A diaphragm clutch and a B&B clutch genrally have the same bolt pattern size for size.

I think most 4 speed GM cars of the 60s are going to have a raised finger diaphragm clutch. They will come in 10.4" and 11" sizes.

I can't promise you they will help but maybe.

 

LOT's OF GOOD INPUT,

AFTER THINKING ON THE TIME THAT A FEW OF US WERE WORKING ON ONE OF OUR STREET RODS. IT ACTUALLY WAS A COLLEGE FRIENDS AND WE WERE UPGRADING HIS 66 CHEVELLE TO AN -11- INCH DIAPHRAGM.

THE BELL HOUSING WAS ALUMINUM ON A SMALL BLOCK ORIGINAL RUNNING GEAR, OBVIOUSLY NOT A TRI-5 HOUSING. WE ENDED UP WITH A BIG BLOCK BELL HOUSING AND LATER CONVINCED HIM TO INSTALL A SCATTER SHIELD,,, GREATLY BASED ON HIS HEAVY FOOT.

RICK, THANKS FOR THE INPUT. ALWAYS GOOD READING.

 

I just checked my stash and came up with 2 different pivot balls for the Chevy bell housing. one is 1.800 in long overall and the other is 1.500. Check the length of your pivot. I will bet that you gramps used the shorter one so he could use the long brg with the B&B clutch. Now that you mentioned it I recall that the cast iron truck throwout fork used a different shaped ball and the fork has a retaining ring to secure it in place. The easiest solution to your problem may be the use of a bent finger pressure plate from a mid sixties performance car. Ask for a pressure plate from a 66 396 chevelle or Impala with a 11 in clutch, and use the long throwout bearing. This is probably not the correct way to do this, but since the long brg worked with the B&B setup should work now. Other option is try to find the correct pivot ball. Let us know what you find.
Tom
https://napaonline.com/Catalog/CatalogItemDetail.aspx?A=NCF1104049_0316531828&An=599001+101966+50012+2012020

 

First, the block mounting surface question. It's the machined surface on the back of the block where the bellhousing mounts. Or the front of the bellhousing.

Now that we've established that you have a truck bellhousing, that makes this whole deal different.

I do think that truck bellhousings were made that were deeper (not all though). Some truck bellhouings also had a bigger pilot hole for the front of the transmission. You may want to check that your bellhousing and trasmission match there before you proceed any furthe. I can't give you any other details such as dimensions and what truck had what.

Also I don't know of a "flat finger" B&B style pressure plate.

So I don't know what to tell you.

Oceangoer, a stock 55-57 b/h will clear most 11" clutches. If there's a clearance problem, the ends of the studs that hold the finger pivots are going to hit the clutch fork (B&B style clutch). An 11" diaphragm should clear nicely.

 

Rick/Belair - as usual, thanks for the prompt and thorough responses!

The current ballstud is:
http://www.classicpartsusa.com/prod...duct/1955_1959_Clutch_fork_pivot_ball_CTH-32_1955/1955_Truck_Parts_Clutch_Items

I searched for hours last night and couldn't find the longer one. I kept finding the longer version of the mushroom one. Something like this:

http://www.4speedconversions.com/3790556.html

But the round one, no luck. Belair - any thoughts?

I am positive the bellhousing and transmission match. Everything (bolt holes) lines up perfectly.

The "flat finger" I was referring to was the NAPA diaphragm clutch after it is torqued to spec. My eyes aren't trained well enough to see the difference between a bent and flat finger diaphragm clutch, I guess. (Edit - After seeing Belair's Napa link I definitely see the difference.)

I have no doubt this is a silly question, but what is the application for the raised-diaphragm clutch? Is it intended to be used as a direct replacement for a B&B (dimensionally, I mean). The kit you linked looks like it uses a small TOB rather than the traditional diaphragm long TOB so I would assume the answer is "yup."

 

The 11 in diaphragm pressure plate will clear a 57 bell housing I have one set up for my 57 project. I would think it would also work on a 55-56 bell also but I do not have any way to check as I only have a 57 bell. The 57 bell does still have the mounts on it. The original post stated that he was working on a 55 truck It may be that the pivot ball is different on a truck bell. If I get a chance I will check my parts stash as I think I have a couple of different length pivots. I seem to recall a buddy of mine having the same problem back in the day when he swapped a V8 in a 56 chevy pickup. After thinking about this for a while I agree with Rick_L all chevy bellhousings up to the 90's are the same depth. Otherwise we could not swap transmissions from one year to the next as easily as we do. I wonder if someone swapped in a shorter pivot some time in the past so they could use the long throwout bearing with the B&B clutch.
Tom

 

I AGREE WITH RICK, GET A DIAPHRAGM CLUTCH, YOU WILL BE HAPPY..

BTW RICK, NICE INFO ON THE BALL DISTANCE TO THE BLOCK !!

I AM CONFUSED, AND IT HAS BEEN A VERY LONG TIME SINCE I DEALT WITH THE OLDER BELL HOUSINGS.

