Inconsistent Brake Pedal Travel

BlackWorksInc

BlackWorksInc

New member
So after replacing my 4Runner's front differential I went for a test drive and found that my pedal was way to soft. We're talking almost bottoming out to get the 4Runner to stop, but pump it up some and the brakes work fairly well again. :roadkill:

So my co-worker and I threw on the TIS Techstream and bled the system a couple times, didn't find any air in the lines. The brakes were good for all of about 5 minutes...

Any of you guys found any solutions for this issue? I have seen a number of threads, but very few solutions or even updates on fixes.

I'm gonna go ahead and try to check the master cylinder tomorrow when I have some time. I am wondering if something is internally leaking or not sealing properly because it seems to work well if you pump it once or twice. Worst case scenario I suppose I'll warranty the MC, but I doubt the warranty company will be happy with me since they just warrantied my front differential. LoL
 
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I sometimes feel like my brakes are inconsistent but I always just thought it was me. Maybe it still is, I dunno. I'd be interested to know what you figure out though.
 
Let us know what ends up fixing it. Hope its nothing too serious. Most things ive seen point to air in the Master Cylinder. and when bleeding having to bleed the MC first.
 
If it pumps up, that doesn't sound like air in the system, as the air would still be there when you pump it up. It sounds more like a classic master cylinder failure.

Mileage?
 
scottm said:
If it pumps up, that doesn't sound like air in the system, as the air would still be there when you pump it up. It sounds more like a classic master cylinder failure.

Mileage?
Click to expand...

Looking at 93k right now... That's what I am leaning towards as well and I am sure my Warranty Company will not be hapy to hear that since they just replaced my front Diff this past week ($1500 part + labor and rental w/ no deductible from me...)

My co worker and I bled the master cylinder and all the lines multiple times via the TechStream scantool. We did notice that the left front caliper is not spurting as much fluid as the rest of them. We're thinking that maybe the calipers are sticking some, so tomorrow we'll take a closer look at it. Hopefully all it is a sticking caliper piston.
 
Update,

Went and inspected the calipers and found nothing abnormal. Went and submitted this to TAS, see what the factory has to input on this. The repair manual gives very little data to diagnose or troubleshoot the master cylinder.
 
So I forgot to update this in he past couple days; I haven't heard from TAS regarding the case I opened up, we did one last bleed to the system and it seems much better now even though no air came out. I am still miffed because the problem seems to have gone away on its own and I have no explaination nor real solution for it and I have no diagnostic methods for testing the master cylinder...

So essentially I got lucky and the problem went away on its own accord, sorry guys really wanted to provide some help since this seems to come up every now and then. I will keep looking for some more information and if it comes up I will post it for you guys, but as is right now I have nothing...
 
The problem seems to have stayed away for now and I got a call from TAS in regards to my ticket.

So basically the conversation went like this:

Me: Hey, so basically we have bled the system multiple times, inspected all the brake components and found them to be functioning properly and have no real reason for why the pedal is having soo much travel. I am looking for diagnostic information on how to test the master cylinder assembly.

TAS Tech: Normally in these cases we find that the Master Cylinder/Hydraboost system is faulty and needs to be replaced.

Me: Okay... we suspect the master cylinder might be the culprit, but we want to test it and qualify it before we go and tell the warranty company it needs a new couple thousand dollar part.

TAS Tech: Sounds like you did everything you could, no way to test them. Just rule everything else out as best as you can.

Me: Okay... Thank you.


So yeah... There we go, if you have excessive brake pedal travel and you have bled the system and know you have no stuck caliper pistons you need a new master cylinder assembly.

Some days I am embaressed to be a Toyota Technician, this would be one of those times...
 
That is odd that it doesn't happen all the time. When a master cylinder goes bad, they usually are bad. Is yours under warranty? Rebuilt master cylinders are in the $150 price range if you can find one compared to new which is closer to $1000.
 
I would love to see a rebuilt MC for our vehicles cost that much...

Keep in mind on the 4th gens they combine a MC, ABS module and solenoids, and vaccuumless power assist all in one. The system actually pumps up the pressure hydraulically to create power assist and those seals tend to leak.

Yeah, worst case scenario the pedal issues coe back, I'll have warranty replace it. They can't argue with me on it because I have gone as far as gotten the ok from HQ to replace it as the culprit. I am just frustrated that they give us all the detailed information to tear the damn thing and rebuild it, but they can't be bothered to provide some diagnostic information...
 
Bwahaha. Gotta love that TAS help line. Not the first time I've heard of them being useless. :D


Those hydro units are crap to diagnose. I even tried looking into my old Toyota training books to find out something for you, but all it said was that some of the parts are now available seperately. Unfortunately, it didn't list any tests besides the bleeding procedure for the master and bleeding the rear brakes using the Techstream.

If you did the 40+ times pumping to discharge the accumulator, then bled them, you should've gotten any air out like you said (I know you said you never really saw any air come out). There really isn't much else to diagnose them like you said that I can confirm or help you out with right now(not easy to get info while at home).

I'm curious if your issue comes back.


*edit* Did you check your brake shims? LOL ;)::p
 
Last edited:
Odd, I thought I updated this thread. I ended up having my extended warranty replace it. I disassembled the old one, I think I made a thread on tearing it down. I'm on my phone right now, but I'll try and look for the threads later. The new unit made a difference in braking performance, but it was different than I expected, but that was because of my unrealistic expectations than anything else.
 
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