I recently upgraded my 88 4x4 chinook to the v6 brake system.

v6 calipers
v6 rotors
v6 broke booster
v6 master cylinder

I've yet to bleed the brake system, but I started it to see how the brakes felt after the install and the rpms drop when I hit the brakes. I'm really hoping this isn't an issue with the new brake booster but it was a remanufactured unit from rock auto. Doesn't appear to be any vacuum leaks with the hose to the brake booster.

4x4 Chinook Brake Upgrade

 

Well I have had an idle surge until its warm for years I gave up, BUT I do like these threads so I can see if you figure it out, so mine surges when the brake is applied so does yours just drop and stay dropped until you let off the brake? Normal recommendation will be a vacuum leak BUT if it didn’t do it before the booster and now it does first thing that comes to mind would be booster issue…. But of course before I went through the return process I would double check EVERYTHING you touched just to make sure

 

I would suspect vac leak at the booster. There are some FSM tests I believe to test the booster that involve pumping brakes and shutting off engine, holding pedal and restarting but I can't recall the exact sequence. I would check those tests and see if it points to a vac leak at booster. Seems like you could also cap the vac line to the booster, press the pedal and see if RPMs still drop.

 

This might help: https://web.archive.org/web/20120316.../3checksan.pdf

 

I need to make time to look into this. Honestly I just had to step away for a few days. The idea the new booster might be faulty and I'd need to try and work with RA for a refund or replacement is just defeating. lol I'll post an update on this

 

thanks!