A brake odyssey

[lazyxj]

When I installed 31” tires, on my 2001 XJ, more braking power was needed, even with the late-model dual-diaphragm booster.
I rebuilt the front brakes and added ZJ rear discs, along with a ZJ proportioning valve's internals. Both the front and rear brakes received new Centric premium rotors, calipers and PosiQuiet pads along with a new master cylinder. A Crown performance braided brake line kit was added along with new Bendix soft lines for the rear calipers.
http://www.jeepparts4less.com/crown-performance-braided-brake-line-jeep-cherokee-198489-p-4707.html
The brake pedal was a bit lower due to the increase volume of the rear calipers even after repeated power and gravity bleeding. Even with the slightly lower pedal, the brakes were much stronger.
After moving up to 33s, the brakes were once again marginal, especially at freeway speeds. Hard braking caused pulling to one side or the other and there was not enough braking power to get the tires anywhere near lockup.
Upgrading to Vanco front brakes, with EBC yellow pads, gave the XJ strong, solid brakes again but hard braking would send the pedal almost to the floor, not exactly confidence inspiring. More MC volume was definitely needed.
The stock XJ MC wad replaced with a RAM 2500 MC. It is a bolt on except for needing a ¾” longer booster rod and the brake lines bent to fit the longer MC. A new rod was made with a cut down ¼” SS bolt, with the tip rounded.
http://www.flickr.com/photos/lwade/3418418553/in/set-72157616348032595/
http://www.flickr.com/photos/lwade/3419228528/in/set-72157616348032595/
The RAM 2500 1.25” cylinder provided a high, solid pedal but hard braking took a lot of pedal pressure. It was too much for my wife to stop so a better solution was needed.
Searching , I found where 53guy had used a 1999 Dodge Dakota MC.
http://www.naxja.org/forum/showthread.php?t=903864&highlight=durango
The Dakota MC has a 1.125” diameter cylinder, in between the stock XJ’s 1” MC and RAM 2500's 1.25” MC.
http://www.flickr.com/photos/lwade/3419228732/in/set-72157616348032595/
http://www.flickr.com/photos/lwade/3419228904/in/set-72157616348032595/
The Dakota MC was an exact replacement for the stock MC. Even the stock booster rod worked without adjusting.This is the right MC for my application. The brakes are now strong, solid and a pleasure to drive. The EBC yellow pads have good initial bite, even when cool.
The RAM 2500 cylinder would be a better choice if running 1-ton axles with big, high volume calipers.
It is important to get the booster rod properly adjusted whatever MC you use.

 

[Cherikon]

Dude- you are a life saver. I am moving up to 35's in the very near future and was wondering how to effectively run my brake setup. I have more confidence now. I will need to switch my rear D44 to disc brakes as time permits, but I was definitely more worried about the front setup as it does more of the stopping.

Thanks again for the info and pics.

Later,
Coullt

 

[rmm727]

I'm seeing on Advance Auto Parts' website that they sell a Dakota MC without the fluid container that is quite cheaper than the one with it. Does it look like they are interchangeable?

 

[lazyxj]

I'm seeing on Advance Auto Parts' website that they sell a Dakota MC without the fluid container that is quite cheaper than the one with it. Does it look like they are interchangeable?

Sorry, the plastic reservoirs are not the same and will not interchange.

 

[lazyxj]

An update to the above old posting. After a year or so, I switched back to the stock cylinder after wanting more brake boost.
To regain some of the lost pedal, due to the increase fluid volume needs of the ZJ and Vanco disc upgrades, I spent a couple hours finding the position, for each wheel's brake rotor, where the lateral runout was the least.
This consisted of cleaning the hubs and rotor surfaces, mounting and torquing to spec, using a wheel spacer instead of the wheel so the runout could be measured with a dial indicator.
Each wheel's rotor was tried in all five positions, noting the postion with the least runout. The starting runout ranged between .003-.005", after all were at .002 or less.
Surprisingly, this adjustment brought the pedal up to an acceptable height and made the brake much easier to use.
Interesting that the tolerances of new parts could stack up so high, when in the right combination, and have such a significant effect on the pedal.

