928ntslow

I did a search and didn't quite find what I was looking for.

On my 82 Euro auto, the brake booster was bad, so I replaced it. The PO did the pads and rotors before I got it, so they look pretty fresh.

In my freshening of the car, I noticed the brake lights didn't work, so I replaced the pressure switches. Turns out that was not the problem, but no big deal, lights work fine.

So what would happen before I changed out the brake booster was when the car was first started, the brake pedal was tight, but it would bottom out. When I say bottom out, they didn't go to the floor, but rather past the point of assisted braking to more of a manual, mash your foot to the floor, hard braking just to get the car to stop. After the car warmed up and ran for a bit, the braking got better. First thought was a vacuum issue. When sitting at a stop light with the tranny in D, you could hear a hiss from the brake pedal area which seemed to be a booster leak. I thought all of this tied in and thats why I replaced the booster.

After the booster swap, I bled the brakes in proper procedure. Much to my surprise, this didn't cure the pedal action and actual braking...though it didn't hiss anymore. Now, I recently got a flashing "BREMSKREIS" light (brake circuit). The light flashes along with the "!" on the cluster and on the console button. This warning cannot be canceled.

What am I missing here? The master cylinder is not leaking and holding my foot on the pedal does not slowly hit the floor. This is a pre-ABS system, so there really can't be much complication to the system.

I checked the brake fluid level and it is fine...fluid is a bit hot though. I guess that is to be expected.

Anyone want to throw some ideas out there for me to double check?

dr bob

Dragging brakes from sticking caliper are just about the only thing that will heat up fluid in the reservoir in casual driving. Shoot the calipers/rotors with the heat gun to see which/if any are hot.

Pads sometimes drag because the MC isn't allowing the fluid to bleed back to the reservoir. Might be that the pushrod is adjusted too long. The heated fluid will expand with no place to go, and eventually may cause a wheel to drag so much that you can feel the anchor dragging as you drive. Telltale of this is the brak fluid circuit light-- one circuit thinks the pedal is pushing down and pressurizing while the other circuit is normal. Imbalanced pressure lights the idiot light and it won't go out until the fluid cools off.

That's my amateur diagnosis.

sharknoob

Like DR Bob said check the calipers.....A frozen one will make the pedal hard i would start with rear ones if the car doesnt pull when hitting the brakes

im new so take it for what its worth

928ntslow

Interesting theory, but that doesn't address the main issue here. However, I will look into the dragging possibility. The car never pulls and you cannot hear/feel anything. Glides quite nicely at speed or crawl.

I can easily adjust the booster rod at the pedal, but I can bet it is fine as I am sure I attached and adjusted properly when the job was done...but will double check.

Thanks for the info Bob!

Now onto the not braking properly issue......

Landseer

What's the condition of the master cylinder? A failing master seal(s) can cause pedal to sink under steady pressure.

nosnow

I replaced the master on my 82 as well as a complete brake job. After my first drive I recieved the same warning light "Brake Pressure" I think is the translation. The only way to clear was to disconnect the battery. After that initial warning I never recieved it again.

I also had a problem with my rear brakes, I rebuilt them and the car seems to stop better. If your brake pedal pressure changes during braking I'd suspect the master. Everytime I repair one component on my car it seams like every wear item in that system needs to be fixed.

ew928

Had a sticking rear caliper on my ex-Audi.
Can't really feel anything driving. But boy did that wheel get warm.
That was my hint at a bad caliper.

Mrmerlin

check the calipers for heat buildup(sticking) and replace the master i would bet its corroded inside

mark kibort

brake master cylinder!

had this issue with my bmw, and it cured it instantly. brakes worked fine, but were dragging. the master wasnt allowing the fluid to go back to the reservoir, hence the dragging pressure and superheated brakes. chancged the master and all was fixed.
mk

69gaugeman

For another weird one, on my daughters 97 neon, brake would be on. bled the brakes and would be free. press the pedal and then the brakes would stay on again. after 15 to 20 seconds it would free up. Turns out the inner lining of the flex hose had de-laminated and created a one way valve. It drove me NUTS! Replaced the flex line and all was just fine.

928ntslow

I guess something must have been lost in the translation. The dragging or heating of the fluid is NOT the issue. That is just something that popped up yesterday.

The issue is the car not stopping and the assisted braking going to a manual feel where the car keeps rolling and you have to put all of your weight on the pedal. The situation gets less as the car warms up or builds vacuum pressure.

This is what I need to figure out.

Mrmerlin

replace the master, my bet is one of the brake circuts has a small leak in the master as it heats up the seals swell and leak less, if the car is old and which one isnt the masters seem to rust where the seals dont run and then if you bleed the brakes then the seals run into the corroded part of the master bore and get cut and this begin to leak.
Usually a new master cylinder will cure this and of course use ATE super blue for the fluid, I think that mixing different brands and qualities of fluid also causes damage to the master cylinder seals, but this is usually over time, so its not as noticable as other things

ew928

Check vacuum?
My S4 went to manual brakes till I fiddled with the vacuum check valve. The blue? plastic valve by the master cylinder (Big piston thingey on driver's side firewall. Forgot if that was slave or master)
Not sure why I lost vacuum assist. Think the check valve jammed open and I freed it up. Fluke on my part maybe.

michael j wright

To check to see if your booster/and or check valve is holding properly- with enginge off pump up your brakes till hard (this bleeds off all vac from booster) with foot still on pedal, start the engine and the pedal should drop (this will be from vac assisting) if not you either have a bad booster-not likley you just replaced it! or bad check valve wich you can also check by seeing if you can blow through one way, but not the other. If both check out you have a bad vac line somewhere.

dr bob

Keith--

Read post #2. Checking is cheap.