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I have a cracked bell-housing in my 56. I found a used bell-housing at the local junkyard, the owner said it was off a 56. It is dirty, but looks sound, and just needs cleaning up the thread for the bolts. I waited until I could pull mine out before getting my hopes up.

Here they are side by side. In both pics, my (cleaned up exterior) original is on the left, the junkyard one is on the right. Bolt holes seem to line up correctly:





Couple pics of the casting numbers. Mine:



And the junkyard dog:




So I lay the two down together, hoping the clutch pivot stud for the clutch fork matches. Uh oh, not a match. Mine screws in from the outside with a 3/8" allen wrench, the junkyard dog screws in from the inside with a 3/4" wrench, both have different thread sizes, so swapping the studs won't work. Both have slightly different profiles to the rounded cap of the stud:

Again, mine on the left, the junkyard dog on the right:



Both of these studs stick up from the machined surface of the bell housing about 9/10ths of an inch (.088, but who's counting LOL)


So, can I use the junkyard bell-housing with my original 56 clutch fork? Since parts guys nowadays can't find anything unless you give them a part number pedigree, if I need to order a new stud for the replacement junkyard bell housing, what do I ask for???? Such as, "I need a clutch pivot stud for a (fill in the blank)".

Did I miss anything important when I compared the two side by side?
 

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No,
I think you covered everything, and I believe the housings are interchangeable. Even bolts up to the horns on the frame and the depth of the pivot for the cluth rod would have been my only concern, but I'm thinking it will work....you'll just have to adjust the length of the clutch rod to match the throw out bearing...:shakehands::anim_25:
 

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Personally, I think you are fretting over nothing, the new bell housing will work fine as is.
 

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The bellhousings should be interchangeable, except for below.

Some truck bellhousings look very similar except the big pilot hole for the trans is bigger, and there is only 1 hole for the rear motor mount on each side. That type would not be interchangeable.

The only difference in the pivot balls is that you can remove the one that mounts from the outside to give you more room when R&R'ing the clutch without removing the bellhousing.

You can use any traditional GM clutch fork in any traditional GM bellhousing, provided the clutch linkage that connects to it is correct for it. 55-56 clutch forks are different from 57, but they all fit the bellhousing, trans, and throwout bearing. How they connect to the linkage is what's different. 55-56 has a spherical nut on the end of the linkage rod, 57 has an eye. Later forks may have a different bend where the linkage exits the bellhousing. If that bend is wrong, the fork may hit the floorboard when the clutch pedal is depressed.
 

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As best as I can tell from the photos, both are casting number 3704922. One was cast in January '56 , one in March '56.

I say - use it.
 

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I thought I had remembered that there were differences between the 55-56 bell housing and the 57 bell housing, something about the clutch fork ball. And I thought I remembered a thread here about the 55-56 ball not being available in the aftermarket. So I went to the Ol' 55 East Coast Chevy catelogue. The ball that installs from the inside of the housing is catelogued as a 57 ball. I don't think it affects interchangeability, but you should probably double check that the 55-56 fork will seat properly on the 57 style ball. I don't know the answer to that question myself, in fact, the older I get, the more I am convenienced that I don't know anything at all, lol! Hopefully one of the fellas here will know.
 

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I am sorry, I got that backwards, the one that installs from the outside is the 57 ball.
 

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I think they made the bellhousings both ways in 56, as evidenced by the date codes on the examples.

The clutch fork works fine with both versions.
 

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The pivot ball that threads in from the engine side is a flat diaphram clutch type. All V8 55's had a flat diaphram the same as 6 cylinder cars. In 56 GM decided the clutch needed help and went to the Borg and Beck 3 finger coil spring clutch with the 4 barrel engines. Since the 3 finger clutch has a taller installed height it uses a shorter throwout bearing, and to facilitate service removal GM changed the pivot ball to one that is able to pulled back the fork from the clutch to allow it to be dropped out the bottom.
Bottom line is that all standard clutches in 55-57 came with the flat diaphram and the front mounted pivot. All 56 and 57 4 barrel and better engines use the adjustable pivot. GM saw they didn't need the front mounted pivot and changed over to the adjustable pivot on all bellhousings. an aside to casting numbers, the 55 and 56 used that 922 but also had an 002(I think) casting. I don't know what the difference is but I have owned them. Another thing to remember if hunting for a bellhousing is that the 55-56 used three threaded holes for mounting the starter but the 57 uses 2 threaded holes on the lower starter holes, usually studded in the middle, and the top hole is a through-hole for the bolt to be put through and threaded into the starter. There is a relief next to the hole to allow a socket to be put over the bolt bead. I had to make that relief and drill the threads out when I put a 56 bellhousing in my 57.
In the 60's I had 2 barrel 57 wagons and I always use 3 finger clutches so to ease the service on the clutches (when I tore the lining off the disc at the strip) I removed the stud and shortened the threads on the stud to allow me to wrench the stud out and drop it out to allow clearance to drop out the clutch. This may be helpful for anyone who had a later style diaphram such as the Centerforce, which is taller than the original flat diaphram. Good luck.
 

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Adding some other info on the bellhousings-
Beware when buying.Watch that the lower starter bolt hole is not missing!It is often removed when using with a later block with block mounted starters.
The truck bellhousings have fins radiating from the top trans mount holes upward to the top of the bellhousing.Tri-fives are smooth.The truck housing has no threads in the 2 lower trans mounting holes-Bolts go in from the inside of housing.The top bolts go in from the outside as the tri-fives.
Lots of these are sold at swapmeets as tri-five bellhousings,but won't work.
Mike.:):bowtieb:
 

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All 56 and 57 4 barrel and better engines use the adjustable pivot. GM saw they didn't need the front mounted pivot and changed over to the adjustable pivot on all bellhousings.
That pivot ball is NOT adjustable! If you thought you wanted to move it toward the trans, the head of pivot ball will not be flush or below with the transmission mounting surface, so the transmission won't slide in fully. And there's no way to lock an adjustment. So you just torque it down.

Now, Lakewood does sell an adjustable pivot ball that screws into the hole for the later V8 version. You should not be using this to adjust your clutch linkage. The reason they make this available is that the adjustment makes up for using their block plate, or for an intermediate motor plate sometimes seen on race cars.

Regardless of what you have, you need to have the furthest forward tip of the pivot ball 4.75" from the block. The stock pivot ball gets you that dimension when there's no extra plate.
 
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