jeepmjga Posted April 12, 2021 Share Posted April 12, 2021 So I've been scouring the forums on a solution, but wondered if the gurus could offer any more advice. Replaced all of the brake components front and rear, new stainless lines front and rear. Did not replace booster or master cylinder. I have bled the system multiple times in the correct order and doing the bypass bleed as well. Cobbled together this replacement adjustable setup for the height valve. The local ACE was out of spherical rod ends so I couldn't do the hornbrod upgrade. So I am getting some pressure build up when the truck is off, but the pedal dumps to the floor when I turn the truck on. It will stop and lock up the rears while driving but I have to press the pedal all the way to the floor. My next thought was to the replace the rear height valve, I have thought about eliminating it but I think its a cool old school feature and want to keep it if possible. An extra came with the truck but unsure if its in working condition or not. Is there a way to tell if its working properly other than just disconnecting it and seeing if the brakes work? Thanks for any suggestions. On a good note, the motor is running well and the clutch is nice and smooth and I drove it up and down the street under its own power for the first time since I've had it! Link to comment Share on other sites More sharing options...
jdog Posted April 13, 2021 Share Posted April 13, 2021 did you bleed the master cylinder? Link to comment Share on other sites More sharing options...
jeepmjga Posted April 13, 2021 Author Share Posted April 13, 2021 No not yet, that was also my thought for the next step. I figure theres still got to be air in the system somewhere. Link to comment Share on other sites More sharing options...
Eagle Posted April 13, 2021 Share Posted April 13, 2021 How do you bleed? Link to comment Share on other sites More sharing options...
jdog Posted April 13, 2021 Share Posted April 13, 2021 6 minutes ago, Eagle said: How do you bleed? the mc? its essentially the same as bench bleeding, I've got some hard lines that I use to go from the fittings back to the reservoir. then pump the brakes. I've heard on older units not to press the pedal all the way to the floor as the m.c bore will have imperfections built up. if you then press the pedal to the floor it pushes the seals past these and ruins the seals. Link to comment Share on other sites More sharing options...
Pete M Posted April 13, 2021 Share Posted April 13, 2021 the MJ has a special bleeding procedure due to the rear prop. the link in my sig will have it Link to comment Share on other sites More sharing options...
mjeff87 Posted April 13, 2021 Share Posted April 13, 2021 Definitely bleed the MC. Also, make sure your calipers are on correctly on each side. The bleeder needs to be at the top, not the bottom. It's not uncommon to put them on the wrong sides (upside down), especially when replacing both at the same time. (been there, done that, got the tee shirt) Link to comment Share on other sites More sharing options...
jeepmjga Posted April 13, 2021 Author Share Posted April 13, 2021 Definitely double checked the calipers when I put them on so they are correct. So I bled it a few times doing the correct procedure for the prop valve but I was still getting pedal to the floor. The procedure I did was this... Bleed entire system normally, pass rear > drivers rear > pass front > drivers front Opened pass front bleeder, press pedal to floor and release Bleed pass rear > drivers rear Close front bleeder Bleed entire system again, pass rear > drivers rear > pass front > drivers front Still getting pedal to the floor, but it will stop and lock up the rear brakes. I was looking at the MC last night and noticed there is no bleed screw, so I am assuming I would need to pull it off and bench bleed? If so I was thinking about just going ahead and replacing MC and booster since its not too expensive. Thoughts? Link to comment Share on other sites More sharing options...
jdog Posted April 13, 2021 Share Posted April 13, 2021 Yeah no bleed screw on the Mc you either have to pull and bench bleed or set up as I Do. Link to comment Share on other sites More sharing options...
Jesse J Posted April 13, 2021 Share Posted April 13, 2021 slightly offtoping but I am stealing that control valve adjustment thing when I lift Link to comment Share on other sites More sharing options...
89 MJ Posted April 13, 2021 Share Posted April 13, 2021 10 minutes ago, Jesse J said: slightly offtoping but I am stealing that control valve adjustment thing when I lift I'd delete it. When you are going down a steep trail, then you won't have much rear braking power at all. Just food for thought. Link to comment Share on other sites More sharing options...
Jesse J Posted April 13, 2021 Share Posted April 13, 2021 Just now, 89 MJ said: I'd delete it. When you are going down a steep trail, then you won't have much rear braking power at all. Just food for thought. we will see it would be super easy to get rid of down the road Link to comment Share on other sites More sharing options...
derf Posted April 13, 2021 Share Posted April 13, 2021 Random thought. I may or may not have been involved in doing this once myself Did you get the front calipers installed on the correct sides? The bleed screw should be on the top. If you swap them, they will fit but the bleed screw will be on the bottom and the air won't bleed out. Link to comment Share on other sites More sharing options...
Pete M Posted April 13, 2021 Share Posted April 13, 2021 4 hours ago, Jesse J said: we will see it would be super easy to get rid of down the road you can disconnect it any time you need. Link to comment Share on other sites More sharing options...
Pete M Posted April 13, 2021 Share Posted April 13, 2021 also, it's possible I would want less braking in the back when pointed down hill. there'd be less weight on those tires. Link to comment Share on other sites More sharing options...
