Need advice on Brake problem.

[AlaskanJack]

Ok so I have been driving my 91 Sport while my Tranny and T-case get fixed in my 93 Sport. I have lost all brake pressure. Here's what I get.

With engine off nice hard brake, turn engine on brake pedal goes to the floor. My RABS wires have been cut at the rear diff so I get a RABS light on dash panel. I was looking at my brake pedal and noticed a vaccuum line with a valve that is attached to the brake pedal. Problem is the vaccuum line is cut past the firewall. I can't find any notes on this in the 91-92 Haynes manual or the 1991 EVTM. I can detect no leaking of brake fluid around any lines. When driving I pump the pedal and it will take like 6-7 pumps before I feel a grab in rt front caliper, then slowly I lose it.

What do you guys think?? I haven't done brakes in over 12 yrs and I feel lost. I don't want to jump into it and replace master cylinder or booster if not necessary. I need new front brake pads so they will be replaced.

 

[Runnin'OnEmpty]

Jack, that vacuum switch and line on the brake pedal is likely to be from an aftermarket cruise control.

Since the brakes will eventually pump up, you are either getting air in the lines, or no pressure from the master cylinder. I'm betting on a bad master cylinder.

 

[AlaskanJack]

Hmmm...Aftermarket cruise control that doesn't sound right since the vehicle has cruise control on steering wheel, now it doesn't work but that a seperate issue.

The brakes won't pump up they will just grab after pumping for a few times, the pedal is still at the floor when they grab. I checked my booster and its pressurized. I also think it is the master cylinder but just checking with others. I thought if the master cylinder was gone I wouldn't get hard brakes with engine off either.

 

[V8BoatBuilder]

One way to test the booster is to press the brakes when the engine is off, and then start it and see if the pedal goes down. then its working.

Another test for the booster is to disconnect the vaccum line from it - there is only one in the engine compartment. You will loose all power braking, and will have "old school" manual brakes. The booster is meerly a diaphram on the shaft that connects the pedal to the master cylinder. The pedal is directly connected to the mc as a failsafe.

But it sounds like thats not the problem here. Your problem sounds hydrualic related. Try getting the RABS system back to stock.
Then bleed the brakes. You might want to have a shop do it, since air might be in the ABS pump. if so, you need a specail tool to cycle the ABS pump to clear the air. regular bleeding will not work.

If that fails, I think the M/C could have lost a seal. If the M/C is replaced, the ABS pump will need to be shop bled as mentioned above.

 

[AlaskanJack]

Can't get RABS back to stock. Rear gearing was changed to 5.13 and then the rear abs sensor was disconnected. Possible that Ithink its the rear abs ring was not installed when gears were changed