Ibby Posted August 13, 2013 Share Posted August 13, 2013 I recently did a bunch of brake work on my 91 MJ. I swapped in an MJ D44 with the larger drum brakes, removed the bed biasing device and ran a single line to the rear through an adjustable prop valve, and I just installed a 95 booster and master cylinder. When I went to bleed the front calipers I broke a bleed screw so I replaced the calipers and rotors. I bled the system quite well and there is a huge difference in braking, but when I first push in the pedal it does feel a bit spongy. Is this normal? Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted August 13, 2013 Share Posted August 13, 2013 That's not normal, no. Re-bleed and if that doesn't work, the MC may be on its last leg (assuming you got it used). Link to comment Share on other sites More sharing options...
1989 Eliminator Posted August 13, 2013 Share Posted August 13, 2013 Make sure you bleed in the order: Right Rear, Left Rear, Right Front, Left Front. Make sure your vaccum hose is on the booster good. Link to comment Share on other sites More sharing options...
skidoo_j Posted August 13, 2013 Share Posted August 13, 2013 What brand of adjustable proportioning valve did you use? Does it hold residual pressure to the drums? Are the Cylinders in the drums good? Did you use a new hose from bed to rear axle? What about the the fronts? I'm just proposing ideas, if you did the dual booster upgrade and kept your old rubber hoses maybe they're swelling some... Link to comment Share on other sites More sharing options...
Ibby Posted August 14, 2013 Author Share Posted August 14, 2013 With the exception of the front brake lines, everything is new. The prop valve I used is identical to this: http://www.coloradomustang.com/ShowItem/100714%20Mustang%20Disc%20Brake%20Proportioning%20Valve%2064%20-%2073.aspx but I didn't think to put a check valve in when I installed it. I wound up making a pump brake bleeder this evening and re-bled the truck (yes, in the right order). Although the cap on the 95 booster leaked a bit of fluid I didn't see any bubbles at any of the wheels when I re-bled things. After the bleed the brakes are a bit more firm. Does the pressur holding vavle for the rear brakes make a big difference? Link to comment Share on other sites More sharing options...
skidoo_j Posted August 14, 2013 Share Posted August 14, 2013 did you keep the stock proportioning valve then? the one you sent a link to is just one line in one line out valve. So if you kept the stock one and eliminated one line did you plug the correct port? The residual pressure valves are often used in hot rod applications where the master is near level with the brakes, but a few people have used them, Not needed was just to see if it could have been a cause for your issue. was the booster used? sometimes it's the simple things, did you tighten all the bolts holding the booster to the truck well? Was the firewall weak? Do any of your bleeder valves leak? Link to comment Share on other sites More sharing options...
Ibby Posted August 14, 2013 Author Share Posted August 14, 2013 Yep, kept the stock prop/combination valve. The adjustable one sits between the stock one and the new single rear line I ran, keeps the rear brakes from locking up. The correct port has been plugged. The booster and all the other parts I installed are brand new. Firewall's in good shape and all bolts have been tightened (and rechecked) to the specified torque in the Haynes manual. The bleeder valves don't leak. I've left the truck in the garage overnight and not a drop has shown up on the floor. I looked at all the fittings and they're bone dry. After I did the re-bleed last night things are seeming a lot better even though I didn't see any air bubbles at all. I can feel the difference in braking power is way better than the stock system. I think it's fine now. I'm just a bit concerned as I'll have a camper on the truck and I'll be towing a fairly heavy load as well, which is what made me put the better braking system in the first place. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 14, 2013 Share Posted August 14, 2013 Yep, kept the stock prop/combination valve. The adjustable one sits between the stock one and the new single rear line I ran, keeps the rear brakes from locking up. The MJ doesn't have a prop/combination valve up front in the stock configuration like the XJs do. It is simply a distribution block; no proportioning or brake biasing happens internally. If you had not installed the adjustable inline valve, full brake bias would be applied to the rear brakes since you bypassed the original load sensing proportioning valve. If plumbed and bled correctly, your setup is fine. Link to comment Share on other sites More sharing options...
Ibby Posted August 15, 2013 Author Share Posted August 15, 2013 Apologies on the bad terminology. I realize the prop/combi device is just a distribution block. I just went with what everyone seems to call it. I read all the articles here on the brake work I did and I am quite happy with the results. The increase in braking power is quite noticeable. The "spongy" feeling at the start of pressing the brake pedal had me concerned. She stops like a champ though. Link to comment Share on other sites More sharing options...
carnuck Posted September 1, 2013 Share Posted September 1, 2013 If you still have rear drums, manually adjusting them usually takes the mushy feel out after the brakes are worn in a bit. Link to comment Share on other sites More sharing options...
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