AS I REMEMBER, YOUR BELL HOUSING APPEARS TO BE A PASSENGER BELL HOUSING AND IT DOES LOOK LIKE AN 11 INCH CLUTCH SETUP.

MY QUESTION IS THAT,, I WAS CERTAIN THAT 55-57 BELL HOUSINGS WERE NOT WIDE ENOUGH FOR 11 INCH FLYWHEELS.

AM I INCORRECT ?? AS YOU DID WRITE THAT THE BELL HOUSING IS A '57 DATE CODE.

ALSO, DID THE 57'S STILL HAVE BELL HOUSING HAVE REAR MOTOR MOUNTING ??

 

Every GM bellhousing for a car from 1955 through cars of the 90s should have a pivot ball for the clutch fork that is 4-3/4" away from the block mounting surface. That's measured from the tip of the ball nearest the block mounting surface to the block mounting surface.

There are different balls. Some mount differently, and some are for other bellhousings.

Not only that, all flywheels that are new and never surfaced should have the clutch mounting surface in the same place. Any variations in the flywheel are on the engine side. (I.e., less metal there for a light flywheel, and more metal there for a heavy one.)

The photo is definitely of a B&B style clutch.

What's confusing me is that every B&B I've ever used (and they were all aftermarket high performance units) used the shortest throwout bearing available.

But maybe they built something else I'm not aware of.

The other question I have is why do you want a B&B style clutch instead of a diaphragm?

If I were you I'd get a raised finger diaphragm clutch from a 60s performance car, a short throwout bearing, and live happily.

Are you sure you have a passenger car bellhousing?

 

Hey guys, thanks for the thorough responses! I never thought about it being the pivot ball. I completely agree that this is a possibility. I have never seen a B&B use a 1-7/8" TOB. I have no doubt that my grandpa (original owner) would make a simple swap like that. A couple ad-hoc mechanics I know said to "throw washers under the pivot ball," but I thought that was a terrible idea.

When you say: "should have a pivot ball for the clutch fork that is 4-3/4" away from the block mounting surface," can you define the block mounting service? Are you talking about the back of the block? The flywheel? The back of the pressure plate?

Can you give me an example of a good raised finger diaphragm clutch? I assumed the one Napa gave me was raised (it was raised until I tightened to 35ft-lb then it went flat). I would much rather have a diaphragm style than a B&B. I'm a bit of a novice mechanic (my grandpa left me this truck when he passed away and I want to fix her up and keep her in the family).

As per the bellhousing - what little information I have tells me it was a 55-59 casting truck bell-housing. I cannot 100% verify this, though. I believe the truck came with the 6-cyl and my grandpa took parts from the 8cyl version he found at a scrap yard (again, can't verify).

As per the pivot-ball - can someone provide me with a link as to the two separate sizes? From what I can see the short TOB is somewhere around 1.3" and the TOB that was being used with the B&B is 1-7/8." Is the longer pivot .55" longer than the shorter one? That seems like a lot. Another thing I noticed was that Napa was trying to sell me a more mushroom shaped pivot ball. The one currently on the bellhousing is spherical.

I have attached a copy of my clutch fork in case anyone is curious. It's the original cast iron.

Thoughts? Thanks for the help guys!

 

Is the clutch a 10 1/2 in or 11 in diameter? If it is 11 inch as your picture looks like it appears that the NAPA clutch is the low diaphragm style and it would use the long throwout bearing. I seem to recall that over the years GM used 2 different length pivots for the throwout fork. I am willing to bet that the bell housing has the short pivot installed that would allow the use of the long bearing with the B&B style pressure plate. I suggest that you try to get the longer pivot for the fork. Another option is to try a high diaphragm pressure plate. A popular GM 11 inch pressure plate is Part # CA5505. it is a 11 in high diaphragm. It was used in numerous trucks and high performance applications. NAPA also list the throwout fork pivots in their on line catalog.

 

There are two types of diaphragm clutches. The trucks used a low performance type witch used a longer type throughout bearing .The B&B clutch used a short throughout bearing as did the high performance diaphragm. you may just need to change to the long bearing. Don

 

The few times I've changed out clutches, it seems I've run into the same problem. I'm never able to get the same exact clutch assembly as I took out. My guess, is that if you have to use all of your adjustment to get it to work, and you have the long release bearing, then the pressure plate is not the correct one. Can you go back to the B&B style? Did they not have that style?

 

Yea, I know there is a height difference between the B&B PP and the Diaphragm style. I am of the assumption that the original owner tweaked the setup. I am not sure why he would have used a long throwout with the B&B.

As for Napa, no they did not have a B&B style kit. Does anyone here have any suggestions on a good B&B for this application? I think it is best I just switch back to B&B without having to go through the hassle of alignment issues with a Diaphragm style PP.

 

adjustment

If your fork pivot point is adjustable try moving it in a bit.