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No front brakes

Discussion in '6.9L IH & 7.3L IDI Diesels' started by slyhog022056, Jul 14, 2019.

  1. slyhog022056

    slyhog022056 Registered User

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    I have searched the forums and cant find the info i need. I have a 91 Ford f350 Diesel I have rear brakes but no front brakes until I mash the pedal 3/4 of the way down I have bypassed the ABS on the system and it has a new master cylinder could this be a proportional valve problem. the front calipers, brake hoses, brake lines, rotors they're all brand new no collapsed lines I don't know what to do. They have been pressure bled and gravity bled with a half gallon of brake fluid, there cant be air in the lines.
     
  2. Knuckledragger

    Knuckledragger blowing chunks

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    Sounds like a blockage. Have you checked the ft. reservoir in the master cyl? If it is high, leave off the cover and hit the brakes. If the fluid sprays everywhere, it is blocked somehow.
     
  3. Slicknik

    Slicknik Full Access Member

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    Is your vacuum booster new? What condition is your one way valve in? How much vacuum is your system making at idle? What your vac gauge read after pressing the pedal?

    When you say brake line you mean from hardline to caliper about 12” of line?

    Check your fitting for the front brakes at the MC and make sure you didn’t smash it
     
  4. Noiseydiesel

    Noiseydiesel Full Access Member

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    I learned to recenter a prop valve, if it is biased to the back, was to open the bleeder on the rear and mash the brake pedal. This should make the prop valve move to the front and center. I also learned you can remove the switch from some of the M/C and using a small pick, physically center the valve. I have also learned recently that a tool has been made to hod that valve in the center position.
    Good Luck!
     
  5. Garbage_Mechan

    Garbage_Mechan Garbage Mechanic

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    There is no proportioning valve in a 91. There is a valve screwed into the rear port on the master cylinder that is a pressure reducing valve.
    The first question is what order did the problem occur in? Did you replace parts due to maintenance and then develop the no front brakes issue or did the issue arise and all of the parts changed so far haven’t fixed it?
     
  6. slyhog022056

    slyhog022056 Registered User

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    When i i t the truck the right front calipers would hang up on heavy braking and very little rear brakes. I replaced both calipers, front rubber lines to calipers, new entirshoes,ade wheel cylinders and hardware on the rear. Had the entire system bled out with pressure bleeder. Hanging caliper problem gone i thought. Had to mash on the brakes 1 day and locked rears up. Check shoes and front pads, shoes worn down to about 1/8 inch left, front pads had no wear on them. Then i replaced the master cylinder, NEW not rebuilt benchh bled it them rebled entire system again. Still no front brakes. Shoes last me about a month. I dont know what else to try.
     
  7. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    It may be time to schedule a trip to the southwest to visit Thewespaul.
     
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  8. MtnHaul

    MtnHaul Supporting Member Supporting Member

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    Have you replaced the brake booster? There is a pushrod that applies pressure to the master cylinder and it's certainly possible that it is out of adjustment. Since you seem to have replaced darn near everything else you might as well as check the booster and scratch it off the list of possibilities.
     
  9. Cubey

    Cubey Full Access Member

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    I had a car, I think a 91 Corolla, where an honest and pretty trust worthy shop replaced the master cylinder, but the brakes were still a bit lousy. I suggested the push rod but they said "oh you should never touch that" or something. They didn't want to mess with it. So, I did it myself and it helped.

    On a beater car a couple years later, I was trying to adjust it and it got out to car and totally locked the brakes when I applied it. Thankfully I was a 2 minute run from home so I ran back, grabbed my tools because I foolishly didn't toss em in for the test drive, adjusted it on the side of the highway enough to get it rolling again and u-turned back home for better adjusting.

    I had to do a minor adjustment on the RV's new booster to get it working well. I got on residential street with almost no traffic. I would drive a couple blocks, brake and stop at the curb, hop out and adjust real fast, hop back in and repeat until it felt right without dragging or locking up. After 3-4 times, I had it good.

    I went overboard on adjusting the F250's push rod s a couple years ago. It was dragging the brakes, literally making the front pads smoke and losing most stopping power.
     
  10. Garbage_Mechan

    Garbage_Mechan Garbage Mechanic

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    The thought about the pushrod adjustment is a good one and one I should never forget.
    If the pushrod doesn’t allow the master cylinder piston to fully return and uncover the fill port bad things will happen. Air cannot be exhausted and the master cylinder cannot refill well. Sometimes it just won’t manually bleed, sometimes the brake pedal just gets lower and lower. There should be detectable clearance between the pushrod and piston. If the piston gets depressed at all there is a problem. Looking down into the reservoir at the fill ports one should see the piston cup completely clear the port to the rear side allowing the MC to fill and vent.
     
  11. snicklas

    snicklas 6.0 and Loving It!! Staff Member

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    The pushrod adjustment can happen if the master and booster as a set. We replaced the master and booster, on our 83 F-150, as a unit from NAPA, already assembled. We installed, connected all the lines and bled properly. First drive, the front brakes would not release completely. The pushrod had to be adjusted, and all was good. So if both were replaced together, or a master and pushrod was replaced, it could adjusted incorrectly.
     
  12. Garbage_Mechan

    Garbage_Mechan Garbage Mechanic

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    The reason I should never forget is I once put a new MC on our 71 Datsun B110 “1200” Coupe on Friday night. Next morning headed out on a drive through Yosemite. Almost never use the brakes in this car since it weighs 1200 lbs or so and has a sweet shifting 5 speed. It is a twisty road rocket you for sure. So as we near the top of 10,000 ft Tioga Pass we notice the brake pedal is low as we pulled off for a photo op. No leaks, full of fluid. Bled it a little...made it worse. Considered it a little and finished the day with the parking brake and gears. Wanted for the tourists to go home and then cruised through 100 miles of Yosemite back country at 25 mph. No foot brakes at all. An adventure we won’t forget. Turned out new MC pushrod pocket was shallower so not getting full return. Needless to say I check my MC pushrods now!
     
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  13. slyhog022056

    slyhog022056 Registered User

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    I guess i need to check it then, that could be it. I always measure from mounting face to back of the part inside, never thought about the cup beinng deeper or shallower. I know i bought the master cylinder seperate from booster.
     
  14. RDieselKid84

    RDieselKid84 Full Access Member

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    In the Ford shop manual it has a diagram of a tool you can make for the adjustment of the mc rod. You can make it out of a piece of sheet metal. And it will make life easier with the mc change.
     
  15. BR3

    BR3 Full Access Member

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    Also, have you considered that the rear is just locking? It's unusual, but entirely possible.

    As well as timely considering your front just locked up
     

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