schmooot

cliffnotes at bottom for the lazy asses.

Crap this truck is mad at me. Here's the deal, I've been slowly losing brake fluid somewhere for the past year or so...no big deal I just kept topping it up when it got low, brakes were a tiny bit spongy but everything was fine...I figured the leak would show itself when it was good and ready.

Well it did....I noticed a bit of fluid hangin out on my rear wheel the other day and finally I knew what I had to do.

I picked up a new wheel cylinder and shoes and went to town...it was a mess, the entire inside of the drum was thoroughly coated with DOT3, surprisingly completely rust free...even the fittings and bleeder on the backside. SO I changed the cylinder on the one side and shoes and figured I'd better change the shoes on the other side at the same time...when I opened that side up I noticed that that wheel cylinder was ready to go as well...so I got a new one of those and changed it as well. Then I bled both rears...starting from the furthest one until I was satisfied with the pedal feel. After starting the truck and the booster kicked in the pedal was uber spongy...and the rears were hardly braking at all.

pulled it back in and proceeded to rebleed them...this time all 4 wheels...no air came out.....I did it again just to be sure. I even went so far as to gravity bleed each wheel. I have now run at least two full reservoirs through and I'm confident that there is no more air in the lines. Still spongy when stopped and obviously 10x spongier when running.

I then bench bled the master cylinder in the truck (as per the fsm) while I was under the hood with a friend pushing the pedal I could hear fluid or something bubbling inside the MC whenever the pedal was depressed. This led me to believe that the MC happened to bite the dust as well.

OK fine so I have to get a new MC. My neighbor happens to be an automotive instructor at the local college so he said he could get me a pretty good deal on a refurb MC and then said his students would love to take it on, sure.....I don't say no to free labour (and it is more of a winter beater/pull my trailer than a dd so time is not an issue).

I dropped the truck off a couple days ago and they bench bleed the new MC and put it in......at which point only one side was working (his words not mine) They have been trying to figure it out for two days now and it has apparently stumped everyone.

I'm suspecting the proportioning valve is buggered (the one right below the MC) and I told them to check that out but are there any other components which could be at fault? Is there a trick to bleeding brakes on a 4runner that makes it different from every other toyota I've worked on? I'd like to go in there with a few suggestions for these guys...they have to learn somehow right.


I'm open to suggestions on things I can tell them to check out.


Cliffs: new rear wheel cylinders, shoes and MC. Brakes still won't bleed properly...suspect proportioning valve or ??? is at fault

BigBluePile

iTrader: (3)

What year?? Don't think it matters, but after all that...

You still loosing fluid? The only proportion valve I can think of is the one above the rear axle, which IIRC, is the last thing to bleed. Also, bubbling sounds at the MC?? Possible booster leak(indicated by lost fluid...)?

scuba

1 Use OEM parts for stuff like this.
2 BBP, the LSPV above the rear axle is normally the 3rd thing to bleed. Start from the furthest away from the master cylinder and move forward.

schmooot

as far as I know I'm no longer losing fluid....it just doesn't seem to want to bleed properly.

So there is a proportioning valve above the rear axle as well as just below the MC correct?

I didn't realize there was a bleeder nipple on the valve?

scuba

There is no prop valve on the master cylinder on any yota I've ever ran in to.

schmooot

what the heck is directly below it then? the two lines go right into it from the MC

Its a 1990 4runner 22RE BTW

thook

I realize some folks are sticklers for using OEM, but I've had good experiences with quality aftermarket brake parts at O'Reilly.

Anyway....

If the fluid is bleeding through lines to the rear on the side that's not functional, then it couldn't be a plugged brake line. So, I would suspect the load sensing proportioning valve. It's at the rear, passenger side, though. As stated, bleed it last. You will notice a detriment in your braking if it still has air and old fluid in it. Note: sometimes the inside bevel on the LSPV bleeder valve can corrode from lack of maintenance of the valve and not give a good seal allowing a small leak at that sight. Something to check for when bleeding it.

In case it's not obvious, the place to start bleeding the lines is at the rear driver's side. It's the longest line and, hence, furthest from the MC. I only say this for clarification even though it hasn't been brought up only because it's been somewhat of a common misconception to start on the pass. side rear.

thook

It would have to be a splitter. That's all I can think of. Although, I have been surprised before.

Here's the FSM diagram for the LSPV and bypass valve...

http://personal.utulsa.edu/~nathan-b...12loadsens.pdf

BigBluePile

iTrader: (3)

ah...well whatever...

Indeed.

Interesting, I've never thought of that...hmmmmm.

Pretty sure it's just a splitter.

schmooot

awesome, so just a splitter below the MC (two lines off the MC run into 4), then there is a lspv above the rear axle. WHat exactly does this valve do? does it adjust pressure between the left and right rear according to the weightload? or does it adjust pressure front and rear?

thook

A google search would tell you that, but for the.....ehem....lazyasses () it adjusts between front and rear according to the weight load.

scuba

You answered your own question

schmooot

got it. I'll pass the info along and we'll see if these college kids can get me back on the road....these kids are our future.....