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Spongy brakes with new MC

weekendmech

NAXJA Forum User
Location
Battle Creek, MI
I did a search and did not find a problem that is exactly like what I am experiencing so I hope some of you can help me.

I have a 1998 Cherokee with ABS brakes. I bought it in January and it has been a ton of fun. The vehicle has 180,000 miles on it and it runs well. The problem I am having is with the brakes. The pedal goes all the way to the floor. It does stop, my daughter usually drives it and I don't want her to get into a panic situation and have them not work.

I bought two new(not rebuilt) master cylinders, bench bled them, and put them on. I thought the first one was bad so I replaced it agian.

Well, it turns out it is not the master cylinder or else I received two new NAPA MC,s that were defective. I am wondering what else it could be.

Has anyone had to replace the HCU (hydrauic control unit) part of the ABS system? If so, what were your symptoms? The only other thing that could be bad might be the proportioning valve. Anyone have to replace that?

I also should mention that the red brake light comes on quite ofter. I get it to go off by pumping the brakes gently. The ABS light only comes on when you first start it up as part of the power on test.

I have a scan tool that is a Snap-On 2500. It has an ABS brake bleed mode. When I enable it, the pedal gets extremely hard to push. Not sure what the scan tool is doing but it eventually times out and I go back to my original pedal to the floor problem.

If you need any other info let me know and I will keep you posted.

Thanks
Andy
 
You indicated you bench bled the MC but did you also bleed the brakes at each wheel? If so, did you also adjust the rear brakes?
 
I did bleed them at the wheels starting at the RR then LR then RF and finally the LF. I did not adjust the rear brakes as I think they are fine. I can barely get the drum off and back on.

Thanks for your reply.

Andy
 
weekendmech said:
I did bleed them at the wheels starting at the RR then LR then RF and finally the LF. I did not adjust the rear brakes as I think they are fine. I can barely get the drum off and back on.

Thanks for your reply.

Andy

If you can "barely get the drum off" without backing off the adjusters, you probably need to adjust the brakes. I'd do that first, and then, just to be safe, bleed them again and see if any more air is in there. If you're getting the brake warning light, one or the other circuit is probably either leaking or still in need of bleeding.
 
Good News

I think I have it fixed. Time will tell if they go spongey and again. What I had to do was bleed them each step of the way as they go to the HCU and then finally to the wheels. I cracked the fittings at the proportioning valve, and then the input to the HCU and then to each outlet of the HCU. The brakes now feel very good and I hope they stay that way.

Thanks for your help

Andy
 
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