n7k1

I've been working on my s4 vert for a year now. I thought everything was done and was about to drive her to the paint shop when I found out the brakes were shot. I have been working on this on and off for weeks now...and need some advice.

As I said, its a s4 vert. The front calipers are 4 piston. I noticed the original master cylinder was severely rusted and the reservoir was empty when I bought her. I immediately put on a rebuilt MC. I bled the lines and expected everything to be good...unfortunately not.

With the engine off, I pump the brakes. They hold about midway down but don't get firmer as I pump. When you start up the engine, the pedal gets softer and then fades to the floor. I figured I had a leak. The right side caliper looked messy, so I rebuilt it. I bled the lines again. Still the same problem. I checked every fitting and tightened it. I checked every caliper for leaks...nothing. The fluid level never seems to drop.

I finally gave up on the rebuilt master cylinder and managed to pay the difference and get a new one. The problem still persists and its kicking my ***! I've run out of ideas.

Did s4 verts come stock with 4 piston front calipers? I read in an older post that it may have something to do with the length of the rod that pushes into the master cylinder. How do I adjust that? Do my symptoms sound like a failing brake booster? Could my second master cylinder be bad?

I'm getting tired of this...I would appreciate any help. I really want to get her on the road.

n7k1

also, there are a few clicking noises as the pedal fades and when you pump it with the engine on, its as if the brake pedal isn't coming back fast enough.

clokker

iTrader: (2)

You could be talking about either of two different adjustments here...the booster>MC pushrod, or the pedal>booster pushrod.
Both are adjustable but highly unlikely to have changed on their own.
The pedal>booster rod can be reached (by an 13 y.o. Chinese gymnast) from the footwell and is the most easily fiddled with ("easy" being a very relative term here).

Getting to the other requires separating the MC from the booster- a task the deficient usually shy from (usually, but not always...check the brake line fittings for evidence of Vice-Grips) and, like the first , can barely be done with intention, much less decide to move on it's own.
Possibly.
Sure.

It's too late for you but I'd recommend a scorched earth policy when approaching a system like brakes (cooling system, too).
Especially given your initial discovery of the rusted and empty master cylinder, the logical conclusion would be that the whole system had been compromised and must be dealt with as a whole.
Instead of chasing problems from one end of the car to the other, overhaul/replace everything at once and viola!, you're done.

The time- and agida- saved is worth it.

misterstyx69

iTrader: (142)

the Reservoir was empty..I think I know what may be going on.
Ok,you have to Bleed all 4 corners..(start with rear passenger,rear drivers,front passenger and then front drivers.) always go from Furthest away from the Master to the closest.
The reason is that there is was no more fluid in the lines and air could have gotten into the Brake lines.
Try bleeding it with either a One man brake bleeding tool or have someone Pump pump,pump and then Crack bleeder, keep Foot Down on Brake pedal,.and tighten bleeder,,repeat.

n7k1

Thanks for the replies so far. I've bled the lines 3 times - it hasn't helped. I think I'm going to replace the brake booster and check valve next. Then I'm going to plug the master cylinder ports and see if the brake pedal is firm. If it isnt, I'll suspect that I have another bummed master cylinder. If it holds, I'll hook up the brake lines, bleed them and see if my problem is gone. If not, I don't know what else to replace except the brake lines and the calipers...

misterstyx69

iTrader: (142)

did you bench bled the master after you rebuilt it?
by the way,if that check valve was on in reverse you would know it..
Extremely HARD pedal.and if you drive the car and slam the brakes on,you almost have to Grab the steering wheel and Pull your Body onto the Pedal..
When parked it feels like you have good pedal but the Booster isnt actually getting vacuum so it is like Hitting a friggin brick wall..(stumped me for about 4 days after a 5 lug swap!).

n7k1

yup bench bled. I'm trying to learn more about this check valve thing on the booster. Where is it? When I look at my brake booster, there is a hose that connects to a metal nipple on the booster and then it connects to a metal line that connects to someplace on the passenger side of the engine bay. I don't see anything that looks like a check valve.

whistlepig87

iTrader: (2)

I would check for a hole in the lines somewhere too. My brother's chevy had the same symptoms, and it was spewing brake fluid from one of the lines.

SoloII///M

iTrader: (13)

Use a 2x4 wedged against the seat bottom to apply constant pressure to the MC. Look under the car an hour later to find the leak. It sounds like it's leaking somewhere.

n7k1

Bloody frustrating...the fluid level doesn't drop at all even though the pedal keeps going to the floor. Right now I'm guessing a torn booster diaphragm.

replacing the booster this weekend with a used one. Then I'll rebleed and put the 2x4 to check for leaks.

oregano

iTrader: (1)

why would you suspect the booster?

the booster helps you apply force to the brake pedal (which would otherwise be very hard to press using your own human strength). it has nothing to do with the actual braking system firmness or hydraulic parts. Symptoms of a failing brake booster would either be no brake assistance (you would have to press very veyr hard on the pedal to make it move at all and stop the car) or way too much brake assistance (you tap the brakes and the wheels lock up).

you say your foot "goes to the floor". This sounds like a failure in the hydraulic part of the brake system. Could be air in the system, or could be something else. The only way its your brake booster is if your foot goes to the floor, but the pedal still feels very firm, and your car slams to a stop as if you had pressed the brakes very hard.

