gearbox noise when clutch released at idle

justinbaldwin · 01-31-2008, 04:55 AM

Hi,
i've been noticing for a while now a new noise, (perhaps it was there before but i never noticed it!)
when sitting at idle, if i push the clutch in, all i hear is a nice clean engine sound, however, when i release the clutch, there is a slight whirring noise, it's not bad, but it's definitely there. just wondering if this is the first sign of anything starting to wear, and what that might be?

many thanks in advance as always.

jb

yelcab1 · 01-31-2008, 07:20 AM

Throw out bearing

justinbaldwin · 01-31-2008, 07:35 AM

thanks,
i've done a quick search through the Throw out bearing threads, but there seem to be two schools of throught:
1. they all make that noise and it isn't a problem.
2. this is wrong and it needs fixing

so my next question is: which is it, and if it the latter, is it something that will just get slowly progressively worse, or something that will almost certainly go BANG!

many thanks as always
j

DaddyGlenn · DaddyGlenn's Garage

Although it is likely the TO bearing, I would try to isolate it a bit more. if you crawl under the car while it is running

with the wheels appropriately blocked, silly. Can you tell where the sound is coming from? If it is the transmission at the end that attaches to the engine the I would suspect the TO bearing, if elsewhere then not.

Another part that moves at idle with the clutch out is the transmission main bearing. Which could make sound if failing.

It probably is the TO but I'd dig a little deeper to be sure.

Assuming it is the TO, they are pretty easy to change.... once you get past that remove the engine and transmission step.

It's the "while your in there" stuff that will kill you.

No matter what it is, it will probably get louder as it gets worse.

bbarrington · 01-31-2008, 05:58 PM

Quote:

Originally Posted by justinbaldwin

Hi,
i've been noticing for a while now a new noise, (perhaps it was there before but i never noticed it!)
when sitting at idle, if i push the clutch in, all i hear is a nice clean engine sound, however, when i release the clutch, there is a slight whirring noise, it's not bad, but it's definitely there. just wondering if this is the first sign of anything starting to wear, and what that might be?

many thanks in advance as always.

jb

Interesting - I've got the same issue (posted 1-28). I suspected it to be the TO bearing, but responses did not seem to reinforce that (as the responses to your post do).

If you gather any more definitive info, I would be interested to know. BTW - what year is your car?

Thanks,

Bill

john walker's workshop · 01-31-2008, 06:30 PM

t/o bearings don't tend to make noise when they are not loaded. the trans mainshaft will be spinning without load also and in turn, rotating the free wheeling gears on the pinion shaft. some rattle would be normal, as long as it was fairly quiet. if it was a 901 trans, and the noise was pretty obvious, i would suggest a mainshaft 4 point ball bearing problem, but 915s don't tend to have that problem.

Ole Petter · 02-01-2008, 12:26 AM

Hi, I had the same issue on a Turbo'ed Volvo...

I had the clutch and bearings renewed, but to no avail. As stated here the bearing rattles when the clutch is not engaged, so that is not the problem.

I asked a mechanic who renovates 915 boxes, and he thought the noise "not dangerous" if it didn't worsen, which it didn't... He stated it would be just about impossible to locate, and probably just was "something" that didn't have "much pressure" on it. In fact there was no noise when the cluch was engaged or if the loud pedal was used "in gear".

I was told to just "drive"...

He had some theory that even afflicted heavy diesel-trucks, that the shere forces on the box made the internals "move" a little, which not uncommonly gave some rattles. I don't know if this is plausible, but he may be right that it could be hard to rectify?

Excuse my fumbly english!

Greetings Ole

dshepp806 · dshepp806's Garage

JW...expound, a bit, on the G50/915 differences (as related to noises) (and I'm not talking about shifter-related rattles)..wouldn't the concerns (or should I say "points") about TOB and tranny bearings be the same, essentially? (i.e.,: clutch OUT noises=NOT TOB, clutch IN noises=(probably) TOB, etc..)

Thanks,..and I do hope you're doing well these days!!! I'm sure all "issued walkers" have been modified for shop use!!!!!!!!!!!!!!!

Best!

dshepp806 · dshepp806's Garage

Ole's post seems to confirm what JW has said ALL ALONG: they (normally) "rattle"(NOT gearbox or shifter rattle,..but "something else"..).....even after remedied issues with tranny bearings AND TOB,..WALA!!! still there!!!?

then the P-wrench states (instructs) to drive the damned thing......................as is,...no worries....

Mine (as stated many times before, a G50) does have a bit of noise w/ clutch OUT and complete dead silence w/ clutch in,..shifts like a dream,.....perfect!

