Strange Rear Brake Problem

C

changedsoul

New member
Im not sure how long this has been going on. This truck was originally from California but recently I made a move to a snow filled state of wisconsin when I discovered my rear tires still spinning on a sheet of ice while my foot was applied to the break at a dead stop. To test I jacked the car up in the rear both tires off the ground about a 1/4 inch. I jacked up on the axle so as to not mess posision of the proportioning valve. I put car in gear, both rear tires begin to spin at an idle around 5mph, I apply break and one maybe slows (hardley) and the other seems like it might want to stop, but doesnt. This is under a low low idle power of the engine. Also I was giving it to the pedel too. If I were driving, I would be in a full on 4 tire lock up, lol. Come on now, my rear tires should stop right?

I pull the e-brake and the rear tires stop...ok, so the brakes seem to work ok, just not getting hydraulic pressure to them it seems.

I inspect further and find both lines coming off the master cylinder and running to the back some proportioning valve. I played with this for a while, ended up zip tying it so it dont move, which gave me brakes again in the rear. Well this has to be the problem.

I go talk to a Toyota mechanic about this and was able to get the line pressure specs they use when setting these things, because if I am going to spend $300 on a new one, i sure dont want to spend even more for them to calibrate it. They say that when the front breaks reach(and Im rounding here), 1000psi, the rears should be at 400psi.

Ok, so I go a buy some gauges, attach one to the bleeder on the front caliper and one to the bleeder on the rear cylinder, get a buddy to read the values as i press on the break. And they are what they should be :O what what what?

How is this possible? How can I be at the spec toyota sets for these brakes and still have no rear brakes? I took it to toyota finally to have them inspect the brakes and they also said they are ok.

But any idiot knows,if you press the brake pedal and the fronts stop and rears dont...um somethings not right.

I pulled the rear brakes apart and the cylinders are not seized, in fact they almost look new. I can squeeze pistons in with very little effort. So what on earth can be causing this behavior?

As I am now, I am ridding around with the proportioning valve zip tied so it dont push out when hit the brakes, this at least gives me some rear breaks. They stop now when doing the test jacked up with rear tires off ground.

Any help on this would be great, I really dont want to keep this zip tied.

Thanks,
 
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If it hasn't been done, I'd definitely go with a fluid flush and bleed before I'd change out the valve. The LSPV is covered in my '99 4Runner paper FSM and it is very straight forward. It does need to be bled just like a wheel and is bled last, after all four wheels are done. Somebody may have skipped this step last time brakes were bled.

In case you didn't have it, there is this hint on how to check the rear fluid pressure:

HINT: The brake pedal should not be depressed twice and/or returned while setting to the specified pressure. Read the value of rear pressure 2 seconds after adjusting the specified fluid pressure.
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Spec: Front 995.6 psi. Rear 393-563 psi. If pressure is low in rear add spring tension by shortening bolt OR sliding it up in the slot. Lock nut torque: 9 ft-lb.

That's about all there is except remove/install instructions.

Somewhere I read that if you HAVE ABS, you DON'T have an LSPV/BV. I know I have ABS and no LSPV/BV.
 
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Well I did bleed the whole system, but was not aware it is to be done last. in fact I think I did it second, after the rear right wheel. Trying to keep with the furthest from master cylinder first thing. But the pedal feels very firm and the braking power as a whole on the truck is great. Almost to great. It doesnt take much and I could lock the front tires up.

Spec: Front 995.6 psi. Rear 393-563 psi. If pressure is low in rear add spring tension by shortening bolt OR sliding it up in the slot. Lock nut torque: 9 ft-lb.
Click to expand...
This is what the toyota tech told me, I just could not remember the exact values off hand. But I did check the rear pressure and it was good. Perhaps it was the way I did it? Maybe Toyota puts a gauge inline with the brake line? I dono. I just used a high pressure gauge that I attached to the bleeder valve.
Now there may have been air in the system when I attached the gauge because my gauge didnt have a bleeder on itself. But since air compresses a fare amount, and I got the pressure that is spec at the rear tire, I can only conclude that A) If there were air, the rear tire pressure is probably higher and B) If there were no air then the rear pressure is still where the spec is.

My rear is adjusted where it should be. The e-brake works just fine. I cant skid out with it or anything, but it stops the truck from rolling down hills. I even went so far as to buy brand new drums and shoes.

It is a 2WD.
This just doesnt make any sense. Even when I took it into Toyota, the mechanic said the brakes were fine, all adjusted properly and everything. So Im not sure what it could be.

If it IS air in the line, then Im sure its a very small amount that isnt noticable by the foot on the pedel. So that being the case, could a very small amount of air cause complete lack of brake power to the rears...even though the line presure reads good?

None of this makes sense, logic tells me, if the line presure is there, the cylinders arent seized and the brakes move freely, shoes are good, new drum, everything adjusted right.....I should have rear brakes.
 
Perhaps the valve is bad, but reads good? Can this be a possibility?

I dont do any serious hauling so my rear is never loaded down to even really use that stupid valve, so is it possible to safely bypass it? I would think the design incorporates it with the design of the master cylinder calipers and rear brakes as a whole. But maybe not. Can I just send the front line outlet from the master cylinder to the front, and the rear to the rear? Would that be safe? Thats how its been done on any older car I worked on.
 
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Did you take the drums off and inspect the shoes? We had this problem (little rear braking power) on ours. It was caused by gear oil leaking into the rear brakes. Seems the differential breather has a bad habit of clogging on these. Also might be your slave cylinders are weak.
 
