Rear disk brake conversion questions.

[LT.]

Once again I am needing the help of the RME folks. Last night I took the Beater out for a maiden voyage on her new legs and with some lower gearing. After noticing that I had a rear output grumbling problem I raised the rear axle off the ground in the shop and put her into drive to find the grumbling. Turns out that with the rear disk brakes I put on the 14 bolt they will not stop the rear tires from turning while in gear. If I put the truck into neutral and apply the brakes it will stop the rear tires sooner or later. I am still using the stock master cylinder and stock proportioning valve. What parts do I need to change?

LT.

 

[blueovalyj]

larger displacement master cylinder. 1999+ ford superduty hydroboost works well.

 

[LT.]

Thank you. Does anyone else have any ideas? I guess that I should add that it is for a 1985 Dodge Ramcharger.

LT.

 

[RockMonkey]

I would suggest that just about any master cylinder should have the capability of stopping the tires right now while the transmission is in neutral and the vehicle is on jack stands. I'd bet you have a lot of air in there, and not much brake fluid, or something is broken.

I had a similar experience with my last build. It turned out that one of my bleeder valves was clogged. I bled the breaks many times, but it didn't fix the problem until I cleared the one clogged valve and was able to properly bleed that caliper. After that my stock XJ master cylinder works fine with Bronco front calipers and Chevy 1/2 ton rears.

I wouldn't be surprised if you end up upgrading your master cylinder, but I don't think you're seeing what your stock master cylinder is capable of yet.

 

[BCGPER]

I just went through this on my Blazer project. I'm still running the drums out back, but the same basic principles apply, I had zip for rear brakes.

Started tossing money at it by replacing the wheel cylinders, then master. After bleeding and bleeding, still nothing out back. The proportioning valves are major bucks, so I figured I had noting to lose by tearing it apart.

Turns out the proportioning valve was full of rusty sludge and seized up. I disassembled it, cleaned it with carb cleaner, and my brakes are now good as new. Well, as good as a 40 year old truck gets I guess.

Anyway, before you start tossing money at it, make sure everything you have now is working properly.

 

[ChestonScout]

I never did anything extra to my Scout brake system when I had the 14 bolt disks on the back.......they would lock up well before the fronts would but in low low I could crawl through my brakes with ease.

When decending steep ledges I usually just popped it in neutral.


Like was said...I would just double check everything over


edit....


They worked well before the suspension mods right??? Something must be wrong

 

[Tacoma]

My stock 1/2t stuff locks mine up just fine. The above suggestions are solid. If none of that works, you may need to gut your stock prop valve, get an adjustable, and dial in more rear. Brake.

 

[LT.]

Sprueitt has video of me locking up the rear brakes with the front brakes while I was still on the half ton equipment. When I switched to one ton axles I also switched the rear brakes from drum to disk. When I did that I have yet to have the rear brakes work well ever. This is even before I re-did all my brake lines so that they would work with the new suspension. This is why I was wanting to know if I was needing a new master cylinder and proportioning valve.

LT.

 

[rockreligious]

Im running d60's with 5:13 and discs on all 4 corners with a stock YJ master, and my rig stops good..my rig is light though. my guess clogged prop, or master.

 

[LT.]

When I get back from EJS those are going to be the parts I look at more carefully. Time is too short to be pulling the rig back apart. I think I will be ordering a new 205 T-case in the morning to get rid of the gear chatter I am having with the final drive. I really can't express how much y'all have helped me not only with this problem but, with all the others that I have had. Thanks so much RME!

LT.