacing the pinion gear and it doesn't sound like its coming from there.

*Note* I didn't try taking the DS off becuase I didn't feel the need to since I'm pretty sure its the tranny.