I'm finally ready to hit the trails !!!
I've been battling "satisfying brakes" since I bought the jeep several years ago (I'm quite slow on some projects). The thing has an unknown but guessable 78 Wagoneer Dana 44 rear axle with the 1985 Cadillac Eldorado disk brake calipers which give integrated parking brake capability (See caliper pic - courtesy of O'Reilly Auto Parts). I've gone through two+ sets of rear calipers, fighting them all of the way, to get sound brake performance (bonus for lifetime warranty service).
Late last summer I tried to see how quickly the jeep would stop from ~40mph on clean, dry pavement. I pushed that brake pedal harder than I ever recall. No tire locked up. It stopped decently but wouldn't take home any participation trophy. From that curious test I graced myself with a sinking brake pedal at stop lights. That hard press had pushed the rubber seals past some rust area in the master cylinder bore and damaged the seals. Time for a new master cylinder (slap my head for the what-were-you-thinking prize). Out to the parts store - brake master cylinder for an 1990 Wrangler please.
Dismount old MC and mount the new (blindly returning the old MC as a core charge) with proper brake bleed of the system... only to have a pedal that hits 90% to the floor to have only 70% brake performance. What the heck?!?! Double check the brake bleed - I'm good (put me as a BIG FAN of the industrial syringe bleed method - see pic). With a "one-pump" of the pedal I have fantastic brakes. High pedal. Firm. No sink while stopped. But it takes one pump to attain that. Not satisfactory. Pinch off the rear brake hose - fantastic, high, firm brake pedal. The front's are good (they're stock I believe) with aftermarket steel braid flex lines. Was the MC I turned in for core charge not a 1990 Wrangler specific MC but rather a specific MC to help with having rear discs??? No telling - water long under the bridge. Time to focus on those danged Cadillac calipers and maybe yet another MC change.
I resolved myself to crossing the issue off of my list.
I poured time into research on how these calipers should operate. I checked the rebuilders' web site (Cardone) for tech documents. I asked a professional mechanic buddy for his knowledge of "adjusting" the calipers and any tech docs he could funnel my way. YouTube has several "try this" / "this worked for me on this project" vids. In the end - I'd install the calipers onto the vehicle and I could not get any satisfactory brake pedal. The calipers would not adjust or function as everything I read or saw said they should. Time to jump into the deep end and conquer.
But then you ask yourself - if you changed the MC why are you focusing on the rear calipers? Shouldn't you focus on the MC? We'll get to the MC. In process of bleeding the rear calipers and trying to adjust with the parking brake actuator arm - caliper in fully assembled mode on the vehicle / ready to be put into service - the driver's side caliper decided to puke out of the p-brake actuator seal. Since I'm already ticked at these calipers and know I have lifetime warranty I just pulled the driver's side caliper and warranty returned it. So now, I'm focused on the rear calipers.
A basic function of conventional disc only calipers is that they automatically self adjust for pad wear. These integrated calipers supposedly do not auto-adjust and require (somewhat routine) use of the parking brake mechanism to adjust for pad wear. Sadly, working the parking brake actuator arm (P-brake cable & return spring removed, caliper removed from vehicle - no pads installed) shows the caliper piston extend out of the piston bore - but then 100% back into the bore as the P-brake actuator is returned to home position. The piston, as I now know, should not return 100% on a cycle of the actuator lever. It should stay "out" more than when the p-brake actuator lever was first cycled. If a piston does not "move out further" with actuation of the parking brake arm the caliper is not working as designed.
Time to disassemble the piston "assembly" (it's not just a plain caliper piston - it is an assembly). Sort of an piston inside of a piston with springs, ball bearings, actuator screws (see my photo of the assembly, disassembled). I come to find out that the assembly as I have from the parts house calipers - the internal parts are locked up and don't move. I make an educated assumption that the internal, piston assembly parts should have some freedom of movement. Why else would the manufacturer put a ball bearing set in it?
The assembly is held together via a friction fit and I'm guessing that at the rebuilding house (which does need to disassemble the assembly to replace one internal square o-ring) simply pushes the assembly together until it can't go together any more. This puts the internal mechanism into a bind where it can't properly operate. Actuation of the parking brake lever, yes, actuates the p-brake but release of the lever does not find "take up the slack" of pad wear on the release as it should.
Time to adjust the assembly for proper operation. Remove the assembly from the caliper. Remove the yellow "dust cap / two way valve" to expose the internal piston. Set the assembly onto a couple 2x4's and with a punch and hammer, push the internal piston (and assembly) out of the major piston enough to free up the internal mechanism's operation. Install yellow dust cap / valve and install the ?properly adjusted? piston assembly into the caliper. Mount the caliper onto the vehicle and cycle the parking brake lever to have the now-properly-functioning caliper take up slack between the pads and rotor. Assemble the parking brake cable, return spring, bleed as typical.
Having the knowledge of how these calipers operate when properly assembled settles my mind. Knowing how to adjust the piston assembly is significant. I've not found this anywhere on the internet (I'll post a dedicated page at my site on this).
Now back to the jeep and its brake pedal - better but still not satisfactory. Was the MC that I returned a custom / specific MC for this application? I'll never know. Time for yet more 1990 wrangler with 85 Caddy rear calipers and "what works" research. Some say go 1995 Wrangler booster and MC. Some say go 1977 Mercury Marquis 4-wheel Disc Brake with Hydroboost MC with 1998 Grand Cherokee proportioning valve. Quick info on the Merc MC - Sub $30, near direct bolt-on, and I can have it in my hands tomorrow - ordered. In my hands this last Saturday. Installed Saturday evening - modify the MC cover hold down bar for reduced space between MC and brake booster - done. OH CRAP - the outlet ports are swapped from what the 90 Wrangler's MC has. Do I make new MC to Prop-Valve lines or cut the ends off of these lines and swap fittings. In the end I came out easy - buy a double flare tool, cut flares and swap fittings and re-flare (and it seems no leaks!). Test drive. High, firm pedal with decent brakes - though the pedal is unusually hard - almost like not having power assist, though, a significant improvement. The 90 Wrangler MC has a 1" bore and the Merc MC an 1-1/8" bore. Now to look into booster-to-MC pushrod length.
I measured distances on the 90 Wrangler MC and the 77 Merc MC and came up with 0.024" difference (MC-Booster mating surface to piston-pushrod mating surface). Dismount the Merc MC and guess at 1/2 turn to lengthen the pushrod might be close to 0.02". Road test - reasonable brakes. I'm calling it done / ready for summer unless I come across some oddity (backward, down hill braking??).
It's been a long, frustrating road but I'm happy with where things are sitting. I know more of the details of the brake system which isn't a bad thing - I just didn't wish to jump into the pool. Having reasonable parking brakes might be a nice thing (I've never used them in 7 years - I recently ordered & installed custom cables as the driver's side wasn't long enough with this setup - something the PO didn't tend [and I was a slacker in tending - I didn't need parking brakes but also didn realize I should use them for decent rear caliper adjustment - a whole ball of badness is getting cleaned out on this project]). I might toy with changing the proportioning valve to a 98 Grand Cherokee to see if there's any improvement. Bleeding brakes is but a 20 min task with the syringe...