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Car Forum / Audi Cars / February 200986 4kq master cyl question
Greetings It's been quite a while since I stopped in here to ask a question. Did manage to change my timing belt and also rebuilt my front end last fall. More recently, in the middle of a coold January, it was an alternator replacement. Question is: if I can't pump anything out of the bleeder on the proportioner (term?), is it a sure thing I've got a bad master cylinder? I also replaced a caliper last summer and never did feel like I had the lines bled perfectly. Brakes got worse this winter. Last weekend I had a helper so I tried to bleed the lines; my helper said the pedal response was erratic--sometimes it would firm up, and the next push was mush. I've got brakes--at the very end of the pedal travel. At the bleeder on the proportioner, neither can I push any fluid through with a pedal stroke nor can I pull any through with a vacuum pump. Gotta be the master cylinder, right? Clogged galleys? Say goodbye to $200? miguelito The installation of a new brake master cylinder is always good insurance!!!!! I would replace one especially since yours is 22-23 years old! When my brakes start to act mushy I will replace the master on my '83 4000s. ;-) Congrats on getting the other work done successfully! later, One out of many daves > Greetings > [quoted text clipped - 17 lines] > > miguelito I had four T44 series and replaced several master cylinders. Each time they failed a symptom was if I pushed the brake pedal down and it didn't hold but slowly faded to the floor, it was a bad MC. > The installation of a new brake master cylinder is always good > insurance!!!!! [quoted text clipped - 31 lines] >> miguelito >> Ok, thanks guys. I'll spring for another master cylinder. > would replace one especially since yours is 22-23 years old! Actually it's only a couple years old. Which is why I wanted some expert opinions before going ahead. While I'm at it I guess I should order an expansion tank, too, since mine's been cracked for about 6 years! I've found that if I just back the cap off a smidge my coolant loss is pretty slow. Well, there goes another $100! I also have some oil leak despite changing the lower seal at the TB change. Could be cam drive seal I suppose. I get a fair amount of oil pooling on the intake casting. I have a valve cover gasket waiting to be installed, but I've been waiting for warmer weather. Since we're going to be around 50! today, maybe I'll do that and listen to the Badgers on the radio instead of watching on tv. Oil, coolant, now brake fluid--can you imagine what my garage floor looks like?! miguelito I had a cracked expansion tank in one of my T44s. I tried a number of things to seal it but none worked. I think that the dealer cost at that time was only about $40. The valve cover seal should correct the intake oil pooling. Just don't over torque the bolts. I don't remember the speck but it is probably around 10 ft lbs. The only time that I changed the crank seal while doing the TB it developed a leak too. I probably didn't set it at the proper depth. There is a special tool for that. If I were to do another one I wouldn't change the seal if it wasn't leaking previously. Have a good afternoon listening to the Badgers. We don't listen to them over here in Minneapolis :-) > Ok, thanks guys. I'll spring for another master cylinder. > [quoted text clipped - 21 lines] > > miguelito Hmmm a 2 year old Brake master cylinder that might be defective is not good! Do you remember the brand, ATE/Girling or ??? Check all hoses/lines/calipers/cylinders to make sure that there aren't any leaks there. The brake hoses may swell up when under pressure. Calipers pistons may retract too far into the cylinders. To test the master cylinder you could purchase enough metal plugs to replace the brakes lines going into the master cylinder. Then step on the brake pedal to see how it feels. Another option would be to isolate each brake line at the master one at a time and plug only that line, then try another. Or deal with any number/combination of plugs you want! You are trying to see if you can get a nice hard steady pedal,one that does not stink or feel mushy. Then if you find a line that gives you that mushy feel then you have isolated the offending system. Well you already know that you need a coolant expansion tank. ;-) You should make sure that the crankcase fumes can get out of the engine properly. If not they could pressurize the inside of the engine and force oil out of the seals and gaskets. JMHO  Signaturelater, (One out of many daves) > Ok, thanks guys. I'll spring for another master cylinder. > [quoted text clipped - 19 lines] > > miguelito Another component to consider is the 'bomb' aka hydraulic pressure accumulator. Is is located under the engine just behind of the air conditioning compressor. This holds residual pressure to assist the power brakes is the engine stops. If it loses pressure the brakes will operate fine when the engine is running but with it off the pressure on the the pads will take a lot more foot effort to stop the car. This might allow pedal fade. Don't mess with this unless you are well versed in its operation it is called the 'bomb' for a reason. It is normally pressurized to about 2500 psi and nitrogen filled. If you suspect this take it to a qualified Audi mechanic (dealer or independent). > Hmmm a 2 year old Brake master cylinder that might be defective is not good! > Do you remember the brand, ATE/Girling or ??? [quoted text clipped - 19 lines] > > JMHO > Hmmm a 2 year old Brake master cylinder that might be defective is not good! > Do you remember the brand, ATE/Girling or ??? Just went and checked my book for the replacement date, and wouldn't you know I didn't write it in. Don't remember the brand either. > Check all hoses/lines/calipers/cylinders to make sure that there aren't any > leaks there. > The brake hoses may swell up when under pressure. > Calipers pistons may retract too far into the cylinders. No leaks. Funny thing--I've got some brakes right at the end of travel and it's not mushy, just the first 95% of the stroke is nada and and I can't pump up pressure at all. The car seems to stop straight, though I haven't had a chance to try it on a slippery surface to see how they lock up. I'm still driving it, by the way. > To test the master cylinder you could purchase enough metal plugs to replace > the brakes lines going into the master cylinder. Then step on the brake > pedal to see how it feels. > Another option would be to isolate each brake line at the master one at a > time and plug only that line, then try another. Or deal with any > number/combination of plugs you want! There's a diagnostic process I hadn't thought of. Great idea. What's weird to me is I can't pump or pull anything through the bleeder on the proportioner/distributor (right below the MC) At any rate, I went ahead and ordered the MC and an expansion tank last night. I'll definitely let you guys know the outcome later this week. miguelito |
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