Transmission Noise
Thread Starter
Instructor
Joined: Apr 2023
Posts: 103
Likes: 7
Transmission Noise
Hey All,
I dropped my 91 six speed at the shop today for an oil leak and some other issues. It’s been making a racket lately when slowing down. the noise is most pronounced when letting off the gas in 3rd or 4th gear and coming down to about 5mph/1500 rpm. It’s hard to describe the sound but it feels like an intense low frequency rumble at my feet. It only happens occasionally. Overall this transmission has been REALLY noisy during my ownership and I sort of chalked it up to it being old and straight cut.
The shop used to own this car and rebuilt the engine so I do trust them quite a bit. Currently they think it’s possibly the throw out bearing and possibly “something internal” to the transmission.
Any thoughts on what this could be / what i’m looking at here? I plan on fixing whatever the issue is. this car has brought me and my daughter a ton of joy this summer and I want to keep driving it. Thus far the car has been running strong and shifting well. Third gear isn’t as smooth as i’d like but there’s never any grinding.
I unfortunately have to sit all weekend with the anxiety about not knowing what’s going to happen to my car. So I was hoping for some idea from you guys.
I dropped my 91 six speed at the shop today for an oil leak and some other issues. It’s been making a racket lately when slowing down. the noise is most pronounced when letting off the gas in 3rd or 4th gear and coming down to about 5mph/1500 rpm. It’s hard to describe the sound but it feels like an intense low frequency rumble at my feet. It only happens occasionally. Overall this transmission has been REALLY noisy during my ownership and I sort of chalked it up to it being old and straight cut.
The shop used to own this car and rebuilt the engine so I do trust them quite a bit. Currently they think it’s possibly the throw out bearing and possibly “something internal” to the transmission.
Any thoughts on what this could be / what i’m looking at here? I plan on fixing whatever the issue is. this car has brought me and my daughter a ton of joy this summer and I want to keep driving it. Thus far the car has been running strong and shifting well. Third gear isn’t as smooth as i’d like but there’s never any grinding.
I unfortunately have to sit all weekend with the anxiety about not knowing what’s going to happen to my car. So I was hoping for some idea from you guys.
Team Owner
Joined: Sep 2003
Posts: 25,373
Likes: 2,734
Have you ever serviced the transmission (changed fluid)? I wouldn't let the shop remove the transmission speculating a throw out bearing. Check all of the u-joints first I'd think is a must. You haven't said that you've done a thing. Have you done anything service related to the car drive train since owning?
Thread Starter
Instructor
Joined: Apr 2023
Posts: 103
Likes: 7
Have you ever serviced the transmission (changed fluid)? I wouldn't let the shop remove the transmission speculating a throw out bearing. Check all of the u-joints first I'd think is a must. You haven't said that you've done a thing. Have you done anything service related to the car drive train since owning?
I did ask about changing the fluid before doing anything. They haven’t done any work yet to the car, just started diagnostics today. I have a newborn at home and a small garage so I’m time and space limited on what I can do on my own. (One promise of getting this car is it wouldn’t be a “project” like prior cars i’ve owned.
The car has had some recent work: under prior ownership It got a new block, refreshed heads, new clutch and a new exhaust system (probably 15000 miles ago). I’ve had the brakes and starter done and an oil change. I’ve put about 2500 miles on the car.
Team Owner
Joined: Sep 2003
Posts: 25,373
Likes: 2,734
Let them check the transmission fluid just to see if there's any, Tell them to remove the fill plug (to check fluid) before draining if they're going to service for you. Be careful of the fluid used to service it. Check the u-joints and drivetrain and think hard about having the transmission removed speculating a throw out bearing. Could it be a release bearing?
Thread Starter
Instructor
Joined: Apr 2023
Posts: 103
Likes: 7
Let them check the transmission fluid just to see if there's any, Tell them to remove the fill plug (to check fluid) before draining if they're going to service for you. Be careful of the fluid used to service it. Check the u-joints and drivetrain and think hard about having the transmission removed speculating a throw out bearing. Could it be a release bearing?
thanks!
