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  #1  
Old December 19th, 2017, 19:59
Dill30705 Dill30705 is offline
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mj highly modified Brake setup help

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 donít 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 Iím bottoming out the master cylinder but this is my first custom brake setup and Iím unsure if that could be a possibility with this setup or not.

Thanks for any input and help anyone can give.
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  #2  
Old December 19th, 2017, 21:31
gordonganders gordonganders is offline
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Re: mj highly modified Brake setup help

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.
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  #3  
Old December 19th, 2017, 21:48
Francesco Francesco is offline
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Re: mj highly modified Brake setup help

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.
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  #4  
Old December 20th, 2017, 00:16
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Johnnie Walker Johnnie Walker is offline
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mj highly modified Brake setup help

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.
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  #5  
Old December 20th, 2017, 07:59
Dill30705 Dill30705 is offline
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Re: mj highly modified Brake setup help

Quote:
Originally Posted by Francesco View Post
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? Iíd really like to see someone else with the same setup but know this is unlikely to find so anything close Iíd 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 donít think so unless I possibly donít 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 Iím not able to move enough fluid to fill the larger front and rear calipers. Thought the Durango master cylinder would fix this, but now Iím unsure. Before I done the new larger master cylinder I could just mash it to the floor and have nearly no brakes.
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  #6  
Old December 20th, 2017, 08:24
Dill30705 Dill30705 is offline
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Re: mj highly modified Brake setup help

I just got done driving to town and I havenít 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.
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  #7  
Old December 20th, 2017, 09:23
RCP Phx RCP Phx is offline
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Re: mj highly modified Brake setup help

Pedal pushrod length can definitely have a impact. Did you bleed the master cylinder on the bench and LEVEL?
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  #8  
Old December 20th, 2017, 10:51
tow hook tow hook is offline
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Re: mj highly modified Brake setup help

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
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  #9  
Old December 20th, 2017, 11:47
RCP Phx RCP Phx is offline
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Re: mj highly modified Brake setup help

Quote:
Originally Posted by tow hook View Post
I will add to the rod length to bring the pedal up off the floor.
It doesn't work that way!
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  #10  
Old December 20th, 2017, 13:42
Dill30705 Dill30705 is offline
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Re: mj highly modified Brake setup help

Quote:
Originally Posted by RCP Phx View Post
Pedal pushrod length can definitely have a impact. Did you bleed the master cylinder on the bench and LEVEL?
It was bench bleed correctly and has no air in the system. I have bleed brakes for years and this is not the issue.
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  #11  
Old December 20th, 2017, 13:50
Dill30705 Dill30705 is offline
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Re: mj highly modified Brake setup help

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 donít 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 ďbottom outĒ limiting peddle travel?

This makes me wonder if Iím possibly not getting complete master cylinder useage because I donít 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.
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  #12  
Old December 20th, 2017, 16:06
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techno1154 techno1154 is offline
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Re: mj highly modified Brake setup help

Quote:
Originally Posted by Dill30705 View Post
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 donít 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 Iím bottoming out the master cylinder but this is my first custom brake setup and Iím 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.
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  #13  
Old December 21st, 2017, 08:55
Dill30705 Dill30705 is offline
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Re: mj highly modified Brake setup help

Quote:
Originally Posted by techno1154 View Post
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 donít 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 donít believe it is truly the issue because the front brakes wonít lock either.

-The front proportioning valve canít 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.

Donít get me wrong it stops very good just wonít lock up the brakes like I would expect. Maybe Iím 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?
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  #14  
Old December 21st, 2017, 20:01
Dill30705 Dill30705 is offline
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Smile Re: mj highly modified Brake setup help

For anyone still hanging around I think I may have found the problem. Iím 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.
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  #15  
Old December 22nd, 2017, 06:05
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Kego814 Kego814 is offline
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mj highly modified Brake setup help

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

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