1995 Ford F150 6 cyl Two Wheel Drive Manual 150287 miles
Customer brought me this truck with a broken left front brake hose and the master cylinder empty. Pulled the front wheels to replace both brake hoses & found the brake pads very thin. Replaced both front hoses, front pads & front calipers. Bled air from front brakes and got decent pedal height; started truck and brake pedal went to the floor every time I pumped it, would not give a good pedal when I had the engine running, only with the engine shut off. I pulled the rear wheels & checked the brake shoes and adjustment, OK; I bled the rear wheel cylinders then the front calipers and still had no pedal height even though the rear brakes were adjusted correctly and I had a good strong emergency brake. I then bled the entire system, including the ABS bleeder valve screw, twice more with the same results (no engine/pedal - engine/no pedal). I vacuum bled the entire system then gravity bled (opened all bleeders) and no change, no pedal when running. I loosened the master cylinder lines & bled it, no air, OK then bled the rest of the system, no pedal when running. I removed the master cylinder nuts & pulled the cylinder away from the vacuum booster; I turned the adjusted on the booster rod out two full turns & installed the master cylinder, no pedal when running. I removed the cylinder and turned out the rod three more turns (total of five turns) and installed the cylinder, no pedal when running. I drove the truck down the road and applied the brake 3 or 4 times; the pedal went to the floor each time but the rear wheels locked up showing that the rear brakes were working normally. I shut the truck off and went to talk with the owner; I asked him if he or his employees had been experiencing any problems before the hose blew and he said they hadn’t, that no one had complained. I returned and started the truck to move to another location and had good pedal! I test drove the truck for about ten minutes; good pedal all the time but I started smelling the brakes like they were getting hot. I brought the truck back and had to leave it to finish tomorrow. I need an opinion on my work and diagnosis of the problem and also any suggestions you might have. I don’t like adjusting the brake pedal height at the booster rod because I believe that is treating the symptom rather than the problem. I plan on turning the rod adjustment back in a couple turns tomorrow and road testing again to see how it performs but haven’t yet understood why I couldn’t get a normal pedal after replacing the hoses, pads and calipers.
No leaks anywhere -Try replacing the master cylinder could have an internal leak with seals/cups. Then bleed the MC/ABS then the wheels in sequence.
March, 20, 2009 AT 3:00 AM
Something else I need to tell you that I just remembered; sorry, was late last night when I first emailed. During the entire repair I checked the vacuum booster operation; first checked for adequate engine vacuum (20" & steady) then hand-pumped the port valve that sits in the booster, OK. I tried to hand-pump up the booster but couldn't get any reading on my gauge even though I pumped 50 times or more in a rapid fashion. Is it possible to hand-vacuum pump up a booster?
By bleeding in sequence you mean the ABS valve first, then right rear, left rear, right front then left front? Will try that first because I don't want to spend the customers' money on a part that doesn't need replacing.
March, 20, 2009 AT 5:10 AM
Bleeding sequences okay-check the booster
To check the vacuum booster, pump the brake pedal with the engine off until you've bled off all the vacuum from the unit. Then hold the pedal down and start the engine. You should feel the pedal depress slightly as engine vacuum enters the booster and pulls on the diaphragm. No change? Then check the vacuum hose connection and engine vacuum. If okay, the problem is in the booster and the booster needs to be replaced.
March, 20, 2009 AT 5:27 AM
Wow, thanks for the quick response. I did do that; I pumped with the engine off until I got a decent pedal height then started the engine up, the pedal went all the way to the floor. My concern about the booster was that after I had run the engine, I shut it off and pulled the check valve expecting to hear vacuum leaking from the booster and the diaphram seating back in place but there wasn't any pressure/vacuum loss. Did you have any thoughts on why the brake system would supposedly/alledgedly work normal before the ruptured hose and then give me the pedal height problems after the parts replacement?
March, 20, 2009 AT 3:49 PM
The pedal shouldn't go all the way down when you start the vehicle maybe an inch or 2-Check the master cylinder thoroughly
March, 27, 2009 AT 5:41 AM
Problem of low pedal height still persisting. Have bled the brakes in sequence repeatedly as you instructed, no air in system. Made certain the rear brakes were adjusted properly, OK. After initial adjustments have booster rod adjustment at 2-3/4 turns out; if I go to three the front pads start staying engaged & you can smell them. Engine off and brake pedal depressed is good pedal approx. Half-way down; engine started takes the pedal to within 1" of the floor. Road test shows good stopping, no lockup or pull but pedal consistently goes down to within 2" of floor, does not have the same pedal height as with the engine off. I haven't replaced the master cylinder yet because I can't afford to replace it and that not be the problem but not sure where else the problem could be.
March, 27, 2009 AT 11:35 AM
The master cylinder creates the hydraulic pressure through out the brakes system the only time it should lose pressure is if its leaking somewhere
October, 1, 2015 AT 2:47 PM
Had exactly same problem until replacing the RABS module.
After replacing MC and calipers it must have gotten contaminated.