Dryheat

I am at wits end with my brakes. Its on a 90 4Runner, 3.0 4x4. Started as a bad master cylinder/brake booster, which was replaced, progressed to bad rear passenger cylinder which was replaced.

I had the system professionally bled but still come to find I don't have very good brakes, low pedal(almost all the way down) and no stopping power in high speed braking.

Took it to a garage close to my house. They said that it needed a new master cylinder(after I had put in a new one from NAPA) When that didn't work they started saying that it was my Booster. I have have checked it for leaks and don't think anything is wrong with it but it is a used one out of another 4Runner. At that point I think that they are grasping straws.

I took to to a Brake shop that I thought would have more experience with this kind of problem. Unfortunately, they said that I just need to adjust the rear brakes and turn the drums and rotors. Brakes still the same.

I then take it to the Dealer and they say on first look that it will be fine if you put in all OEM parts. I tell them that I don't think thats the problem. They then say that they just need to adjust the back brakes and bleed the system. I let them but when I came to pick up the car the service person brought it up and realized that the brakes were even worse then when I brought it in. After 3 techs look at it they settle on new rear shoes and new front rotors and pads. The also adjusted my brake pedal such that the vacuum was always bleeding. I found this out while driving it and getting alternating high and low pedal. I fixed that but afterwords I checked my reserve pedal height and found it to be only 1" above the min. that they call for in the service manual. I will probably take it back to them on Monday but this weekend I will see if I can find any bulging rubber hoses.

Sorry for being so long. Any other ideas about things that I can check or have them check.

Thanks in advance.

Paul

ThomasJ

let me give you a few tips for next time you take it somwhere so you dont have to waste any more money.

The rear brakes being out of adjustment will cause a low pedal. The rear brakes are self adjusting. Every time you pull your parking brake the rear brakes adjust if they need to. If you never pull the parking brake the brakes will never adjust. The adjusters can stick and stop working. In most cases they just need cleaned and greased.

Them telling you that the rotors and drums need turned is complete BS. This has no effect on pedal travel and if it did it would make it worse due to the material being removed from drums and rotors. The booster just gives you the power assist. If the pedal is easy to push but just travels too far it is not the booster. If the booster goes bad the pedal will feel stiff and your braking power will be minimal.

From what I gathered you have new rotors, pads and shoes. The possible causes for the low pedal are air in the system, bad master cylinder, rear brakes out of adjustment.

You should focus on the low pedal issue first.

I would

Check for leaks
Adjust the pedal height according to the factory service manual
Adjust the pushrod on the booster.
Bleed whole system including master cylinder and LSPV. Do the master cylinder FIRST.
Check adjustment/adjusters on rear brakes.

If these steps are dont correctly and you have no leaks anywhere including the calipers and rear brake cylinders it should fix you low pedal. If it does not then I would say you still have a bad master cylinder.

Dryheat

Thanks for the reply. I agree with you on every point. I don't see any leaks. I have adjusted the pedal correcly and I have used the e-brake. In fact, they incorrectly ajusted it as it was leaking vacuum constantly. Rears have been adjusted manually to begin with. Rotors and pads and shoes are new. New rear cylinders were replaced (one bad, the other just to make sure it didn't blow out later) I see no leaks Ihave checked all components down to pulling the boots back and looking for fluid. The master cylinder has been replaced first with a rebuilt one, then a new one, then another new one at the garage with no change. The new rotors and pads have raised the pedal only a small amount. I finally can get the brakes to lock up on in the dirt. I couldn't before. I know it does feel like its a bad master cylinder but 3 out of 3 bad master cylinders is pretty bad luck. I was even careful to not depress them all the way in case there was debris in the piston bore that might rip the seal. I opened up one of the supposedly bad ones and checked the deals for rips or tears but found nothing.

I checked the pushrod length and checked it for stroke with the master cylinder unbolted. It pushes out the full stroke, so that's adjusted correctly. I can't see that any of thoses are cracked or bulging.

