clutch

[Noel K.]

Okay,

Facts: 1965 roadster - 327/365 hp 4 speed muncie.

Since replacing the throw out bearing last fall without completely removing the transmission didn't make the noise go away(see below) - I've now pulled the complete assembly out from the flywheel back.

We've discovered:

the pilot bearing was very dry and probably "gaulding" a little when the clutch was depressed.

It appears the incorrect clutch/pressure plate and throw out bearing combination was installed. The pressure plate iwas the diaphram type (10.4") and the "taller" throw out bearing was used. I had very little, if any, clutch adjustment which was also a sypmtom of the incorrect parts I believe.

I ordered a complete new Borg and Beck clutch kit from NAPA - with what i believe is the correct 3 lever pressure plate, 10.4" clutch, bronze pilot bearing and 1 1/4" tall throw out bearing.

Would welcome any comments re: anything else i should be looking for. The transmision front spline has a little wear we hope to clean up with emery cloth. Initial attempts to remove the pilot bearing have proven unsuccessful - looking for suggestions re: removal.

At least I believe I have now defined the cause of the problem ( which presented itself as a noise and vibration felt in the shifter when the clutch was depressed)_

Thanks all in advance.

Noel Kendall

[Mike M.]

Re: clutch

to remove the pilot bearing, get a bearing puller with two or three fingers facing outboard. a slid hammer with similar outward facing fingers also works. you may have to chisel the bearing out but be careful not to damage the crankshaft. good luck, mike

[Jim T.]

Re: clutch

It has been addressed before on this board about the incorrect and incorrect installation of the throwout bearing. If you need a drawing it should be available in the archives.

[Joe L.]

Re: clutch

Noel-----

No 1963 or later Corvette ever originally used a Borg & Beck 3 finger style clutch. All 1963+ Corvette cluches were diaphragm type clutches. 1957-62 Corvettes were the only ones that originally used the 3 finger style clutches.

If you had the "long" clutch release bearing installed, that was the cause of all of your problems. That bearing was NEVER used for ANY 1957+ Corvette. It is often incorrectly supplied by parts countermen for Corvette applications.

[Mike McKown]

Re: clutch

Check the new pilot bushing you just purchased from NAPA. I bought one the other day and it wasn't bronze. It was some kind of iron with a bronze color. That may be what you had in there that was causing the noise. The man behind the counter said it would do no good to try another, all NAPA pilot beushings were of that material. This is second hand info. I don't know if that's a fact.

Run a tap in the pilot bushing and when it bottoms in the crank it will jack the bushing right on out. You can do the same with a large lag bolt. Run it in a little and reef it up and down a few times and the bushing should pop out.

I don't know why you couldn't use the Borg/Beck clutch with the proper throwout bearing in your car but like Joe says, your car came with the diaprahgm type.

[Bryan L.]

Re: clutch

I use the same method McFast uses. I think 5/8" is the correct size for the tap and use the coarse thread instead of fine. Use a 3/8" 8 point socket and run it in with a ratchet. It will push the old pilot bushing out in a heartbeat. I used the GM roller bearing version on my car. An old input shaft is an excellent way to get the new one back in without boogering it up.

BL

[Chris Shanahan]

Re: clutch

There are 2 types of diaphram clutchs. The older, original style had "flat" fingers that are low down and go about flat to the plate. Now there is another style diaphram clutch that has higher fingers that form a "cone" shape that sticks up farther. Both types take a different length throw out bearing.

[Noel K.]

Re: clutch

just to follow up - received the new clutch kit from NAPA. The pilot bushing was .030" oversized ( measured 1.094" O.D). After a bit more research and discussion with the NAPA dealer we found what was hoped to be the correct busing from the Balkamp supplier in Indianapolis. I asked them to order two (just in case) and when they came in, sure enought there was .006" difference in the two. Was able to use the bushing that measured 1.066" and now putting everying back together with hopefully better results than the last time.

By the way, sure would like to talk to the Corvette engineer that decided the crossmember should be welded in rather that bolted so that the transmission and bell housing have to come out and go back in at the same time !

Finishing up the assembly this evening. Am keeping my fingers crossed !

Thanks all for the comments and suggestions.

My suggestion - if you need a new pilot bushing, make sure you measure the crank and measure the replacement bearing being supplied in the clutch kit or as a separate part.

Noel

[Ken Edmunds]

Re: clutch

I have never seen a Borg and Beck clutch in an original midyear. Should be a diaphram type with a short throw out bearing.

[John H.]

Re: clutch

Noel -

1.094" is the correct design O.D. dimension for Chevrolet pilot bushings.

[Joe L.]

