Th400 important question.

[Nick88]

Hey yall, I'm rebuilding a 1986 4x4 HD case th400 to hold power. Upon pulling apart the front pump I found there was some scoring where the outer pump gear rides, enough to feel with a finger nail. On the shelf I have an unknown year 2wd solid yoke th400 apparently out of a mini school bus. No history on it but I pulled out the pump to see the condition and it was flawless. (Was told it was a low mile transmission looks like it was factory low miles never rebuilt it is immaculate) the pump housings look identical but my 4x4 is labeled 34 inside, the other is labeled 33. Are they interchangeable??? Which is better?

 

[Matt69olds]

There are certain combinations of pump halfs (meaning the COVER and PUMP) but complete pumps can interchange. There are also certain combinations of pressure regulator valves that aren’t compatible, so either keep the pump parts together, or be VERY careful mixing and matching parts.

The only issue with swapping complete pumps: there are pumps with 8 and 6 mounting bolts, and cases that have 8 and 6 mounting holes. You can use a 6 bolt pump in a 8 bolt case, but you can’t use a 8 bolt pump in a 6 bolt case. Make sense??

Nick has an excellent thread on the 400, I don’t recall if he covered the pump part interchange, if not that’s definitely something that need to be added.