Hotrodder

Hi guys, I've got a brake problem on my 95 4runner I was hoping to get some help with. I bought this truck recently and it had funny brakes. I thought no big deal, old truck it will need brakes. I ordered everything to do the brakes, pads, calipers, rotors, drums, shoes, cylinders, etc. Got the truck up and to my surprise the brakes on it looked brand new with nice even minimal wear. So, I took the brakes back and started hunting down the problem. I tested the vacuum, perfect, tested the check valve, perfect. Next I tested the power booster and it seemed to fail so I thought, ok, it's 200.00 but let's replace that. Not a dang thing changed. So now I'm going to try replacing the master cylinder. The one on it looks newer but we will see.

My question is, do these symptoms sound like a master cylinder?
1) brakeing at idle speeds is great, nice hard pedal
2) get up to about 40ish and hit the brakes and hard pedal but barely any brakes
3) get up to about 40ish and pump the brakes, they work fantastic

Could the reason the brakes are so touchy be that the rears are not adjusted properly? Theyre all bleed correctly but I understand the rear brakes are adjusted via the e-brake? Well the previous owner removed both rear e-brake cables...could this be the problem?

Any thoughts? I'm at my wits end with this problem and I've searched for days with nothing sounding like this.

Please help

angrybob

SOLVE THIS FIRST! I think this is key. And you are correct, the drum brakes are adjusted by the park brake. Yours are not adjusted. My thought is to first check the cage diameter and subtract it from the drum diameter. Divide that difference by 2. That clearance spec is 0.6mmm or 0.24".

Check that first.

Replace the cables and check that they adjust correctly by turning the adjuster in so its a lot smaller than the drum diameter. Apply the PKB until it stops adjusting and measure the clearance again. See if that fixes your problem before you spend any more money.

Just curious but specifically, how did you test the booster? With the brakes applied, does the pedal drop when you start the truck?

For the master cylinder, does the pedal go to the floor or move at all when you hold constant pressure while at a stand still?

Hotrodder

I will definitely check the rear brakes first as you say. I checked the booster three ways. Engine off held the brakes after pumping a couple times to firm it up, started it, and yes, it dropped. Then I had the truck running, pumped the brakes, held them firm, turned the truck off, and brakes went to the floor. Next I removed the booster hose, applied manual vacuum with a mityvac with engine off. Applied 12 lbs of vacuum. Hit the brake once, dropped 6 lbs, then hit the brake a second time, dropped to 0 lbs of vacuum. I was told by a mechanic that this meant for sure a bad booster. Was he wrong?

angrybob

In general a failed booster will give a hard pedal and low output and will not drop when you start the truck with the brakes applied. Likewise, a failed master cylinder will have the pedal slowly go to the floor with a constant pressure. Both happen, but both are somewhat rare.

Even without you PKB cables, set the running clearance to spec above and take it for a drive.

#1 is normal
#2 is a failed booster symptom
#3 could be a bunch of things

Hotrodder

To clarify the "this" above, I was told all three test results meant a failed booster. So one other thing too, when in park, if I pump the brake it doesn't much firm up but when I'm driving and pumping the brake, it firms up well. So when I did he test of engine running, pump up the brakes, engine off, and the pedal went to the floor, there was only about 1/4 inch of travel from holding to floor.

I think I'll adjust the rear brakes and then see how it is. If it feels better, I think I'll redo these tests.

I'll post results of adjusting the rear brakes.

I really appreciate the help angrybob. Thanks

Hotrodder

So I adjusted the rear brakes with the self adjuster by taking the rubber plug out and turning the adjuster with a screw driver (turning the adjuster away from the truck on both sides).

They both clicked about a dozen times. Took it for a drive and no real noticeable difference.

angrybob

It does sound like your booster was bad. The three main booster tests are to check its functionality by pumping it with the engine off about 4-5 times then start the engine. The pedal should drop a little bit. This indicates a build in vacuum from the engine side.

The second is what you did I think. With the engine running, push the brake pedal in and turn off the engine. It should not drop further to the floor (very slow is OK) for say 30 seconds. Mine drops to the floor in about 10 seconds, but my brakes are fine.

The third is let the engine run for about a minute and shut it off. Press the brake pedal slowly a couple times. If the first stroke was the longest, then slight shorter on the second, then slightly slower on the third then your good.

I don't know what your mechanic told you, but if nothing changed and you failed the second test badly, you probably still had a bad booster...just masked by the main problem.

angrybob

With new brakes that you did not install, I would check the system bleed because many people have problems bleeding the LSPV. Do it last. LR, RR, RF, LF, then LSPV. Its easy to do and a good idea with not knowing.

Second is to make sure that the wheel cylinders are functioning properly. New probably means reman' and they are not the most reliable component...even new.

Third would be to ask how you set/confirm the pushrod length when you installed the booster. Not sure how this would contribute, but its also often overlooked and worth checking while your hands are dirty

Finally and related to #3, I would check your brake pedal free play (3-6mm) just to make sure that the brakes are fully disengaged.

These two things usually are not part of the same problem.

Hotrodder

I'm pretty sure the booster was fine. Put the old one back in and I'm going to change the master cylinder. I bleed the master cylinder really well and found the front line bleeds like crazy almost sprays out while holding the pedal but the back line barely drips. I think that is why it seems my back brakes aren't getting any juice...right?

I'll hang onto the booster for a bit before returning it but im pretty certain it's the master cylinder.

However, I've got bigger problems now. I've got exhaust bubbling in my radiator meaning..finally the head gasket gave out. Sigh, I can't win with this truck. Bought it cheap and I'm payin for it now but oh well, more work and more money at least the truck will be solid mechanically for a while after a rebuild...hopefully.(knock on wood)

willyt4r

First Bear Down.
My own trying experience was that the LSPV was clogged. I couldn't bleed the rears. I tried two different MC's- thinking Ive got a faulty one the first time. Replaced both calipers-againd thinking that they were at fault. I'd checked and recheck the Booster- replaced the check valve and hoses. After these repairs I went to the dealer and purchased the LSPV. That solved the mysterious brake pedal problem that I had.
91 4runner 3.0 4WD

angrybob

Yeah, that doesn't sound right.

If so, good thing is that you've fixed a couple things along the way and now *know* your brakes are right. I never like previous owners new brake jobs...but that's just me.

Head gasket - 22RE or 3VZ?

Hotrodder

It's the 3vz..I think what happened was, the previous owner used the crappy cheap bars leak in it (gold flakes in the coolant when I got it). so when I used sea foam in it, it ran like a brand new truck but must have cleared away the bars leak. So, in hopes it will last through winter, I'm going to try the good bars leak or blue devil or something and hope it plugs up the leak for a bit. If not, time for a rebuild.

Depending on how that goes determines how much more I do with the brakes of course.

Is there any way to pressure test or otherwise test the lspv?

Thanks guys!

Hotrodder

Update: got the motor rebuilt and she runs like a champ. Still going to need to figure out the brakes though. I'm trying the master cylinder this weekend. I'll let you know. Thanks again for the trouble shooting help.

vasinvictor

iTrader: (3)

x2 DO THIS

sechott

Just curious what level rebuild did you do, anything interesting to share?

Hotrodder

I missed that the first read through! I didn't know the lspv can be bleed. I'll try that first.

I blew a head gasket so I rebuilt the motor from the heads up. Nothing too exciting. Runs like a champ. Replaced the timing belt, water pump, gaskets, every hose I could, all filters, pcv, plugs, wires, the usual. Again, nothing exciting just a rebuild.