Would tranny fluid be a contributor to this noise phenomena? Or would this be more shifter-related (vibrating/unused gears)? Has anyone here seen any differences by simply changing out the fluid? Just curious....I would have to assume that it's NOT related.

Best to all,

red-beard · red-beard's Garage

Quote:

Originally Posted by john walker's workshop

t/o bearings don't tend to make noise when they are not loaded. the trans mainshaft will be spinning without load also and in turn, rotating the free wheeling gears on the pinion shaft. some rattle would be normal, as long as it was fairly quiet. if it was a 901 trans, and the noise was pretty obvious, i would suggest a mainshaft 4 point ball bearing problem, but 915s don't tend to have that problem.

A lot of the trannies I pulled apart had this bearing bad, with the brass cage shattered. That being said, it could be the TO bearing and that is a lot easier to check.

justinbaldwin · 02-01-2008, 02:08 PM

my tranny has recently been treated to a slap up meal of swepco, so it's not a fluid issue. Actually, i've known about this noise for a while and it's really quite quiet and hasn't got any worse, but you know how it is, once you've heard it, it sounds louder, and fear worms its way into the back of your mind. so i just thought i would check with the big wide world to make sure i wasn't missing anything.

next time i have the car up i'll try and isolate it a bit more methodically, and if necessary revitalise this thread.
many thanks as always to all contributors.

j

myfast911 · 02-01-2008, 02:13 PM

do you have a regular flywheel (steel) or a lighten one(alum).if you have the latter,you may have spun it.

justinbaldwin · 02-01-2008, 02:53 PM

I have no idea which i have, but suspect bog-standard steel.

rgofast · rgofast's Garage

I have a custom 901 transmission with all of the goodies. Custom ratios, CA motorsports billet plate, retainer, side cover, wave track diff, etc. I have a slight brushing noise when the engine is at idle and in neutral with the clutch out. The free play adjustment is correct. When I push the clutch in the noise goes away. Transmission has about 700 miles on it since built. Does this sound like the main shaft bearing?

T77911S · 03-30-2017, 10:01 AM

I had a rattle on my 88 325is like you have.
found out on trip down to florida that there was NO oil in the tranny.
I just bought the car ($800) just a few months before.

I thought TO bearing also.
I have a LOT of respect for what JW says but sometimes I have to see things along with being told. me? I would drive it but plan on an engine pull to inspect the TO bearing. no disrespect, sometimes I just have to see for myself, that's how I learn.
I would also check the oil level.

BTW, that was an incredible tranny in that car. drove a few hundred miles with no 5ht gear, tranny making noise.
THEN drove it another 4 months missing 5th and maybe another gear along with making one hell of a noise in 1st and 2nd.
when I pulled it out there was NO front bearing. MAYBE 2 balls in there. the others were gone.
and NO oil.

cudabnu · cudabnu's Garage

Any follow-ups? I also have a new rebuilt 915 (new billet plate, bearings, wavetrac side cover etc.) with the same issue: at idle makes some noise, clutch in, no noise. It's behind a 3.6 with all new clutch components.

uwanna · 07-20-2017, 11:48 AM

Quote:

Originally Posted by cudabnu

Any follow-ups? I also have a new rebuilt 915 (new billet plate, bearings, wavetrac side cover etc.) with the same issue: at idle makes some noise, clutch in, no noise. It's behind a 3.6 with all new clutch components.

Same noise here! I also have a 964 3.6 in my '80SC. When I put in the 3.6 I also
installed a brand new out of the box 915/70 transaxle. It now has appox 40K miles on it
and at idle in neutral it sounds like some rocks rumbling around in the tranny. It disappears when clutch is pushed in. If I take off the shift coupler cover plate it seems the noise is coming from the "nose cone" end of the tranny where the 5th gear and reverse gear stuff is. So I don't think it has anything to do with TO bearing or clutch
stuff.
I think I concur with John Walker that with the the driven shaft running and all the
pinion shaft gears whirring around it's going to make some noise.
That said, this trans has been flawless since new and shifts like a dream.
So, it may have bothered me for a while, but now I just ignore it.

hillsprint · 04-30-2023, 09:34 AM

I know this is an old thread, but I have a similar issue at low idle speeds (eg 800 or less rpm). The noise disappears when the clutch is disengaged and then also if idling and you move the gear lever a little in the 3rd 4th plane where I assume you are starting to engage the synchros ( with the clutch still engaged). However if the idle is raised to 1100 rpm the noise disappears. I have use a mechanic’s stethoscope and the sound is coming from the area of the 1st/2nd gears and the case bearing. This beating was replaced about 15 k miles ago and looks fine, they are in metal sleeves in the 915 alu case due to some ovality that was found at that time. The other 4 main bearings at the diff end of the case were replaced a year ago.