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FixItMan
FixItMan, Master Technician
Category: Car
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Experience:  AA DEGREE AUTOMOTIVE/DIESEL TECH
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Tracker: stopping..master cyl and abs ubit..booster

Customer Question

1996 GEO Tracker with ABS, brake pedal goes to floor with out stopping vehicle. Master Cyl and ABS ubit are one piece mounted to booster and fender skirt. Bleeding makes no difference.XXX@XXXXXX.XXX
Submitted: 2 years ago.
Category: Car
Expert:  Techman replied 2 years ago.
Hi, are you getting fluid from all the bleeders? Which lines were replaced?
Customer: replied 2 years ago.
rear lines from junction block on frame to real wheel cyl. Yes fluid was flowing from all bleed screws
Expert:  Techman replied 2 years ago.
Have you done manual bleeding with a person pumping the pedal?
The vacuum bleeding will sometimes not work when manual bleeding will. Manual bleeding will also let you see which brake circuit is building fluid pressure.

If you've done that, then I would remove the rear drums and inspect the wheel cylinders for leaks.
Also check the condition of the rear brake shoes, and the adjustment. if they are worn out or out of adjustment, then it will allow excessive pedal travel.

Also inspect the front calipers closely for leaks.

Let me know your results.
Thanks
Customer: replied 2 years ago.
Shoes and pads were previously replaced. Yes also tried manual bleeding with two people. No leaks at rear wheel cyl or front calipers. Yhis was all done a few hundred miles ago and wehicle worked well for many miles, the pedal failed and vehicle did not stop correctly and in a day or two pedal was going to floor with no loss of fluid and no leaks.
Expert:  Techman replied 2 years ago.
How many miles on the vehicle?
Customer: replied 2 years ago.
about 75,000
Expert:  Techman replied 2 years ago.
Ok, thanks. At this point, with no leaks or fluid loss, all signs point to the the master cylinder. A faulty seal in the 16 year old mc will cause the pedal to go to the floor with no pressure build up.
The master cylinder should be removable and replaceable separately.
Check rockauto.com, which will have pictures to match up the part with the one on your vehicle, there are several options.
Customer: replied 2 years ago.
Two things here. The entire unit (master byl with ABS unit) was replaced about 15 months ago when this happened and it worked for 15 months and now failed again. The replacement master cyl listed A1 11-2765 is not the correct unit as it is only a master cyl and the one on this GEO is all one piece with the ABS unit (one casting)
Expert:  Techman replied 2 years ago.
Ok, that is a very odd poor design. But if the same issue happened before, and was fixed with a new unit. A new complete mc/abs unit will be needed again. What was the condition/brand of the last mc/abs unit?
What type/brand of brake fluid was used?
Customer: replied 2 years ago.
unit was new from GEO. Brake fluid was dot 4 from advance auto and dot 4 from NAPA
Customer: replied 2 years ago.
Relist: Answer quality.
You had no new answer from anything that had already been tried. I hoped that since my ASE Cert. was from the sixties you may have had more answers than I could come up with myself. I'll continue on my own and thank you for trying.
Chuck
Expert:  Techman replied 2 years ago.
Good luck.
Expert:  FixItMan replied 2 years ago.
Hello JACUSTOMER, will the pedal pump up and get firm? What bleeding procedures have you followed?

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