The Stovebolt Site Forums The Parking Lot '60-'66 Trucks 1970 4spd Manual into a 61?

Will a tranny from a 1970 GMC 3/4 ton 2wd 4spd fit the bellhousing hole in my 61 Chevy with a 235?I understand that at some point the OD of the bearing cover on GM manual trannys increased. I need something with a PTO opening.

The short answer is no. In 1968 they went from the SM420 to the SM435. There are two differences the OD on the bearing retainer is 5+ inches, and it also sits higher. The bellhousing can be opened up or I believe the bearing retainer can be turned down.

Larry

Thanks I have a lot of miles on my 4 spd and am looking for an affordable option that still allows me to use my PTO.Is it possible to swap retainers?I've heard of opening up the hole in the bellhousing as well.I live in a remote location and don't have access to a machine shop.

I haven't heard of anyone swapping retainers. The only other option I can think of is swapping the bell housing, but that won't work for you because of the hydraulic clutch. The only other thing would be to get another bell housing for the 61 and have it opened up. Then you could do a fit check before you tear it apart.. You might also look into rebuilding the 420. I've read it's not difficult, but that could lead to problems too if you haven't done one. There's a great group of stovebolters here to help, and I can check the Inliners International roster to see if there is anybody in your part of Canada.

Larry

I put a late 70's early 80's three speed in my 61 and had to replace the bearing retainer to a smaller one. Not sure if you can do that to a 4 spd.

the bearing retainer size has to do with the bellhousing hole, the larger opening and retainer are truck, the smaller retainer fits the car bellhouse .... it would be that way with a 4 speed, you'd need to have the truck bellhousing to fit it, a car one would have too small an opening

Bill

why not just rebearing your sm420. they are pretty tough old trans. a sm365 doesn't give you that much more. it has a little higher ratio in first, but is still quite low
ron

My original bell housing was cut with a torch by the former owner to replace the original 3 speed to make room for a 4speed
I bought a replacment bell housing on E-bay and not sure what it came out of.

I believe all the bell housings car or truck up to 1967 had the same size hole for the bearing retainer. I'm going by having swapped 3spd to SM420, and passenger car 4spd. In 1968 GM went to the SM465 and 435 in their trucks which have the larger bearing retainer. The 68-72 truck bell housing should be able to replace those in earlier trucks with the exception of the hyd clutch and 235 engine. If I'm wrong I'm sure I'll hear about it.8-)

Larry

283 eng also used the pass side clutch opening
ron

I dont believe there is a 235 bell houseing with the larger hole for the SM465. If it was a V-8 you could use the later bell houseing. I think rebuilding your trans will be the best route.

yes for a 283 you could use the later bellhousing.. but then you would lose the use of the hydraulic clutch setup.
ron

Oleschool,
Find a brigeport or a similiar device,center the hole and open it up to fit the larger retainer.I converted several years ago with no issues.Being from Canada the local farmer probobly has the equipment you need dont waste your money on another bellhousing .