Eagle Posted April 13, 2021 Share Posted April 13, 2021 18 hours ago, jdog said: the mc? its essentially the same as bench bleeding, I've got some hard lines that I use to go from the fittings back to the reservoir. then pump the brakes. I've heard on older units not to press the pedal all the way to the floor as the m.c bore will have imperfections built up. if you then press the pedal to the floor it pushes the seals past these and ruins the seals. No, I want to know exactly how the OP (jeepmjga) bled his system. One person or two people? Suction bleeder? Pressure bleeder? Step-by-step procedure. If the brakes have been bled and there isn't a good peddle, something's wrong -- and it's usually in the way the brakes were bled. Link to comment Share on other sites More sharing options...
Eagle Posted April 13, 2021 Share Posted April 13, 2021 4 hours ago, derf said: Random thought. I may or may not have been involved in doing this once myself Did you get the front calipers installed on the correct sides? The bleed screw should be on the top. If you swap them, they will fit but the bleed screw will be on the bottom and the air won't bleed out. Good point. Often overlooked. Link to comment Share on other sites More sharing options...
jeepmjga Posted April 14, 2021 Author Share Posted April 14, 2021 13 hours ago, Eagle said: No, I want to know exactly how the OP (jeepmjga) bled his system. One person or two people? Suction bleeder? Pressure bleeder? Step-by-step procedure. If the brakes have been bled and there isn't a good peddle, something's wrong -- and it's usually in the way the brakes were bled. Calipers are installed correctly with bleeders on top. Two person bleed every time used clear tubing into bottle with a some fluid already in it. When bleeding individual wheel it was pump and hold, open bleeder until i see solid fluid coming into tube then close bleeder. Repeat process for each wheel at least 3 times. Then check fluid in master cylinder. This is process i used... Bleed entire system normally, pass rear > drivers rear > pass front > drivers front Opened pass front bleeder, press pedal to floor and release Bleed pass rear > drivers rear Close front bleeder Bleed entire system again, pass rear > drivers rear > pass front > drivers front Link to comment Share on other sites More sharing options...
Pete M Posted April 14, 2021 Share Posted April 14, 2021 with my truck, pressure-when-off-but-none-when-running was a bad booster Link to comment Share on other sites More sharing options...
derf Posted April 14, 2021 Share Posted April 14, 2021 2 hours ago, jeepmjga said: Opened pass front bleeder, press pedal to floor and release Bleed pass rear > drivers rear Close front bleeder Having a bleeder open when you release the pedal sucks air in through the bleeder. Link to comment Share on other sites More sharing options...
jeepmjga Posted April 14, 2021 Author Share Posted April 14, 2021 1 hour ago, Pete M said: with my truck, pressure-when-off-but-none-when-running was a bad booster Yea mine is pretty rusty like fluid has been dripping down the front of it for a while, makes me think the master is leaking out of the seal where the rod goes into it. 19 minutes ago, derf said: Having a bleeder open when you release the pedal sucks air in through the bleeder. From my understanding you need to leave the front bleeder open to simulate a front brake failure so the bypass valve will activate, otherwise you won't be able to fully bleed the entire system. I ordered a new master and booster anyway since it's likely they are still originals. Going to put all four on jack stands tomorrow and then try bleeding one more time tomorrow just for kicks and see what happens. Link to comment Share on other sites More sharing options...
Eagle Posted April 14, 2021 Share Posted April 14, 2021 6 hours ago, jeepmjga said: Two person bleed every time used clear tubing into bottle with a some fluid already in it. When bleeding individual wheel it was pump and hold, open bleeder until i see solid fluid coming into tube then close bleeder. Repeat process for each wheel at least 3 times. Then check fluid in master cylinder. This is process i used... Bleed entire system normally, pass rear > drivers rear > pass front > drivers front Opened pass front bleeder, press pedal to floor and release Bleed pass rear > drivers rear Close front bleeder Bleed entire system again, pass rear > drivers rear > pass front > drivers front Sounds right. Pete's comment about the booster may be the answer. Link to comment Share on other sites More sharing options...
mjeff87 Posted April 14, 2021 Share Posted April 14, 2021 If you do end up replacing the MC, bench bleed it before you install it. It "should" come with a little kit of parts for you to use to do that, but if not you can either buy one or make one up out of some spare fittings and short pieces of brake line. Bench bleed it, install caps on the outlets, install it on the booster and then quickly remove the caps and screw the lines into it. Then bleed the whole system again as normal. Link to comment Share on other sites More sharing options...
fiatslug87 Posted April 14, 2021 Share Posted April 14, 2021 6 hours ago, derf said: Having a bleeder open when you release the pedal sucks air in through the bleeder. The purpose of opening the front bleeder is to get the system to think there's a leak and move the pressure differential valve so the rears with the height sensing valve can be bled correctly. That's why after the initial rear bleed with a front open, the front is closed and the system is bled again. I had a similar issue, I rebuilt the MC (yes old school) and all was good. From '92 FSM: It also says not to pump brakes, just depress pedal. Link to comment Share on other sites More sharing options...
derf Posted April 14, 2021 Share Posted April 14, 2021 Makes sense. Link to comment Share on other sites More sharing options...
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