No rear brakes

[RedJeepster1]

Hey guys. So I was working on my YJ this week. Having fixed the leaks in the 9” rear axle, I was hoping to also get the rear brakes working better. Since I put this Jeep back together last year, the brakes have always been horrible. Pedal engages where it should but is very soft all the way to the floor. It does harden up near the floor, but basically feels like I blew a rear brake line.

The current setup:

The rear axle has brakes off of a Cadillac Eldorado. They are single piston calipers with a lever for the e brake. These were on the axle when I bought it.

All brake lines were brand new last year. From the master to the calipers.

Booster is stock for an early YJ.

I changed the master cylinder to one off of a 78 Grand Marquis. It’s 1.125” bore, direct bolt in to the stock YJ booster, and designed for front and rear disk brakes.

Proportioning valve is summit racing brand adjustable. Currently bypassed because I wanted to rule it out as a culprit.

Brakes have been bled multiple times. I get a good flow of clean fluid out of the rear bleeders. On both sides. This was the case with the stock 1” bore master as well as with the new 1.125” bore master. I currently have bypassed the proportioning valve to rule it out as the culprit. It made no difference. Line from the body to the rear axle is stainless braided and new last year. Only parts I have not replaced are the calipers themselves and the short section of rubber line that runs to them. Neither the calipers or the lines look very old.

Any thoughts? Anything I am missing? I can lock up the front wheels currently, so rod length appears to be correct. Distance to engagement is nice and short. After trying to lock up the brakes multiple times, rear brakes are still cold. I can see the calipers quick but it’s such a small amount it isn’t doing anything.

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[massxj]

Sounds like a residual pressure issue.  2lb for disk

 

[redjeep]

Can you set the proportional valve to 100%rear and see if the calipers lock up?

 

[JeepinMaxx]

That short section of rubber hose you mentioned may be weak/spongy and expanding under pressure.  Maybe replace it with section of new line to rule it out

 

[RedJeepster1]

Can you set the proportional valve to 100%rear and see if the calipers lock up?

I can only reduce the pressure to the rear. Currently 100% of what’s coming out of the rear outlet of the master is going directly to the rear brakes without being throttled down.


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[RedJeepster1]

That short section of rubber hose you mentioned may be weak/spongy and expanding under pressure.  Maybe replace it with section of new line to rule it out

It’s certainly possible and I probably will replace it, but right now I’m not sure it’s building any pressure to begin with.


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[Red Rocker]

Maybe swap the front and rear lines at the master and see if anything changes for the better

Look up the brake system for the eldorado donor calipers and see if it has anything different from a normal system

 

[RedJeepster1]

Maybe swap the front and rear lines at the master and see if anything changes for the better

Look up the brake system for the eldorado donor calipers and see if it has anything different from a normal system

The idea about swapping the lines in gonna have to try. That would help me rule out a lot of potentially bad parts.


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[joe98tj]

This is probably a stupid question and something you have already ruled out but are you sure the calipers are on the correct sides?

I accidentally swapped mine when I put the explorer axle in and it gave me a soft pedal and weak rear brakes.

 

[RedJeepster1]

I wouldn’t say it’s a stupid question. That’s a mistake I’ve made before and now I always check that my bleeders are up before bolting new calipers on.

In this case they definitely are facing up.


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[clarkie]

It seams like it could be
Air?
Proportioning valve?

I know you’ve bled it multiple times. Maybe try a vacuum bleeder to be sure. Or even a long gravity bleed.

With the larger piston you increased the amount of fluid with each stroke. (But it actually decreases psi applied to the calipers) Seams like that would work good. I don’t know if it’s possible to actually limit the flow to the front to see if the rears work?

 

[beaker]

I've dealt with those calipers many times.  Did you adjust the caliper by rotating the piston to get it close ?  Those calipers have a ratchet mechanism to tighten the e brake.  One trick that sometimes works is holding the brake down and operating the e-brake lever.  I've not been particularly successful with them.  Years ago on my 79 bird or my current jeep.  Good luck and in a pinch chevy 3/4 ton early 80's front calipers drop in place.  Atleast for the large versions.  There's a metric size one two.  Both operate equally poorly.

 

[beaker]

The ratchet adjustment may take multiple cycles to adjust it right.

 

[beaker]

If you've got the metric size, swapping to regular chevy monte Carlo calipers 85 ish would eliminate the problem but lose the e brake.  Need disc residual pressure valve no matter what.  Even without e brake crap.