• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

mj highly modified Brake setup help

Dill30705

NAXJA Forum User
Location
Georgia
I have a Jeep comanche 1992 with Ford 8.8 rear disk brake axle and front is a custom G2 dana 44 with Jeep WJ knuckles and brakes.


Setup so far:
-late model xj large brake booster
-Dodge Durango 1.125 bore master cylinder
-factory comanche proportioning valve with rear load leveling valve held wide open for max braking power.
-ford 8.8 disk brake rear axle
-Jeep WJ front calipers and rotors.

Brake pedal is a bit stiff but nothing bad at all. Problem is I can mash it to the floor and brakes don’t lock up. I have factory 2012 Jeep jk rubicon wheels and tires 255/75r17 I believe. Should I be able to lock these up? It stops good but I really expected the rear to lock up with the tire and brake combination on the comanche at a minimum.

To me it seems I’m bottoming out the master cylinder but this is my first custom brake setup and I’m unsure if that could be a possibility with this setup or not.

Thanks for any input and help anyone can give.
 
Just finished WJ brakes on my 98xj. Also my first time getting into brake mods. I have the opposite problem: can lock up 33s no problem, but the pedal is soft. Doesn't quite make it to the floor but its close.

I will be following this thread and hope to learn a thing or two.
 
Personally, I'd remove the proportioning valve in the rear entirely, and put an XJ prop valve in the front - I have a very similar setup to you and it will lock up 35s no problem.
 
I have had my Exploder 8.8 for a bit, just recently swapped a WJ 30 in.
LSV still installed, before the WJ swap brakes weren't spectacular.
Brakes are meow better, haven't tried to lock them up though.
I do still have factory MC/booster.
As others have stated, I say delete the lSV, and run a ZJ or adj. prop valve.
 
Personally, I'd remove the proportioning valve in the rear entirely, and put an XJ prop valve in the front - I have a very similar setup to you and it will lock up 35s no problem.

What exactly is your setup? I’d really like to see someone else with the same setup but know this is unlikely to find so anything close I’d like to compare different peoples successful setups.

I need to remove the rear load sensing valve but have a trip coming up the 30th just trying to make due til after the first of the year before making any new brake lines.

I also had to cut and reweld the end of the brake booster arm that attaches to the brake peddle because the new larger 2000 xj brake booster rod was longer. Would this have any effect I don’t think so unless I possibly don’t have enough throw in master cylinder now? So effectively I might only have says 70% of the usable throw in master cylinder before the peddle bottoms out?

It just seems to me that I’m not able to move enough fluid to fill the larger front and rear calipers. Thought the Durango master cylinder would fix this, but now I’m unsure. Before I done the new larger master cylinder I could just mash it to the floor and have nearly no brakes.
 
I just got done driving to town and I haven’t drove any other xj in a long time to be able to compare peddle travel but mine seems very short not sure if this might give any insign to the possible problem but the first bit seems very soft then it gets hard and I have about 1-2 inches or peddle travel before it bottoms out. This is a rough estimate I doubt I even have 2 inches of travel.
 
Pedal pushrod length can definitely have a impact. Did you bleed the master cylinder on the bench and LEVEL?
 
when I did the ruff stuff disc conversion, I used a zj prop valve, my pedal goes to the floor but my 37s lock up no problem, I will add to the rod length to bring the pedal up off the floor. both play a part in getting it to work
 
If the rod length was any longer it would have to peddle super high. It was cut and welded to be exactly the same length as the factory single diaphragm booster. I have heard talk about a spacer that goes between the booster and the firewall could this be part of the the issue? If I used the 1/4 or 1/2 spacer I don’t remember what that spacer thickness was I had read about. But if I used it to lower the peddle then lengthen the rod back longer so that I would have more throw would this possibly gain me more peddle travel?

I guess I need to look and see what the peddle is bottoming out on the bracket or something else?
Can the booster “bottom out” limiting peddle travel?

This makes me wonder if I’m possibly not getting complete master cylinder useage because I don’t have enough peddle throw thus causing the issue. Because this Durango master cylinder is used on a large vehicle with comparable sized calipers front and rear.
 
I have a Jeep comanche 1992 with Ford 8.8 rear disk brake axle and front is a custom G2 dana 44 with Jeep WJ knuckles and brakes.


Setup so far:
-late model xj large brake booster
-Dodge Durango 1.125 bore master cylinder
-factory comanche proportioning valve with rear load leveling valve held wide open for max braking power.
-ford 8.8 disk brake rear axle
-Jeep WJ front calipers and rotors.

Brake pedal is a bit stiff but nothing bad at all. Problem is I can mash it to the floor and brakes don’t lock up. I have factory 2012 Jeep jk rubicon wheels and tires 255/75r17 I believe. Should I be able to lock these up? It stops good but I really expected the rear to lock up with the tire and brake combination on the comanche at a minimum.