Yes the brakes are dry, no oils or anything. In fact I replaced both shoes and drum thinking that may be the problem, but that didnt solve anything.
 
changedsoul said:
Maybe Toyota puts a gauge inline with the brake line? I dono. I just used a high pressure gauge that I attached to the bleeder valve.
Now there may have been air in the system when I attached the gauge because my gauge didnt have a bleeder on itself. But since air compresses a fare amount, and I got the pressure that is spec at the rear tire, I can only conclude that A) If there were air, the rear tire pressure is probably higher and B) If there were no air then the rear pressure is still where the spec is.
Click to expand...

No, the FSM just shows two gauges, one attached to a front and the other to a rear wheel, so your test set-up sounds fine.

I agree, air should reduce the pressure at the wheel, and you have pressure. It just seems like fluid is the only component not changed or tested. The LSPV definitely needs to be bled last.

If you want to get rid of it, here is a how-to:

Project Tacoma Removing Toyota LSPV Load Sensing Proportioning Valve : Off-Road.com
 
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changedsoul said:
Yes the brakes are dry, no oils or anything. In fact I replaced both shoes and drum thinking that may be the problem, but that didnt solve anything.
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Basically, 3rd gens have crap for brakes. If you get a chance try this. Take the drums off and check the surface of the brake linings. What percentage of the lining is making contact with the drum?
 
What percentage of the lining is making contact with the drum?
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Well when I first changed to new drums and shoes, I would have to say it was only around %50, maybe less. But I have been riding now for a few months with my valve zip tied and I took a look at the brakes a few days ago and it looks like its contacting on almost the entire surface. They wore in nicely it seems.
Now that you brought that up, I havent yet checked to see if the rears still keep spinning after pressing the brake. I will have to do that soon and get back.
I found this forum for another issue and thought I would ask about my brake problem not even thinking if it still is a problem, lol. Its been so long riding on a zip tied LSPV that I forgot I had break problems till I stumbled in here. hehe.
 
changedsoul said:
Its been so long riding on a zip tied LSPV that I forgot I had break problems till I stumbled in here. hehe.
Click to expand...

Why did you zip tie the LSPV? Was it loose causing braking problems? Maybe a lift made it unusable?
 
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I zip tied it because from the way it looks on the car, when the brake pedal is pressed, that lever moves. When the car is loaded down, this puts mor tension on the spring making it harder for the lever to move, thus giving more brake power to the rear. So since I had no brakes in the rear without a zip tie, and what seemed to be brakes that would at leasts top the rear wheels with it zip tied...I just left it zip tied. :)
 
notrayray said:
Are the rear brake shoes adjusted properly?
Click to expand...

I have the same issue with mine and I'm going with the adjustment first. Just tighten the adjuster until you can hear the shoes scraping the drum while spinning and then test to make sure it stops the spinning wheel, and back off a touch to get rid of the noise.
 
89 4runner brake problems

I have an 89 4runner. If I press the brake pedal slow and steady the pedal will go to the floor and not stop the truck. However, if I press the pedal to make a quick stop it will stop fine. I have bled the brakes thinking it was air, but the problem persist. Any ideas on what it could be? I’m also not seeing any break fluid leaks.
 
Old thread, hopefully new tricks

I'm experiencing similar to the problems explained but do not have enough forum cred to start a new post and do not have a proportioning valve.

My 4runner has had weird rear brakes since I became the owner. Recently, I decided to tackle the issue and rebuilt my rear brakes and did the large Tundra brake upgrade at the same time.

Issue was, and still is but not with the dash brake light, my rear brakes haven't been working working well. I can press the brake to a stop and the rear brakes barely engage. Pedal is soft, not spongy, and firms the lower I press. On my short test drive, if I stopped two times in relatively quick session, the second stop firmed up and braked batter. The first stop felt like it bypassed the rear and the front did 95% of the work, I don't think I felt the rear grab, only the front which would dive.

I've adjusted and bled at all 4 ends, both traditional way and gravity. Master cylinder hasn't been dry, at least since I've had it. There are no leaks, yet the brake light now goes on and off for short periods at, what I feel, are random times. I haven't checked the mc yet, nor bled the abs motor.

Any ideas?
 
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Parallelephant said:
I'm experiencing similar to the problems explained but do not have enough forum cred to start a new post and do not have a proportioning valve.

My 4runner has had weird rear brakes since I became the owner. Recently, I decided to tackle the issue and rebuilt my rear brakes and did the large Tundra brake upgrade at the same time.

Issue was, and still is but not with the dash brake light, my rear brakes haven't been working working well. I can press the brake to a stop and the rear brakes barely engage. Pedal is soft, not spongy, and firms the lower I press. On my short test drive, if I stopped two times in relatively quick session, the second stop firmed up and braked batter. The first stop felt like it bypassed the rear and the front did 95% of the work, I don't think I felt the rear grab, only the front which would dive.

I've adjusted and bled at all 4 ends, both traditional way and gravity. Master cylinder hasn't been dry, at least since I've had it. There are no leaks, yet the brake light now goes on and off for short periods at, what I feel, are random times. I haven't checked the mc yet, nor bled the abs motor.

Any ideas?
Click to expand...
Soft brakes/front brakes doing all the work indicates the the rear drums are not adjusted correctly

Is your brake fluid reservoir at the full/max mark?
 
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