The Stovebolt Site Forums The Shop Area Driveline SM420 need to be rebuilt?

Have a 1950 3800 thats been parked for about 7 years. Owner said transmission is good but I've never driven the truck personally, and am in the process of restoring it. With the trans out, are there any tell-tale signs on a SM420 that I should look for to see if it warrants a rebuild?

Easier to do now while its out, but I don't want to fix something that ain't broke. Advice? Thanks!

Make sure there isn't any large wiggle in the front drive gear at the splined end. Check to be sure the snout that the throwout bearing sits on is not cracked. Pull the top and check to make sure there are no large metal pieces or chipped gear teeth inside and that the forks all slide appropriately. Cycle through the gears and make sure the yoke and splined end turn appropriately. And probably just replace the seal at the yoke end just because.

Drain the fluid and as long as there are no tell-tale signs of trouble, re fill and reuse her.

Those transmissions are tough as nails.

Jeff

Thanks Jeff, I'll check it out. Any recommendations on a good refill fluid?

I think that year had a neoprene shaft seal in the front, which was a real improvement. I would remove the front retainer and put a new seal in. Getting tranny fluid on the clutch is really nasty.

Edit:*** I thought your post said 1958. A 1950 would not have the seal in the front.

I would use GL4 which is somewhat hard to find. Most everything now commonly found is GL5 which is good for the rear end.

This is what I use in a SM420
http://www.summitracing.com/parts/RED-50304/

GL5 should be the next better version of GL4. The way I was explained, the higher the number the better or newer version.

GL5 has additives that eat the brass parts found in a SM420. Same thing with the new motor oil, not good for engines with flat tappet cams.

IF it's not too late.... and the transmission has been drained, you might remove the transmission side cover to inspect the magnet in the bottom of the transmission to see what may have accumulated there over the years.

GL-1 90 wt.
That's the stinky stuff. I get mine in 5 gal buckets at Agri-Supply. They will even order GL-1 140 wt. if you want that.

I understand that GL-5 is supposed to be bad for brass or bronze components.

Kurt