To me it seems I’m bottoming out the master cylinder but this is my first custom brake setup and I’m unsure if that could be a possibility with this setup or not.

Thanks for any input and help anyone can give.

Well, I do not know for sure what the problem is with your brakes but I do not think the size of the calipers or the fact that you are using 4 wheel disc contribute to the problems.

My XJ have been outfitted with WK (2005 to 2010 Grand Cherokee) front brakes, ZJ rear disc except the calipers themselves were taken from an Explorer (they have metal pistons unlike the ZJ) an adjustable proportioning valve and the same old 1996 XJ master cylinder. My XJ stops on a dime and the break pedal travel is less than half way.

I know you said the brakes have been properly bled,.. could you by chance be over looking something,...air leaking into the system, calipers not positioned properly i.e. the bleeder valve down instead of up, old ballooning rubber hoses? Maybe the problem is the load sensing brake valve allowing too much fluid to bypass. I am not sure you mentioned whether or not it is properly adjusted.
 
Well, I do not know for sure what the problem is with your brakes but I do not think the size of the calipers or the fact that you are using 4 wheel disc contribute to the problems.

My XJ have been outfitted with WK (2005 to 2010 Grand Cherokee) front brakes, ZJ rear disc except the calipers themselves were taken from an Explorer (they have metal pistons unlike the ZJ) an adjustable proportioning valve and the same old 1996 XJ master cylinder. My XJ stops on a dime and the break pedal travel is less than half way.

I know you said the brakes have been properly bled,.. could you by chance be over looking something,...air leaking into the system, calipers not positioned properly i.e. the bleeder valve down instead of up, old ballooning rubber hoses? Maybe the problem is the load sensing brake valve allowing too much fluid to bypass. I am not sure you mentioned whether or not it is properly adjusted.


I wish it was this easy to diagnose.

-I don’t believe it is air as the brakes have been like this for months without getting worse making me believe they system his not loosing fluid or having air introduced.

- all calipers have been installed correctly no doubt about that.

-front hoses are new extended stainless braided lines

-rears are brand new

-load sensing valve it tied vertical. This should have is functioning in the wide open position. I don’t believe it is truly the issue because the front brakes won’t lock either.

-The front proportioning valve can’t be the issue because in a mj it is basiclly just a splitter with no internal valves to limit pressure. Their is a built in rear bypass Incase the fronts go out the rears get full pressure. But otherwise it does not limit pressure.

Don’t get me wrong it stops very good just won’t lock up the brakes like I would expect. Maybe I’m overlooking something simple like brake pads? They are the nicer metallic set house brand from oreillys. Maybe I should put better pads. Yellow stuff from EBC?
 
For anyone still hanging around I think I may have found the problem. I’m going to try it out tomorrow. I was unaware until just now that the rod between the booster and MC is adjustable. From reading other threads about adjusting and issues that can cause the need for adjustment. I think I have found my problem. And that is the rod need lengthen ever so slightly to better match the Jeep booster to the Durango MC. I will update if this fixes the issue.
 
In my experience at the shop, When a booster fails, it won't fully travel and no matter how hard you push, you can't lock them up. I'd replace the booster and try your luck

Sent from my LG-LS777 using Tapatalk
 
In my experience at the shop, When a booster fails, it won't fully travel and no matter how hard you push, you can't lock them up. I'd replace the booster and try your luck

Sent from my LG-LS777 using Tapatalk


I have experience a failed booster not sure that is the problem but likely will be the first thing I replace if adjusting it doesn’t work. The booster is a reman from autozone and is about 6 months old.

Can anyone confirm that a 1995 or 1996 cherokee brake booster has the same length push rod as the earlier single diaphragm boosters?
 
WJ front brake with 8.8 years with stock 97 XJ booster/master and prop running 35s. Thing has better brakes than my 2006 Tacoma. And it will lock all four up if i mash on it. Its a scary event when you do that because of the weight transfer the ass likes to walk around. But it stops like a beast.

Its not a super hard pedal and it has a nice amount of push before the brakes really kick in.
 
I'm also running 8.8 disc brakes with wj front brakes. Still using the stock booster and master. Only thing I have done is pull the prop valve o-ring to even out the braking. Will lock up 35's and has good pedal pressure. The pedal shouldn't be bottoming out mechanically at all.
 
I seriously wonder if you don't just have a master that's too big. While the bigger one will reduce pedal travel it will reduce pressure at the calipers. Maybe the Durango uses a larger booster to compensate for that? I'm not sure. Might be worth looking for a 1 1/16 master
 
Back
Top