ourkid2000

Good day all,

A recent thread about TH400 rebuilding has me thinking about rebuilding a TH425 (someday!). Has anyone rebuilt one? If so, how did you find it?

Now they say a TH425 is just a TH400 with the 90 degree chain & gears added for the FWD feature but I guess my biggest question is the parts.......are the guts of the 425 completely interchangeable with the TH400? A couple parts pop into mind that wouldn't be the same (i.e. the governor is different). Would the re-build be just about the same as the 400?

Thanks!

OLDSter Ralph

I had a shop familiar with TH400 and TH425 rebuild the one in my Toro. I had a Trans-Go shift kit added. I had a problem with shifting and it took a while to find the cause. It ended up being a problem with the Trans-Go piston that was installed. When the old piston was put back in, everything worked fine. Now it shifts beautifully.
There are a few parts that are "special" to the TH425, but most is TH400.

ourkid2000

Interesting Ralph. Strange there's not more out there on the 425's thought isn't it? GM used them on quite a few high end models so they're pretty popular. Between the Eldo, GMC motorhome, and the Toros, I'm surprised that information, parts, and rebuilding guides aren't more plentiful. Maybe there is and I just haven't stumbled across it yet? Certainly not much on the Youtubes out there that's for sure. Not that Youtube is always to be trusted but it's great to have visual references.

I should say, other than the CSM.....which is actually very good.

OLDSter Ralph

The "basic transmission is like a TH400. The differences are in the transmission output and final drive. The Toro, Eldo, motorhome are different from rear wheel drive cars. The parts in most cases is out there. YouTube might have some helpful video's.

This guy actually has Toronado parts on hand. I will have them rebuild my 57 Olds transmission when I get to it. Bob wants me to bring the 57 Olds tranny so he can tech his son to rebuild them. They also have the tools to work on the 61-63 Olds Cutlass (Roto5) transmission. I believe Bob is the "Dad" and Chuck is the son. They are good people.
https://bobtransmn.com/

matt69olds

I have never rebuilt one, I have torn down maby for parts. There are many parts that will interchange with a 400. Just be sure to pay close attention to the sprag rotation! It’s opposite of a rear wheel drive application.