maddogs1965

So to make a long story short, i have had front braking issues on my 2000 Grand Cherokee. For the last month, my front brakes would start dragging for no reason. So after replacing both front calipers, both rotors and both front brake lines, the problem was still not taken care of.

So i ordered a new Master Cylinder and installed it yesterday after bench bleeding it. After removing the reservoir to install it on the new master cylinder and looking inside, i guess i should count my lucky stars the brakes worked at all, the bottom was so dirty it looked like the bottom of a oil pan that had 300,000 mile on it with out a oil change.

So after trying to bleed my brakes for 45 minutes yesterday, and another half hour today to no avail, i finally broke out the repair manual and read that if air enters the HCU (hydraulic control unit) i need to take the Jeep to authorized deal ship that has a DRB scan tool to purge any air from the HCU...( guess i should have read that before replacing the master cylinder)

So has anybody else ran into this issue? and now that the Jeep is 14 years old, does any mechanic shop have a DRB unit or am i still stuck going to the dealership or is there anyway around this for me to still bleed the brakes?

dave1123

When I bought my '00 WJ, I had trouble with the front brakes not working on occasion. The calipers were free and all the pads and rotors were good, they just once in a while refused to work. I noticed the brake fluid was dirty and decided to change the fluid by sucking out the reservoir and bleeding the brakes. My friendly mechanic did this for me. He bled the rears but couldn't get any fluid out of the front calipers. He tried leaving all 4 bleeders open and pumping the brakes. We had fountains on all 4 wheels! Then he restarted the brake bleed the right way. He must have gotten the air out of the ABS unit or something because everything has worked since. I have replaced all 4 calipers since that time and everything bled normally.

People don't think about brake fluid as wearing out and needing to be changed once in a while. Brake fluid absorbs water and allows the inside of calipers and the master cylinder to rust. Also, the working parts of the ABS unit can seize up. IDK about reprogramming it. I DO know it's very expensive to replace.

maddogs1965

Thanks for the info, it sounds like to me the new master cylinder i installed might be faulty, i can not get it to pump at all, no pedal what so ever. I am going bench bleed it on more time and see if i missed some air in it, then if i get the brakes to work at all, i will deal with scanning the ABS system to get all the air out of it

Cherokee_Mike

I changed the front calipers on my 2000 WJ about 18 months ago, bled the front brakes but they still didn't feel right so carefully took to my local garage to have them bled out again. They took about 4 attempts at bleeding to get the pedal pressure correct. I also got the local garage to change the rear discs & calipers earlier this year and again they had to bleed the brakes a few times to get the pedal pressure correct. The guy who runs my local garage used to have a Jeep dealership and told me that this was not uncommon once they get air in the system.

dave1123

One other thing. I recently changed the brake pads on all 4 wheels at the same time. I used a c-clamp type compressor to retract the pistons. When I started pumping the brakes to reset the pistons, it took FOREVER to get a petal feel. I fired up the engine to see if that would help and instantly had a hard petal. It most have something to do with the ABS.

maddogs1965

After doing some more research last night, correct me if i am wrong, but i should be able to get the master cylinder to bleed up/pressure even with out the ABS being scanned. Then if the brakes feel mushy i will need to hook up the scanner to open the solenoids to bleed the ABS system.

I guess good minds think alike, i even tried starting the motor with the booster to build up pressure, but still nothing. I also read that a shop had to open all 4 bleeders on the calipers to start getting brake fluid from the master cylinder to start moving, so i am going to try that tonight., if that does not work, i will try bench bleeding the master cylinder again.

I will keep you updated on what i find seeing how this seems to be a JEEP issue.

Still blows my mind and makes me angry that you need a computer to bleed your brakes these days..... but then again that is why i still drive a 57 Chevy, 69 GMC and a 65 L.C. I guess i am lucky my 91 Cherokee does not have ABS on it

dave1123

If you buy anything newer, you're REALLY in for a treat!

maddogs1965

So i tried having all of the calipers open at once to no avail....

I also removed the front brake line from the master cylinder and had my son hit the brake pedal with my thumb over the hole AND IMAGINE THAT, NOT A DROP OF brake fluid cam out.

So either i still have air in the M/C, or i have a faulty one...of-course it does not help that the little clear hose that they give you to bleed the M/C in the kit are too short to reach down inside of the reservoir to bleed it. I had a longer hose, but i must not have gotten all the air out. I will remove the M/C and bench bleed it again tonight.

maddogs1965

So i finally figured out why my brakes would not pump up after installing the new brake master cylinder,and i am going to say 50% of the problem was on me, and the other 50% is on Jeep for such a **** POOR DESIGN....

As most of you know, the older brake booster's were a sealed unit, meaning that they were sealed from the factory and held there own vacuum, were as the the brake booster on the G.C. uses the brake master cylinder to seal of vacuum since the brake booster has a gaping hole in it once your remove the master cylinder, and the new M/C has a O ring on it and plugs the hole back up once you re-install it back o the B/B.

When i installed the new master cylinder, the rod that comes from the brake booster to press the master cylinder piston in & out missed the hole on the B/C. This is the reason why i was not getting any brake pedal what soever. As soon as i removed the new M/C, i could see were the rod was rubbing up against the new M/C instead of depressing the piston in and out. So this time i tried to use a flashlight to look inside of the hole of the brake booster as i was re-installing the M/C.....MISSED IT AGAIN... The rod is so far inside of the B/B you cannot see it once the M/C is half way in to make sure you have the rod aligned correctly.

So this time i had my son come out and press the brake pedal down so it would move the rod out from inside of the B/B so i could make sure the rod was inside of the M/C hole. IMAGINE that, i have a rock hard brake pedal again. So i proceeded to bleed the brakes, and lucky for me no air made its way into the ABS system and after a half hour test drive the brakes still feel great, and even better, my calipers on not dragging or hanging up any more

So needles to say the G.C. is parked until the new owner i sold it to comes up and picks it up next weekend, I am glad this Jeep is out of my hair once and for all. At least i don't have to plug my old 91 Cherokee into a stupid computer to bleed the brakes

I hope this thread helps somebody else out so they don't pull there hair out like i did.....

dave1123

Duh!! I should have caught that one myself!