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Cant get a firm pedal after upgrading brakes

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Cant get a firm pedal after upgrading brakes

Old 01-03-2019, 09:25 PM
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Default Cant get a firm pedal after upgrading brakes

Alright yall, I have used this forum for searching and learning countless things on my 1990 XJ but even after searching the bowels of the Internet I still have to post because I am stumped. I have a 1990 XJ 4.0 Limited that was my sonís until he went off to college. Now I am upgrading the brakes to a 1995 XJ MC and Booster ( non ABS)( both from rockauto). I can get a somewhat firm pedal while the Jeep is off but absolutely no resistance when running. It doesnít even attempt to stop the wheels when I have the rear wheels off the ground.
So far I have replaced both front calipers and pads (yes they are on the correct sides with the bleeders on top and the pads are seated correctly), it has new rear wheel cylinders with hardware and new shoes all adjusted correctly I believe, I upgraded to a new power booster from a 95 XJ as well as a 95 XJ MC (Iím on the 2nd 95 XJ MC because I was getting the same result with the first one), I have bled the brakes with a Motive power bleeder as well as a Phoenix reverse bleeder and have gone through at least 2 gallons of DOT3 so far. I have no leaks and I have not been getting any air bubbles. None of the lines seem blocked and all bleed well. I also bench bled the MC before installation until I was no longer seeing bubbles.

Since my pedal goes down very easy when the Jeep is running, I am convinced the power booster is functioning correctly. Do you guys think I should try a 3 rd MC? Any other ideas that I havenít seen yet would be much appreciated. And just a note, I am currently stationed up in Ft Wainwright, Alaska so junkyards are pretty much non-existent.
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Old 01-03-2019, 10:17 PM
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Make sure the rear drums are adjusted properly, I take the drum off and adjust them to where the drum will only slide on with a little bit of persuasion from a hammer. Will the parking brake stop the rear wheels?
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Old 01-03-2019, 10:27 PM
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Iíll adjust them out a bit more and I hadnít tried the parking brake so I will do that as well. Iíll let you know shortly. Thanks
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Old 01-03-2019, 10:34 PM
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Ok the parking brake holds them tight and they donít move but adjusting the rear shoes to a tighter tolerance with the drums didnít help.
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Old 01-03-2019, 10:41 PM
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How did you adjust the pushrod?
New same length as the old?
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Old 01-03-2019, 10:48 PM
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I didnít mess with the pushrod and didnít even think about that. I did put about 3/8Ē worth of spacer between the booster and firewall to keep my pedal height manageable and never thought about the pushrod. Is that a simple threaded adjustment?
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Old 01-03-2019, 10:55 PM
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yes
You'll have to fool with it but try the new same length as the old for starters.
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Old 01-03-2019, 11:03 PM
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Thanks, I was definitely out of things to try and my wife is sick of me coming back into the house and giving a verbal play-by-play out loud on everything Iíve done and tried lol. Iíll jump into that as soon as I get home from work tomorrow.
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Old 01-04-2019, 10:41 AM
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I had the same problem when replacing the booster on my daughters XJ. It has to be adjusted to match your old unit.
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Old 01-04-2019, 07:27 PM
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So I did some measurements and put the pushrod to where it was just touching the cylinder in the MC and the pedal when the Jeep was off was much firmer and it would stop the rear tires from me spinning them by hand but still a very loose, all the way to the floor, pedal when the Jeep is running. So I adjusted the pushrod again so when it touched the cylinder in the MC at the point where it still had about 1/8 to 1/4 inch until it was seated all the way on the power booster. That made it a little better and it at least slows the rear wheels down when running but the pedal still goes to the floor without much resistance.

So my question now is, should I adjust the pushrod out more even though it is engaging the MC by about 1/8Ē when I tighten it to the booster? I canít go off of the old unit because that was the stock 1990 MC and booster (single diaphragm) and this is the ď upgradeĒ from a 1995 XJ (dual diaphragm). Should I take the 3/8Ē spacers out from in between the booster and firewall and then have a high pedal but more stroke distance?

thanks again guys, I at least feel like Iím getting somewhere again lol
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Old 01-04-2019, 08:41 PM
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Yes adjust out a little at a time, the push rod should have some preload on the master cylinder. You just don't want to adjust too far at one time because it will block the relief port when the fluid/system warms up and then the brakes will start dragging. Not sure about needing a spacer between the booster & firewall...
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Old 01-04-2019, 10:49 PM
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Ok Iíll do some more adjusting out in the morning. I put spacers in because the 95 boosterís rod that connects to the pedal is about 1/2Ē longer than the original 90 single diaphragm booster. I donít think it would make a difference in my current issue but who knows.
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Old 01-04-2019, 11:10 PM
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Thatís how I adjusted them per the previous recommendation and yes the parking brake stops the rear wheels very well.
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Old 01-06-2019, 03:12 AM
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Alright, the pushrod is preloaded into the MC by about 3/8Ē. I put all 4 wheels up in the air on stands and started checking in 4Hi so I could see what the fronts were doing as well. I am to the point where it will stop the fronts seemingly well and is now stopping the rear but much slower and if I put it in N and have my wife press the brake I can slightly move the rear wheels if I put some heft into it.

Just wondering if you guys think it is time for a test drive or if I should bring that pushrod out some more. Also, does anyone know where to get some flex lines so I donít have to remove my lines every time I do this and then bleed the system for the millionth time lol?
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Old 01-06-2019, 08:48 AM
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I would lengthen the rod just a hair more before you button it up.
Then as long as you can get a firm pedal without bottoming out the master cylinder I would call it good and take it for a spin. Does the parking brake still function as well?
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