clutch diameter

[awg]

I have recently purchased some stock from a vendor who has some
left over parts from his fathers CCKW.

He advertised a complete clutch,
but on inquiry he advised it was 10 &3/4 inch diameter.

I advised him the GMC clutch is 11 &1/2 inch diameter, and that the clutch
he has is likeley a Chevrolet, and that it would NOT be suitable for a GMC.

I advised him i could double check this, and he asked me to do so
( another customer stated that it CAN be used in a GMC)

regards tony

[John V Cliche]

Hi Tony
From memory I thought the clutch disc in my Chevy was 11 inches but it may have been 10 3/4 inches.
As you know the smaller the dia from orig. the less surface area for the pressure plate to clamp down on ,therfore, the quicker the wear or slippage.
But if the splines are the same and the hub design similar then it should fit/work but it may have a shorter life span.
So the info you have gotten although somewhat different may indeed be correct
Hope this helps
John

[dr deuce]

The 10.75" Chevy clutch will not fit the GMC without a custom flywheel.

The GMC clutch is an 11.5" unit that has the plate inside the flywheel. In other words, the flywheel is not flat like a normal flywheel. There is the rub with a CCKW clutch. There is nothing to replace it these days.

A 10.75" Chevy clutch would work fine if you could mount it. You cannot

To complicate matters, the WW2 GMC 270 engine has a 4 bolt crank/flywheel. The 1950's GMC 270's have a 6 bolt crank/flywheel and more importantly, a flat flywheel for the clutch to mount to.

My 50's GMC 302 engines have a 50's 270 flywheel (the original 302 flywheel is too big in diameter to fit in the bellhousing) and a 1974 Chevrolet Corvette clutch of 11 inches. It all bolts together like it was made to! There is actually more room in the stock bellhousing with this set up than on the original with the recessed clutch.

[John V Cliche]

Sorry Tony
I misread your post.
I understood your question as using A Chevy clutch DISC with a CCKW pressure plate.
I have to agree with the good Doctor on the uniqueness of the CCKW sys. and the inability to use the Chevy pressure plate.
Hope this helps
John

[awg]

Hey Doc,
your excellent answer just made me think, if the flywheel
is the problem, is there any reason why a custom flywheel cannot be
made and the original ring gear fitted?

My knowledge in this area is a little bit slim,
however, about 7 years ago, I fitted a 5 speed Toyota Supra gearbox to a automatic V12 Jaguar, (I still have it!)
and that is what was done. I distincltly remember drilling and tapping
the blank flywheel to recieve the ring gear.
The cost was only $200-300.

It may be that it cant be done, I dont know how the GMC flywheel/ ring gear are mated, but i think the GMC flywheels and
ring-gears come as seperate items?

There is an engineering company over here that specialises in mating
differnt boxes to various motors, they use the 11" GM clutch a lot, also
the clutch out of Toyota Dyna small trucks.

I can still get original parts, and that would probably prefer,
however, as yourself and others have alluded to, the GMC clutch
is not so reliable with the diaphram spring.

It would be good if an alternative was available, especially in the future,
or where parts are less available...you could even soup your CCKW up with a custom, lightened aluminium flywheel!

The other consideration is the method of actuation, of course.

regards tony

[dr deuce]

If you could get a flywheel made like a 50's 270 one but with 4 bolts to the crank, you could drill it for the Corvette clutch and you would be all set. I have tried to find a company that would do this for a reasonable $$ but have not had success.

To me, this is the long term solution to the "GMC clutch"

[awg]

I will make enquiries. My Jag flywheel was machined steel, made especially for the Supra box/V12 jag conversion.
( the V12 never had an original 5 speed box). The person that supplied it had them made up.

As the cost was very reasonable, I can only assume that the process was
relatively straightforward. Maybe there are listers who have sufficient
engineering/machining knowledge to comment on this

There are several companies locally and overseas that advertise aluminium flywheels, for jags (and other vehicles),
once again the cost is not too high.

As I recall, the ring gear must have been recessed, to allow the flywheel centre to be drilled and tapped
(mine was an auto ring gear, so only had a sheetmetal centre to attach to the torque convertor)

If the ring gear is shrunk on, or press fitted and has no recess, that would
complicate the process

[dr deuce]

The 10.75" Chevy clutch disk "Might" work in a CCKW. The spline is the same. I just wonder what effect the smaller sidk would have on the pressure plate with "that spring" that is the source of the problems.

[John V Cliche]

Hi Tony
I just checked on Rex Ward's web site and he has all the clutch related parts avail. I know he is 1/2 a world away from you but machining costs may outweigh shipping costs.
Have you also checked with Ross?

Rex's web site www.dukw.freeserve.co.uk
Hope this helps
John

[awg]

Hi John & all
I"m fairly sure Ross has the correct parts, my question
arose mainly because I got the chance to buy the parts cheaply, as
spares for the future, a good thing to have consumables such as clutches on hand. I was able to buy a Zenith carb and governor off the owner of the 10.75 clutch, (to replace my Carter) also an exhaust manifold

I wanted the seller to have the correct info also, for his benefit as well as any future CCKW owner.

The machined flywheel musings only came into my head when i read Doc"s answer and remembered what i did with the jag flywheel