[jchavis 1975]

Hi Guys, I have a 1975 Corvette with 4-speed Borg Warner Super T-10 Trans
Issue When I drive for a while (say about 30min or so ) when I stop at a light I can hear a noise from the car when I push in the clutch it seems to continue only a slightly different sound and even when I put in neutral and let off the clutch
Sounds like the tranny isn't disengaging completely (With clutch pushed or in neutral with clutch disengaged). Sounds like its scrapping like the surfaces are touching on each revolution when they shouldn't be (Like in Neutral or clutch disengaged)
Any help would be greatly appreciated
THANKS!!!

[T-bucket23]

Sounds like your throw out bearing may be going

[jchavis 1975]

Thanks Chet for the quick reply
I greatly appreciate your input

[cobalt327]

Usually when a TOB is going you will hear the rumbling kind of noise when the clutch is depressed just enough for the TOB to contact the pressure plate. When the clutch pedal is all the way out, there should be no contact between the TOB and the PP- unless the linkage is out of adjustment and/or the entire clutch assembly is worn. If adjusting the clutch doesn't help it's probably time for a clutch, etc. If that's the case, don't neglect to have the flywheel turned. A new clutch can still slip if it's not turned.

Another thing you should check is the pilot bearing in the back of the crankshaft. It's what the tranny input rides on.

[jchavis 1975]

Thanks for your help!!!

I am suppose to have a rebuilt tranny with new clutch etc.. but I am not so sure he looked at everything.
Thanks again for the help

[cobalt327]

Originally Posted by jchavis 1975

Thanks for your help!!!

I am suppose to have a rebuilt tranny with new clutch etc.. but I am not so sure he looked at everything.
Thanks again for the help

If it's been worked on recently, be sure to check for easy things first: rubbing dust cover, starter adjustment, that sort of thing.

[jchavis 1975]

Will do
It only seems to do it after about 30 to 45min of driving
The noise will start (Or that is when I notice the noise) when I stop at a light and seems like the more I use the clutch and change gears but of course that may only be my thinking

[AutoGear]

Probably not your issue; but make sure the TOB is seated properly in the fork.

A good litmus test is with the car AT REST, try to get the trans into - and out of - reverse nice and clean. If you can, the clutch is adj properly. This doesn't necessarily rule out the clutch but its a good indicator that the adjustment is proper. Do you have a Centerforce clutch with those little weights wired on? Sometimes those little wires can cause problems.

If none of the previously mentioned things in this thread solve your issue; check that pilot bushing and the pilot on the input gear (the smooth tip on the input shaft rides in that bushing or bearing that's in the back of your crank). If you have a needle bearing in there; get it out. If you have a bronze bushing in the crank, check it with a magnet. if the magnet sticks; get it out. Replace with a premium bronze bushing that DOES NOT stick to a magnet. We make them; but if you're not in the northeast, its more cost effective to drive to Napa and rummage through their box, checking the inside dia AND the outside dia with your favorite magnet.

Needle bearings are great if you want to futz around with a dial indicator, trying to dial the bellhousing register within .002. The bushing can take a small amount of misalignment and still work properly. Do NOT use grease on the pilot or the ID of the bushing.
If the tip of your input is discolored, scratched or pitted...it should probably be replaced, although in reality, a bushing shouldn't be bothered by this if the damaged area is very small and localized.

Since you'll be under the car anyway, drain the lube from the gearbox and inspect it. Refill with GL4 multi viscosity 90wt NON Synthetic. We like Sta-Lube's SL24229 (1qt bottle) from Napa
Sorry for the lengthy post

[lmsport]

Originally Posted by AutoGear

Probably not your issue; but make sure the TOB is seated properly in the fork.

A good litmus test is with the car AT REST, try to get the trans into - and out of - reverse nice and clean. If you can, the clutch is adj properly. This doesn't necessarily rule out the clutch but its a good indicator that the adjustment is proper. Do you have a Centerforce clutch with those little weights wired on? Sometimes those little wires can cause problems.

If none of the previously mentioned things in this thread solve your issue; check that pilot bushing and the pilot on the input gear (the smooth tip on the input shaft rides in that bushing or bearing that's in the back of your crank). If you have a needle bearing in there; get it out. If you have a bronze bushing in the crank, check it with a magnet. if the magnet sticks; get it out. Replace with a premium bronze bushing that DOES NOT stick to a magnet. We make them; but if you're not in the northeast, its more cost effective to drive to Napa and rummage through their box, checking the inside dia AND the outside dia with your favorite magnet.

Needle bearings are great if you want to futz around with a dial indicator, trying to dial the bellhousing register within .002. The bushing can take a small amount of misalignment and still work properly. Do NOT use grease on the pilot or the ID of the bushing.
If the tip of your input is discolored, scratched or pitted...it should probably be replaced, although in reality, a bushing shouldn't be bothered by this if the damaged area is very small and localized.

Since you'll be under the car anyway, drain the lube from the gearbox and inspect it. Refill with GL4 multi viscosity 90wt NON Synthetic. We like Sta-Lube's SL24229 (1qt bottle) from Napa
Sorry for the lengthy post

Hate to hijack, but why dont you like the roller bearing pilot? THey are the only thing that I have found to work in racing apps. I have seen some fall apart on high mileage street cars, though.

[AutoGear]

Heres the Auto Gear company answer:

Aftermarket needlebearings can be cheap. Not necessarily a problem, however as you alluded to, they can fall apart in high mileage situations. Also, the NB doesn't like ANY misalignment. Bellhousing alignment is critical for their long term survival. Several of our customers had their inputs torn up by an improperly installed NB. The needles were trying to skew, stopped rolling and started sliding. For a home mechanic, installing a bronze bushing is easier, one less thing to worry about. If the drivetrain alignment isnt spot on, the bushing will accept some misalignment.

A lot of the off the shelf bushings have too much iron in the sintered bronze. The large amount of iron can score the input, weld itself to the input and then tear up the crank, or weld itself to the input AND the crank. Hence the magnet check. We use genuine self lubricating Oilite bronze. But, some of our customers don't want to ship an $8 bushing across the country, so I usually have them look for the more expensive 'HD' or 'Premium' pilot bushing at the parts store, and check with the mag.

This of course doesn't apply for OEM ballbearing applications.

[T-bucket23]

Originally Posted by jchavis 1975

Thanks for your help!!!

I am suppose to have a rebuilt tranny with new clutch etc.. but I am not so sure he looked at everything.
Thanks again for the help

New clutch could equal cheapest clutch they could find. I have seen some pretty poor quality bearings in some of the cheap kits. I have actually changed a few clutches for a garage I work at that buys the cheapest kits, with them I usually will re-use the factory TOB.
never make the mistake of assuming new is good !!!!

[cobalt327]

A short page on pilot bearings is here.