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disk brake conversion

W

wagoncase

NAXJA Forum User
Location
monaca pa.
Ive done a disk brake conversion to my xj, it stops good but not as good as i'd think, i still got the drum brake master cylinder in the truck,I changed the proportion valve to a 4 wheel disk one from summit. my question is what other master cylinder will work with my brake booster? thanks ..
 
I have heard that a 98 Dodge Durango master will bolt right up and moves a bit more volume than the XJ cylinder, though most people that go to the Durango master have also gone to WJ front brakes.

What parts did you use for the disc swap? What year XJ?
 
To me, going from drum to ZJ disk in the rear of my XJ did nothing to improve stopping ability. A good working set of shoes in the XJ OEM rear drum stop the XJ just fine. What make the swap to disc a worth while swap is the ease of maintenance and the ability stop the XJ better when they are wet. Drum on the XJ were always finicky and require lots of maintenance.

For the proportioning valve, I swapped the interior from the donor ZJ which included the entire break setup from the rear axle.
 
wagoncase said:
Ive done a disk brake conversion to my xj, it stops good but not as good as i'd think, i still got the drum brake master cylinder in the truck,I changed the proportion valve to a 4 wheel disk one from summit. my question is what other master cylinder will work with my brake booster? thanks ..
Click to expand...



Thanks for your post.
We’re here to help but you must understand that all Jeeps are not the same.
In order for us to give you more accurate advice and help, we must know the following, along with detailed information as to the symptoms/problems etc:
Year
Model
Engine
Transmission
 
Re: Re: disk brake conversion

techno1154 said:
To me, going from drum to ZJ disk in the rear of my XJ did nothing to improve stopping ability. A good working set of shoes in the XJ OEM rear drum stop the XJ just fine. What make the swap to disc a worth while swap is the ease of maintenance and the ability stop the XJ better when they are wet. Drum on the XJ were always finicky and require lots of maintenance.
Click to expand...

Same here. My old XJ stopped about as well with new drums & shoes as my current one does with ZJ discs. But the disc brakes seem to stop the Jeep well even as they wear much better than the drums did. The increased ease of maintenance also made it worth doing the swap to me.

I didn't change the proportioning valve though. It stops fine so I just haven't bothered.
 
Red91Laredo said:
Same here. My old XJ stopped about as well with new drums & shoes as my current one does with ZJ discs. But the disc brakes seem to stop the Jeep well even as they wear much better than the drums did. The increased ease of maintenance also made it worth doing the swap to me.

I didn't change the proportioning valve though. It stops fine so I just haven't bothered.
Click to expand...

Try swapping the guts from a 4 wheel disc ZJ into your prop valve. Works better.
 
Originally swapped 95 ZJ rear discs into a 95 XJ. I have the proportioning valve as well, but never used it as the XJ stopped fine with just the brake swap.

When the 95 got written off, I swapped the rear axle into the 99 XJ i got as a replacement and she stops just as well. Again, I have the donor prop valve but have not installed it as I don't feel it is needed.
 
My suggestion since you have only experienced the braking with the stock prop valve and not with the ZJ "guts" , try it so you CAN experience the difference. I did.
 
cdn_xj said:
Originally swapped 95 ZJ rear discs into a 95 XJ. I have the proportioning valve as well, but never used it as the XJ stopped fine with just the brake swap.

When the 95 got written off, I swapped the rear axle into the 99 XJ i got as a replacement and she stops just as well. Again, I have the donor prop valve but have not installed it as I don't feel it is needed.
Click to expand...


The reason I changed the proportioning valve internals was to prevent the rear from early lockup on wet surfaces.
 
If you are just swapping the rear drums with ZJ parts you don't need to touch the MC. Same MC is used in the ZJ w/discs. Larger bore will not help with ZJ rear and stock fronts.
 
Below is a link to a long posting I made 5 years ago about various sizes of master cylinders and how well they worked with my XJ's brakes system.
I just updated it to reflect the present usage.
http://www.naxja.org/forum/showthread.php?t=991378&highlight=master+cylinder+diameter
My XJ presently has ZJ discs, in the rear, and 15" Vancos, with the larger 48mm calipers, up front, as well as the ZJ proportioning valve and a stock master cylinder. It will lock up the 33"s at freeway speeds.
At present, I'm thinking about an adjustable proportioning valve for the rear brakes. With the powerful front brakes, there is a lot of weight transfer to the front, lightening up the rear and
allowing rear discs to lock up in wet conditions, even with the ZJ proportioning valve.
Grand Cherokee can take full advantage of their rear discs since they all have ABS, which prevents lock up.

My present thinking is the ZJ brakes are not all that useful an upgrade if the front brakes are being upgraded. Drum brakes, in good shape, might be all that is needed.
Discs are easier to work on, never need adjustment and stay cleaner in muddy conditions.
 
I put a manual prop valve in mine. I went with a Wilwood prop valve, 260-10922 with 3/8-24 flare fittings. I used the following adapters from Royal Brass (mine has ABS so it may be a bit different).

Brake prop valve adapters:
2x BQ260 - 1/2-20 female thread w/ 3/16" tube to 3/8-24 male thread
1x 240CB - 7/16-24 female (w/ 3/16" tube) to 3/8-24 (w/ 3/16" tube) male thread
1x 42IFHD-3 - 3/8-24 union (w/ 3/16" tube)
 
Talyn said:
I put a manual prop valve in mine. I went with a Wilwood prop valve, 260-10922 )
Click to expand...

Where did you mount it? After the initial adjustment, do you change it often or at all?
Without spending some time looking, I wonder if bringing up through the floor is a good idea.
I like the idea of being able to change it quickly. In dry conditions, rear lock up usually isn't a problem, only when wet.
 
Where the stock one was.

DSC_1467.jpg


It took a bit to get dialed in but after that I only change it if I am towing or hauling something. Not pictured is an aluminum bracket that supports it as it was in the way for the test fit.. You don't want it vibrating or bouncing around as that will fatigue the lines.
 
As Cruiser noted, a properly balanced braking system will make a difference. Will the car stop without it? Yes but in reality you will be using the front brakes to stop and the rears will just be along for the ride and won't really be doing much. Drum brakes require much less pressure than disc brakes so the stock proportioning valve will be directing too little pressure to the rear disc system. Under slippery conditions this can be hazardous, particularly with an automatic transmission, because the brakes are fighting the road as well as your drivetrain that will continue to try to turn the wheels. Even brand new cars with the latest ABS systems still include proportioning systems to get the balance right.

As I said above, it will stop with improper front/rear balance but when you really need the stopping power, you will find that having the right proportioning valve will make the difference between a wreck and a close call.
 
I swapped in the spring from the ZJ disc brake rear axle prop-valve, works great under hard braking.
 
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