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Hi... I have a 1990 XJ, I have Ford Explorer rear disc brake conversion on my Currie nine inch Ford rear axle. My front brakes, master, propotioning valve, and single diaphragm booster are stock. I have 33x12.5 x15 tires. I want good braking!
Anyway the stock booster is leaking vacuum per my hand vacuum pump test, so time to replace it. That leads me to perhaps replacing the master while I am at it, and perhaps the proportioning valve too.
What upgrades are suggested if any?
Different bore master? Different booster? What about the proportioning valve?
I see Quadratech offers an upgraded booster and master kit for "rear disc brake conversions" , see link below...
Engine: 4.3L with headers and full 3" exhaust system
Stock is 15/16" I believe. I have WJ brakes front and rear and used the stock ZJ master which is that size. Works well. A different proportioning valve is recommended. Mostly that controls when the rear brakes are applied when you push the pedal. I am also running the ZJ dual diaphragm booster.
Stock is 15/16" I believe. I have WJ brakes front and rear and used the stock ZJ master which is that size. Works well. A different proportioning valve is recommended. Mostly that controls when the rear brakes are applied when you push the pedal. I am also running the ZJ dual diaphragm booster.
ok, thanks when you say the ZJ master is that size are you referring to the xj stock15/16" size bore or the larger 1 1/8" bore diameter?
Yes, Cruiser54! But which dual booster?
1. later model XJ which years?
2. ZJ which years?
3. WJ which years?
4. Other?
Then what of the master cylinder?
1. retain my stock master?
2. use master that goes with the ZJ or WJ booster, if so is one better than the other, remember I have rear discs? I assume the bigger bore is better for discs, right?
3. Other?
As for the Propotioning valve,
1. keep mine?
2. Use one off a disc brake equiped WJ or ZJ?
3. no valve?
4. Other?
Recall I have 33 inch tires, and disc rear brakes (Ford rear disc from Explorer)
Also ease of install is important, and being a 1990, I want to retain my wiper fluid wash bottle if possible, moving it into the wheel well like later XJs did is probably not an option as my tires and wheel travel will possibly hit it, or thrown rocks may smash it. I wheel in my Jeep. I wheely do! haha. but if I need to relocate it, I suppose I can, a small price to pay for best brakes.
I do not mind bending the firewall pinch seam if needed to fit the booster.
I have the stock aircleaner housing and wish to retain it, as I need it to pass smog. It has the smog required thermostatic preheat valve on it.
I also prefer to know everything up front I need to change, so everything can be gathered before I start, such as modified brake lines, and their end fittings. So info on that will be helpful!
Althoigh I can pull an used one from the wrecker, I much prefer to buy new parts for this, rather than used parts that may not be much newer than mine. (my stock single diaphragm booster now leaks)
I couldn't use the WJ master because the reservoir was too tall and hit the hood, or the other way around
Oh, I will need to be aware of that, although other poster has not had this issue. Maybe it is a year model difference with in the WJ series? or perhaps
what you used had the a replacement master lt reservoir, or cap rather than a stock WJ set up? I wonder, are you sure of the pedigree of the parts from your WJ swap attempt, or do you think maybe another part was swapped or something like that, or maybe an aftermarket unit sold as a WJ compatible part rather than an exact match?
Thanks for that input, something to look out for.
Photo of WJ reservoir... https://en.m.wikipedia.org/wiki/Jeep_Grand_Cherokee_(WJ)#/media/File:4.7_Powertech_engine_Jeep_WJ.jpg
99 to 2004 WJ booster/master with the flexible tubes.
Keep your PV and swap out the guts from inside the WJ PV.
OK that is great info. Thank You Cruiser54
Do you recall what flare end changes if any need be done on the flare ends of lines for your suggested plan? i.e. 99 to 04 WJ, and using the xj proportioning valve with the valve's internals changed with that of my XJ? Do I need to purchase new ends or adaptors, or couplings or such for the lines ?
In doing this Proportioning valve modification, what am I accomplishing? Increasing rear bias, or decreasing rear bias? I am trying to wrap my head around this, the swapped rear discs are more effective than the drums, so bias should be reduced to the rear? or do disc calipers require more fluid volume to work than drum cylinders and hence more bias is need to the rear when discs are used?
I understand some conversions require either a spacer added, or a spacer removed, to / from between the firewall and booster, what in this case of the 99 to 04 WJ booster put in my XJ?
I plan to document this conversion and generate a complete parts list, right down to the part numbers if applicable, and include a modifcation list and some photos to post on the forum.
Engine: 4.3L with headers and full 3" exhaust system
Originally Posted by robsjeep
Oh, I will need to be aware of that, although other poster has not had this issue. Maybe it is a year model difference with in the WJ series? or perhaps
what you used had the a replacement master lt reservoir, or cap rather than a stock WJ set up? I wonder, are you sure of the pedigree of the parts from your WJ swap attempt, or do you think maybe another part was swapped or something like that, or maybe an aftermarket unit sold as a WJ compatible part rather than an exact match?
Do you recall what flare end changes if any need be done on the flare ends of lines for your suggested plan? i.e. 99 to 04 WJ, and using the xj proportioning valve with the valve's internals changed with that of my XJ? Do I need to purchase new ends or adaptors, or couplings or such for the lines ?
You will cut the Bubble flares off the WJ lines. Put the original fittings from the prop valve tubes over the WJ lines and then Double flare the lines to fit the prop valve.
In doing this Proportioning valve modification, what am I accomplishing? Increasing rear bias, or decreasing rear bias? I am trying to wrap my head around this, the swapped rear discs are more effective than the drums, so bias should be reduced to the rear? or do disc calipers require more fluid volume to work than drum cylinders and hence more bias is need to the rear when discs are used? The "guts" are matching the prop valve to the rear discs.
I understand some conversions require either a spacer added, or a spacer removed, to / from between the firewall and booster, what in this case of the 99 to 04 WJ booster put in my XJ? Trim the flange behind the booster.
I plan to document this conversion and generate a complete parts list, right down to the part numbers if applicable, and include a modifi
cation list and some photos to post on the forum.
02-15-2021, 03:15 PM
Brake Upgrades for Rear Discs
