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Almost no pressure to front brakes

Discussion in 'Early CJ5 and CJ6 Tech' started by Strider380, Apr 11, 2011.

  1. Apr 11, 2011
    Strider380

    Strider380 Can I have a zip tie?

    New England
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    I have a power booster/master cylinder from an 87 wrangler (4 cylinder). My rear brakes are 11" drums on a tapered 44. front axle is a d30 with disc brake knuckles from a 78 cj5. All calipers, wheel cylinders, rotors, pads, shoes, hoses and lines are new.

    I finally plumbed in my front brakes (had the fronts plugged at the master cylinder), bled the crap outta them for a half hour, but I couldn't get any pressure to the fronts. The rears work perfect. The pedal basically drops halfway down till it hits the back brakes. If I pump the pedal 5 or so times I get good pressure to both.

    I immediately changed out the master cylinder. Bench bled it, installed it, and I have the same exact problem.

    I have no proportioning valve. I ran all my lines in 3/16 brake line. Could either of these be my cause? I also have a pressure switch "T"ed into my front line near the master cylinder. Could this be my problem?
     
  2. Apr 11, 2011
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    Make sure the rear drum brakes are adjusted properly. If not that is probably your issue as the shoes have to come out and make contact with the drums before the front can build much pressure.
     
  3. Apr 12, 2011
    napaguy

    napaguy Banned

    goldendale wa
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    I just went through something similair and it turned out that the master cylinder wasn't getting a full stroke because the rod from the pedal was too long

    I built an adjustible rod and now have good pressure at all four wheels
     
  4. Apr 12, 2011
    Strider380

    Strider380 Can I have a zip tie?

    New England
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    Both excellent ideas. I'm gonna check them both out. Everything is custom so it could be anything.
     
  5. Apr 13, 2011
    scott milliner

    scott milliner Master Fabricator

    Seattle Wa.
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    It sound like the same problem I had. I found one of my used calipers were stuck. I replaced them and it solved the problem.
     
  6. Apr 18, 2011
    Strider380

    Strider380 Can I have a zip tie?

    New England
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    So I can't figure it out. Is it possible that 3/16 line is too small? I disconnected the front line at the master cylinder and replaced it with a plug. The Master cylinder held perfect pressure, just like it should be, with a nice firm high pedal. Like I was expecting. Hooked my front line back in and Its just like before. The pedal goes halfway down straight to the back brakes. If you pump it 4 or 5 times, you get good front brakes too. The hydraulic switch (plumbed into my front brakes) won't even turn on the brake lights unless you pump the pedal.
     
  7. Apr 18, 2011
    napaguy

    napaguy Banned

    goldendale wa
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    3/16 is what you should be using
     
  8. Apr 19, 2011
    eddiememphis

    eddiememphis Knuckle Buster

    Colorado
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    Pull out the pressure switch and install a proportioning valve. You must have one for a disc/ drum setup. The drums need a pressure valve to keep the spring from squeezing the fluid out of the wheel cylinders, and having to pump them up.
     
  9. Apr 19, 2011
    scott milliner

    scott milliner Master Fabricator

    Seattle Wa.
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    You will have to push the brake pedal down farther with the disk brakes. This is because more fluid is needed for the pads to contact the disk.
     
  10. Apr 19, 2011
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    Proportioning valves control the amount of pressure going to the rear brakes to help keep them from locking up too soon, they have nothing to do with what you describe. A residual pressure valve holds pressure on a drum system that does not use the spring and cup expanders in the wheel cylinder to keep pressure on the seals so fluid doesn't leak past them. Stock systems with the cup expanders typically do not use a residual pressure valve. Our Jeeps have a residual pressure valve because from the factory they did not use cup expanders in the wheel cylinders.
     
  11. Apr 19, 2011
    Strider380

    Strider380 Can I have a zip tie?

    New England
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    This is driving me nuts because its all I have left before insuring this 5 year project. Thought it'd only take a day to install the front brakes (i've been using just back brakes to move it around the garage/yard).

