Greetings everyone. I purchased a project Cummins 6bt conversion with a trashed original th400 transmission. I just finished the transmission rebuild and attaching the custom driveshaft so i took it out for a drive and hit a whopping 40 mph Is this normal for this transmission or is something wrong. It is shifting smoothly, so I have a feeling a new transmission is in my future if I ever want to drive it on the highway.

Any info would be appreciated.

 

The TH is a 3 speed transmission. With factory gearing and the TH400 the original 6.2 will do 65-67 but it won't like it. 55-57 is my normal highway speed in the 92. With the Cummins you should have more power so duplicating the OEM performance should be easy. If you want to 70-75 on the highway a 4L80 and regear are in your future.

 

Update.

Well, I have been busy. I put in a 47RH tranny behind the cummins with a NP241DHD transfer case so I can select 2wd/4wd. I have it set up so I can manually switch the overdrive and torque lock up at my leisure. I has been working very well since adding 4000 fuel pump governor springs (over the top - I know) which was preventing me from going faster than 55 mph - now i can go as fast as I want!

I can now pull my military M105 trailer loaded without difficulty. Now to insulate the beast as I cannot drive it on the freeway without earplugs.


cheers