After spending far too many hours trying to figure out what's going on with my brakes, I still have no idea what's wrong. Can anyone help? 1985 4Runner, new to me so no prior experience. This is a long one, but I'd really appreciate the help.

I only have front brakes and BARELY this at best. With the truck on stands and the brake floored, you can turn the drums easily by hand, but the fronts hold. On the ground, you can hardly keep the truck from rolling with the brake floored. So, basically I have no brakes, very low pedal, pressure does not build at all. Here's the two tricky things that have me baffled.

1) Rear doesn't get any pressure.......when I open the bleeders on the drums, the pedal does not drop at all and fluid barely comes out. When I move up to the BPV and do it, the pedal drops like it should. The calipers bleed properly also. So, I thought maybe a rear line was clogged.....nope, I disconnected it and blew through it and fluid movely freely. So, I thought the BPV was messed up, so I switched it with my parts truck's......nope, no change at all. So, for whatever reason NO PRESSURE is making it to either rear drum, it IS making it to the BPV and calipers, but thats it.

2) Air bubbles in master cylinder.......they are always there. For 30 seconds after pumping with motor off, air bubbles comes up just like it was carbonated, lots and lots of bubbles streaming up. Even after a while, the occassional bubble comes up. I don't think the MC should have any bubbles in it. No leaks that I can find anywhere in system.

I've bleed the system properly many many many times, so its not that. I've broken open many of the connections to see if air was trapped at joints and found no problems. The truck has new calipers (not related to this problem, and did this before new calipers) so that's not the problem.

My only guess is that the MC is bad and somehow not pressuring the rear of the truck. Those air bubbles (lots of them) doesn't seem right. Also, whenever I pour fluid in it, the level increases and then drops a good bit. Does this every time, I'm not sure where the fluid goes, but it has to go somewhere.

I am not positive how the BPV works, but this is what I'm thinking....one line runs to the BPV from MC to feed it and one line runs out of the BPV it back to the MC, with the third line actually feeding the drums. Does this sound right? I had always thought the two lines connected to the BPV were one for each drum, but after looking carefully, I don't think this is true. I guess the one line that returns to the MC is to monitor pressure from the BPV. I think the problem lies either within this line or withing the operation of this in the MC.

Alright, that's my story........I am pretty frustrated <img src="/forums/images/graemlins/angry.gif" alt="" /> with this truck. Seems like one problem after another (now it won't even try cranking over...starts with popping clutch, and the radiator is leaking), more on these later if I run into questions.

Thanks for the help <img src="/forums/images/graemlins/confused.gif" alt="" />.

First off I think you have a bad master cyl, bubbles like you describe should not be happening. You can upgrade to a 1" bore master cyl from a 89+ V6 truck. Also the LSPV (the thing you called BPV?) is a Load Sensing Proportioning Valve, it controls the amount of fluid getting to the rear brakes and increases the flow when you have a heavy load in the bed because it moves the rod attached to the axle. If you have a lift on the truck you need to raise the end of the rod that attaches to the axle a like amount. You can actually strap the rod full up to the frame and it will be fine, you will have maximum rear braking all the time so make sure your rears don't lock up before the fronts or you could swap ends when panic braking. Definitely change the master cyl and then bleed the crap out of the whole system, shoudl work fine.

<img src="/forums/images/graemlins/confused.gif" alt="" />Do you have a repair manual for the truck?The 2 things I would check would be the proportioning valve adjustment and the rear drum brake adjustment.You may not be getting a lot of fluid to the rear brakes because the valve is closed off,not allowing fluid to the rear.Also,there's a small inspection plug near the bleed valve on the rear wheel.Pull this off and shine a light in the hole.You will see the teeth on the adjustment wheel.Take a small flathead screwdriver and push the gear teeth upward.Keep checking the play in the wheel your adjusting.When you feel the wheel start to drag,your done with that side.Then check the other.The lspv has an adjustment attached on the diff.pumpkin.You want it adjusted up.Hope this helps you out!Good luck! <img src="/forums/images/graemlins/cheers.gif" alt="" />

I had this SAME exact problem on an '88 toyota truck several years ago...if my memory serves me right the master cylinder was bad. I remember thinking it was odd too...because it didn't exibit the typical bad master cylinder symptoms. Even with the new one installed I had a Hell of a time getting it bled. I ended up have to use a pressurized brake bleeder to force fluid through the system via the resevoir. That rear axle proportioning valve was a pain to deal with during the bleeding. Good luck.

Thanks guys. The rear brakes and BPV are adjusted properly, so I'm still thinking its the MC. I guess I'll have to swap that out also. I surely hope that's it, but I'm still wondering............

remeber to bleed the poportion valve as I forgot on my last brake and plumb job and took me 1 big bottle of fluid to remeber it messy to say the least

Jim Ed