Troubleshooting very soft brakes (1 Viewer)

[digital]

91 FJ80 - Have to press the brake pedal to the floor to get any braking.

Here is what I've done/checked so far;

Bled all 4 brakes and the LPSV (with the engine running)
Brake fluid looks normal
pads have about 3k miles on them
new rotors in the front
Rear pads are adjusted correctly

I don't lose any brake fluid from the master cylinder, looks normal.

When I press the brakes with the engine off, I can faintly hear fluid going through the MC, is that normal or is that a sign that it needs to be rebuilt/replaced?

 

[digital]

Anyone who has rebuilt their MC, have you had good results with the Toyota rebuild kit?

 

[jonheld]

Have you checked the pistons in the calipers for freedom of movement without pain?

 

[digital]

Have you checked the pistons in the calipers for freedom of movement without pain?

Hey Jonheld, I haven't done that, how would I go about testing them?

 

[Grench]

I had similar symptoms and replaced my MC. It didn't fix the issue. Bleeding them another 4 times and running 1.5 qts of fluid through was the key. It sounds to me like you might still have a bubble in them somewhere.

YMMV.

 

[peepers]

this is the other reason for me... i think that when the stainless brake lines were put on it was never bled all the way out.

 

[digital]

I had similar symptoms and replaced my MC. It didn't fix the issue. Bleeding them another 4 times and running 1.5 qts of fluid through was the key. It sounds to me like you might still have a bubble in them somewhere.

YMMV.

At the time that you were having the issue, could you press your brake pedal all the way to the floor?

 

[Grench]

Nearly. It was downright frightening trying to stop the thing.

Fixing it was a -long- process of bleed the brakes, didn't help, check/change something, bleed the brakes, didn't help, check/change, bleed, check/change, empty wallet, bleed...

Pads, master cylinder, front/rear axle service, caliper inspections, noggin scratching, etc... It didn't make any sense that my '96 with bigger brakes and ABS was so bad and my wife's '92 was -good- by comparrison. It took nearly 2 years to figure it out.

We (takes two) bled 1.5 quarts of brake fluid through it 2oz or so at a time rotating around the valves starting with the LSPV, then rears, then fronts, then around the block twice braking as hard as possible at each corner, then repeat. We did this a good 6 times, but I count this as one 'instance' of bleeding the brakes. Around the 3rd time it started to firm up.

The previous 5 or so times we did what would be 'normal' for any other vehicle and just pulled through three or so presses per corner. (I/we didn't know about the LSPV for the first few.)

YMMV. What worked for me may not work for you. These are brakes and messing with them is at your own risk, etc...

 

[peepers]

These are brakes and messing with them is at your own risk, etc...

well the way i see it is that i have had mine looked at by local landcruiser experts and the deal and they all came up with nothing. now, its up to me.

digital, you and i are in the same boat. i just replaced my MC. the test i read about on the board for a failing MC is pump up the brakes (while parked) to build up the pressure. when you have some good resistance, press them hard and keep em pressed. if the pedal eventually goes to the floor, replace the MC.

that is what i did. i still think they are soft. i am calling cdan tomorrow for some 100 series front pads and i am just going to jump in and get that abs control box or whatever it is officiall called. i am about to embark on a 2,500 mile road trip with a loaded truck and the !

anyway, back to you, if your pedal goes to the floor and you cant build pressure? i think that points to a lot of air in the lines.

 

[digital]

well the way i see it is that i have had mine looked at by local landcruiser experts and the deal and they all came up with nothing. now, its up to me.

digital, you and i are in the same boat. i just replaced my MC. the test i read about on the board for a failing MC is pump up the brakes (while parked) to build up the pressure. when you have some good resistance, press them hard and keep em pressed. if the pedal eventually goes to the floor, replace the MC.

that is what i did. i still think they are soft. i am calling cdan tomorrow for some 100 series front pads and i am just going to jump in and get that abs control box or whatever it is officiall called. i am about to embark on a 2,500 mile road trip with a loaded truck and the !

anyway, back to you, if your pedal goes to the floor and you cant build pressure? i think that points to a lot of air in the lines.

