M21 gearbox whine
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
M21 gearbox whine
I have a noticeable whine in my M21. 2000mi since rebuild. Whines in neutral when I give it a rev, and noticeable in 1st and 2nd. Too much car and road noise to hear it in higher gears. Whine disappears when clutch disengaged and car stationary.
It's in a 69 427 Coupe.
Only mods to gearbox by the shop was use of longer needle rollers in one place (can't remember where).
No other problems. I had removed the transmission tunnel insulation, so it could be my imagination, but think the whine is getting worse, and don't remember it being so bad after the rebuild. Fresh gearbox oil is now dark/grey. No sign of metal in oil.
Any thoughts? Am I just being paranoid!?
Thanks...Joe
It's in a 69 427 Coupe.
Only mods to gearbox by the shop was use of longer needle rollers in one place (can't remember where).
No other problems. I had removed the transmission tunnel insulation, so it could be my imagination, but think the whine is getting worse, and don't remember it being so bad after the rebuild. Fresh gearbox oil is now dark/grey. No sign of metal in oil.
Any thoughts? Am I just being paranoid!?
Thanks...Joe
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
Re: M21 gearbox whine (1bad69)
While I'd like to have an M22, My car has the original 427L36 / M21 / 3.08 setup and has 60k miles. I only had the gearbox overhauled because it was out of the car. It had no problems.
I had to rebuild the motor because the nylon/alloy camshaft sprocket failed and the cam stopped turning at 5000rpm. Wish I'd known about this weakness beforehand! Luckily I could use the original matching# block bored 30thou, fresh pistons, valve gear etc. etc.
So the car is back together and running very strong.....just this whine.....!!
I had to rebuild the motor because the nylon/alloy camshaft sprocket failed and the cam stopped turning at 5000rpm. Wish I'd known about this weakness beforehand! Luckily I could use the original matching# block bored 30thou, fresh pistons, valve gear etc. etc.
So the car is back together and running very strong.....just this whine.....!!
Burning Brakes
Joined: Aug 2000
Posts: 1,211
Likes: 6
Re: M21 gearbox whine (jyounane)
I wonder if it's the throw-out bearing?
I had my M-20 rebuilt locally (very few miles since) and I have a noise coming from the front of the tranny. This sounds loud enough to hear at idle even with a loud exhaust. Goes away when I press in the clutch. A friend suggested the input shaft was perhaps not aligned or the bearings were failing? Also, I have small leaks from shifter seals on the side plate as well as at rear seal (can't see front seal but it looks like a bit of a leak up front also)!!
This was not a cheapo rebuild and the guy does a lot of race trannys (mostly Fords though !!).
I should have and now will send it off to "4 Speeds by Darryl" for a proper rebuild. I don't know if your noise is that serious or not. You could call Darryl and describe the noise and he could perhaps give an opinion. He's busy, but still willing to talk most of the time.
Good Luck! Just remember, when it comes to 'Vette repairs sometimes it takes one or more trys to get it right! (and extra $$$$).
Regards,Mark :flag :chevy
I had my M-20 rebuilt locally (very few miles since) and I have a noise coming from the front of the tranny. This sounds loud enough to hear at idle even with a loud exhaust. Goes away when I press in the clutch. A friend suggested the input shaft was perhaps not aligned or the bearings were failing? Also, I have small leaks from shifter seals on the side plate as well as at rear seal (can't see front seal but it looks like a bit of a leak up front also)!!
This was not a cheapo rebuild and the guy does a lot of race trannys (mostly Fords though !!).
I should have and now will send it off to "4 Speeds by Darryl" for a proper rebuild. I don't know if your noise is that serious or not. You could call Darryl and describe the noise and he could perhaps give an opinion. He's busy, but still willing to talk most of the time.
Good Luck! Just remember, when it comes to 'Vette repairs sometimes it takes one or more trys to get it right! (and extra $$$$).
Regards,Mark :flag :chevy
Burning Brakes
Joined: Aug 2000
Posts: 1,211
Likes: 6
Re: M21 gearbox whine (oger)
Yes Oger, it's a noticible "turning of the gears" while engine is running and in neutral. I put it on a lift with engine running in search of exhaust leaks and thats when I noticed it. I can now hear it while sitting inside the car if I listen closely. Car shifts fine otherwise and leaks are minimal but this can't be normal. Thanks. Mark
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
Re: M21 gearbox whine (marky mark)
Mark,
Mine wasn't a cheapo rebuild either. And I also have minor leaks as you describe. It is not the throwout bearing because that is not loaded when clutch pedal is out.
I suspect input bearing or cluster shaft bearings.
Many thanks,
Joe - Melbourne Australia
Mine wasn't a cheapo rebuild either. And I also have minor leaks as you describe. It is not the throwout bearing because that is not loaded when clutch pedal is out.
I suspect input bearing or cluster shaft bearings.
Many thanks,
Joe - Melbourne Australia
Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
Re: M21 gearbox whine (oger)
Thanks Oger,
I'll check with the gearbox rebuilder on the longer roller bearings and where they were fitted. I plan to take it back to him so he can hear the whine.
I just hate the work involved in getting that gearbox in and out.....
It is a Corvette after all.
Joe
I'll check with the gearbox rebuilder on the longer roller bearings and where they were fitted. I plan to take it back to him so he can hear the whine.
I just hate the work involved in getting that gearbox in and out.....
It is a Corvette after all.
Joe
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Thread Starter
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
Re: M21 gearbox whine (marky mark)
Mark,
I'm told a bit of gearbox "whirring" and slight knocking at idle is very common and normal. Bigger cams can create an uneven idle which causes the cluster gear to rattle and bounce.