Re: clutch

Noel and John-----

Yes, that's correct. The GM #3752487 pilot bushing that was used on literally millions of Chevrolets in the period of 1955 through the early 90s was exactly 1.094" in OD. This is not only the spec dimension, but it's the dimension that I've determined empirically (i.e. measured) on several NOS GM #3752487 bushings. Some of the replacement bushings on the market are about 0.001-.002" bigger in OD than original. These may make for a tighter fit than the originals.

If you obtained a bushing that was 0.030" smaller in OD than the above-referenced, then you have a non-Chevrolet bushing. No Chevrolet bushing was ever of this OD. I cannot imagine why you would need such a bushing on any Chevrolet crankshaft.

[David W.]

Re: Pilot Bearing

Just a tip worth repeating that I learned on this board. I couldn't get the pilot bearing after trying all normal methods including a puller, tap, etc. The tip was to fill the bearing opening with as much wet paper towel as you can get in there. Then take the plastic dowel used for aligning the pressure plate, insert into the hole, and whack hard with a hammer. The bearing came flying out like you wouldn't believe. Water pressure (hydrostatic might be the term) is a powerful tool!

[Noel K.]

Re: Pilot Bearing

Arrrghhhh - it just never seems to stop. I now have the clutch and transmission reinstalled and the clutch will not engage and I'm out of "travel" on the adjustment rod. I've measured the dimensions of the z-bar, adjustment rod from under the dash, the rod from the z-bar to the clutch fork, etc. However, I have no reference re: what the correct dimensions are supposed to be. The mechanic helping me with this project has suggested it may even be an incorrect ball pivot stud in the bell housing that is incorrect.

Any resource or other suggestions about how to determine where i still have a problem.

Again, thanks in advance.

Noel Kendall

[Verne Frantz]

Re: Pilot Bearing

That's an old trick David, but the one I heard of 20 years ago said to fill the pilot with grease and do the same thing. Either way, it's hydraulics at work. It's the same principal that makes your power steering and your engine hoist work.
(not to mention your brakes!)

[Joe L.]

Re: Pilot Bearing

Noel-----

The problem has to relate to one of two things----either there has been some deficiency in assembly or there are incorrect components being used.

The most common error in assembly is the incorrect articulation of the release bearing and the fork. The fork and the end "tabs" of the attached u-shaped, flat spring MUST reside WITHIN the groove on the release bearing. The spring "tabs" MUST NOT reside outside the release bearing groove.

As far as a release bearing goes, the 1-1/4" long bearing IS the correct one for your application. Period. Several slightly different length release bearings, including the 1-1/4", were used on Corvettes over the late 1955-81 period. ALL have been replaced by the 1-1/4" bearing and the 1-1/4" bearing is the only one currently serviced by any manufacturer. The 1-1/4" bearing WILL work properly in any late 1955 thru 1981 Corvette. No matter what anyone else says. Period.

The clutch release fork used for 64-81 Corvettes is a bit difficult to describe. However, it uses a "slot-and-pin" design for attachment of the fork push rod. Most other Chevrolets (and 1963 Corvettes, too) use a "ball-and-socket" design. So, if you have the fork which uses the "slot-and-pin" design (i.e. the fork push rod has an eye on the end which passes through a slot on the end of the fork and is attached thereto by a clevis pin with cotter pin), then you likely have the correct fork.

The bellhousing-mounted fork ball stud is critical to the whole clutch release system. For Corvettes over the L55-81 period there have been 2 ball studs used. One is 1-3/8" long; the other is 1-1/2" long. 1965 may have used either the 1-3/8" stud or the 1-1/2" stud. No matter; the 1-3/8" stud was long ago discontinued and replaced by the 1-1/2" stud. As far as I know, no one currently manufactures a 1-3/8" stud, so the only way to get this length is to use an aftermarket adjustable ball stud. You don't need to, though. The 1-1/2" stud will work just fine. No matter what anyone says. Period. Any stud other than a 1-3/8" stud (if you happen to have one installed) or the 1-1/2" stud, WILL NOT WORK. No L-55 through 1981 Corvette EVER used a stud that was anything other than 1-3/8" or 1-1/2" and a stud of any other length will not work in any of them now. There WERE different length studs used on some other Chevrolets, though. These other studs were LONGER and will NOT work on a Corvette (regardless of what some parts store countermen might think).

The clutch fork pushrod for your application should be 10-9/16" overall length. It is GM #3844209.

I cannot describe the cross shaft to you. All 1963-81 Corvette clutch cross shafts appear very similar. The only difference is the angular relationship between the levers on either end. This difference is hard to measure since it is quite small between all the different cross shafts.

Your clutch pedal pushrod should be 18" overall length.