Driveline issues

[jim_in_fl]

I've got a couple of driveline problems, and I'd like to see if anyone has any ideas.

First, there is a rattling sound from the front of the tranny at idle when the clutch is engaged (like when sitting in neutral). Sound goes away when I push the clutch pedal. I've assumed this is a throwout bearing, or maybe the clutch pivot arm (or whatever that thing is called). It has done this since I bought the car (about 15K miles ago), I don't think it has gotten worse, but it has certainly gotten more annoying. Would it be something other than the throwout bearing? Should it be fixed, or will it likely wait until the clutch needs to be replaced as well?

Also, I've got some sort of driveline vibration. I just replaced the driveshaft, and it is now somewhat smoother, but there is still something wrong somewhere. Previously, on hard acceleration in 2nd/3rd gear, there was a driveline vibration you could feel in the car. It was also noticeable at highway cruise speeds (85-90). The driveshaft I removed seemed fine, except there was no bushing in the coupling nut, so the 2 parts could slide in/out with no resistance.

Now, there is still a slight vibration, kind of a shudder, on hard 1st/2nd gear acceleration. However, it seems like something I hear rather than feel, and I can't pinpoint it. I haven't had the car on the highway yet to see how it feels at higher speeds. The (time-based) frequency of the sound still points to a driveshaft problem. The axles are almost new, and the old ones made bad noises at a much lower frequency.

I just thought this evening that maybe the motor or tranny mounts might be going bad. If they were allowing too much movement could that cause the driveshaft to make noise/vibrations? I looked at them (but not carefully) when replacing the driveshaft and they looked fine, no sagging or cracks. Maybe it is worth another look.

[shifty]

The first problem definitely sounds like the TO bearing. It's really not cool that you would have to pull the tranny to replace the TO bearing if the clutch is just fine, so maybe you'd want to wait a little while until the clutch is ready to be replaced, too.

The second problem could be anything in the driveline, really, but my vote is on either the guibo or the center bearing, if they weren't replaced with the driveshaft.

[Threeshifter]

I just replaced my driveshaft and I have a vibration that I believe is the result of bad transmission mounts. My vibration is at about 80mph. I thought the transmission mounts were ok but after taking a second look the one near the exhaust is really crappy. Planning on installing them this week.

There are 3 types of transmission mounts so check to see what you have if you want to change them. They are relatively inexpensive.

[a]

Swap the tires front to back just to eliminate an out of round tire. AMHIK. The classic symptom of a bad TO bearing is noise when the clutch pedal is depressed. When the pedal is up, the TOB isnt loaded. I s'pose the forks that hold the TOB could be worn or a pivot bushing could be the culprit. I'd live with the noise until something breaks or you replace the clutch and all the associated wear components.

[C.R. Krieger]

[QUOTE="a"]The classic symptom of a bad TO bearing is noise when the clutch pedal is depressed. When the pedal is up, the TOB isnt loaded. [/QUOTE]

IME, it's the opposite. When the bearing is loaded, the parts are held together enough that it doesn't make noise. When it's unloaded, the parts are able to rattle around so you hear them. At least, that's what mine did up until I yanked it last summer ...

[Velocewest]

Getrag trannys are not the quietest. If you are running a light oil like ATF or Redline, it will be more noticable. Every 265 I have owned was noisy in neutral with the clutch engaged, regardless of mileage. Ignore it, or switch to heavier lube.

[Tammer in Philly]

[QUOTE="a"]The classic symptom of a bad TO bearing is noise when the clutch pedal is depressed. When the pedal is up, the TOB isnt loaded. [/QUOTE]

[QUOTE="C.R. Krieger"]IME, it's the opposite. When the bearing is loaded, the parts are held together enough that it doesn't make noise. When it's unloaded, the parts are able to rattle around so you hear them. At least, that's what mine did up until I yanked it last summer ... [/QUOTE]

I think it depends on failure mode. In my E36, the TO bearing got cocked in its place and was putting stress on the input shaft when loaded, making a sort of oscillating screech. It was fine with the clutch engaged.

The second problem, the driveline vibration ... did you preload the Center Bearing properly when installing the new D/S? That is a small but very important step!

-tammer

[jim_in_fl]

I didn't replace the guibo, but it looks fine. Does it fail or go bad before there are visible tears and fuzz?

The center bearing was new with the driveshaft, and I did preload it according to the service manual (~4mm toward the front of the car).

It is raining today so I haven't been able to go look under the car at the motor and tranny mounts yet.

[Tammer in Philly]

[QUOTE="jim_in_fl"]I didn't replace the guibo, but it looks fine. Does it fail or go bad before there are visible tears and fuzz?[/QUOTE]

In my experience, no. I ran one with visible radial cracks in my E36 for several months before I got around to replacing it, with no problems. The only one I've seen that was the true cause of a vibration (and it was making a racket) was completely trashed and barely holding together.

I'll be interesting in learning the result of your diagnosis.

-tammer

[jim_in_fl]

I checked out the motor and tranny mounts. All appear to be in very good shape, no cracking, tearing, or sagging, and all were mounted securely.

I had a friend ride with me this morning to try to help isolate the source of the vibrations. He couldn't pinpoint anything, but seemed to think the most likely suspect would be the center bearing. That is new, though, and the one on the old driveshaft wasn't bad either.

The vibration is mainly felt in first gear as a fairly low-frequency vibration (guestimate around 5 cycles/sec), and in 3rd gear at a much higher frequency (guestimate 20-40 cycles/sec). It only occurs in the midrange on boost, when the motor is cranking out ~350 ft/lbs torque (about 310 to the wheels).

My friend has quite a bit of experience with turbo rwd Nissans, and since the center bearing and rubber coupler seem to be ok, he suggested it might be the tranny. If the bearings are wearing out, the shafts could move around and cause some vibrations under the high torque load. There isn't any noticeable lateral play on the output shaft, though.

The tranny was rebuilt at Korman around 60K miles ago. I guess I don't really know what the expected lifespan of a tranny in a higher-powered car is. It appears to be a 265 (removable bellhousing). I'll be changing the tranny and diff fluids tomorrow, I guess I'll see what comes out.



[Edit by jim_in_fl on [TIME]1111166160[/TIME]]

[dworthy]

Did you seperate your drive shaft when you replaced the center bearing? If not put together properly, then it could be out of balance. Also did pre-load the bearing? That could also leave a little slack in the shaft as well.

[jim_in_fl]

I replaced the whole driveshaft. I never separated the new driveshaft, and it came with a new center bearing which I did preload.