Help: Weird trans vibration

[AX75F92]

I did some searching and couldnt really come up with anything to explain this so here it is:

I just finished up installing a new ACT clutch kit on my '91 240sx (with SR20DET). The clutch is a 6 puck disk with the "Heavy duty" pressure plate. I also installed a new Toda flywheel at the same time. I replaced the T/O bearing and pilot as well.

Note: Everything was fine before switching the clutch. (well....everything except the for the clutch slipping...)

After the installation, everything seems fine except I am experiencing a rather hard vibration and noise. The problem only occurs between 2000 and 3000 RPM while decelerating in 1-4th gear only (not in 5th). All the gears are OK while accelerating and during steady crusing, the problem only happens under decel. There also has to be load on the drivetrain, I tried decelerating in gear with the car raised on a lift and there is no vibration at all. No problem in neutral either.

Is it possible that the clutch is misbalanced and is encountering some sort of resonance at that particular RPM range? I talked with Toda and they have never heard of a problem like this being caused from the flywheel. I checked the mounts, exhaust to transmission bracket, and everything else under the car and it all seems to be good and tight. I am confident that it is not something that is rattling from under the car. It seems like the vibration is being transferred through the trans as you can feel it through the shifter. I would place blame on the transmission, but all was good before the clutch install and I didnt touch anything on the trans.

Any help you guys might be able to provide would be greatly appreciated. This problem is getting really annoying and I would really like to solve it and prevent any potential engine or transmission damage.

THANKS.

[NISTECH]

sounds more like a drive shaft problem. did you get the carrier bearing reinstalled properly. seriously take a good look at your driveshaft.

[AX75F92]

Yeah. That is exactly what Im thinking now too.

I took off the center consol and shifter boot yesterday so I could look down at the trans while the problem was occurring. It seems to be coming from right in that area where the driveshaft yoke enters the transmission. It is definitely not coming from the front of the gearbox. What could possibly go wrong with the driveshaft? It did fall off the diff and whack my friend in the head when he was trying to put it back on. Hahaha. Is it possible it has become unbalanced? I also replaced the seal that goes in the back of the trans and around the driveshaft yoke. If this was somehow misaligned, not pushed in far enough, or pushed in too far, could it cause the problem? Sorry for the ingorance but, where is the carrier bearing? The only bearings I replaced were the T/O and pilot.

Thanks for the help Nistech.

[NISTECH]

When you guys removed the shaft did you mark its location on the diff flange so all 4 holes would line up where they were before you removed it? If you didnt that could cause it to be imbalanced. If thats the case unbolt it from the flange on the diff and rotate it 180 degrees rebolt it and recheck it.

[AX75F92]

No, I didnt mark the shaft. I have heard of this before, but since I have removed it numerous times with no problems, I didnt think it was necessary. I will try unbolting and rotating 180 on Monday. Ill let you know if it works.

So, you are saying it is more effective to change the orientation of the shaft on the diff side...not the trans side, right?

Also, is the carrier bearing you referred to the large black bushing/bearing that secures the driveshaft with two U brackets?

Thanks allot man.

[NISTECH]

So, you are saying it is more effective to change the orientation of the shaft on the diff side...not the trans side, right?

Yes on the flange at the diff. I have seen this mistake made by rookies many times. But with rookies we sometimes like to make them think they hosed up and stick a tape weight or 2 on the shaft to throw it out of balance on their final R/T...lol

Also, is the carrier bearing you referred to the large black bushing/bearing that secures the driveshaft with two U brackets?

Thanks allot man.

Yes it is the one right in the center of the drive shaft make sure you put any of the spacers on the mount bolts in the correct locations. The spacers typically go between the braket and the body of the car.

[AX75F92]

Well, yesterday I tried unbolting it at the diff flange and turning it 180. After a quick test drive, the vibration is still there. I guess the next step would be to turn it 90, test it and if that doesnt work, turn it another 180. If it still persists in all four possible combinations the problem must be with the carrier bearing then, right?

I dont remember any spacers on the carrier bearing brackets or bolts. Should there be any? If all else fails, I guess I will just pull the entire driveshaft and brackets off and reinstall it. Any other suggestions? Thanks again.

[NISTECH]

If its not your shaft alignment it could be the one of the ujoints as well. Your shaft shouldnt be able to bolt up in all four positions.

[AX75F92]

Ill check it out tomorrow. Is this something that I should really be worried about, or is it more of an annoyance?

I have a drift event this sat at Buttonwillow that I cant miss....

[NISTECH]

potentially the vibration could grow worse and what ever the problem is could grenade and send the shaft into peices. very unlikely though. that is just worse case senario. You would probably be ok letting it go for a little while. But the vibration from the shaft could amplfiy when you stress the rear end while accelerating causing you to hop in your drifts.

[AX75F92]

I think Ill just take everything out tonight and reinstall it. If nothing seems to work, I can get ahold of another driveshaft to swap in and see if that fixes it. Ill let you know how it goes.

[Chingon]

I have a similar problem and it also occured after doing my clutch swap. my driveshaft vibrates in 3rd gear a little and also at about 50-65mph on the freeway when i let go off the gas; as soon as i step back on the accelerator the vibration goes away. I have disconnected the shaft from the differential and rotation many times and the vibration goes away for about a day and then comes back. i will take it completely out and reinstall it more carefully, but i, like AX75F92 do not recall any spacers on the u-joints nistech. and my shaft is able to be mounted in all four positions, ill take another look at it today or tomorrow.

[NISTECH]

It might be the Z or truck on the spacers I am thinking of.On your diff input flange you should see an imprint on how the shaft was originally mounted, by matching that imprint to your shaft there are only 2 ways the shaft will match that imprint exactly.

[AX75F92]

I still havent figured it out. Ive decided to try and take the easy way out and buy an aluminum one piece drive shaft from Phase 2. I figure I can kill two birds with this as my stock 240sx drive shaft comes up a little short on the SR transmission (oil leaks out from where the shaft enters the trans when I beat on the car). Plus the one piece will eliminate the carrier bearing so spacers (I really dont remember any) should be obsolete. Plus I will save a little weight in the rotating assembly which is a cool side bonus.

I have found some cool tricks to get around with it though. My newest one is left foot braking through the vibration range, no vibration at all.

[AX75F92]

...The Phase2 shaft was designed around a 240sx...it will still come up short. Damn...

I think I will try a JDM S13 one instead.

[AX75F92]

I have a similar problem and it also occured after doing my clutch swap. my driveshaft vibrates in 3rd gear a little and also at about 50-65mph on the freeway when i let go off the gas; as soon as i step back on the accelerator the vibration goes away. I have disconnected the shaft from the differential and rotation many times and the vibration goes away for about a day and then comes back. i will take it completely out and reinstall it more carefully, but i, like AX75F92 do not recall any spacers on the u-joints nistech. and my shaft is able to be mounted in all four positions, ill take another look at it today or tomorrow.

Chingon, did you ever find out or fix your problem?