Tranny swap in '71 GMC B-series school bus

[Gary Gable]

Hi All,

This is my first post, though I've lurked and read quite a bit on this site relative to my bus. Lots of excellent information and helpful replies offered by members. I hope to be as helpful in the future.

I have a set of questions. My bus, a 19000 GVW B-Series school bus about 26' long, came stock with a 350 mated to an SM465 with a parking brake on the output of the transmission. Although the motor was replaced with a Goodwrench within the last 50k, the tranny is original and the synchros are shot plus it leaks pretty bad. Additionally, the bus winds out at 50 mph, which is pretty much unacceptable if I ever care to drive on the freeway.

To remedy this I bought an NV4500 5 speed in good condition, and since it was out of a Chevy 3500HD it too had a parking brake on the output.

I want to pre-run as many of the swap issues as I can before I start. I know in advance I'll need to shorten the drive shaft, but as I've done this on previous occasions with my Jeep and there is a local shop that's excellent I'm not worried about that. The NV4500 is some 9.5" longer. I know I'll need to fab a cross brace. No problem, I'm a metal fabricator by trade. The output shafts, pinion diameter, and bell housing hole diameter are identical, so no problem there I think. Although the NV4500 had a hydraulic T/O bearing and my stock bus has mechanical, since I'm retaining the stock bell and replacing the flywheel, clutch, pressure plate and T/O bearing with stock parts I think it should mate right up. The NV4500 has no speedo attachment so I'll need to change my speedo to full electric vs cable driven.

Here are my questions:
1) The NV4500 drum diameter is 9.5", and the SM465 drum diameter is 11.5". As I need this drum to hold the bus on a hill, does anyone think (as I suspect) that a parking brake drum that is essentially 20% smaller will pose a problem? The bus GVW is 19000, and a 3500HD series pickup comes in at a max of around 13000 I think when all loaded up.
2) Do these transmission mounted parking brakes tend to have similar mounting interfaces? My wet dream fantasy is that the drum assembly on the SM465 will bolt right up to the NV4500. Has anybody had any experience with this?
3) No matter what, the parking brake cable will be too short for whatever parking brake assembly I use. Has anyone here had a custom cable made up, or have knowledge of other longer cables being commonly available for other applications that may work here?

Thank you for any and all help and advice, in advance. Feel free to weigh in with partial answers. I'm happy to sift through. I've found some fairly decent schematics but nothing that is approaching the detail I need to answer my questions.

Sincerely,

Gary