Hard pedal after full floater w/ disks conversion (1 Viewer)

[cruisedeisel]

So this has been going on since I installed a fj80 full floater with disk in my 83 bj60. All new brakes, rubber lines, axle lines. Did not replace chassis lines. I have tried two bj60 boosters with no luck. Just installed a early 90's 4runner brake booster. The only way it fit was upside down with an extended vaccum line. I have a proportioning valve on the rear line. I have tried dialing it in and out several times.

If you pump the brakes, the brakes get worse and the "Brake" light indicator comes on on the dash. I have 30 (psi or inches?) vacuum at the booster. Could be more. It just maxes out my vacuum gauge. I tried switching vacuum lines with the clutch booster and seem to get worse. Vacuum line off the vacuum pump reaches max vacuum on my gauge super quick compared to at master.

I also have changed the master cylinder to a an non-abs fj80 steel one. Same problem, it started leaking so I replaced it with an aluminum fj80 master cylinder. No luck there either.

I have talked to two different mechanics and they both say its probably my brake booster but I tried 3 different ones.

So can I have too much vacuum? I really doubt it.

Thanks!

 

[cruiserpilot]

Try to delete the rear proportioning valve. Run a bypass and see what happens. Didn't you recently change an
alternator with vacuum on the back? Maybe I've mixed you up with someone else. Did you make sure the
pedal to booster adjustable rod is the proper length?

 

[robmobile73]

If your brake lines are not leaking, the system has had the air bled out, you have plenty of fluid in your MC and it is working then it sounds like a vacum problem. So assuming it is a vacum problem:

question-After you drive or run the vehicle a little bit is your first pump of the brake pedal good and slow the truck down well? After the first push/pump of the brakes the pedal keeps getting harder to push and the brakes less effective? Your pedal is not going to the floor down to metal as if the fluid is out or your sucking air in the MC but travel is consistent just harder to push each time and less effective braking?

Years back I this symptom in a FJ40. I know it's a different vehicle, but it happened in similar circumstance and the symptom sounds the same. I had been working on the engine and had pulled the vacum line out of the booster and the plastic check valve got ripped off and the check disk inside fell out somehow in the grass without my knowledge(at that time I didn't even know it was a check valve, just thought it was a plastic elbow fitting of some sort). I put it back on without the guts and my problem started. I thought my booster had gone bad. Got a booster with the valve and piece of line going to it off a old cruiser at the salvage yard(you could find FJ40's in the salvage yards in 1990). When I pulled the check valve off the booster I noticed it looked different from mine and that mine was actually missing a part inside. I installed the new check valve and my brakes went back to normal again.

Your engine and/or vacum pump doesn't produce enough vacum all the time to instantly draw down the booster to full vacum. There has to be some sort of check valve to help it store up the vacum. If you have a in-line check valve that is leaking/cracked/not working or missing you only get one good push on the brakes. You say you had to put the booster on upside down-perhaps there is a internal check valve with a verticle free floating check that must be right side up to work properly. Since you tried 3 different boosters I am guessing you either have a bad check valve, or perhaps you didn't put it back in the line thinking it was just a plastic fitting and installed some genaric vacum fitting that wasn't actually a check valve.