Question-------------------------
Followup To
Question -
Re: Brake failure -1996 Dodge Caravan ES-72,000 miles
I purchased this van new and have not had any brake trouble before this. I recently had a complete brake failure when the peddle went to the floor. I took the van to my local mechanic, he bled brakes added a vent block and two rear brake cylinders. It was okay for about a week then the peddle again was on the floor. I manually bled the brakes with no luck and returned the van to my mechanic. He installed a used ABS unit and power bled the brakes. Okay for another week and then another brake failure. It seems like the brakes continue to get air in the lines and it causes the brakes to go out.
When I have bled the brakes, I can pump the brake peddle and air blows out both back bleeders the most. After bleeding , the peddle will come up somewhat, but the rear wheels build up so much air in the line that a full peddle does not return. All brake lines have been checked for leaks and none were found. In addition, there is no brake fluid leakage. The ABS unit has not been recycle bled, is this possible or should it be done? Below are more parts that have been replaced on my van:
Two (2) rear wheel cylinders
ABS unit (used)
Vent block in rear
New booster brake unit
Three (3) new master cylinders
Brake pads, drums and shoes
Manually bled 4 times
Power bled 3 times
Both my mechanic and I are at a complete loss and it is getting very expensive. Any ideas?
Answer -
Hi David,
At a distance this is not too easy to give advice about. But first, do both warning lights come on the, the red and the amber? or just one and which one. That will perhaps direct you to focus on the convemtional part or the ABS part of the system. Second, before you bled the brakes have you always depressurized the hydraulic accumulator portion of the ABS (you do that by pumping the pedal at least 40 times with the ignition key off)?
Sometimes the power brake unit is at fault and one way to go about diagnosing this is to press on the brake pedal very lightly and try to get the unit to catch, then press progressively harder and observe when the warning light(s) come on which is of diagnostic significance:
If you don't get the brake warning light coming "on", the two possibilities are the booster runout point is mistaken for the bottom of pedal motion... so open a bleed fitting and see if it goes any further to the floor. Then check booster vacuum hose for crack or leak at either end, then test again; and then remove lines (and plug their ports) for the cruise control and heater/A.C. units in that big vacuum line if those are present, and retest. Measure the vacuum in the line at one of the ports, then clamp off the main hose and see if the booster unit holds the vacuum (no more than 3 in. Hg drop in 15 seconds).
If the red and the amber ABS light are "on" then the ABS system needs to be checked out (a longer desrciption that would best be xerox copied and mailed to you by US mail). Also if the red warning light comes "on" only when you actuate the pedal, try to apply the brake Very Slowly and if you get some resistance keep applying pressure and note the degree of pressure that you are applying when the light comes "on". Then write back with the results.
All the above is from a couple of pages from the shop manual for '93 vans that I have. I could copy and snail mail these to you.
Roland
Roland,
Thank you for your timely response. The red and amber lights come on when I start the engine, then go off. The red light comes back on when I bleed the brakes to the refill point, then goes out when refilled. The brakes have been power bled, manually bled and I took your advise about pumping the peddle 40 times with the engine off. Nothing has worked yet. I am still having the same problem. I most recently tried to bleed the brakes by opening the bleeders and let them sit open and letting the fluid run out via gravity (another piece of advise I had received). Again, after a test drive, the brakes were good for about five miles then became spongy. Additionally, I checked for fluid leaks, air leaks and cracks on everything including the booster hose and cruise control vacuum hose lines.
I cannot imagine how the air is getting into the lines? If you can think of anything else, I would really appreciate your input.
Thanks,
David
AnswerHi David,
The only other possibility I can identify is that the master cylinder has not been bled properly when first installed. Did you use one of the kits that allow you to hook up the output ports to little hoses that recirculate the fluid back up to and into the filler reservoirs and then pump the pedal repeatedly until all the air is out of the master cylinder? If not, that would be a persistent source of a soft pedal.
Other than that you may have to find a brake shop with a really skilled mechanic to figure this one out.
Roland