Drifting
Joined: Jan 2021
Posts: 1,312
Likes: 383
From: Northern California
When you say "recent work" "new clutch", it makes me wonder if the reason for that was A/ the clutch had worn or was problematic somehow, and they B/ found that the dual-mass flywheel was bad, so they C/ changed the flywheel for a conventional type and used a different style/brand pressure plate and clutch disk. If they did that, and they changed the car over to a conventional flywheel and a different clutch type, it's possible that the noise/vibration from the transmission has been stronger because it doesn't have the OEM damping capabilities of the dual-mass flywheel.
That would also explain partly why you think the gearbox has been particularly noisy/clattery during your ownership of the car.
Ask the shop to remove the flywheel/clutch area inspection plate (stamped metal at the front of the bellhousing lower side) and take a photo / post here / assess what kind of flywheel/clutch combo you've got in there. Worth a shot.
That would also explain partly why you think the gearbox has been particularly noisy/clattery during your ownership of the car.
Ask the shop to remove the flywheel/clutch area inspection plate (stamped metal at the front of the bellhousing lower side) and take a photo / post here / assess what kind of flywheel/clutch combo you've got in there. Worth a shot.
Thread Starter
Instructor
Joined: Apr 2023
Posts: 103
Likes: 7
When you say "recent work" "new clutch", it makes me wonder if the reason for that was A/ the clutch had worn or was problematic somehow, and they B/ found that the dual-mass flywheel was bad, so they C/ changed the flywheel for a conventional type and used a different style/brand pressure plate and clutch disk. If they did that, and they changed the car over to a conventional flywheel and a different clutch type, it's possible that the noise/vibration from the transmission has been stronger because it doesn't have the OEM damping capabilities of the dual-mass flywheel.
That would also explain partly why you think the gearbox has been particularly noisy/clattery during your ownership of the car.
Ask the shop to remove the flywheel/clutch area inspection plate (stamped metal at the front of the bellhousing lower side) and take a photo / post here / assess what kind of flywheel/clutch combo you've got in there. Worth a shot.
That would also explain partly why you think the gearbox has been particularly noisy/clattery during your ownership of the car.
Ask the shop to remove the flywheel/clutch area inspection plate (stamped metal at the front of the bellhousing lower side) and take a photo / post here / assess what kind of flywheel/clutch combo you've got in there. Worth a shot.
Last edited by fastbanana; Jul 22, 2023 at 09:50 AM.
Thread Starter
Instructor
Joined: Apr 2023
Posts: 103
Likes: 7
So the shop called. The car needs a new clutch and TOB. They think the flywheel is to blame for some of the noise but they are having trouble sourcing the correct fly wheel, and given the cost of the clutch i’m going to just hang onto the current flywheel.
Also needs a new ball joint which makes sense with some of the road noise i’ve been getting.
They will also change out the transmission fluid.
Hopefully it’ll ride like a new car when i get it back.
Also needs a new ball joint which makes sense with some of the road noise i’ve been getting.
They will also change out the transmission fluid.
Hopefully it’ll ride like a new car when i get it back.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Thread Starter
Instructor
Joined: Apr 2023
Posts: 103
Likes: 7
They started working on the car on monday or early tuesday to replace the clutch and a ball joint.
What do you think an expected time for this job to be completed would be? They initially told me friday maybe monday, but then said later next week.
How long would a job like that take? seems like a 5 business days is a long time? Maybe I just don’t have a great idea on how these shops work. I plan on calling on Monday to check in.
What do you think an expected time for this job to be completed would be? They initially told me friday maybe monday, but then said later next week.
How long would a job like that take? seems like a 5 business days is a long time? Maybe I just don’t have a great idea on how these shops work. I plan on calling on Monday to check in.
Safety Car
Joined: Nov 2008
Posts: 3,715
Likes: 551
From: Seattle Washington
You need to find out what Flywheel and Clutch the shop put in it the last time they had it apart. If it is a one piece Flywheel its recommended to install a shim kit in the Transmission from ZF-Doc.com. These Transmissions are a very good but they are also very expensive to repair and very few can do them. I recommend you do your homework both on ZFdoc.com and here on the Forum 5 Days should be the least of your concerns.