The Stovebolt Site Forums The Shop Area Driveline SM420 4 speed seal replacement

Hello everyone I have finished putting in the rear seal in my SM420 thanks for the information it made it so easy. Now I would like to do the front seal any info on that would be greatly appreciated.
Thanks Mike

Depending on the year of transmission there may not be a front seal. Don't park facing down a hill. Check out the differences on the Novak SM420 transmission page.

Here is the page from Novak

Thank you for the website.. mine does not take the seal awesome. I posted a couple pictures all I need is a knob and of course the install.

Thanks again.

Mike

No ribs on mine.

Just looked at you 54 GMC very nice I had a 55 first series loved the truck for many years almost the same color.

Merry Christmas

Now you just have to figure out where all that oil is coming from!

Hello Otto I spilt it all over my work table when I took of the back plate to tap out the seal lolI have a mess to clean up now.

The new gasket worked great no leaks, all the gears are smooth and the two ball bearing were very nice, I gave it a good cleaning out when I took the drain plug out. Thanks for all the help It sure makes a difference

Mike

I have a question Otto is the pilot shaft at the end whereit goes into the bushing


the same size in. the Muncie 318 as the SM420 it looks like it is. Thanks Mike

Mike, that's probably a better question for Kevin. My truck is a 3 spd. I have no experience with the 4 spd.

The pilot bushing is the same for either 3-speed or 4-speed transmission.

If you wish the Novak website has an upgrade to a newer model with seal .It involves purchase of a new cover and the shaft will have to be sent to them for machining were the seal rides. My origional 4 spd had a few broken pieces inside and I was lucky to have from years ago not knowing it but a spare from a 1967 chev truck that has the reverse light and the seal up front .

I did the Novak conversion on the front seal of my Muncie. Best decision I made considering it’s the only part of the trans that doesn’t leak. The shop who did mine was horrible.

Thank you Kevin I was leaning that way it just looked the same

Mike

I have the earlier trans with no seal. So far as I can tell the front seal has never leaked despite being parked nose down on a fairly steep hill for months at a time.

The rear, however started leaking when the splines got loose. I tried a speedy sleeve on the yoke but eventually ended up replacing the yoke, which also cured an annoying vibration. They are NLA new but I found an NOS one on ebay.