I'm having some issues with my brakes... I'm pretty sure it's related to either the brake booster, the booster hose (the one with the check valve), or some kind of vacuum issue.

My engine is a S4 NA 13B with a Large Streetport. The whole braking system is out of a S5 Turbo2 (not some weird swap, my car came out of the factory with it... long story), but I removed the ABS unit and ECU.

Engine had a lot of stuff removed (rats nest, BAC, air pump, etc).

So... this is what happened... I was driving on the freeway and gently touched the brake pedal, feeling it a bit hard. Brakes reacted, but the pedal was strangely hard. Every time I slightly touched the pedal, I felt it getting harder, barely moving. Then I started to feel as if the engine was getting weaker... it was the brakes being stuck "on". So, revving a lot and going nowhere, I luckily got off the freeway and stopped. Brake pedal was impossibly hard, and the car wouldn't move. Brakes were on, really on.

I popped the hood, disconnected the hose that goes from the brake booster to the hardline... tried to blow into it, nothing. Sucked in, perfect. With that... I assume the check valve is doing what its supposed to.

Started the car again, and voilá, the brake pedal works again. Consequently... I assumed my booster was shot.

Took the car to the shop... they took the booster out and noticed it was full of brake fluid. My previous brake master cylinder had a leak, and seems like it leaked into the booster itself... thus... the booster was in terrible shape internally.

Ok great... so they rebuild the booster and got it back in place.

So I've had the rebuilt booster for a couple of days... and this same thing has happened to me already twice. Car starts to feel slow... brake pedal gets harder and harder with each press, until the car won't move at all.

Called the shop on this, and they tell me that the booster was properly rebuilt, that's been tested, etc... and that "something else" might be causing the issue...

Now... is this a possibility? Even through the booster hose's check valve seems to be working properly... is it possible that its not? What about vacuum leaks... would a vac leak cause issues with the booster?


Thanks in advance for any kind of info or feedback you may help with

 

I think your booster input shaft may be incorrectly adjusted (this is the pedal>booster connection with the clevis).
So, try this...

Loosen the pushrod at the pedal till there is significant freeplay before the booster gets moved.
(Make sure you can still brake...)
Drive a few miles- speed does not matter, nor do you need to brake heavily- then stop and readjust the pushrod, taking out most of the freeplay.
Now drive some more and see if the brakes still lock up/drag.

In essence, I think you're adjustment is preloading the MC and as the fluid heats up, the brakes begin to drag.

 

the shop probably sucked the brake fluid out, clean it up and just told you they "rebuilt" it so they could charge you some money. they should've replaced it not rebuilt it.im a mechanic and i've never even heard of a rebuild kit for a brake booster. if they say it could be something else then i would go back and raise hell and get your money back for the "rebuild". you brought them the car to fix and they did not fix it.

 

Yeah, I'm not sure how a booster would be rebuilt either.

 

Black Dragon Automotive offers refunds for "Rebuildable Cores", when selling Brake Boosters...


I forgot to mention something... when the brakes lock up, I do the following to "unlock" them.

I turn the engine off, disconnect the rubber hose that goes from the engine to the booster... connect it again, turn on the engine... and that's it. Brakes working again.

Now... considering that doing this actually unlocks the brakes again... would input shaft misadjustment still be a possibility?

 

there is a Check valve in that Rubber hose that attaches to the Booster,and it could be sticking from all that Brake fluid being sucked in.??
My guess anyways Danno!..how ya doin?

 

Yes.
Without changing anything drive till the brakes begin to drag again.
Then, see if there's any freeplay at the pedal.
If not, you've probably found the problem and adjusting in some slack at the clevis will probably fix it.

 

Hehe, hi Dave!

Thought about that... and like I mentioned before, I tried blowing/sucking through the hose, and it only lets me suck. I assume that means it's working properly. Is there any other way to check if its working properly?

 

You really need to listen to clokker. In my own brake-swapping shenanigans I replaced a perfectly good booster because I over-tightened the clevis.

 

So... I haven't had the time to test what clokker suggested (I will, I promise...)