 

[XJEEPER]

An update to the above old posting. After a year or so, I switched back to the stock cylinder after wanting more brake boost.

The Dakota MC was an exact replacement for the stock MC. Even the stock booster rod worked without adjusting.This is the right MC for my application. The brakes are now strong, solid and a pleasure to drive. The EBC yellow pads have good initial bite, even when cool.

Care to expand and further clarify? Seems to contradict.........

 

[lazyxj]

Care to expand and further clarify? Seems to contradict.........

Simple explanation, my right leg is lot stronger than my wife's..any questions?

The Dakota MC worked fine for me but did take more force than the smaller diameter stock cylinder and my wife wanted the lighter pedal back, not liking or feeling safe with the harder pedal.
So, in an attempt to maintain marital harmony, I took another look at the MC. After reading a few articles on brake systems and then calculating the volume needs of the calipers, it appeared the stock MC should be adequate.
I had installed the Dakota MC because the pedal height was so low. It was evidently losing pedal height from having to move the caliper pistons too much before the pads made contact with the rotors, a function of lateral run out.
I measured and found the rotor run out to range between .003-005. By finding the best location of the five possibilities, on each wheel, run out was reduced to .002 or less at each wheel, also reducing the amount of brake fluid volume needed for the pads to make contact with the rotors.
This was enough to allow the stock MC to work, even with the oversize front calipers ...now everyone is happy.

It was a eye opener for me, that's why I updated the old posting. I never realized how much run out effected pedal height. Now I know better.
If I had done more research, before attempting to find a fix, it would have saved me a few bucks. Maybe this will save someone else some money.
Hydraulics is a science and it is possible to calculate what size MC is needed to satisfy the requirements of the calipers and/or brake cylinders without guessing. It just simple math.

The Dakota MC works fine if you need more fluid volume but, in return, you give up some of the mechanical advantage.
What's needed is a bigger booster but there's no available room. A hydroboost is an expensive option if a larger MC and more boost is needed..

 

[XJLI]

So you'd want the Dakota MC and a larger booster? Idk if you have that right, I'm running the stock booster in my 98 with a dodge 3/4 ton master and my pedal is perfect with larger brakes than what you are running. Perhaps you just need(ed?) a longer rod on the master to raise the pedal up. If your brake pedal was a stuff as you're saying, you have too big of a master.

 

[MoparManiac]

So you'd want the Dakota MC and a larger booster? Idk if you have that right, I'm running the stock booster in my 98 with a dodge 3/4 ton master and my pedal is perfect with larger brakes than what you are running. Perhaps you just need(ed?) a longer rod on the master to raise the pedal up. If your brake pedal was a stuff as you're saying, you have too big of a master.

There's more to it than just master cylinder to caliper bore sizing.

You also have 12.5" rotors compared to a D30's 11" rotors. I'm not sure what size the Vanco brake kit uses, but in order to fit in a 15" rim it can't be much more than that.

Since you have more leverage than him with the caliper further away from the center of the wheel, you don't need as much effort to provide the same stopping force, but with the larger calipers you need more fluid volume. Hence why that diameter master cylinder works out in your case.

 

[XJLI]

All I heard was blah blah read the brake bible on pirate lol

 

[lazyxj]

So you'd want the Dakota MC and a larger booster? Idk if you have that right, I'm running the stock booster in my 98 with a dodge 3/4 ton master and my pedal is perfect with larger brakes than what you are running. Perhaps you just need(ed?) a longer rod on the master to raise the pedal up. If your brake pedal was a stuff as you're saying, you have too big of a master.

You are comparing apple to oranges
You have larger calipers, then you do need a larger MC to produce the fluid volume.
I needed a smaller cylinder to product the pressure needed to push the small diameter caliper pistons. The piston rods on the various MC I tried had properly adjusted rods.
.

 

[tow hook]

so you find that the dakota m/c works fine for your rear disc brakes ? and what year dodge 2500 m/c did you use ?

thanks