cjs07office

I'm a Jeep newbie be gentle - bought 93 Grand Cherokee Laredo 4.0 for my son as a fixer. Last brake job I did was in the 80's on an early 80's car NOT ABS.

When I purchased this Jeep the front bakes felt like they were tight, they were even smoking. So here's what I've done

- Replaced front calipers and pads. Had the rotors turned
- Replaced rear brake cylinders, shoes, springs, auto adjust - did not turn the drums cause there was no pitting or grooves.

Bleed the brakes starting with passenger rear, driver rear, passenger front then drivers front. Had my son pump the brakes and resulted in apparently micro bubbles cause it was milky white. Let set a day and re-bleed in same order this time NO pumping NO milky fluid. Brakes go to the floor when engine on. Re-bleed again and again and again and again....still going to the floor.

REMIND YOU THE BRAKES WERE NOT SPONGY BEFORE I DID THE BRAKE JOB.

After bleeding so much (keeping the reservoir capped off) when I turned the engine on it would build up stopping power AFTER I pumped the brakes several times.

So - took a brake spoon and adjusted the rear brake shoes as far out as they would adjust. Bleed them again. Brakes were firmer so I thought "success" until I cranked the engine - TO THE FLOOR

I will say in the forums I've researched there is a common denominator, replacing front calipers and spongy brakes.

One more thing - I have the original service manual and in the replacing caliper section it mentions using a DBR-II to bleed ABS. I do not have a DRB-II. I'm trying to exhaust all ave before taking (hauling it) to a dealership that has the DRB-II.

I've been working on this for 2 weeks surely someone out there has had the same problem and found a solution.

Thanks

XJPat

As you say the Jeep is a project, had it sat for a while? I wonder if you took out the master cylinder seals when bleeding the brakes. Pump them all the way to the floor? Also kept the reservoir full?

cjs07office

XJ Pat - Thanks for the reply

The previous owners had it 19 years and keep a service record on it. They replaced the alternator 4/2015 so it was on the road at that time. It could be the original MC. I guess my "hummmmm" would be the brake pedal was solid before we changed the calipers. But will keep that in mind.

From many forums I've read it seems a common denominator is changing calipers and then this mysterious problem appears :-) Yet I haven't seen a forum yet that gave the solution.

XJPat

And after changing the calipers, they bleed the brakes. The extra travel of pumping and bleeding the brakes sometimes pushes the piston into the part that usually isn't used which can get gummed up and that tears up the seals. I always lay a 2x4 under the brake pedal to limit the travel. At least thats how it was explained to me.

Bustedback

Solid advice. Pushing the brake pedal too far on an old master cylinder will destroy the seals in a heartbeat? Master cylinders are cheap and easy to replace, it couldn't hurt to change it.

zjWaggy

Bleeding the master cylinder could help, there may have been air bubbles that traveled their way up there