Brakes locking up after hydroboost replacement

[okiebenz]

I replaced the hydroboost on my 96 6.5 and afterward the brakes are partially applied which progresses to fulling applying as they heat up. I have concluded the rod in the hydroboost must be slightly longer and when the master cylinder is bolted down it pushes in the piston. I have read online about a washer that can be missing that allows the rod to fall off center and not insert into the center of the master cylinder piston. It appears the washer is on the replacement booster and the rod is centered. I am going to also replace the master cylinder as well because it appears it was leaking slightly but I do not think that will cure this problem. Is there some sort of adjustment of the length of the rod I missed maybe from the pedal side? Otherwise what might I do to correct this? Can I insert a washer or 2 on the studs before mounting the master cylinder to shim it up? Or did I get a bad hydroboost?

[DmaxMaverick]

Welcome aboard!

It could be a bad HB unit out of the box. Not common, but I've heard of it before. Could also be the lines are installed incorrectly. I'm not going to advise from memory, but we had a recent discussion about it with details within the last couple months. Try a search or just scan through previous threads. If you don't find it, post back and I'll find it.

The bore for the pushrod is narrow, and there is a deep detent in the MC piston, so having it misaligned is unlikely. It may have a bushing in the bore, but I don't recall. If it were possible, just once, we'd see them like that all the time. It would only take a MC piston slightly slower on the return.

[okiebenz]

Thanks! I searched and scrolled and did not come up with anything, but I could be blind. If you happen to run across the thread in question and pass it along, that would be great.

[DmaxMaverick]

Hydroboost line routing:
PS pump connects to the HB inboard port, and the HB outboard port connects to the steering box. The forward HB port is the return.