JReed

iTrader: (18)

well if your lip seal failed on the pirmary piston it very likely could have pushed fluid into the booster and then your diaphragm would most definitely be beat :/

n7k1

Yeah, that's what I'm thinking right now. The paint on the booster under the MC was gone when I took off the original MC - so I'm guessing it got into the booster.

Oregano, you described it better than I did, pedal is firm while it fades to the bottom and then the brakes grab suddenly. The clicking noise I was referring to is coming from the left front caliper and while its not leaking - I'm going to rebuild it for good measure anyways.

Thanks everyone. Hopefully I can get things sorted out this weekend. I'm getting a used MC, booster and a 13B for $100! hopefully the parts are good.

SoloII///M

iTrader: (13)

A booster would not cause the problem you describe.

You have air in the system somewhere. If I had to guess I would suspect something with the calipers since the 4pot calipers are notorious for failing when they're not maintained properly (i.e. regular fluid flushes).

Or your bleeding technique needs work. It's important to bench bleed a master before installation, or use a pressure bleeder to do it when it's on the car. Even if you use the pressure bleeder, it can take three or four go-rounds to get ALL the air out of it if you don't bench bleed it properly.

It could be a number of things, and your booster may be hosed, but the booster isn't causing THIS problem.

Makenzie71

If I were you I would first make sure there are no leaks in the system. Then, individually, use a vacuum to bleed each of the slaves. Make sure you top off your reservoir each time you move to a new caliper. And by "bleed", I mean you need to suck the reservoir, from full, down to about 1/4 each time. Just keep recycling your fluid.

If you're sure you have no leaks in the system, and doing an aggressive vacuum bleed does not correct the issue, you need to go to a shop and have them flush and pressure bleed the system...cost like $30 and it's done the best way possible.

JReed

iTrader: (18)

#1 you never ever reuse brake fluid... i mean its dirt cheap , and once you bleed through the system it brings contaminates with it out through the caliper.. even if it a sealed system, once air is introduced into the system, the boiling point drops, etc... point being dont reuse brake fluid

#2 You bleeding your brakes vs a shop doing it....virtually the same except the price u pay (def more than $30.00, my shop is close to $65.00)

my $ .02

Makenzie71

Such a post is either from idiocy or ignorance...I'll assume ignorance and explain a couple things to you.

By the time you suck the new brake fluid from your master to your slave and get ALL of the air out you'll have used nearly twelve ounces on just one of the front...which is about the capacity of the entire brake system when properly fed and bled. You're either going to have to use several jugs of brake fluid, a giant jug of brake fluid, or you can just do the smart thing and use the right size jug of brake fluid and use it all correctly.

First, your shop isn't the only shop. Second, your shop is charging too much. Third, you sitting on your *** at each wheel well sucking bubbles from the system is about as distant as can be from hooking a pressurized system to your reservoir and forcing brake fluid through to all of your slaves.

JReed

iTrader: (18)

do you have your ASE certification in Brakes ?

not being a dick, but ASE clearly states not to reuse brake fluid at all, and who really cares if u use a big bottle of brake fluid its like 4.00-6.00 at auto zone (or equivalent)

SoloII///M

iTrader: (13)

Once the fluid is through the system it should not be re-used.

I somewhat scientifically measured the capacity of the brake system when I was replacing everything in mine this winter. The farthest corner took about 5 fluid ounces. In other words - not much. The ones closer to the master were a bit less.

Point being, if you're going after a flush of the system and doing it properly, you only need a maximum of 20 fluid ounces plus what's in the reservoir (which you should suck out before hand). Not much fluid. It's cheap. Don't re-use it.

Makenzie71

Maybe I wasn't clear...I assumed new fluid is being used. I read back now and do not see that being said. If the system is clean, taking new fluid that's been sucked from the reservoir to the caliper and reusing it will cause no harm...this is all assuming your storage and vacuum setup is clean.

misterstyx69

iTrader: (142)

the check valve you are looking for is IN the rubber "s shaped" hose that goes from the Booster to the Hard Steel line on the firewall.

n7k1

I just wanted to say thanks to everyone. I swapped out the booster and the pedal doesn't drop/fade anymore. The clicking sound was still there so I suspected it was the pads - I replaced them and the clicking went away. The brakes still felt a bit spongy so I power bled the lines. I took the advice of one of the posters and bled each line until the reservoir was down to a 1/4, sometimes, I filled it up and did it again. I never reused the fluid...I didn't want to have to suspect the quality of my brake fluid if the problem persisted. After bleeding, the brakes felt better - but I still didn't like the feel/play of the pedal. I played with the brake pedal free play adjustment and its miraculous how a few mms can make the pedal feel so much better.

I learned alot and all the advice I received was good. Now I'm thinking of upgrading to a 929 MC...but first I hope to get her on the road *finally* and hit the paint shop! Thanks again.

RXnos1200

iTrader: (24)

check your flexible brake lines when you get a chance. I've seen them swell up but not leak causing a spongy type feeling to the brake pedal. we replaced them with the ss braided lines and it was much stiffer........