Transmissionbearing needing replacing?

[mjlisz]

Hi everyone,

I have a 1990 C-4 with a six speed manual transmission. I am starting to hear rotional noises when sitting at a stoplight in neutral with the clutch out. If I push the clutch in the noise goes away. Someone told me that this is the main bearing in the transmission going bad. The car has 105,000 miles on it which seems a little soon for a main bearing. Can any of you with more experience tell me if this seems like a reasonable diagnosis? If it is, can the bearing be replaced without tearing the transmission apart? And, could this problem be unique to this bearing only, or is this an indication that all the bearings in the transmission are going bad?

If the bearing can be replaced without tearing the transmission apart and this is likely to be the only bearing needing replacement, I might be tempted to only replace the main bearing. It seems to soon for bearings to be going out.

Your thoughts on this are appreciated.

Regards,

Mike

 

[gmjunkie]

Hi everyone,

I have a 1990 C-4 with a six speed manual transmission. I am starting to hear rotional noises when sitting at a stoplight in neutral with the clutch out. If I push the clutch in the noise goes away. Someone told me that this is the main bearing in the transmission going bad. The car has 105,000 miles on it which seems a little soon for a main bearing. Can any of you with more experience tell me if this seems like a reasonable diagnosis? If it is, can the bearing be replaced without tearing the transmission apart? And, could this problem be unique to this bearing only, or is this an indication that all the bearings in the transmission are going bad?

If the bearing can be replaced without tearing the transmission apart and this is likely to be the only bearing needing replacement, I might be tempted to only replace the main bearing. It seems to soon for bearings to be going out.

Your thoughts on this are appreciated.

Regards,

Mike

6 sp's are noisier than other transmissions as a rule anyway!! Dose it have the right lubricant in it??Has it ever been changed?? If it's not ever been changed that would be to first thing I would do!! I have 2 6 sp c4's here at the time and there both a little noisier, but I heard allot of them worse!! The ZF in C4's are really noisy and MM 6 in C5's are allot noisier than say a regular 4 or 5 sp!! My C5's have noisy transmission's,My 03 Z-51 new I really didn't Notice it ,till I quit Cranking up the Bose System !!

PS The input shaft bearing can be changed without complete disassembly,but if I went that far I'd go ahead and tear it down and check it out!! Your already 3/4 way there!!

 

[Hrtbeat1]

One other thing to think about is the flywheel. Does it have the original dual mass flywheel? Or has it been replaced with a single mass flywheel? This is a pretty common thing to do, due to the cost of the original dual mass. If it has been replaced it will be noisier, especially with the clutch out.

This is probabally the best ZF expert ... www.zfdoc.com

 

[mjlisz]

Hi their qm. And thanks for your help. Here is the skinny on the transmission lubricant. I changed the lubricant when I bought the car 5 years ago with 60,000 miles on it. I remember being confused as to what to put in it as the manuel said SAE 5W-30 which I remember thinking was motor oil. I can't remember if I actually put motor oil in it or not. I had the fluid changed again about 6 months ago and the technition insisted that it shold not be motor oil but rather synthetic synchromesh transmission fluid. I remember wondering if I may have contributed to premature wear of the transmission by putting motor oil in it. What do you think?

Anyway, It has been changed twice in the last 45,000 miles - most recently about 6 months ago. I also remember thinking that it was a lot quieter when I first bought the car. But then, as you point out, I almost never drove it back then without the stereo being cranked up. The transmission shifts great and otherwise works flawlessly. But I am worried that one of these days the bearing may fail altogether and leave me stranded somewhere.

Do you have a suggestion as to how to proceed next? I was going to take it to the local Chevy dealer (there is only one here in Flagstaff) but they are not certified to work on vettes.

I have no idea what flywheel might be in it. But it seems like that would be spinning whether or not the clutch was in or out and be noisy all the time.

Thanks for your help so far. I am not opposed to leaving it alone if the noise is normal.

Mike

 

[John Robinson]

With the mileage you have on the car I would be more inclined to think the throw out bearing on the clutch is the culprit. As you say the noise goes away when you push the clutch down. When you do that you are engaging the clutch throw out bearing. If that is the case a clutch replacement with a new bearing would solve you problem.

 

[mjlisz]

John,

It is just the reverse. It is noisy when the clutch pedal is not pushed in. It is actually amazingly quiet when the clutch pedal is pushed in. But it begs the question, how long does the typical clutch last in a corvette?

Mike

 

[John Robinson]

As you say the noise goes away when you push the clutch down.

As for the milage a clutch will last that normally depends on the way it is used. I have seen clutches gone in 15000miles and I have also seen clutches lasting up to 150000 miles.

When you push the clutch pedal down you engage the throw out bearing. If the noise only occurs when you have your foot off the clutch pedal and then goes away when you engage the clutch that is because you are putting pressure on the bearing.

 

[Hrtbeat1]

The reccomended transmission lube is a motor oil. Its made by Castrol and used in the BMW M class motors, from what I have heard the actual reccomended oil can be purchased at any BMW dealer.

Check out the zfdoc site he has some very good information on the transmissions, clutch hydraulics, ect. Oh and by the way I think he is located in Prescott, but it may be Flagstaff, so he is relatively local to you. More so than a lot of us.



G

 

[Hib Halverson]

The reccomended transmission lube is a motor oil. Its made by Castrol and used in the BMW M class motors, from what I have heard the actual reccomended oil can be purchased at any BMW dealer.

Check out the zfdoc site he has some very good information on the transmissions, clutch hydraulics, ect. Oh and by the way I think he is located in Prescott, but it may be Flagstaff, so he is relatively local to you. More so than a lot of us.



G

In fact, the original lubricant designed for the ZF by GM was a Texaco Havoline 5w30 engine oil. Texaco no longer supplies that to GM.

There is a replacement available from GM dealers for 89-96 six-speeds but it's expensive and really not a very good choice.

The best to put in a ZF is Red Line MTL a synthetic, low-viscosity, GL4 gear lubricant designed specifically for spur- and helical-gear, manual transmissions. It may give you an improvement in shift feel, however, if you have a developing noise (ie: one that used to not be there but has appeared and is getting worse) going to MTL, or any lubricant for that matter, won't help. You need to repair whatever is making that noise.

The best lube to put in a ZF for severe duty, is Red Line Light Shockproof Gear Lubricant. That's what I've used in my two ZFs since about 1996.

A post above references the ZFDoc's site. The ZFDoc is Bill Boudreau, one of the top ZF repair, overhaul and modification experts in the country. He's a bit south of Flag in Cave Creek. You can reach Bill with ZF questions at 602.319.6575 or billb@zfdoc.com