Svenska Posted January 17, 2012 Report Share Posted January 17, 2012 I'm still working on my friend's 1992 240 with 192,000 miles on it. I've replaced the front brakes for him... Both front calipers were really rotted, one was seized, the other was working but in rough shape. Here's the problem, The brake job is done but the pedal goes to the floor. I have spent HOURS on these two front wheels. New rotors, pads and calipers. The back wheels have not been touched. I have bled many, many calipers over the years, I don't understand what's happening. It seems that the driver's front caliper is dead - it has no activity. With the engine running, I can look under the front door while using my hand to depress the pedal, there's no closing of the pads on the rotor. I have bled both front wheels about five-times now with a Motive pressure bleeder up to 20 p.s.i. and blown through about two-liters of brake fluid too. I do not see any leaks of any kind, it's all dry. I can't see the passenger-side though to see if those pads are closing on the rotor, I swapped the old caliper on the driver's side back in place of the new one thinking it was a caliper issue - no difference. When I drive the car in the two-inches of snow we just received, it feels like I'm braking with three-wheels. The ABS kicks in when it should though and the car will stop, it's just that the pedal isn't right. With the engine running, the first time you depress the pedal it goes to the floor. If you pump the pedal quickly, it seems to feel normal, wait two-seconds and reapply, and the pedal goes to the floor. I'm at the end of my rope with this. It definitely sounds like air in the lines. The brakes will stop the car although not as comfortably as you would want them to. This doesn't seem like a master cylinder... It's a matter of the driver's front caliper not closing. Link to comment Share on other sites More sharing options...
Three Fat Tigers Posted January 17, 2012 Report Share Posted January 17, 2012 When driving in dry conditions, if one side is working anywhere below the pressure of the opposite side, the steering wheel should be pulling toward the higher pressure side, especially as you near a full stop; where the greater the pressure differential, the harder the pull. Otherwise you might need someone to lightly press the pedal (or a 2x4 wedged between the pedal and the drivers seat cushion) while you have both front wheels in the air to try and see if one side is different than the other. If it is, and it's not the caliper, then odds are it a problem with the ABS unit, and if so you might try taking the cover off and rapping on it with a dead blow hammer while bleeding. If the pressure is the same, then odds are it's a worn out MC or you need to bleed the rear brakes. I would have suggested rapping on the caliper as you bleed it with a dead blow hammer but as you've changed the caliper again, that's probably moot. I would also say there is a high probability that you will still need to bleed the rear brakes at some point. Link to comment Share on other sites More sharing options...
Svenska Posted January 17, 2012 Author Report Share Posted January 17, 2012 I couldn't try that pull technique last night with all the snow, I would have gotten a skewed result. I didn't think of rapping the ABS unit to rid it of air bubbles. I wear I've never had this problem before, even with clutch slave/master cylinders. If the suction/ Vacula venturi method doesn't work (and it almost always does), then I use the Motive pressure bleeder at 20 p.s.i., it always works. I was hoping not to have to touch the rear brakes since they are also rotted and the bleeder screws look very fragile... Link to comment Share on other sites More sharing options...
Svenska Posted February 17, 2012 Author Report Share Posted February 17, 2012 Last month, I replaced a pair of front brake calipers on my friend's 1992 240 (w/ABS). After replacement, I bled the two calipers one at a time with a Motive pressure bleeder at about 20+ p.s.i. I noticed then that the brake pedal went down to the floor which it never did before. I also noticed that if you pump the brake pedal just once, the pedal feel is normal and the car stops the way it should and the travel feels normal. When you let go of the pedal and reapply two-seconds later - it's the same scenario, the pedal travels to the floor (the car always stops though every time - it's just a little unnerving). Pump it just once, and the pedal feels great. I ended up bleeding all four-calipers, even though I only opened the front calipers. I went through about three-liters of brake fluid. The pedal was still the same. I tapped lightly on the ABS unit to free up any bubbles while bleeding. No go. I finally assumed it was the master cylinder. I replaced it with a brand new ATE-brand cylinder from Eeuroparts.com. I bench bled it for about 15 minutes/about 70+ strokes. It progressively got harder to push and the bubbles stopped appearing in the reservoir. (The reservoir came attached to the cylinder too). I installed it on the car and the same thing happened, pedal to the floor, pump once, pedal OK. I bled the hell out of the system with both the pressure bleeder and the Vacula suction bleeder. Finally, at some point the pedal seemed to work, (although I didn't think it felt right) and all was well. Last week, we discovered that the cheap caliper I installed was defective in the way that it caused the pads to touch the disc while the car was being turned at very low speeds left or right - sort of a horrific moaning sound. I replaced the suspect caliper with a good remanufactured one. The sound is gone. The pedal now goes to the floor. I wish I never meddled/opened up the system. My only thought is that the master cylinder is bad. There's not much left to this braking system. The calipers and hoses don't leak, the reservoir is full. I don't get it. Tonight I bled the system again, all four-wheels, two-liters of fluid. I even used both the pressure bleeder at 20 p.s.i. AND at each caliper I attached the Vacula suction device (at the same time) and pulled the fluid through each caliper. I started at the passenger-rear caliper, the driver's back, passenger front, etc. I can't imagine a rogue air bubble trapped somewhere in the system still. What are the chances that it's the brake booster check valve or the brake servo check valve????? Link to comment Share on other sites More sharing options...
DVolvoguy850T5 Posted February 19, 2012 Report Share Posted February 19, 2012 I suspect a bad master cylinder. The symptoms where the same in the 81 DL wagon I had. Brakes always felt spongy even after replacing all the calipers, rotors, pads, and throurally bled. Wife had an accendent as a result of brake failure. After replacing the core support, the right left fender and both head lamp assemblies, went to test drive and car had no brakes. Even though I knew that I replaced them just two weeks before. Turned out the master cylinder's seals where shot. Replaced and the brakes where very effective. If this is the cause of your issues, make sure you bench bleed the cylinder before installation. Link to comment Share on other sites More sharing options...
Three Fat Tigers Posted February 24, 2012 Report Share Posted February 24, 2012 I've merged the two threads where post #4 was the start & end of the second thread. Not sure what to say but I would try bleeding the brakes via pumping the pedal, pump them up like 5 times, hold, open-close the valve; repeat. Link to comment Share on other sites More sharing options...
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