But today, this happened...

I'm on the freeway, and I start feeling the brake pedal get harder and harder, each time with less and less travel... so a point in which it was actually dragging down the car... had to stop, had no option.

Pedal was, obviously, impossibly hard. Almost no play... not like when you turn the engine off and pump it... much harder than that -- would only feel a small play when pressing it with my hand.

So I popped the hood... disconnected the booster hose, got into the car and turned it on. No luck, brakes still locked...

I connected the booster hose again. Nothing, brakes still super locked.

The pedal got a little play, but the brakes where still on.

Disconnected and connected the hose a couple of times (was desperate...) -- and eventually the brakes went "off" a bit... car would move... so I drove very slowly for less than 1/4 mile, to a safer location.

Brake pedal was still hard, and had very little travel.

So... once more I disconnected the booster hose... but this time I tried to blow/suck through it. Tried, couldn't do either.

I connected the hose again, turned the engine on and... the pedal released completely. So did the brakes.

Now... could really blowing/sucking through the hose achieve this!? Should I assume that the hose's check valve is simply getting randomly stuck... and causing all this?

 

quote>Now... could really blowing/sucking through the hose achieve this!? Should I assume that the hose's check valve is simply getting randomly stuck... and causing all this? <unquote.
..
De javu?..or victory?

 

Try bypassing the check valve

 

If it is indeed the check valve... do I need to get one specific for our cars? :P

Do I need a new booster-to-engine hose altogether?


Really? Wouldn't this hurt braking, or the booster itself?

 

Damn it, it's NOT your check valve, it's NOT the vac hose...it's the adjustment.
All of your experiences still point to that very thing.
Just loosen the locknut on the clevis and take her for a spin.
As the brakes begin to drag, loosen the pushrod instead of screwing with the vac line.

Speaking of the vac hose/checkvalve...no, you don't need a Mazda specific part...it's just a simple one way valve.
Every car in the junkyard is a potential donor...

 

Okay! Okay!

So... I should...



- Slightly loosen "D"
- Take her for a spin, and when the brakes start to drag...
- Loosen "C" until... the brakes unlock and work normally?
- Tighten "D"

Should I adjust "C" when I start to feel the brakes drag? or should I wait for them to lock completely?

 

ok did they rebuild the brake master cylinder? because i have never heard of rebuilding a brake booster. those are just replaced.

either way if they did not fix the leaky brake master cyl its just going to push fluid back into the booster and mess it up again..

either way i have a master cyl and booster off a s4 laying around 65 bucks shipped

 

Man, I'm going to feel stupid if I'm wrong here...
Loosen the locknut and drive.
When you feel the onset of drag, stop and spin the pushrod till there's a bit of play in the pedal, drive again...repeat till the brakes no longer lock up.

Or, you could save some time by just increasing the amount of freeplay beyond spec and then driving about the distance that has caused the problem before. Stop and adjust freeplay to spec and you should be done.

 

Master Cylinder's been rebuilt as well, no leaks.

T2 Master Cylinder and Booster... 65 bucks shipped to... Argentina?


Hahaha, why's that?

Thanks again for your time and explanation... will give that a go on saturday

 

Your car is an NA, you can simply remove the check valve and eliminate that as a possibility. The check valve is to prevent boost pressure from reaching the brake booster.

I do not think the check valve is your problem, but if you are in doubt just remove it.

 

Um, no.
Even NA cars (pretty much ALL of 'em) have check valves.
The valve allows the booster to retain enough vacuum so there is still assist if the engine dies.

 

Even with some overlap (Large 6-PI Streetport, and huge sleeve-less exhaust porting), I shouldn't worry?


So... you're with clokker? Pedal adjustment?

 

ah man so what happened? im in the same boat. same things goin on with my car. bought a rebuilt master cylinder from auto zone but i havnt installed it yet. was about to buy a brake booster and take it to my mechanic to put it all in but im going to have to try this first. cars been sitting for over 2 months so now i need a new batt too. everytime it sits it kills my batteries smh...