94 4RUNNER Brake issue

9

944runner

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Wifes vehicle. I am historically a Chevy guy, familiar with the square body's C/K and right now knee deep in an 89 GMC K5 Jimmy.

Anyhow, she called me today and said her brakes feel like she is pressing a brick. I am assuming that she has lost the "power" brake feeling when pressing on the brakes. Now in my previous experience I want to start looking for a bad or cracked vacuum line, or one has come off completely. What ever it is, it happened fairly suddenly, and she say's the brakes still function, just doesn't feel like it used to. (That's wife talk for FIX IT NOW.)

Can you guys point me in the right direction please, where to start and what I am looking for. I have all of the service manuals for my truck, but have yet to aquire the Toyota service manuals. I am hunting though.

Thanks in advance guys!


Sorry guys. 1994 4 Runner, 3.0, 2wd, stock everything.
 
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Id check the vacuum line to the brake booster, could be a blown out booster its self but thats rare. It's dang near the same as a chevy or any other car that produces vacuum.
 
Thanks GonOvr, headed home shortly. I figured as much, but as I said, this will be the first wrenching on a Toyota. Well except the trans sensor I replaced after we bought it. PO thought tranny was bad and head was bad. Nope on either one.

Thanks again, I appreciate it.:cheers:
 
Booster???

Okay got home, checked it out first. No obvious vacuum lines off or cracked, no leaks at any hard lines, calipers, etc. I put my foot on the pedal, prior to starting the engine, felt okay, semi soft for about 1/2", then real firm. Started it up and with foot on the brake, into reverse, vehicle moved backwards. I had to nearly stand on the pedal to stop it.

Any affirmative checks to do on the booster to verify that is it? I'm not much of a "parts changer", I'd like to correctly diagnose first, then change what I need to.

Any help is greatly appreciated guys.

Thanks again.
 
Little more info, more questions

Okay after some more digging, investigating this is what I have.

Searched 12 to 15 pages of posts that came back searching both brakes and brake booster. Seems eerily similar to a few booster related threads.

I went back down after some of this research and I do have plenty of vacuum at the booster. No actual gauge reading but it feels sufficient, I think it should have about 15-20 inHg (healthy engine, this one has 175,000 miles, maybe not a picture of health, but healthy as say a 35 yr old who smokes a pack a day???).

When I depress the brake pedal I can hear a hiss. The noise seems to be coming from internally from the booster and traveling down through the steel of the brake pedal.

I turned the engine off again and removed the vacuum line at the booster. If the booster has failed, I imagine it would be the diaphram that has a tear (symptoms). However, when I checked vacuum originally and after running it for a while, there was a distinct hiss once the vacuum line was disconnected at the booster. That leads me to believe that the diaphram is holding vacuum and does not have a tear. SO, why is the pedal hard to push AND brakes acting as if there is no booster working.

Perhaps I do not have my head wrapped around the booster internals.

Anyone give me some guidance here??? I'd feel sick throwing $200 booster on this thing and giving up time with the family this weekend to find out the booster is okay.

Anyone?

Thanks in advance for the help.
 
Info and testing

Throught some internet exploring and research I found several checks for the booster and brake system.

Engine OFF- depress pedal several times, there should be no change to the reserve (amount of space between bottomed out and pedal position) This is good, there is no change

Run engine for several minutes. Turn OFF. Depress pedal several times slowly. 1 st time should go down further, the second a bit higher, third higher yet.
This is also good, it does go down further the first time, and a bit higher each subsequent depression. Not a ton of seperation here, I would have liked to see more, but there was seperation.

Depress pedal with engine RUNNING. Turn it OFF. If no change in pedal after holding pressure on it for 30 seconds. Another good test result here.

These should have revealed something if the booster was the culprit.

I also noticed that sometimes during repeated depressions and / or holding the pedal down the engine will bog down a little (as if there is a vacuum leak). Yet other times it will not affect engine idle at all.

Another note: maybe nothing but I did it several times to make sure there was some sort of connection. My garage is flat, did the testing in there. Rolled it out of the garage onto the driveway that slopes fairly quickly. This is where I noticed the engine idle bogging and heard the hissing. Pulled it back into the garage, no hissing, no engine idle affected. Repeated this 3 or 4 times, same result.

:wtf:
 
Nothing

Wow, nothing......no help huh?

I guess I'm going after the booster, that's all it can be. Perhaps the double diaphram is throwing the results of my testing off a bit, i.e. one diaphram punctured, one is okay???? Strange inconsistency though.

I will try to let folks know what I come up with, hopefully it will help someone else out. Noticed during my vast searches thru threads here that there are so many open ended threads, no results posted.

I am open to any suggestions or guidance if someone is so inclined to help a guy out.

Thanks.
 
On the vacuum line going into the booster, there is a check valve. Try replacing that. Sounds like its stuck to me.
 
It seems to me that if the booster was bad, simply disconnecting the vac line to it and comparing the feel/stopping to with the vac line connected would tell you. If it felt the same whether the vac was connected or not, then the booster would probably be bad.
 
Update: It was the booster

Got a used booster today from the scrap yard and threw it in this afternoon. $100 used, vs $300 - $600 reman unit, or $935 from the stealership.

I still do not have an answer for the tests performed on the booster I described above indicating the booster was okay, but it clearly was not. The brakes feel great, in fact they feel better than prior. My guess is that the diaphram or what ever failed in the old booster was on it's way for some time, just gradually over time we didn't notice it.

Anyhow, hope this helps the next person down the line with a similar issue. Very hard, high brake pedal. You may notice a hissing noise when depressing the brake pedal. Noise actually sounds as if it is traveling down the steel of the brake pedal hardware, from interally within the booster assembly.

If anyone has any questions in the future just send me a message. I'd be glad to help.
 
Good info

944runner - appreciate you posting your troubleshooting and solution (even though its from 2011 - its still relevant information).

Anyone experience idle fluctuation or engine stalling due to a faulty brake power booster?
 
Caspice- idle stability

I, too, am addressing a suspected brake booster failure (Thank you for the posts, 944Runner!). Regarding the idle stability, there is a distinct difference in my idle speed when I disconnect the vacuum hose going into the booster- it slows and gets only a little bit rough, but still runs. I did not experience a change in idle while hose was attached- same before and after booster failure.
 
The diaphragms in the booster can get small tears in them from age. Think of a tire with dry rot. It can hold air but it can leak as the rubber moves. I have experienced a high/ stiff brake pedal from brake calipers that have stuck pistons. Easy to check. Stuck pistons won’t affect your idle though.


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Privateer383 said:
I, too, am addressing a suspected brake booster failure (Thank you for the posts, 944Runner!). Regarding the idle stability, there is a distinct difference in my idle speed when I disconnect the vacuum hose going into the booster- it slows and gets only a little bit rough, but still runs. I did not experience a change in idle while hose was attached- same before and after booster failure.
Click to expand...

Hhhhhh
 
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