So, I've had my '53 3/4 ton for 24 years or so now, and been using it as a DD most of that time. Since '04 I'm running a stock 216 that was a free gift from a nice gent back in Colorado who was going the SBC route. Well, the 216 was finally showing its age--low compression, almost no power, leaking lots of oil and coolant... so I decide it's time to swap in the sweet-looking 235 I picked up at a local auction for $90. I had the 235 up on blocks, got it all cleaned and painted nice, put in the flywheel from the 216 and a brand new clutch, and finally hoist it into place on the truck.
I'm itching to get everything hooked up to see how she runs. Fiddle with the timing for a few hours (should have realized the timing mark on the flywheel would be useless, as I put my original 216 flywheel on the '53 Powerglide hi-pressure 235), but finally got her to purr! So, let me slide the tranny back in place and get everything else buttoned up. Or so I thought; I've got the SM 420 4 speed up on blocks at the correct height under the truck, ready to just slide back into place. It takes some wiggling of course to get the splines into the clutch disc and then the front of the input shaft into the pilot bushing, but she finally snugs up.
And then the HORROR strikes me: the bellhousing on the new 235 does not align with the bolt pattern on my '53 SM 420!!! And here I was thinking all 1950s GM manual transmission bolt patterns were the same! The darnedest thing about it is it's only off by a little bit, probably less than an inch, so it's not really noticeable on just a casual visual inspection. I actually did measure the width of the bellhousing at the rear engine mount points, to be sure the old mounts would work, but I never even thought about checking that transmission bolt pattern!
Argggh, now I have to yank the whole engine back out, set it down on blocks, pull the clutch and flywheel, pull the bellhousing, install the 216's bellhousing on the 235, put the flywheel and clutch back in, and drop it back into place. I think I just added 3 or 4 hours to an already interminable project! Oh well: lesson learned: CHECK THE BOLT PATTERN!
Which bolt holes aren't lining up- - - -top or bottom? I've never seen a car/truck trans that wouldn't swap, unless it was a pre-1953 car bellhousing. The 1954-up cars and trucks, 3 and 4 speeds, are supposed to have the same bolt pattern. The only difference is in the transmissions- - -trucks have threaded bolt holes at the bottom while car transmissions have threaded holes in the bell housing and the trans bolts in from the back with 4 bolts. You might be able to drill the threads out of the car bellhousing on the bottom and not have to swap. Jerry
The murder victim was drowned in a bathtub full of Rice Krispies and milk. The coroner blamed the crime on a cereal killer!
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
I had the same problem when I made the same swap in my 1952 3100 with a SM 420. I was trying to use the bell housing that came with the 235 I purchased. Not sure I correctly remember the details but I think I determined the bell housing was originally for a much earlier truck. Fortunately I was installing the engine and trans as a unit in a bare frame.
I seem to remember playing this game when I put an SM 420 into my 46 Panel truck. One of your bell housings is probably for the original non synchro 4 speed. When you switch everything around to get the SM 420 to match the bell housing, you may need to check that the starter and flywheel work together and that the clutch and brake pedal assembly still bolt up to the right places. This may not be an issue for you, but I had to fight that battle with a modified bell housing. Think it was something between 46 and 47 body styles.
Mike, I got everything back together. I just put my original 216 bellhousing on the 235. I do happen to have an older 4 speed (pre-SM420, don't recall the model # off the top of my head) laying around, so I'll check for curiosity's sake to see if it matches up to that bellhousing.
The older 4 speed, the one with the lever for reverse, doesn't match up with the SM 420 bolt pattern. But the old bell housing will will bolt to a 235. So the front is compatible but the back isn't. I am not sure if there was another 4-speed between the reverse lock out model and an SM 420, I don't think so but I am not too familiar with the transmission development process.
Right you are--I held up my earlier 40's 4-speed (the one with the lock-out reverse as you noted) and yep, it's a match for the bellhousing I initially had on the 235. The p.o. of this engine must have had it in an earlier truck with that 4 speed. From what I've read, that trans went up to '47, and then the SM 420 came out in '48, if I remember correctly.