I have a question that has been bugging me for awhile so here goes. First some basics............I have a fully manual T400. No upshift or downshift capabilities. Starting in 'drive' means starting in 3rd gear. It's basically a race transmission I run on the street and I love it. It's just beastly when it shifts and I like that.

So here's the question. Why does it have a vacuum modulator on it? I have it hooked up and it doesn't seem to effect anything but I've always wondered. I got the transmission 20 years ago and I've forgotten what the instructions said at the time. I do have it hooked up to manifold vacuum but I was just wondering if anyone has any insight as to why it's on a full manual transmission?

 

So it doesn't leak trans fluid. If you had a trans brake it would be hooked up in place of the modulator.