zomeizter Posted March 10, 2021 Share Posted March 10, 2021 Dudes, I'm about to complete the 8.8 swap on the 'manche, all that is lacking is the rear sway bar links to frame mounts and lower shock mounts. Since now I have discs all around, I'm wondering if I need to bother with a master cylinder replacement. I have it all hooked up the way it came from the factory with a properly working rear leveling valve. I was able to take the truck for a quick test drive and the braking system is working pretty well, pedal feel is unchanged and I can stop without the need of any more pedal effort than before the mods. I am running 31" tires with steelies but will eventually go with 33" or even 35" tires. I do have a corvette 4 wheel disc MC ready to go since I thought I was gonna have to swap it in if the stock braking system was inadequate. I keep reading about some o-ring in the prop valve that should be removed to allow more brake fluid flow to the rear, does my setup even have this? Did y'all have to swap in a different MC after your rear disc axle installation? Once I'm back home from TDY, I'll get the truck aligned and give it some hell on and off road to break things in and see how it all behaves after continuous use...holler. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 10, 2021 Share Posted March 10, 2021 Those particular rear disks need more pressure to equal the same braking force the stock drum brakes had (if they were in perfect working order and adjusted properly). The distribution block is a choke point for fluid flow for sure. The original prop valve may or may not let enough volume through. Either way, either replace the distribution block with a good prop valve and eliminate the load sensing valve or, if your load sensing valve can provide adequate flow, raise the linkage to provide more pressure to the rear disks than the drums would have had. You’ll have to play around with your braking bias to get it right. Regarding your master cylinder, with a single diaphragm booster you won’t want much more than a 7/8” bore. 15/16 is the max I’d recommend if everything else is perfect. Since you don’t have much assist to the pedal, you need all the hydraulic advantage you can get. Those calipers shouldn’t need any more volume. If you put a 1” or larger MC bore on your stock booster you will decrease overall braking performance. The better setup is to upgrade the booster and MC to a dual diaphragm setup and eliminate the distribution block and load sensing valve. Add a good Wilwood or similar proposal valve and adjust your braking bias. It’s a not too much work and will give you significantly better brakes with your existing setup. Assuming this is going in your 86 MJ, you will have some slight mods to do. Write ups on the swaps with both WJ and XJ boosters are a plenty. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 10, 2021 Share Posted March 10, 2021 This info may be helpful: Link to comment Share on other sites More sharing options...
Minuit Posted March 10, 2021 Share Posted March 10, 2021 I have rear disc brakes from a ZJ on my 91's D35 (as I understand it, the ZJ discs are practically if not identical to Explorer discs) and I actually needed to reverse an adjustment I'd done previously to the factory load-sensing valve that sent more fluid to the rear to prevent premature rear lockup after the disc conversion, for what it's worth. Pretty sure I ended up putting it right back in the factory location. Otherwise the rear end would try to swing around every time. Stock master cylinder and booster too. From what some people say here you'd think I'd just about be better off opening the door and trying to stop with my foot than pushing the brake pedal, but it seems to be working just fine for me. YMMV - as the demands you put on your braking system increase (tire size being a big one), you'll cross a point where the stock components just don't cut it anymore. But I can say that 29" street tires and ZJ discs out back isn't that point. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 10, 2021 Share Posted March 10, 2021 2 minutes ago, Minuit said: I have rear disc brakes from a ZJ on my 91's D35 (as I understand it, the ZJ discs are practically if not identical to Explorer discs) and I actually needed to reverse an adjustment I'd done previously to the factory load-sensing valve that sent more fluid to the rear to prevent premature rear lockup after the disc conversion, for what it's worth. Pretty sure I ended up putting it right back in the factory location. Otherwise the rear end would try to swing around every time. Stock master cylinder and booster too. From what some people say here you'd just about think I'd be better off putting my foot out the door than pushing the brake pedal, but it seems to be working just fine for me. YMMV - as the demands you put on your braking system increase, you'll cross a point where the stock components just don't cut it anymore. Yeah that does happen sometimes. All depends on how well adjusted and what kind of shape the original drums were in. The stopping power of drums is typically better than disks given the show to drum surface area. But disks definitely are superior for maintenance, adjustment and overall performance (cooling, self-cleaning etc.) Link to comment Share on other sites More sharing options...
