I am cleaning my sm420 trany up and installing new gaskets. I saw online that there is an upgrade to the front shaft by Novak that replaces the front input housing, and they grind a new seal area on your own shaft. I have the ability to do this myself, as, I have a universal tool and cutter grinder, a nice Romi lathe and Bridgeport mill. I can grind the shaft between centers, make a new input housing, and install a new lip seal. Has anyone done this upgrade recently? I would need the seal number, and the shaft dimension, that way I can do it myself. This is a 1948 sm420 that is in really great shape. I am also considering a Gear Vender overdrive unit. The truck is a 47 3600 with the 4:56 ratio, but in very good shape too. I found a 4:11 center carrier, but the guy is a little hard to deal with, so an overdrive will be my next choice for better road drivability. Any info will be appreciated.
Instead of fabricating a new bearing retainer, why not simply machine the old one to accept a seal? I'd be tempted to clean up the OD of the input shaft to get it round, and press fit a thin machined ring onto the shaft to act as an inner seal surface, also. Bearing and seal manufacturers such as National, Chicago Rawhide, and SKF publish progressive size charts for seals that list the ID and OD, as well as the lip material and design. Just pick one that meets your needs. Since the SM 420 has survived for decades without a front seal, not all modifications are "improvements"- - - -especially if you're not going to encounter extremes of up and downgrades like the rock crawlers do that might let the lube leak out of the front of the housing. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Well, I went out just for fun and machined a left-hand internal sleeve to fit on the input shaft. It fit the first time trying the shaft into it...That has happened more than once when I make threads for special nuts. So, I'm not sure what I'm going to do yet, but it was fun to run my lathe and challenge myself. Jerry, the bearing retainer does not look to be thick enough for a seal counter bore. It is only about 1/8" thick between all the dimensions. With the bearing nut and the oil slingers, not much room left to fit a seal in it.
The newer sm420 have a seal you may be able to find the front retainer for a newer one mine is a 67 or 69 transmission ,also has the reverse switch on the top cover the seal is available.
I have not run the truck yet. The transmission was covered in greasy dirt so I thought it might need some new gaskets and maybe a upgrade to the front seal.
I ordered a new bearing retainer front for my SM420 From Novak. It came with a standard input seal in it, but mine being an older trany the seal will be replaced with a 1 1/8" bore instead of 1 1/4" that the newer trany must have. I machined the left-hand threads back to get a very nice area for the new seal. So my new seal is 1.750 OD X 1.125 ID X .250
