Yes, another brake question - JeepForum.com

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post #1 of 17 Old 02-04-2013, 09:26 AM Thread Starter
mntbkrguy
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Yes, another brake question

Background:
94 YJ, 8.8 swap w/disk brakes. Master Cylinder out of an old Mercury Grand Marque, stock proportioning valve with the o-ring removed.

Symptoms:
1) When first started I hit the brakes and it takes a while to slow to a stop so I usually hit the brakes a few times when I first start moving to warm them up (figure of speech).
2) Once warmed up the brakes are touchy, if I press to hard the jeep nose dives and I have been wearing my front pads down quick. I need to replace the pads and rotors this week.
3) The pedal goes all the way to the floor, when I replaced the Booster about a year or so ago I adjusted the push rod to the point where I think that is the point where the pedal stops.
4) when I really need to stop and have the foot to the floor it seems to take a longer distance than I feel comfortable stopping.

I have bled the brakes many times with little improvements. The last time I used a hand vacuum pump to pull fluid up to the master from the passenger front and got just a few little bubbles from the front which I think may have been stuck in the proportioning valve which helped a very little.

I have read every post I can find and it seems like everyone has had different results. I am ready to put in a ZJ Proportioning valve when I change the brake pads and rotors, I have also considered a 95 booster.

I can deal with the touchiness, and the soft brake pedal but what really has me concerned is the short stopping distance and it taking time before the brakes really start working after initial startup.

Any experienced input would be a huge help, Vancopbs, any suggestions.


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1994 YJ 4.0
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post #2 of 17 Old 02-04-2013, 09:45 AM
SeanB95YJ
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This is what I did back when I had my XJ and swapped to rear discs....

4-wheel disc MC (which you have already)
dual diaphragm booster (you mentioned new booster, but didn't say if it was stock replacement or upgraded dual)
removed stock prop valve completely
ran front directly from MC through a T fitting to each of the front wheels
ran the rear through an adjustable prop valve I bought from Summit Racing
bled/flushed system fully
initially had the prop valve fully open (full flow) and took it to a deserted shopping center where the town dumps all excess plowed snow (after it's melted, there's lots of sand on the pavement)... did some slow test runs SLAMMING on the brakes locking up the tires... kept making prop valve adjustments (reducing flow) until the fronts would lock BEFORE the rears did

on 33s I swear it stopped better than most cars on the road

Good luck

Sean B. - Schenectady, NY - 95 YJ, 350/700r4/NP241, JB Shorty SYE, 8.8 rear, 2" BDS, 1" homebrew shackles, Daystar 1" BL, TJ flares, 35x12.50 General Grabber AT2 on 15x10 Bart D-Truckers, Polyshield polycarbonate windshield, HD over/under crossover steering
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post #3 of 17 Old 02-04-2013, 10:24 AM Thread Starter
mntbkrguy
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I have the stock booster and thought about upgrading to the dual. I haven't heard of removing the proportioning valve for the front that is a different idea. I looked at the adjustable valves for the rear it sounds like you have had good luck with that. That may be back on the list.

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post #4 of 17 Old 02-04-2013, 10:37 AM
jbolty
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I did the 95 booster swap a couple years ago and had a lot of problems; low pedal mostly. I adjusted the push rod, swapped the master and bled gallons of fluid. Turns out to have been a bad booster. I got three in a row that were defective rebuilds from Cardone. Eventually mrblaine made a custom bracket for me and put in a 98 TJ booster. With that and EBC pads in the front I can stand the jeep on its nose with the brakes. Never touched the proportioning valve. Not long after this the black magic pads came out and I have some experience with those and highly recommend.

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post #5 of 17 Old 02-04-2013, 10:58 AM
NHfireLJ
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Running the same set up as you, (O ring still installed) No issues at all, on 35's

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post #6 of 17 Old 02-04-2013, 04:33 PM
JeeperDon
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OP, to me your '1)' item is screaming air-in-line. I just added the axle with discs and nothing else but a good bleed. My brakes were fine before and are fine after, with zero differences in any particular press at any time. On any brake work done right with good working parts, the overall stopping performance may be different as you play with MC's, prop valves, and boosters, but it should never change from stop to stop. You said you did the air, and I'm not saying you don't know what you're doing, but to me it's an air issue.

'93 YJ, '02 GM 4.3V6, SOA, dual ARB's, 8.8+D30(WarnHubs), 4.88s, 35" BFG KM2s, AX15, NP231+4:1+SYE+2LO, York OBA, Warn M8000.
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post #7 of 17 Old 02-05-2013, 08:47 AM Thread Starter
mntbkrguy
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JeeperDon I think you are correct although I have no idea how that could be so after all the effort I have put into bleeding the system.