Minuit Posted March 10, 2021 Share Posted March 10, 2021 7 minutes ago, ghetdjc320 said: Yeah that does happen sometimes. All depends on how well adjusted and what kind of shape the original drums were in. The stopping power of drums is typically better than disks given the show to drum surface area. But disks definitely are superior for maintenance, adjustment and overall performance (cooling, self-cleaning etc.) I probably spent more time trying to get the rear drums working on my 91 than anything else. I don't know if they worked for more than 2 months at a time between me getting the truck and the disc conversion. Every part was new, sometimes replaced more than once. Two of the wheel cylinders I installed leaked within a year of me putting them on, and the final thing that led to me putting discs on was a wheel cylinder just straight up blowing apart. The drums on the D44 and non-C clip D35 aren't bad. Haven't had any trouble out of those beyond typical drum brake stuff. The ones on the C-clip D35 can eat $#!& and die in a fire for all I care. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 10, 2021 Share Posted March 10, 2021 2 hours ago, Minuit said: The drums on the D44 and non-C clip D35 aren't bad. Haven't had any trouble out of those beyond typical drum brake stuff. The ones on the C-clip D35 can eat $#!& and die in a fire for all I care. True Link to comment Share on other sites More sharing options...
Dzimm Posted March 10, 2021 Share Posted March 10, 2021 Easiest fix is to find yourself a disc brake ZJ prop valve and swap it in place of the original. These are factory tuned for disks all around and are an identical setup to what the MJ has when you swap rear disks in so it works as intended. Go out and get up to about 25mph and stop on the brakes, if your fronts lock up first you're good to go. I would recommend you upgrade to the dual diagram booster and master from a later XJ as well since you'll have it apart. I would also say to remove the rear prop valve but you can retain it if you'd like to, may require some fine tuning though. Link to comment Share on other sites More sharing options...
zomeizter Posted March 10, 2021 Author Share Posted March 10, 2021 ZJ prop valve and dual diaphragm booster is what I will go for later on I reckon. Ima run it as is for now, the drum setup on the D35 was adjusted properly with all new components before I pulled it. I did have the rear load sensing valve at about the 2 o'clock position as well. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 10, 2021 Share Posted March 10, 2021 The ZJ prop valve is ok for a ZJ which has better weight distribution than our trucks. It does work well but to really dial things in get the Wilwood or similar. Just my $.02 Link to comment Share on other sites More sharing options...
zomeizter Posted March 11, 2021 Author Share Posted March 11, 2021 I reckon an adjustable Wilwood prop valve is the ideal component? Link to comment Share on other sites More sharing options...
Dzimm Posted March 11, 2021 Share Posted March 11, 2021 My ZJ prop valve without the load sensing valve works perfectly in the 92. Fronts lock and the rears lock shortly after when unloaded. This truck will never see a loaded bed but regardless without a rear prop valve it will still behave the same. An adjustable valve like the Wilwood has been done many times and is proven to work. It requires manual adjustment though so be careful you get it setup correctly. Do as much research as possible and you'll have to do testing in all scenarios with the truck loaded and unloaded to get the proper adjustment especially if you retain the rear prop valve. You may even need to adjust the valve based on your trucks load when you load it, you may not be able to set and forget. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 11, 2021 Share Posted March 11, 2021 2 hours ago, zomeizter said: I reckon an adjustable Wilwood prop valve is the ideal component? Yes. The ZJ valve is not adjustable and if you delete the load sensing valve it is just a standard prop valve. The Wilwood has the best flow for quicker pedal response. Also, you can adjust the bias based on future mods like larger tires or heavy bumpers. And in regards to frequent adjustement, it’s not different than the ZJ valve. Once you get it setup you leave it alone. The advantage is the initial adjustability to tailor it to your rig. Link to comment Share on other sites More sharing options...
