Need Help Diagnosing FZJ80 Brake Issue

[TurbodreamZ]

I think so, hard to tell when the engine is running. Are you thinking about if I can hear the air rushing in on the pedal side to create the pressure inbalance?

I think what happens is the brake booster diaphragm leaks internally and can’t hold vacuum pressure and you can hear a hissing or whooping sound. one way I knew my brake booster was leaking was to see if the brake pedal feel was better if I pressed the brake pedal while building vacuum pressure by revving the engine. What happened was that during the second or two the revs were going up (negative pressure) the brakes felt normal. as soon as the rpm went back down or stayed consistent, the brake booster lost vacuum and brakes became mushy.

BUT.. that was with a gas motor. I’m not too familiar with how diesels make vacuum.

 

[Therealtotodile]

I think so, hard to tell when the engine is running. Are you thinking about if I can hear the air rushing in on the pedal side to create the pressure inbalance?

Hey sir any updates or resolutions here? Shop told me I was losing pressure and they replaced the master cylinder. No change. New rotors and pads and shop promised they did a full flush. San Diego shop called the truck shop that usually does well working in the ole girl. I have never had good braking and can’t seem to make any sense of the booster being the issue. But my symptoms are exactly what yours are.

Thanks bud

 

[Fosters]

Has anyone checked booster rod length?

 

[Squash]

A lot of work here.
No mention of calipers, a stuck caliper will cause a hard pedal.
Typically happens after a pad change because the caliper pistons/piston get pushed back in, and now live within the crud accumulated over time.
Never trust a caliper...

 

[Rubiclone]

In the end I think it was a combination of a stuck caliper on the front passenger side and s***ty brakes. I ended up just using OEM pads and getting my rotors resurfaced. In the process I noticed the pistons not retracting properly on the caliper. Originally it was not a suspect as under had braking it didn't not pull one way or the other. I can still trigger the low pressure light at idle if I quickly kick the brake pedal a couple times but suspect that might be normal as I have nothing to compare if too. Brakes are much better now and I can stop with confidence.

 

[Therealtotodile]

In the end I think it was a combination of a stuck caliper on the front passenger side and s***ty brakes. I ended up just using OEM pads and getting my rotors resurfaced. In the process I noticed the pistons not retracting properly on the caliper. Originally it was not a suspect as under had braking it didn't not pull one way or the other. I can still trigger the low pressure light at idle if I quickly kick the brake pedal a couple times but suspect that might be normal as I have nothing to compare if too. Brakes are much better now and I can stop with confidence.

Looks like I’ll have to take a look at the calipers. Just tried to go get pizza, and had a super hard brake when trying to back out of a spot, thought I was going to crash into a light pole, took foot off and was able to get it to respond. Keeps happening at low speed.

 

[ppc]

Hard peddle is going to be the booster failing or vacuum leak in the attached hose.

 

[Therealtotodile]

Hard peddle is going to be the booster failing or vacuum leak in the attached hose.

Sounds like it’s booster time…. Already did the damn master cylinder because it was losing some vacuum over time.