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stickshift_or_walk · 11-11-2004, 12:23 AM

Bozracer,

Welcome to the board!

Your '70 should have a cast iron bellhousing, with a supporting crossmember that attaches to some ears on the side of the bellhousing. The 3spd hangs from the four bolts, and has no support under the transmission tailhousing. Factory 4-speeds came with the same configuration, just hanging from the bellhousing with no support. There will be a few issues to deal with.

First, your driveshaft will need to be lengthened, since the 4spd is shorter. Your 3spd has a slip yoke at the rear, and the 4spd likely has a solid (no-slip) u-joint trunion. If you're changing from a rear slip joint on the tranny to a non-slip mount, you'll need a slip joint at the center support, like this which is common in 3/4 & 1 ton trucks with 4spds:

Then you can find a longer front shaft that will mate to the u-joint on the rear of the 4spd, and swap the front half of the slip joint (the splined shaft, shown above) from your old front shaft to the replacement shaft. A competent machine or driveshaft shop can do this change for you. Balancing may or may not be needed, in my experience it usually isn't. Just remember, you need to have some slip in the driveshaft to handle the compression from suspension travel.

Second, the rear your bellhousing has two threaded holes at the top, and two open holes at the bottom. This is because the lower ears on the 3spd are threaded. The top bolts go in from the rear, and the lowers go in through the bottom front of the bellhousing. If your 4spd does not have threaded lower ears, you will need longer bolts and nuts for the inside of the bellhousing. Watch the length - things are pretty tight in there and you don't want anything hitting the flywheel or ring gear.

If you're looking at a GM donor, the '64 1-ton probably has a SM420 transmission, which has threaded lower ears. Another suitable transmission is the SM465, which came in later models. I used the SM465 in my '69.

One other thing to watch for is the size of the locating hole in the bellhousing vs. the front bearing retainer on the tranny. These sizes are listed on the above links, and easy to compare to your bellhousing.

Here is a good picture of various manual transmissions for comparison purposes.

Hope this helps. I've probably left something out, but someone will chime in and correct me or add on.

SSOW

11-11-2004, 12:23 AM	#2
stickshift_or_walk Left Foot Functioning Join Date: May 2004 Location: Duncan, OK Posts: 351	Bozracer, Welcome to the board! Your '70 should have a cast iron bellhousing, with a supporting crossmember that attaches to some ears on the side of the bellhousing. The 3spd hangs from the four bolts, and has no support under the transmission tailhousing. Factory 4-speeds came with the same configuration, just hanging from the bellhousing with no support. There will be a few issues to deal with. First, your driveshaft will need to be lengthened, since the 4spd is shorter. Your 3spd has a slip yoke at the rear, and the 4spd likely has a solid (no-slip) u-joint trunion. If you're changing from a rear slip joint on the tranny to a non-slip mount, you'll need a slip joint at the center support, like this which is common in 3/4 & 1 ton trucks with 4spds: Then you can find a longer front shaft that will mate to the u-joint on the rear of the 4spd, and swap the front half of the slip joint (the splined shaft, shown above) from your old front shaft to the replacement shaft. A competent machine or driveshaft shop can do this change for you. Balancing may or may not be needed, in my experience it usually isn't. Just remember, you need to have some slip in the driveshaft to handle the compression from suspension travel. Second, the rear your bellhousing has two threaded holes at the top, and two open holes at the bottom. This is because the lower ears on the 3spd are threaded. The top bolts go in from the rear, and the lowers go in through the bottom front of the bellhousing. If your 4spd does not have threaded lower ears, you will need longer bolts and nuts for the inside of the bellhousing. Watch the length - things are pretty tight in there and you don't want anything hitting the flywheel or ring gear. If you're looking at a GM donor, the '64 1-ton probably has a SM420 transmission, which has threaded lower ears. Another suitable transmission is the SM465, which came in later models. I used the SM465 in my '69. One other thing to watch for is the size of the locating hole in the bellhousing vs. the front bearing retainer on the tranny. These sizes are listed on the above links, and easy to compare to your bellhousing. Here is a good picture of various manual transmissions for comparison purposes. Hope this helps. I've probably left something out, but someone will chime in and correct me or add on. SSOW __________________ 69 C10 (#1 son's ride) 72 C20 (Dad's farm truck) 82 K30 (Ex - brush pumper project)