Brake Pedal Soft When Running, Firm When Not (1 Viewer)

[mphilleo]

Recently, I replaced the front pads on my '92 FJ80 and bled the whole system twice (even the LSPV) in the correct order. After test driving it, the brake pedal was nice and firm. The only issue was a wandering idle while parked. I later found out there was a decent-sized separation on the section of intake hose from the air cleaner to the central elbow. Aside from that, the test drive went so well that I decided to center my steering wheel and replace my drag link ends and steering dampener. I also took the chance to attempt mending the intake hose leak and check for any other possible vacuum leaks, loose ECU fuse, cleaned the AFM, etc.

This all went pretty well. After doing this work, I took it for another test drive tonight. The steering felt nice and tight and had all its original articulation. Problem was with the brakes. The pedal feels fairly firm when the truck isn't running, though not as good as after I bled it, but it's down right soft and has a lot of travel while running and driving, definitely not like the first time. I'm not sure if my intake hose mend didn't work out and I still have a vacuum issue - but that wouldn't make sense since my idle was a rock solid 650 RPM, never wandering.

Now, I turn to the bright Mud crew for some shared experience and potential insight!

 

[Pin_Head]

Your description is a little too loosey goosey to make a guess, other than you don't like the way it feels.

 

[DARKNESS]

Sounds like you fixed the leak and your booster is now fully effective.

 

[Golgo13]

^ This

 

[mphilleo]

In my defense, it has been a while since I drove it before all that work.

FWIW, I did some additional research and found someone with similar complaints was told to gravity bleed the brakes. I just finished bleeding all four corners and the LSPV, and the pedal feels a lot firmer (didn't try it while idling since it's 11pm here). There was some air coming out of the rear bleed nipples, but the most was coming out of the front bleed nipples. My theory is that there was some left in the calipers from when I changed the front flexible lines and bled the brakes. I will test drive it after work tomorrow to see if there's any improvement and report back to this thread for posterity's sake.

 

[maxamillion2345]

Yeah I was going to say air still trapped in the lines.

 

[DARKNESS]

Try activating the ABS a few times and then re-bleeding. Sometimes air gets trapped in the ABS unit. You can activate it with wires, but it's probably easiest to just do a couple hard stops on a gravel road.

 

[mphilleo]

Try activating the ABS a few times and then re-bleeding. Sometimes air gets trapped in the ABS unit. You can activate it with wires, but it's probably easiest to just do a couple hard stops on a gravel road.

Thank you for the suggestion, but I don't think my '92 80 has ABS. Or at least, I didn't see any sensor in the knuckle.

 

[DARKNESS]

Nope, it doesn't.

 

[mphilleo]

Took a lengthy test drive and had the same result. The brakes work well enough, but the pedal simply has a good bit of travel before the brakes bite and it's fairly soft in terms of resistance. I have another 32oz of DOT3 at my disposal, so I will do a two man bleed, taking great care to close the bleed nipples in mid-stroke.