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Jul 21st, 2025 | | | | Joined: May 2005 Posts: 235 Shop Shark | | Shop Shark Joined: May 2005 Posts: 235 | I found 2 sm420 transmissions for sale on craigs list. Thinking that I should build a new transmission to go with the new 261 that is going into my 3800, I went over to the guys house and bought them for a good price. But darn, when I got them into the shop and set them on the bench I realized there were 2 PTO covers!
After e few minutes I realized I had purchased sm465....
I thought it felt heavy!
What I can see is that these are the 4 speeds that were in the late 60s suburban and 1 and 3/4 ton trucks... Would this be a good replacement / upgrade for the sm420?
Thanks,
Jeremy | | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | The sm 465 came out in 68. It is a stronger trans, but they are harder to work on. It would make a good replacement but the hole in the bell houseing is larger. You will need a later bell houseing or its seems someone mentioned at one time to turn down the retainer. The early 465 up to 73 had the lower mounting bolts come infrom the inside of the bellhouseing. They didn't have the pad on back for a mount. You can drill out the holes if nessesary or you can use bolts & nuts if you put the 73 up in an older truck.
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: Jul 2001 Posts: 3,887 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Jul 2001 Posts: 3,887 | newer is likely better in this case, but 6 of one - half dozen of the other .... Bill | | | | | Joined: Dec 2004 Posts: 1,897 Shop Shark | | Shop Shark Joined: Dec 2004 Posts: 1,897 | The bearing retainer of the sm465 can not be turned down to fit the 261 bellhousing. You will need to have the bellhousing bored from 4.686 inches to 5.125 inches. A later bellhousing will not bolt up to the 261, without some sort of adapter plate. | | | | | Joined: May 2005 Posts: 235 Shop Shark | | Shop Shark Joined: May 2005 Posts: 235 | I did a bit more research and am tearing apart the "bad" one now to learn more about it.
I like that it actually uses "modern" seals rather than grooves to keep the oil in.
I have the milling ability here so opening that hole will be cake.
I'm wondering if I'll have to shorten the drive shaft as this trans is at least 2" longer than the sm420.
Thanks for all the help here!
Jeremy
| | | | | Joined: Dec 2004 Posts: 1,897 Shop Shark | | Shop Shark Joined: Dec 2004 Posts: 1,897 | You might have to shorten the driveshaft, but I would probably put it together and see how much free movement you have first. | | |
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