I have a 93 toyota pickup the rear brakes are in good shape and the fronts are brand new. Sometimes the rear brakes will work, sometimes for seconds sometimes for hours then i will get a long pedal again. It seems they will start working and not working on the very rough roads that i drive quite a bit. Any ideas?

Thanks

 

Verify that all hardware is in good shape, lubed and free, and that there are no leaks allowing air to enter the system, this includes the reservoir. And make sure rears are adjusted properly so the pedal has the least amount of movement necessary.

 

Did you have the problem before you replaced the front brakes? How are you sure it's the rear brakes that aren't catching?

 

And verify that your LSPV (load sensing proportioning valve) isn't jacked up. There should be a long skinny rod going from the diff up to a gizmo on the passenger frame rail. It will have brake lines going to it. Verify its operational and not leaking also. There is a bleeder on it as well.

 

I have never had a LSPV that worked .

Except for the one I tried to bleed and had to buy a new one.

The intermittent problem is quite interesting .

Sometimes you have a good pedal other times it goes almost to the floor.

Then you have no loss of brake fluid.

Do you need to pump the pedal a few times to get good pressure again ??

Does the 93 have that early style of Anti lock brakes tied into the power steering ??

Could be a problem with that if so.

 

That's a good point Wyo. My LSPV just kinda flops around internally. The little pin that is activated by the rod just free rides... I don't even think I am using my rears... Guess I had better find a proper prop valve...

 

Do a brake booster test too!

 

Probably a silly question...did you try bleeding your brakes? It sounds like you might have air bubbles in the lines.

Here's how to bleed them easily...

 

Ok so i adjusted the rear brakes and they worked for the 1 mile i drove it. Parked came back an hour later right back to just front brakes. With the truck off i can het a could firm pedal but one i start up it goes way down. I looked at the lspv and just from looking at it appears to be all intact at least. I just get why i can get a good hard pedal sometimes when im driving down real rough roads and then i completely lose it. Doesnt that say that it is a mechanical problem and not a hydrolic problem if you get my meaning. Could my brake adjusters be moving in and out somehow? If my lspv is messed up and making it brake full in the front wouldn't i still have a hard pedal? Im baffled

 

Test your brake booster and the check valve in the booster vacuum line.

http://www.ehow.com/how_7507543_test...-boosters.html

 

So i tested the brake booster and it all checks out. I was unable to do a vacuum test because i dont have a tester. I brought it into a shop they adjusted the rear brakes and confirmed that all the air is out of the lines and also installed a new master brake cylinder. Still the pedal goes to the floor almost. Without losing any fluid. What else can i check?

 

Did the shop measure your drums?/

If the are worn to the point all the wheel cylinder travel is taken my just having the shoes adjusted up

Another thing Master cylinder O rings could be leaking allowing fluid to leak internal giving you the low pedal without fluid loss.

 

I think they would have probably looked at the drums when they did rear brakes but even so what could possibly be happening that i have no rear brakes and a long pedal then if i hit a hard bump (and its got to be pretty hard) i will then have full braking power with a high pedal? I am toitally at a loss. The only thing i can think of is the lspv and thats mostly because i dont know much about them and ive exhausted every other possibility that comes to mind. Because this is something that must be moving to cause such drastic changes. Any input?

 

the load sensing proportioning and bypass valve has a rod which physically moves and adjusts hydro pressure depending on how much load is in your truck bed. it will actually bypass some rear hydro force up to the front if your bed is sitting high, to prevent rear lock up. (this not the same as the later rear PSPV [abs] system).

when a hard bump is bouncing your truck, its also actuating that valve. it may be sticking instead of operating freely.

the valve also must be mounted appropriately for your truck if youve modified the ride height with some lift accessories. a bracket extention is often required to maintain full function of the valve. that valve also has a bleeder, and the system must be bled in correct order for the best feel. im having trouble w mine at the moment too. good luck

 

If you find a resolution for this I'm all ears, for it sounds almost identical to the brake issues I have been experiencing for quite some time, and have yet to figure it out. Sometimes I have good brakes and at other times the pedal goes almost to the floor. It never fails to stop but the inconsistency leaves allot to be desired. Have replaced master cylinders, lspv, pads, shoes, no fluid loss, bleed and bleed and bleed, etc...94 4x4 3vze

 

If you have a u pick yard close by go grab a lspv and slap a different one on there. It could have gone bad. Just seems that if you have full breaks after a hard hit. Then something is sticking.
Good luck

 

Have someone sit in the cab and press on the brakes while you watch the booster if it moves forward or not.
Look over the pedal bracket while its being pressed and make sure its no contortioning out of shape (From cracks).

Wonder if there is any chance the ALB actuator has possibly gone faulty.

 

Incorrect front calipers on one or more sides...?

Verify brake caliper bleeder valves are at the top of each caliper and not at the bottom.

Verifying you have a RF Caliper on the RF and a LF caliper on the LF....

 

Agreed. Bleed, bleed, bleed. Sometimes it takes a buddy-bleed no matter how much you bleed them with pressure or suction. Just don't let the pedal travel all the way to the floor when doing a buddy bleed.

Rich