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Technical Touchy F100 brakes

Discussion in 'Traditional Hot Rods' started by sdroadster, Apr 30, 2014.

  1. sdroadster
    Joined: Jul 27, 2006
    Posts: 327

    sdroadster
    Member

    I have a 48 Ford sedan that has really touchy brakes. The car is a new build with all new brake parts, including drums. It has the stock Ford pedal, and if stepped on too quickly will lock up the front tires. It has F100 Ford internal expanding brakes in the front, and Ford truck (9") in the back. The master cylinder is a 1" bore 1967 Mustang dual chamber drum/drum, with a Chassis engineering power brake booster. This is all pretty common stuff, I'm wondering if I should put a proporating valve to the front brakes and reduce the line pressure. I hate to discard the booster. Have any of you guys had this experiance? Thanks
     
  2. Mart
    Joined: Mar 3, 2001
    Posts: 4,191

    Mart
    Member

    I don't think using a proportioning valve on the front is a good idea.

    The brakes would probably be fine without the booster. Is it a remote unit or mounted with the master cylinder?

    I would either try running without the booster or try with a slightly larger master cylinder. 1-1/16" or 1-1/8".

    Or just get used to pussy footing the brakes.

    Mart.
     
  3. fender lizard
    Joined: Jan 4, 2010
    Posts: 164

    fender lizard
    Member
    from mcallen tx

    What if you change the ratio of the pedal swing
     
  4. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,658

    V8 Bob
    ALLIANCE MEMBER

    As already mentioned, your pedal ratio is probably too low for power assist, especially if you're using the stock '48 6:1 pedal, ...and...Do NOT proportion the fronts. :eek:
    Are the front brakes assembled correctly, with short linings to the front and adjusted properly?
    You mentioned the 9" rear, but what size are the brakes? Do you know the wheel cylinder sizes? :)
     

  5. sdroadster
    Joined: Jul 27, 2006
    Posts: 327

    sdroadster
    Member

    Thanks guys. The wheel cylinder size in the front is 1 1/16. I don't remember the rear size. It's a Chassis Engineering booster that is attached to the master cylinder. This car is a new build. I removed the 4 door body from the frame, and saved the Earl Shieb paint, and original interior. I built a chassis using mostly Chassis Engineering parts, and a Okie Joe dropped axle. I drive it everywhere, but I have to do something with these brakes....
     
  6. Mart
    Joined: Mar 3, 2001
    Posts: 4,191

    Mart
    Member

    You don't really need the booster with the drums. If you had discs, then, yes, it would be a good idea.

    Either rework it without the booster or make the master cylinder diameter bigger.

    Mart.
     
  7. i have basically the same brake setup on my `36 except they are not boosted, brakes work great. ditch your power booster
     
  8. DrJ
    Joined: Mar 3, 2001
    Posts: 9,418

    DrJ
    Member

    It's not the booster.
    Sounds like you just have more brake in front than the puny 9" ones in the back.
    Put bigger diameter wheel cylinders in the back for a better % gain and it might even out.
    It's NOT the booster!
     
  9. Do you know for a fact that the outlets from the m/cyl are plumbed correctly for the front and rear brakes? Could having them reversed cause the problem you're describing?
     
  10. sdroadster
    Joined: Jul 27, 2006
    Posts: 327

    sdroadster
    Member

    Just for clairification when I said 9" I meant a 9 inch Ford pick-up rear end with 5 on 5 1/2 lug pattern. I rear brakes are intended for a big pick-up or van. It seems like I have way too much brake on the front. Of coarse like most hot rods I have big tires on the back, and smaller ones on the front. The smaller ones provide less traction which makes the problem worse. Sounds like I need to ditch the booster. I hate modern stuff, and am being stubborn on the disk brake idea. Thanks
     
  11. machine1967
    Joined: Mar 24, 2014
    Posts: 8

    machine1967
    Member
    from oshawa

    I have the same problem with my 67 camaro .it has power brakes , front tires will lock up with little effort. it is dangerous not sure what to do
     
  12. seb fontana
    Joined: Sep 1, 2005
    Posts: 6,592

    seb fontana
    Member
    from ct

    Actually the brakes are pretty much the same at 11" diameter...F100 fronts are maybe 1/4" wider than the rear..The rear brakes wheel cylinders are probably around 15/16" but brake parts listing will show other sizes available, I would put larger ones in...As in previous post check plumbing to MC [not that I am conviced it really matters] as it might react different with boost...
     
  13. Mart
    Joined: Mar 3, 2001
    Posts: 4,191

    Mart
    Member

    The front to rear weight bias of a 48 sedan is probably quite a bit different to a F100. The truck is probably underbraked on the rear to prevent rear wheel lockup when unladen. You may be able to get some 1" cylinders for the rear which would improve the front locking problem by making the rears do more work.

    You can still ditch the booster though.

    Lots of guesswork, but as yours is a not standard application, you will need to experiment until you hit on a combination that works.

    Mart.
     
  14. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,510

    Mr48chev
    ALLIANCE MEMBER

    Sometimes we have issues with the brakes on a rig if they don't work like the brakes on our daily or the other rigs we drive. Watch a guy climb out of his four wheel disk Audi into a Model A V8 running 40 drums on all four corners and that becomes quite obvious but it can work the other way too.

    On the booster it's learning the feel of the booster and knowing how it affects the brake feel. That shouldn't be a big issue and should come with time.

    On the brakes not hooking up evenly, Somewhere in the system it isn't balanced front to rear. A search shows that most mid 60's full size Ford Sedans run 1-3/32 front wheel cylinders and 7/8 or 15/16 rears and that most Ford pickups run the 15/16 rears.