    I have the back brakes going to the front of the master cylinder (smaller reservoir) and the front brakes going to the rear of the master cylinder (larger reservoir). I've done some research and as far as I know this is correct for a 87 wrangler master cylinder.

    A little more background info for this problem. Back brakes always worked great. I even tightened them yesterday to a little tighter then I prefer. But now that I think of it, the fronts always had this problem. Let me clarify.

    For years, coming out of the front reservoir was about a 6 inch piece of brake like, going to an adapter for pipe thread then a pipe thread "T". Out of the T is a pipe thread pressure switch (reason I used a pipe thread T) and the other side was a pipe thread plug until some day I plumbed the rest of the front brakes (now!). And the pedal was the same way as now. It would have no pressure and drop halfway down immediately to the back brakes. Tho since there was no front system, it would turn on the pressure switch no problem for whatever reason (doesn't require much pressure? nowhere else for the pressure to go) Didn't think much of it, figured when I hook up my calipers everything would work fine since brakes are very simple and always came easy to me. Hooked up the front lines and same thing, no pressure to the fronts unless I pump it. this time the pressure switch won't turn on unless I pump it for whatever reason (fluid has other places to go?)

    Point of the story is, when I plug the front reservoir at the master cylinder itself, instead of at the 6inch piece of line, T, switch contraption I have going, theres ton's of pressure, works perfect. Bypassed all the T business and ran the line straight to cylinder and no pressure again. Tho I only bled the calipers quick and no air came out.

    Does this mean I have air stuck somewhere That I can't find?

    Driving me nuts!! Thanks for sticking with me guys, I'm sure most of you know the feeling.
     
  12. Apr 19, 2011
    Warloch

    Warloch Did you say Flattie??? Staff Member

    Falcon, CO
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    If I am reading right - you have always 'kinda' had this issue, only now it's worse. I would toss the current front pluming and do it right with brake parts one section at a time. I would even go so far as to plum one caliper at a time to see if you have a bad caliper.

    Also - verify that the Disk rotor itself is the right one. What I am getting at is I have seen this when the thinner disk was used with calipers that needed the thicker rotor.
     
  13. Apr 20, 2011
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    I have heard of the rubber flex lines to the front wheels developing internal blockage. Breakdown of the lining material, or some such issue.
     
  14. Apr 22, 2011
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
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    I have had similar trouble with my front dana 30 with disc brakes. In my case the problem turned out to be that I have two left calipers so the pass side caliper has the bleeder in the wrong spot and it will not bleed the air out. The brakes were spongy until I removed that caliper and rotated it so that the bleeder was higher so I could get the air out. I put it back on and I'm still running it several years later. Some day I'll get the correct caliper on there.

    Another idea would be for you to research the residual pressure valves. I have read somewhere that you may need them for both the rear (drum) and front (disc) brakes but they would be different psi.

    I guess it's worth noting that the calipers may require a lot more volume than the drums. It seems like your problem is volume not pressure.

    Let us know.
     
  15. Apr 22, 2011
    54cj3b

    54cj3b Member

    evergreen colorado
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    try gravity bleeding I had that happen to me a while back just keep a eye on fluid level in master
     
  16. May 2, 2011
    Strider380

    Strider380 Can I have a zip tie?

    New England
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    AKCJ....i didn't see your post until it was too late. Thought I was going to be a help on this forum but looks like you beat me to it. The parts store had the number mixed up for the drivers and passengers calipers. resulting in the bleeders being on the bottom of the calipers. A buddy told me to try switching them around. I did. I then let them drip bleed for a few seconds and had more pressure then needed. Can't believe how this thing stops compared to the manual front and rear drums I am used to. Figured I post this up incase anyone else had the same problem.
     
  17. May 3, 2011
    AKCJ

    AKCJ Active Member

    Fairbanks, Alaska
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    Good to hear you got it working.

    Having the backwards caliper really drove me nuts. I was stumped so I had a buddy come over one night and we went inch by inch over the entire brake system. Then my buddy who was laying on the garage floor under the jeep started laughing when he spied the problem. I had already removed and rebuilt both calipers without seeing the problem.
     
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