Originally I just thought it needed to be bled but after this last go around it seems that its something else. I grilled the tech about it before he did the work he was certain that this would fix it. We'll see what he says when I take it back

I'll post back when I find the real problem Thanks

Paul

Dublin

ThomasJ is right on for the most part. just a few things to add. the rear brakes do self adjust by the parking brake, but they also adjust by wheel movement in reverse when the foot brake or ebrake are used. As for the powerbooster it could cause some odd occurances and normally should act as ThomasJ stated, but just in case try this. Depress the brake several times with the engine off (there should be no change in travel) then start the engine and depress and hold the the pedal (should be no change). Don't blame the booster right away check out all the line connections and make sure the vacume is correct. I'm thinking you should bleed the system again and make sure all the air is out of the lines.

NY T100

I took a quick look at a FSM for toyota trucks and these are the suspected areas for a low pedal:
-fluid leaks
-air in system
-pistons seals worn or damaged
-faulty hydraulic brake booster

How are the seals on the front brake caliper pistons?
Did anyone bleed the LSPV?

Dryheat

I already checked the booster out. It holds vacuum and according to the service manual test procedure it checks out fine. With the engine off, the pedal still feels a bit mushy but but it doesn't bottom out. When I start the engine with the pedal depressed the pedal pulls right down to bottom. Dublin, what does this mean?

I have no leaks that I can find or 5 other techs can locate. Seals are not showing any fluid leaks. I've used both the reverse method and handbrake method to make sure the rears are adjusted.

Thanks for the help

Paul

ThomasJ

Was the master cylinder bled before it was put on?

NY T100

Possible leak in one of the vacuum lines? If they are original they may have some cracks in them.

Dryheat

Thonas J, I didn't put the last one on myself but I assumed that it was bled. It feels like it did before I replaced it the first time. Another bad Master cylinder?

Vacuum seems good. The unit holds vacuum until the peddle is depressed a very small amount then you can hear the air bleed back in. If I had poor vacuum or cracked vacuum line I would have a hard peddle correct. Thats what I had when the peddle was adjusted too low and the peddle would be soft then hard then soft again depending on how often I would use the brakes. Right now its adjusted to manual specs and it does hold vacuum.

Thanks for the input

Paul

Dublin

The pedal could go down a bit after it's started but after a few pumps it should come back up. If it doesn't it most likely is the booster, if it does your master cylinder may not be bled properly. I'm afraid I don't know the exact proceedure for toyota master cylinder bleeding, but some require a front first back second to center the proportioning valve.

Dryheat

Thanks Dublin. I'm not sure I understand about the booster. The height does come back after I pump a few times quickly. That I assume is due to the loss in vacuum . I assume that the booster pulls the pedal down using vacuum pressure of the engine on the booster diaphragm, and that the return spring and the springs in the master cyl. push it back up. The booster only pulls when the valve is opened when the pedal is depressed. At least that was my understanding of it. It's going back to the shop tomorrow to see if they can do it right this time. Hopefully, it just needs to be bled better. We'll find out soon.

Paul

Dryheat

Well I got it back. The pedal is firmer(it did need to be bled) It stil feels a bit low but it'll work for now. Apparently, I still need a booster. The junkyard one leaks, not as much as the old one but still leaks. The dealership wanted ~$1000 for the booster, installed. I guess I'll go with a rebuilt one. I still don't think that changing the booster is going to change the pedal height. My understanding of the way that the booster works is that the vacuum pulls the pedal down but the pressure of the system prevents it from going to the floor, as long as you have no leaks in the system. So the pedal height shouldn't be any different with new booster or in fact it would be a bit lower. If my reasoning is correct, then I still have the problem. I'll post back when after I put the new booster in. In the meantime, does anyone else have an idea? Thanks

Paul

Dryheat

I put the new booster in and in the process found out that the tech that put the new master cylinder in(independent garage) didn't adjust the pushrod to the correct insertion depth in the master cylinder. I just assumed that he had adjusted it. As it was it was way short. I now have decent brakes. Thanks for all that replied.

Paul