    As some said, are all the shoes on correctly with the smaller shoe in front and the one with more contact area in the back? Primary/Secondary just like a carb the secondary almost always is the larger of the two.

    Are the rear brakes adjusted correctly? The lining may have to move too far before it contacts the drums.

    Are the brake lines the correct size front and rear for the application? The wrong size may cause reduced pressure to the rear brakes.
     
    My1964ford likes this.


  15. DING ! DING !

    Check this first. Front and rear.
     
  16. I hate guessing-
    First - check your pedal ratio
    If you use a manual brake pedal with a booster you'll likely put yourself into the windshield or ditch. If you use a power brake pedal with manual brakes you'll likely not stop, hit a object then go into the windshield. The idea is to avoid hitting the windshield.

    For 50.00 you can eliminate a lot of guess work and trial and error parts accumulation.
     

    Attached Files:

  17. I put custom pedals/arms in my '42 pickup and found out that I didn't do enough homework on the pedal ratio and booster, good brakes but "touchy". My fix was a cheap adjustable regulator spliced in the vacuum line between the manifold and booster and dialed it in to what I wanted. Its been working great for over a year.
     
  18. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    JohnEvans
    Member
    from Phoenix AZ

    Change the MC to a 1-1/8 or remove the booster. The bigger MC will have less line pressure for a givin input force making less touchy brakes.
     
  19. sdroadster
    Joined: Jul 27, 2006
    Posts: 327

    sdroadster
    Member

    Thanks for the response. I keep my parts boxs so I can refer to the part number of the suspect pieces in the future. I discovered the rear wheel cylinders are 13/16. I'll go to the auto parts store in the morning and see if i can get 7/8 or 15/16. I have suspected all along the rear brakes wern't doing much. Now I know why. Thanks again, and keep the ideas comming.
     
  20. 48ford
    Joined: Dec 15, 2001
    Posts: 435

    48ford
    Member

    If you want to try a bigger master ,I used one from a full size ford van it has 1 1/8bore.
    Let us know how this works out.
    Were all just guessing and we all need knowledge
    Russ
     
  21. mechanic58
    Joined: Mar 21, 2010
    Posts: 681

    mechanic58
    Member

    This is a pedal swing ratio problem, without a doubt. I have experienced this very same issue in the past after adding a vacuum booster to a 4 drum setup.
     
  22. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,510

    Mr48chev
    ALLIANCE MEMBER

     
  23. Halfdone
    Joined: Feb 27, 2005
    Posts: 237

    Halfdone
    Member

    Front brake lockup is always tough to diagnose as it can have so many causes

    In your case you have Lockheed style non-self energising 11 x 1 3/4 on the front and self energizing 11 x 2 on the rear.
    That should give you significantly more rear brake than front

    You then have more leverage on the rear (larger tires), which reduces brake effectivness at the rear

    You then have different wheel cylinder sizes.

    If it was my car, I would fit bigger wheel cylinders in the rear AND then install an adjustable proportioning valve in the rear circuit and adjust it so the car stops right
     
  24. Mart
    Joined: Mar 3, 2001
    Posts: 4,191

    Mart
    Member

    He has f100 brakes on the front which are self energising.

    Mart.
     
  25. sdroadster
    Joined: Jul 27, 2006
    Posts: 327

    sdroadster
    Member

    The rear brakes have 13/16 wheel cylinders now, I just bought 15/16, but haven't installed them yet. Maybe the first of the week. I'll keep you guys informed. thanks
     
  26. sdroadster
    Joined: Jul 27, 2006
    Posts: 327

    sdroadster
    Member

    I spoke to a nice guy that runs a front end, and alignment shop about the touchy brakes on my sedan. He said F1 or F100 brakes were not intended to be power boosted, and I had an "over active braking condition" He said to reduce the wheel cylinder size on the front brakes. I had 1 1/16 and I reduced the size to 15/16. I used rear wheel cylinders intended for a Ford pick up with a 9" rear end. The wheel cylinder bolted on the F1 backing plate, but I had to grind or relieve the top area of the spindle for hose clearance. I tried the new brakes out this morning, and what a difference!! The brakes still work well, but now they don't skid the front tires, and try to launch you through the windshield. The rear brake wheel cylinders are 13/16. I have always thought the rear brakes wern't being fully activated, so I am going up in wheel cylinder size on those to 15/16 to bring the braking action up a little. I'll keep you informed. So far, so good...
     
  27. Mart
    Joined: Mar 3, 2001
    Posts: 4,191

    Mart
    Member

    You might want to leave the rears alone. By reducing the fronts you have increased the rears, if you see my logic. If they're working ok now leave them alone.

    Mart.
     
  28. Ddooce
    Joined: Oct 27, 2010
    Posts: 132

    Ddooce
    Member
    from Memphis Tn

    I had F100 brakes on the front of my avatar with pickup rears servo assist. They would put you through the windshield - worse than air brakes. Without the servo perfect. Just take the vac off the servo and drive it - you will be surprised! F100 brakes and vacuum booster will not work.
     
  29. manyolcars
    Joined: Mar 30, 2001
    Posts: 8,367

    manyolcars

    I had the exact problem as the OP. I called Master Power Brakes and they told me I needed a hold-off valve. All of your parts are the correct size, but the hold off valve does not apply pressure to the front until the rear reaches ((I think) 125 pounds of pressure. You want the rear brakes to come on first so the car doesnt swap ends when you hit the brakes
     
  30. manyolcars
    Joined: Mar 30, 2001
    Posts: 8,367

    manyolcars

    wade-a-minit! Of course you can add a booster to F100 brakes. I did it to my 1960 F100 several years ago and have been driving it every day
     

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