zomeizter Posted March 11, 2021 Author Share Posted March 11, 2021 Thanks for the insight my dudes... Link to comment Share on other sites More sharing options...
zomeizter Posted March 12, 2021 Author Share Posted March 12, 2021 Anyone have a part number for the adjustable prop valve for rear disc brakes? I just saw a Summit store near the hotel I'm currently at... Link to comment Share on other sites More sharing options...
zomeizter Posted March 12, 2021 Author Share Posted March 12, 2021 Never mind the P/N request, I found what I need and will order/pick up the prop valve this weekend. I reckon I'll be installing this valve soon and deleting the rear load sensing valve too. I will run the MC currently in the truck and see how the braking system behaves but I believe I should install the corvette disc/disc MC I have, what do y'all think? Link to comment Share on other sites More sharing options...
BeatCJ Posted March 12, 2021 Share Posted March 12, 2021 Do you know the bore? What @ghetdjc320 said is absolutely fact. If the MC doesn't match the system, performance is poor. Link to comment Share on other sites More sharing options...
89 MJ Posted March 12, 2021 Share Posted March 12, 2021 I wouldn't. It probably wouldn't be an upgrade at this point and may actually be counterproductive. Link to comment Share on other sites More sharing options...
zomeizter Posted March 13, 2021 Author Share Posted March 13, 2021 Currently running a 1" bore Ford F series MC, the corvette MC is 1.125" bore. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 13, 2021 Share Posted March 13, 2021 6 hours ago, zomeizter said: Currently running a 1" bore Ford F series MC, the corvette MC is 1.125" bore. On the stock booster you don’t want anything larger than 15/16. Dual diaphragm can go to 1” but anything larger will be problematic. Hydroboost could probably get away with 1.125 but 1” would still be superior with stock brakes including ZJ or Explorer rears. Only time you’d go bigger is if the caliper piston surface area increases by a lot Link to comment Share on other sites More sharing options...
BeatCJ Posted March 15, 2021 Share Posted March 15, 2021 The larger diameter will move more volume than stock, but build less pressure in the same stroke. If you were changing to brakes with larger slave cylinders, it could be advantageous, but you would really need to know the volumes. You would also need to improve your mechanical advantage or the reduced line pressure could result in less clamping force. Link to comment Share on other sites More sharing options...
zomeizter Posted March 17, 2021 Author Share Posted March 17, 2021 In its current state with 31s pedal feel and stopping power is great so I will break the suspension in and give it some use for a while. I will eventually install a set of 33s or 35s and I'm sure I will need to tweak the braking system then. I am a fan of hydroboost so I will pursue that option (like a setup off an Astro van maybe), we shall see my dudes... Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 17, 2021 Share Posted March 17, 2021 1 hour ago, zomeizter said: In its current state with 31s pedal feel and stopping power is great so I will break the suspension in and give it some use for a while. I will eventually install a set of 33s or 35s and I'm sure I will need to tweak the braking system then. I am a fan of hydroboost so I will pursue that option (like a setup off an Astro van maybe), we shall see my dudes... There is no going back from hydroboost Link to comment Share on other sites More sharing options...
zomeizter Posted April 3, 2021 Author Share Posted April 3, 2021 After a long work trip I finally got to take the 'manche for a spin to test things out and not one minute on the street, someone cut me off and I had to slam on the brake pedal. To my surprise, I was able to lock all four wheels with ease! I guess the brakes are great the way they are so they shall remain as set up. I was also able to get the rear sway bar installed, I used some brackets I saved that came off my K5 side step rails. I ran a couple hot beads and called it a day... Also, redneck rear brake line relief... Link to comment Share on other sites More sharing options...
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