goingjag

Posted this is the wrong group earlier, appologies if it's a dupe to most.

I inherited a 1989 100 that I haven't used much until my A4's water pump took a hike. While I'm working on that I started driving the 89 again. Out of the clear blue the brakes are locking up sort of. It's as if I'm riding the brakes, and the farther I go the more the brakes seem to be applied. I didn't even realize it until I had a hard time accelerating. Got off the main road and noticed that the car wouldn't move at idle. Limped it home, checked it out and couldn't find any obvious problems. It doesn't exhibit any of the "bomb" problems, the brakes work fine. At first I thought it might be ABS related and switched them off and the problem seemed to go away. Then a couple of days later it was back. Then it seemed if I started the car with my foot on the brake it would be okay. Two days later and the problem croped up again. Checked the Pentosin fluid level, and it was fine. I determined I might have overfilled it when I topped it off when I first got the car, so I vacuumned some out. I was surprised to see that it was black instead of green.

I since found posts on draining the system, so I drained and cleaned the fluid holder, turned the stearing a few times to clear it and pumped the brakes to clear them. Refilled with CHF11S, and it seemed fine for a little over a day. Fluid was a little dark again, so I decided to do another flush. This time I was very sure to clear everything out of the stearing rack and brake, I even used a vacuum pump to clear anything left in the hoses. Drove 30 miles, wheels were cool as could be. Driving home that day, had to get off the highway again, and smoke was coming from the left front tire by the time I got home on the back roads. It seems that if I hold the brake pedal down hard for a few seconds while stopped, it frees them up, but only briefly.

Someone suggested master cylinder problem in the other forum. Thought I'd check for some suggestions here as well as that poster had suggested.

cuatrokoop

It's not the hydraulic assist that's at fault, it's the actually hydraulics. Namely the Brake Master Cylinder.

Changing the MC isn't hard at all. Getting the system bled is a two-man job unless you have a pressure bleeder (NOT a Mity-Vac vacuum pump, that will not work!).

Check with a local parts store first, but you can buy brand new ATE brand (original equipment) MC's for around $100. I just did this on the 5kq a few weeks ago. I used Valvoline synthetic DOT4 fluid along with the new MC, and the car stops better than it did when I bought it back in 1996!

moving violation

A faulty MC will heat up and lock up the brakes. To verify that the MC is the one diong this, take a very cold bottle of water with you and when the start to lock up, pour it on the MC to see if they unlock.
Mike

rooster 2

replaced the master cylinder, and it fixed the problem...Rooster

goingjag

I do have a power bleeder (treated myself, but I've only used in on a friends motorcycle so far!). I guess I'll get to see it in action. By the time I get through with this I probably could have finished the water pump on my A4...Oh well that's why we own cars right!

Thanks again for the help.