Am I supposed to do the MC test with the engine running?

thanks for the reply, I'll do some more bleeding, I did notice a bunch of sparse air bubbles in the left rear while bleeding yesterday (using clear tube), there still may be some air in there...I hope that's it, if not, I'll do the MC...

 

[hadji_85]

the soft noise should be ok, i posted something similar about the noise a little while ago.

 

[digital]

Ok, I carefully bled the lpsv and the 4 brakes again, used an entire 32oz bottle of brake fluid. I'm very confident that my lines are air free...I also checked the adjustment of the rear brake drums, they are good.

The brake pedal still goes to the floor , I can't build up any resistance pumping the brakes.

 

[peepers]

are you losing fluid anywhere? that could be it as well... i leak someplace.

other than that i can only speak to the things i have tried and done and i am so sick of the soft pedal i am just go to throw money at it and get that damn ABS modulator or whatever it is. that and bleed the hell out of all 5 points until i get clear new fluid out of each bleeder.

 

[digital]

....

 

[digital]

are you losing fluid anywhere? that could be it as well... i leak someplace.

other than that i can only speak to the things i have tried and done and i am so sick of the soft pedal i am just go to throw money at it and get that damn ABS modulator or whatever it is. that and bleed the hell out of all 5 points until i get clear new fluid out of each bleeder.

I have clean brake fluid and no air at all 5 points after bleeding last night, that I'm sure of...When I saw the worn rubber around the caliper piston and the oil below the knuckle, starting to make me wonder about the calipers??? I'm not leaking anything at the MC, tracing the brake lines, I don't see anything leaking either...Wish I could get a little more help from the board here...

thanks peepers.

 

[Atoyot1031]

I don't know if this will make you feel better, but it may help...

For the sake of PM, I was swapping out the pads on my minitruck and flushing the fluid. ~$80

Well, I found I had two frozen pistons. So a few days later, I replaced the calipers. ~$200

When I went to bleed the LSVP, I broke the adjusting bolt (unlike an 80, my '87 minitruck had a fixed nipple with a blot that is loosened to allow bleeding, this broke off clean to the surface). Rather than replace with a LSVP (which probably was ineffective anways with my lift), I installed a manual valve off of the MC, which also abandons a couple of the old lines as well, further simplifying a simple truck. ~$100

Only one problem when I got finished. I (like you) could not get any pressure to build up. I tried EVERYTHING!!! So, I disconnected the two lines for the F&R at the MC and checked pressure (by covering the holes with my finger and having someone pump the brakes per FSM). The pressure to the rear SUCKED!!! So, I bought a reman'd MC. ~$60

That fixed it, although at that point I was convinced that I would have a problem with the rear drums as they were the only part of the system that I hadn't replaced!

Anyways, hope it helps. Try testing your MC first...

 

[digital]

I thought I would post this after taking it to a mechanic.

A very simple way to locate where your braking problem lies is to use vice grips and clamp off your brake lines to locate the trouble.

For example, use a vice grip to clamp down the brake line that goes to the rear brakes, right before the LPSV. Now, Press down on the brakes, if your pedal still goes to the floor, leave the vice grip clamped down on the rear brakes and clamp down your front left brake line right before the caliper and press the brake pedal again. Now the right side, press down on the brake pedal, if it still goes to the floor, and your FJ80 isn't equipped with ABS, 99% chance you have a bad master cylinder. You have eliminated the possibility of any air behind the vice grip clamp and any potential problem with brake adjustments, leaky calipers, etc.

I will be ordering a master cylinder from C-Dan and report back here in a couple days.

I hope this will help anyone in the same boat I am in, I did a LOT of searching before I posted this and I read a lot of posts on here, but never read about this method to troubleshoot for a bad MC. I'm sure people on here have done this before, I'm just posting as I learn

 

[digital]

Reporting back, just replaced the MC, brakes are good to go..

 

[Atoyot1031]

Sorry I didn't post up earlier and save you the mechanic's fee...

 

[landtank]

Reporting back, just replaced the MC, brakes are good to go..

same here. But in sub zero weather and the Brake fluid having the consistency of vegetable oil made for bleeding the fronts a real PITA.