Topic: Disk brake upgrade question...

[TahoeYJ]

I remember a family friend telling me way back when that when adding disks brakes to a YJ, you've got to either get a new Master cylinder, or add say a proportioning valve? I'll be hooking up my disk brakes for my 9" sometime this next week after they arrive, and I figure if I'm going to be doing work on my brakes (front end is out and calipers are off, so all 4 corners will be bled anyway) I might as well get it done in one shot.

I don't know what exactly I'll have to change (if anything) and I imagine every Jeep will probably react differently to a brake upgrade, but would it be worthwhile to add something such as this Wilwood proportioning valve? It's fairly inexpensive...http://www.summitracing.com/parts/WIL-260-8419/

I'm definitely not a brake expert, I know how to change them and bleed them but that's it... I just want to make sure I tackle any possible issues before my rig sees the road...

[Jeffy]

A new proportioning valve is a good idea BUT you'll want to take the pill out of the stock proportioning valve.  You might try driving it with just the pill removed and see if it needs one.

Setting up the proportioning valve will take some time and testing as you will have to turn, test, turn test...  You don't want the rear to lock up before the front nor do you want the rear to make the front do all of the work.

[TahoeYJ]

A new proportioning valve is a good idea BUT you'll want to take the pill out of the stock proportioning valve.  You might try driving it with just the pill removed and see if it needs one.

Setting up the proportioning valve will take some time and testing as you will have to turn, test, turn test...  You don't want the rear to lock up before the front nor do you want the rear to make the front do all of the work.

Where would this pill be located in the stock valve? I assume it must be easy enough to remove?

I figured it'd take some time to get the proportioning valve just right, but if I run into any problems I figured it'd be my best/cheapest option.

I guess I'll just hold off on an aux. valve until I know whether or not I need one. Even if the brakes do feel a bit off, it shouldn't be a problem driving around town I assume

[Jeffy]

You can probably remove the whole piston and spring instead of leaving parts in there.  Otherwise you'd remove the proportion valve all together then connect the front lines together with a T fitting and add the new proportion valve to the rear.  Or you could leave the stock valve and take the piston out then tape the new one into the rear brakes.

http://www.lunghd.com/Tech_Articles/Suspension_Steering_Axles_and_Brakes/Proportioning_Valve_Mod.htm

[Jesse-James]

I plan on gutting mine and adding a single line proportioning valve on the rear if needed.

[neale_rs]

If you are willing to eliminate your brake warning light it is pretty easy with the T, like Jeffy mentioned.  I may do this if new rear shoes don't fix my rear lockup problem.

[jfrabat]

In the race car some friends made, they actually have a lever proportioning valve, so they can adjust according to the conditions.  In case of a Jeep, I also think something that is easily adjustable would be beneficial, as you can increase the rear proportion if you are towing or have a tone of equipement in the rear, but can then take off some "bite" if you are running with no top and nothing on the back...

[Bounty Hunter]

I went with a '78 Grand Marquis master cylinder for 4wheel disc and hydroboost, you get a larger piston and a MC valved for discs.  Then installed a Grand Cherokee prop. valve designed for 4whl disc, easily installs in place of the stock prop. valve.

The stock setup has too much residual pressure on the rear drums, too much for rear discs.  The stock setup also doesn't push enough fluid to the rear for the larger fluid capacity of the calipers.

You can also run the front brakes straight from the master cylinder, and install the adj. Wildwood prop. valve inline with the rear brakes.

[TahoeYJ]

I went with a '78 Grand Marquis master cylinder for 4wheel disc and hydroboost, you get a larger piston and a MC valved for discs.  Then installed a Grand Cherokee prop. valve designed for 4whl disc, easily installs in place of the stock prop. valve.

The stock setup has too much residual pressure on the rear drums, too much for rear discs.  The stock setup also doesn't push enough fluid to the rear for the larger fluid capacity of the calipers.

You can also run the front brakes straight from the master cylinder, and install the adj. Wildwood prop. valve inline with the rear brakes.

For what I highlighted in red, would this be a viable/safe solution? It must be safe, otherwise you wouldn't recommend it right?  Also, would there be any issue with the front wanting to lock up without running them through the stock P.V? Seems like the most cost effective way to go for now. I'd have the money within a matter of weeks, but right now I just really need to get my rig finished (Hoping it's driving before next Saturday...) as I've been without it for 2 months. Plus I've got plans to buy new steering linkage too... And I'm due for tires...

I like what jfbrat mentioned as well, although the lever prop. valve is almost double the price I'd just go with the knob style prop. valve, even if it takes more time to adjust. But I do tow from time to time, so it'd be nice to be able to adjust the brake bias during towing periods.

[drunkencityworker]

i grabbed a prop valve from a cherrokee with rear disc at the junkyard for $8.will go in when i do 8.8. if not enuff going to change master cyl like bounty hunter suggested

[neale_rs]

I was told by a Jeep fab shop owner that the TJ (rear drums) and TJ Rubicon (rear disks) proportioning valves are the same.  I also looked on Chrysler Direct just now and they do not list a separate Rubicon proportioning valve. This may help you.

[TahoeYJ]

I think I'll try and run up to Pick N Pull and find a GC prop. valve, if there's any GC's there... Either that or just try removing the front from the stock prop. valve and adding the rear one like Bh suggested. I can get a Wilwood knob style valve at a local race car parts place for about the same price as Summit, so I figure it's worth a shot. Definitely going to weigh out my options this weekend though and think about which way I really want to go...

[drunkencityworker]

almost as many rear disc cherokees at u pull it in chicago as explorers. bring line wrench and go on half price day. should take ya no time and no pricey bling...

[TahoeYJ]

You can probably remove the whole piston and spring instead of leaving parts in there.  Otherwise you'd remove the proportion valve all together then connect the front lines together with a T fitting and add the new proportion valve to the rear.  Or you could leave the stock valve and take the piston out then tape the new one into the rear brakes.

http://www.lunghd.com/Tech_Articles/Suspension_Steering_Axles_and_Brakes/Proportioning_Valve_Mod.htm

So I just took the o-ring out but left the piston in, what you're saying is to try it with the whole pill removed? It sounds like I'll need the whole thing out anyway if I'm going to install an aftermarket rear proportioning valve. I'll have to try it with the whole pill removed I guess and see what it feels like before I know if I need the prop valve. If I do need one, a local performance parts store carries them so I can get it installed the same day.

Pretty dumb question, but I leave the spring out too, right?

[Mr_Random]

Here's a link to an 8.8 swap into an XJ, very detailed and should help (considering all 8.8's past ~96 were disk).

http://www.naxja.org/forum/showthread.php?t=1000520