Brakes

DaGr8Tim

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This is about my 97 Cherokee, but it should apply to about any other vehicle made from the 80's through the late 90's. I'm working on my 97 Cherokee, no abs, front disk, rear drums. I'm asking here because I know there is alot of collective experience that I trust.

About two weeks ago, I lost all of my braking. No loss of fluid, so I assumed it was fluid getting past a piston. The fluid in the reservoir was black and smelled like rubber. I made the assumption that the master cylinder was bad and replaced it. After bleeding the brakes (and completely flushing the system), they were great for about 3 weeks. Firm pedal, less than an inch of travel before before the brakes engaged.

Yesterday the pedal got soft and travel increased a great deal. I can still lock the front disks up in my gravel driveway and based on the skid marks, they look like I'm getting pretty even pressure on both sides. Would this indicate a problem in the rear?

With 300,000 on the Jeep, I was planning on overhauling the brakes before this happened. Right now I've got new soft lines, calipers, pads, and rotors for the front and so far new softline, wheel cylinders, and hardware kit for the rear. I still need to order the drums and pads.

I'm not losing a drop of fluid. I even made a marker mark on the reservoir and the level does not move from that spot when it's cold.

Any suggestions or should I just keep working through the system?
 
Hope you flushed the whole system out good when you installed the new master if not you will need too. Next also check the distribution block / front to rear bias is probably not centered. From what you are describe it sounds as though the valve may be sticking or has over centered during the master cylinder failure so that now only the front brakes are working it will require bleeding to get the front to rear bias balanced again (the valve back to center). Good luck :nod:
 
bubba22349":nhcrnkw6 said:
Hope you flushed the whole system out good when you installed the new master if not you will need too. Next also check the distribution block / front to rear bias is probably not centered. From what you are describe it sounds as though the valve may be sticking or has over centered during the master cylinder failure so that now only the front brakes are working it will require bleeding to get the front to rear bias balanced again (the valve back to center). Good luck :nod:

When I flushed/bleed, I first filled the master cylinder and then ran hoses up to the reservoir. I was working in my inlaws driveway, so I had to bleed the MC on the Jeep. After that I hooked the lines back up and started at the rear passenger. I had my FIL pump until the fluid was clear (new) and then started bleeding. I worked my way closer to the MC from there.

I drove it home (2 hours) and wasn't completely happy with the brakes and rebled them again.

I'll have to check the distribution block when I get home tonight. I do not believe there is any adjustment in the block and I have never heard of them going bad.

I did just do some googling and found this info.

Here's the distribution block mounted on the vehicle. One line for both fronts and a common line to the rear that splits on a junction block on the rear axle.
PropValve1.jpg


Here's the whole thing off the jeep with what was described as a "bleeder" fitting on the front.
PropValve2.jpg


Also, here's the article the pictures came from. I'm still trying to figure out what the "mod" is. I know they are doing something to increase rear braking after installing rear disks.
http://www.lunghd.com/Tech_Articles/Sus ... ve_Mod.htm

Also, do you think I might want to try either bleeding the distribution block, or even pulling it apart and cleaning it like in the article. I've also got the valving parts from a grand cherokee with rear disks that I was saving for a rear disk conversion on my Jeep, but I may pull it out and see if can swap it now to increase line pressure in the rear.
 
If you look at that valve in the center is the brake warning light switch (dose your light still happen to work on the dash)? You can remove the switch and look into the port to see if it's centered. There is a grove machined into the valve that is centered when it's balanced front to rear and the warning light will be off. When it moves either direction during a brake failure (front or back) the switch turns the light on. I think you may be able run some more clean brake fluid through it to clean it out, or else if the system was really dirty (had sludge and crude from neglect) then it might be better to remove it to clean it good and also rebuild or replace the wheel cylinders flush all the lines as you go. If it's not centered you will need to bled the opposite side a little so the pressure can bring it back to center. The valve should move easily unless there is some crude in it to gum it up. One other thing since you mentioned that you had to bleed the master on the truck you may have air in the system the master cylinder on most later model cars needs to be bench bled good first before installing. Good luck :nod:
 
bubba22349":axhulyv4 said:
If you look at that valve in the center is the brake warning light switch (dose your light still happen to work on the dash)? You can remove the switch and look into the port to see if it's centered. There is a grove machined into the valve that is centered when it's balanced front to rear. When it moves either direction during a brake failure (front or back) the switch turns the light on. I think you may be able run some more clean brake fluid through it to clean it, or else remove it to clean it good. If it's not centered you will need to bled the opposite side a little so the pressure can bring it to center. Good luck :nod:

Thanks for all your help. I was planning on bleeding all 4 wheels tonight. I think I'll try to bleed the distribution block first just to see what happens. Worst case, I have the distribution block from my parts Jeep that I can pull, give a good cleaning and then swap.

I am getting a brake light on the dash, and I assumed it was because it was sensing a pressure difference between the front and rear circuits. Thanks for the tip about removing the switch from the block. In all my searching on Jeep websites, nobody else has been able to explain how the system works like you were. :beer:
 
Thank you for the kind words I learned all of this hard way back in the late 1960's doing a brake job. It happened to be my first duel master system and it caused me a lot of grief to figure it all out in the end it taught me the lesson of how these spilt systems work and though the parts are a little different for the most part they work the same on all brands with or without ABS. If you can find or barrow a power bleeder it will help you get all the air out of the system. Good luck :nod:
 
bubba22349":ppxoc6vt said:
Thank you for the kind words I learned all of this hard way back in the late 1960's doing a brake job. It happened to be my first duel master system and it caused me a lot of grief to figure it all out in the end it taught me the lesson of how these spilt systems work and though the parts are a little different for the most part they work the same on all brands with or without ABS. If you can find or barrow a power bleeder it will help you get all the air out of the system. Good luck :nod:

I've been playing with building one. I've seen some setups were they take a garden sprayer and install a pressure gauge in it and then drill a hole in an old master cylinder cap, and route the hose from the sprayer to the cap with some fittings.

They seem to work pretty well.
 
bubba22349":34p4i4rb said:
Sounds like a great idea!

Thanks for all your help. I took my spare distribution block apart and see what you mean about the separator that moves when you have a failure. I was running out of daylight and only got the back brakes bled, but that seems to have resolved the pedal and the light. I was surprised that there was still air in the system.
 
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