C3sharp

Ok, here’s the deal:
89 GTU. The problem is a loud grinding noise upon fully disengaging the clutch (pushing the pedal all the way in), accompanied by a drop in RPMs. From all the information and threads here describing similar problems (and believe me, I’ve probably read them all at least five times at this point), I was lead to believe that this was likely a problem with the throwout bearing or the pilot bearing & dust seal. I was leaning towards a pilot bearing issue, since the grinding noise only occurs when the clutch is fully disengaged, whereas I would expect to hear whirring/grinding at any point during disengagement if it was the throwout bearing since it would be contacting the pressure plate long before the pedal is all the way to the floor. The fact that the RPMs drop also seems to be an indicator that there is improper friction between the eccentric shaft and trans input shaft. I pulled the trans and replaced both bearings (and the dust seal) and was careful to add the proper amount of grease to both (taking care not to over grease the pilot). I also swapped in a newer clutch plate.


After putting the transmission back in, the grinding noise is still there, only now it only lasts for a small duration even when holding down the clutch pedal, and I also cannot shift into gear while the car is running. It seems as if the clutch is now not fully disengaging (perhaps I’ve made a mistake during reassembly, since the issue is worse than before in that way). The clutch fork seems to be getting actuated properly by the slave cylinder, and I bled the clutch ensuring there is no air in the system. So my question now is, what is left that could possibly still be causing that grinding? Improper clutch disk alignment? Worn pressure plate? Bent/damaged trans input shaft (how can I check this)?


Other things:

-The transmission was difficult to mate with the engine. I used the trick of aligning it, and while in gear, rotating the driveshaft to make sure the splines were aligned and that seemed to work. However, I was not able to get the bellhousing flush with the engine side, there was still about 1cm of space before I put the bolts back on, not sure if that matters. Slightly worried that the pilot bearing may have been fouled while doing this, but the old one suffered worse when the trans was removed and it still seemed not to be damaged (curiously).


-Just learned that the pressure plate has 2 out of 4 bolts that are longer ‘pilot’ bolts. Does orientation of the pressure plate matter when bolted to the flywheel? How important is getting the torque absolutely correct when putting the pressure plate back on?


-My eccentric shaft has some scoring on the inside, but the pilot bearing seemed to install correctly (I have the installation tool). The dust seal should be installed such that it just contacts the pilot bearing, correct?


I’ll gladly answer any other questions or post any info that might lead me in the right direction.


Thanks to any one who takes the time to read this and may have a suggestion or two.

professionalpyroman

My $0.02, you can ruin the seal/pilot bearing by ramming the transmission in when it is misaligned. The bell housing on the transmission should shove all the way in to the block before you put any bolts in (I'll leave it to your imagination whether or not this is from experience). If it doesn't mate up and you use the bolts to crank the bellhousing into place, you are using the pilot shaft to crush itself in place. It will likely be difficult to pull back out. I would imagine you've crushed either the seal, or partially crushed the PB.

Were you replacing the transmission from underneath the car? A trick I use to make sure the transmission goes in is to loosen (not undo) the motor mounts so the engine pivots backwards and have a buddy use a prybar to tip the engine back so that I can get it to slide straight in. You have a wider range of movement without the intercooler or throttlebody on top pushing against the firewall.

Also, if you don't have it, get a clutch disk alignment tool to have everything lined up before you go to install the transmission

That's my suggestion

C3sharp

Thanks a lot professional. Yes I was replacing it from under the car. I've heard variations on that trick, like jacking up the front of the engine to get some tilt, but undoing the mounts sounds like a much easier idea, I'll give it a try. I do have the clutch disk alignment tool. Is it possible that the clutch disk became unaligned, and that's causing mating difficulties? Also, how badly damaged should the pilot bearing be before I replace it? The last one I took out actually looked fine and still was able to spin.

professionalpyroman

Well, if its distorted enough, you will get the bearing binding cyclically as the two parts rotate at different rates. The other thing is that if it is distorted, it could cause alignment issues with the input shaft, resulting in wear on mating surfaces and improper gear alignment. The bearing and seal are cheap enough to replace that I would redo it, if nothing else to inspect for damage and ensure that you don't end up stranded.

C3sharp

For anyone who may happen to look upon this thread, I'll post what the actual issue was:

Although the symptoms did mimic a fouled pilot bearing, the grinding noise actually had nothing to do with the pilot bearing at all, but was due to the starter gearing being engaged with the flywheel when it should not have been. This was, in turn, due to a broken ignition cylinder, which allowed the key to stay in the starting position, rather than return to the on position, after starting the car. I saw mention of this in one other post amongst many threads describing pilot bearing replacement techniques, so if you're experiencing this same grinding when the clutch is fully disengaged, check that your key isn't engaging the starter while the car is already on before you go for the pilot bearing replacement, it will save you a transmission drop and several not fun repairs.

The clutch issues I described were due to the fact that I had swapped in a new clutch, but not readjusted the clutch pedal height, free-play, and throw. Once the pedal had been adjusted, the clutch operated properly.

professionalpyroman

Glad you figured it out. Thanks for updating us!

FührerTüner

iTrader: (5)

Thanks for following up. Did you drive it like that? Is the starter toast?