I'm currently working on my 65 c20 and I'm trying to decide if i need to rebuild the trans. Never got to drive the truck before teardown so don't know what shape its in. Think its fine? Or should i tear it apart and get it cleaned and new parts? What's everyone's opinion? And if i need to rebuild wheres the best to get rebuild kit? Thanks, Justin! Posted using the Full Custom H.A.M.B. App!
Its a truck...plenty of room to pull it out easily later if need be. Run it as is, you may get lucky. Spend the $$$ else where. Save for the OD ******.
I ***ume it's a manual? If so, those are tanks and I wouldn't think it needs rebuilt......then again, what do I know
The SM420 is a tough trans, but most of them lead a tough life. I'd take it for a drive first, then figure out what to do. If you can find a few cheap/free extra transmissions for parts, it might be wise to snag them. But also consider that when you do get around to driving it, you'll get tired of the non-overdrive, combined with the 4.56 gears in back, pretty quickly. And you might decide you want something else.
I'm planning on swapping the rear for a 3.46 i believe. So I'm sure it won't be as tough on it! Any ideas on getting all that old grime off. I tried that heavy duty engine greaser only thing that did was make the grime shine sandblasting it...? ? Posted using the Full Custom H.A.M.B. App!
I'd probably change the gear lube in it and run it as-is. If it breaks, I'd replace it with something more highway friendly.
As others have said that transmission is tough and it would be ease to pull if it doesn't work as you would hope. As far as rebuilding it I would look for a more driver friendly transmission if it's bad,as any other transmission ,they are expensive to rebuild. HRP
Does your truck have coil springs in the rear or leaves? Is there a lot of rust? Some guys swear by the GM 14-bolt as it came in so many trucks from the 70s - 00s. But I don't think they have gears as high as 3.46.
It has coil. Its actually 3.42 local yard has one from 72 c20 Posted using the Full Custom H.A.M.B. App!
I'm putting in a 350 and going with larger tires(like that look) 3.73 better for that? Posted using the Full Custom H.A.M.B. App!
I think so. But it's something you have to figure out for yourself. I had a 57 with the SM420 and a stock 454, I swapped in a 3.73 fourteen bolt, it worked out pretty well. with that engine I could have got away with the 3.21s. My son has a newer 3/4 ton Suburban with a TH400 (no overdrive), 235/85R16 tires, 3.73 gears, and the stock 350 engine. It works very well.
Do you know what ****** i have? If its the stock ******. Do the 350 bolt right up? Posted using the Full Custom H.A.M.B. App!
The original 4 speed was the SM420. The 350 engine should bolt up to it no problem. But if the engine is a newer one with the one piece seal, you'll need a different flywheel.
When i was asking earlier about rebuilding the ******, should the clutch plate And disc be replaced? Posted using the Full Custom H.A.M.B. App!
Try oven cleaner on the outside, pull the cover and rinse with kerosene, drain and blow out well, new gear lube, new gasket.
I don't know, I can't see them. If they are not "like new", then yes they should be replace. Along with the release bearing and pilot bushing. And have the flywheel machined, after you decide that it will fit the new engine.
The SM420 is a strong unit and they'll take a lot of abuse. As long as they don't do things like pop out of gear, some noise is tolerable from them. The rock-crawler crowd loves them. If you ever want to replace it with something newer, the SM465 is the way to go. Bob
I've driven 420s quite a bit, and have a 465 in my "new" truck. The 465 is harder to shift, although the 420s were worn out more (very common for a transmission that has been out of production for almost 50 years). I'd say it's a toss up. also, I installed a 465 in a 65 truck, had to trim the bellhousing crossmember to get it to fit.
I seem to have some higher pitched rattling in my SM465 when downshifting in 3rd and 2nd gear. It's not very loud, but you can hear it over the exhaust. Anyone had this issue? It idles fine.
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