The problem goes away when you put the clutch in because the gears stop turning.
One way to check this out is to ease the gearshift towards first gear gently from neutral without depressing the clutch. Just put a little pressure on the synchros, don't try to fully engage first. The slight load on the synchros will take up any backlash and the noise will stop if it is caused by the problem above.
Doesn't sound like you have a problem, though I'm no expert. Hope this helps.
Joe
I'm told a bit of gearbox "whirring" and slight knocking at idle is very common and normal. Bigger cams can create an uneven idle which causes the cluster gear to rattle and bounce.
The problem goes away when you put the clutch in because the gears stop turning.
One way to check this out is to ease the gearshift towards first gear gently from neutral without depressing the clutch. Just put a little pressure on the synchros, don't try to fully engage first. The slight load on the synchros will take up any backlash and the noise will stop if it is caused by the problem above.
Doesn't sound like you have a problem, though I'm no expert. Hope this helps.
Joe
Race Director
Joined: Aug 1999
Posts: 18,126
Likes: 174
From: WI
Re: M21 gearbox whine (marky mark)
marky mark,
"Just remember, when it comes to 'Vette repairs sometimes it takes one or more trys to get it right! (and extra $$$$)."
Why would it take more than "one try" to get a simple M-20 trans rebuilt correctly?? The M-20 you have is the same as every other M-20, and there are zillions of them out there in all kinds of GM cars. If the person doing the job "knows what he is doing" it`s no problem. Assuming all you need is a "rebuild kit" or new "brass" when your have a bad gear, that`s the real problem. ...redvetracr
"Just remember, when it comes to 'Vette repairs sometimes it takes one or more trys to get it right! (and extra $$$$)."
Why would it take more than "one try" to get a simple M-20 trans rebuilt correctly?? The M-20 you have is the same as every other M-20, and there are zillions of them out there in all kinds of GM cars. If the person doing the job "knows what he is doing" it`s no problem. Assuming all you need is a "rebuild kit" or new "brass" when your have a bad gear, that`s the real problem. ...redvetracr
Burning Brakes
Joined: Aug 2000
Posts: 1,211
Likes: 6
Re: M21 gearbox whine (jyounane)
Joe, thanks for the tip. I'll give it a try. It (the noise)does seem more obvious at low idle...Hmmm???
Red, You would think once would be enough to do a re-build. But, given my leaks I described and the noises (whether normal I'm unsure about) I'm given to doubt the rebuilders performance on this particular re-build. He tells me I have an M-21, not an M-20. I point out to him the "A" after the serial #'s but he insists he had to order M-21 parts due to the input shaft or some other shaft, I forget which (this was a year ago). At that point I lost confidence in him, but the job was already done by then.
My point is that any mechanical procedure can be screwed up, even by highly experienced people.
How about this idea: Is it possible that the bellhousing alignment is off and causing the tranny/clutch to line up wrong? I'm going to post that 'cause I don't understand.
Thanks!!! Mark :chevy
[Modified by marky mark, 11:04 PM 2/24/2002]
Red, You would think once would be enough to do a re-build. But, given my leaks I described and the noises (whether normal I'm unsure about) I'm given to doubt the rebuilders performance on this particular re-build. He tells me I have an M-21, not an M-20. I point out to him the "A" after the serial #'s but he insists he had to order M-21 parts due to the input shaft or some other shaft, I forget which (this was a year ago). At that point I lost confidence in him, but the job was already done by then.
My point is that any mechanical procedure can be screwed up, even by highly experienced people.
How about this idea: Is it possible that the bellhousing alignment is off and causing the tranny/clutch to line up wrong? I'm going to post that 'cause I don't understand.
Thanks!!! Mark :chevy
[Modified by marky mark, 11:04 PM 2/24/2002]
Race Director
Joined: Aug 1999
Posts: 18,126
Likes: 174
From: WI
Re: M21 gearbox whine (marky mark)
Marky mark,
"Anything" is possible including a streched case that needs to be rebushed. Tell me how many grooves on your input shaft?? Also tell me stock bell housing or scattershield? You are right that everyone is capable of making a mistake but it`s the "novice" rebuilder that misses the bad parts and has to "re-do" his trans because he does not know what to look for, I am not saying that your guy is a novice but someone who has to re-do a trans more than once is. ...redvetracr
[Modified by redvetracr, 6:49 AM 2/25/2002]
"Anything" is possible including a streched case that needs to be rebushed. Tell me how many grooves on your input shaft?? Also tell me stock bell housing or scattershield? You are right that everyone is capable of making a mistake but it`s the "novice" rebuilder that misses the bad parts and has to "re-do" his trans because he does not know what to look for, I am not saying that your guy is a novice but someone who has to re-do a trans more than once is. ...redvetracr
[Modified by redvetracr, 6:49 AM 2/25/2002]
Burning Brakes
Joined: Aug 2000
Posts: 1,211
Likes: 6
Re: M21 gearbox whine (redvetracr)
Joe, you are right!
I tried what you said about pushing the gear lever towards first without pushing in the clutch and the noise goes away. I guess it takes the "slop" out. Also, if I engage the clutch the noise also disappears. Thanks for the tip pal!
I still have the leaky seals issue but that may be something I can tolerate. Maybe the re-builder didn't do a bad job after all!!
Thanks And good luck with your tranny!
Mark :flag :chevy
I tried what you said about pushing the gear lever towards first without pushing in the clutch and the noise goes away. I guess it takes the "slop" out. Also, if I engage the clutch the noise also disappears. Thanks for the tip pal!
I still have the leaky seals issue but that may be something I can tolerate. Maybe the re-builder didn't do a bad job after all!!
Thanks And good luck with your tranny!
Mark :flag :chevy