I have just ordered new rotors premium pads a tee for the line and adjustable proportioning valve. I saw an adjustable one a while back but it was expensive so I kind of gave up on that but after seeing them for only $35 on Summit I figure that is the best way to eliminate one of the biggest parts of it. I also think replacing the pads and rotors will make a huge difference since they are looking pretty rough. obviously I will have to bleed the whole system again and another temptation is to use a homemade version of this.
http://www.motiveproducts.com/

It is really just your typical garden sprayer with a plate to force fluid through the system.

I will keep an update if anyone wants to know how it all ends up.

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1994 YJ 4.0
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post #8 of 17 Old 02-05-2013, 09:08 AM
JeeperDon
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A caliper may be hanging up too. Also look for the little notches in the brake hanger, where the pad notches hit the hanger. There is not stainless steel cap there on a YJ as on other vehicles, so the hanger gets wear notches. I had that and recently welded the notches up and ground them smooth.

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post #9 of 17 Old 02-05-2013, 09:16 AM
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I am running somewhat the same system is you.
I did install the 95 booster and a proportioning valve from a 4 disk GrandCherokee at the same time as the master though.
If I remember right don't you have to change the lines on the master?
They are switched on the Marquis master. (front and back)
I also had a few problems with one of the lines going into the master. (leak)
As always make sure your bleeders on the calipers are on top and start with bleeding the passenger back first.
You may want to tap on the calipers the same time you are bleeding them. Sometimes air will get trapped in them.

93 YJ SOA 2" springs front, XJ springs rear w/main leaf added, High pinon 9 inch rear detroit locker front Dana 44 ARB 4.56 Gears, 36 inch Irok tires too much to list.
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post #10 of 17 Old 02-05-2013, 09:16 AM
kjg26
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I swapped discs brakes from a 98 grand cherokee into my 93. I swapped a 95 booster and master cylinder and 97 grand cherokee prop valve and it stops wonderfully. Locks up 33s.

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post #11 of 17 Old 02-05-2013, 01:04 PM
87TPIYJ
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Quote:
Originally Posted by jbolty View Post
I did the 95 booster swap a couple years ago and had a lot of problems; low pedal mostly. I adjusted the push rod, swapped the master and bled gallons of fluid. Turns out to have been a bad booster. I got three in a row that were defective rebuilds from Cardone. Eventually mrblaine made a custom bracket for me and put in a 98 TJ booster. With that and EBC pads in the front I can stand the jeep on its nose with the brakes. Never touched the proportioning valve. Not long after this the black magic pads came out and I have some experience with those and highly recommend.
Not to hijack the thread but can you post a pic of that bracket you had made for the tj booster? Did the bracket keep you from having to cut and extend the plunger?

YJ 350TPI NV4500 SOA 8.8 Flat skid

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post #12 of 17 Old 02-05-2013, 01:25 PM Thread Starter
mntbkrguy
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JeeperDon, another great suggestion I will take a look

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1994 YJ 4.0
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post #13 of 17 Old 03-25-2013, 10:24 AM Thread Starter
mntbkrguy
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Here is the update. I decided to go with the adjustable rear proportioning valve and T off the front. So far so good, I took the jeep up tp Rousche Creek for a weekend with my club and felt a lot more compfortable. I think in the long run I could use a little extra power from a dual diaphram booster will help but being able to stop facing down a very steep grade in 4x4 low without my foot mashed to the floor gives me a lot more confidence.




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post #14 of 17 Old 03-25-2013, 04:34 PM
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Quote:
Originally Posted by mntbkrguy View Post
3) The pedal goes all the way to the floor, when I replaced the Booster about a year or so ago I adjusted the push rod to the point where I think that is the point where the pedal stops.
Classic symptom of a master cylinder with bad seals
Did you get a rebuild from the store or a used one from a yard?

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post #15 of 17 Old 03-25-2013, 07:23 PM
87TPIYJ
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Quote:
Originally Posted by mntbkrguy View Post
Here is the update. I decided to go with the adjustable rear proportioning valve and T off the front. So far so good, I took the jeep up tp Rousche Creek for a weekend with my club and felt a lot more compfortable. I think in the long run I could use a little extra power from a dual diaphram booster will help but being able to stop facing down a very steep grade in 4x4 low without my foot mashed to the floor gives me a lot more confidence.
I can't even explain how much better the dual booster is!

YJ 350TPI NV4500 SOA 8.8 Flat skid

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