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Brakes not working

Cobound

Cobound

Legacy Registered User
City
Twin Cities
State
MN
My Scrambler has some brake issues, they need to be fixed shortly or my EJS trip is a bust.

Fronts work great, rears not so much.
Front - D44 w/ discs
Rear - D60 w/ discs

Rear has a 2lb residual valve inline...when I remove it it just locks up my rear brakes.

It appears I have a Jeep proportioning valve:
http://www.4wd.com/aux_incl/images.ashx?i=4WD_52003118.jpg&partNo=INL&w=400&h=400

I had a stock master cylinder, replaced it with a Corvette one, didn't help.

Not sure why I can't get the rears to work properly. Might I need a different proportioning valve, maybe buy one that is meant for disc/disc and replace the one I have. Change my mc back to stock...the rod in the booster too short. Buy a booster and master cylinder kit...

I've looked at some brake diagrams so I think I need to double check that my lines are going to the right leads...but I'd like other input so I'm open to looking for some things while I'm under it.

What is recommended as the first thing to try...suggestions.

TIA,

B
 
What size tires? Stick or automatic?

I would think that the Jeep proportioning valve is wrong, since it's probably disk/drum. Consider removing it and using an adjustable valve to the rear. I'd definitely suggest a duel diaphram booster with a matching m/c; I have the Navaho from Off-Again, but Vanco has a good one, too. You may need hydro-boost if your tires are 38's or bigger (but I don't know your tire size). Automatics need a stronger boost since they tend to creep, especially with low gears and/or a 4:1 t/c.
 
I found through trial and error with my rear disks that the parking brake must be perfectly adjusted for the service brakes to operate...at all!

I am using the stock master/booster and proportioning valve with 80's Eldorado rear calipers.

I dont know what brakes/kit you are using...but that got mine to stop on a dime with 33" TSL's!
 
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37" Goodyears
Auto
4.56 gears
Dana 300 xfer

I used the Vette mc to accommodate for the rear discs, but didn't work like I thought it would. Calipers are most likely single piston from a Chevy, haven't looked in some time and simply don't remember.

It has a booster, solid pedal.

Thinking I'll replace the proportioning valve w/ an adjustable and go from there.

B
 
Im having the same problem. I have a pedal, but I have to push my foot through the floor to stop.

35's
Stock J20 diffs/gears,
Stock booster
Vette master cylinder
New calipers,
Old discs/drums/shoes (all with plenty of meat left on them.)

Could this be caused by a vacuum leak?
 
I just poke my feet through the rusted out floor and do the Fred Flintstone thing to stop.
 
Bogged said:
Im having the same problem. I have a pedal, but I have to push my foot through the floor to stop.

35's
Stock J20 diffs/gears,
Stock booster
Vette master cylinder
New calipers,
Old discs/drums/shoes (all with plenty of meat left on them.)

Could this be caused by a vacuum leak?
Click to expand...

Yes....but it would have to be huge.....sounds like you need a new booster.
 
Update:

Front calipers are OE Jeep, they work just fine.
Rear calipers are '95 Ford Explorer, looks like a Teraflex kit was used by previous owner.

I removed the 2lb residual valve from the rear line, installed an adjusable proportioning valve just after the factory prop valve for the rear only. The driver side wasn't completely stopping so I replaced with a new caliper, no change.

I'm thinking the original prop valve simply isn't sending enough pressure to the rear so the adj valve does nothing. Thinking I need to replace the original prop valve with a disc to disc unit...leave the adj prop in place...any suggestions on what prop valve to use to replace the OE one in place now, which is probably the OE Jeep unit that was disc/drum.

Any thoughts, experience?

B
 
Throw the original Jeep prop valve in the bin (trash to you:D) and just use the adjustable one in its place.
You will have to adjust it in to the correct setting by slowly adjusting it up (or down) and doing test runs up the road to find out if the front or rear locks up first and adjusting to suit. :smokin:
Just hope that your master cylinder displaces enough fluid for the explorer calipers as well (i have no idea how big they are.:shrug:)
 
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Dave The Sparky said:
Throw the original Jeep prop valve in the bin (trash to you:D) and just use the adjustable one in its place.
You will have to adjust it in to the correct setting by slowly adjusting it up (or down) and doing test runs up the road to find out if the front or rear locks up first and adjusting to suit. :smokin:
Just hope that your master cylinder displaces enough fluid for the explorer calipers as well (i have no idea how big they are.:shrug:)
Click to expand...

This!

Although I'd recommend this valve- it takes the place of the original prop/distribution valve
http://www.jegs.com/i/JEGS/555/63025/10002/-1
55563025_2-1.jpg
 
Fronts are fine so what if i left my OE in place for them, I have a single adj valve on the rear line already, thinking I'll loop the rear prop holes on the OE together (essentially a plug) and union my rear lines from the mc and through the adj valve...straight from the mc now.

Then I can adjust the rear if needed, just in case it's needed, since its already set up. This essentially does the same thing, right...all while leaving my working fronts alone.

The valve I have now sits under my seat, I can adjust as I drive, if needed. That valve would be under the body...making it tougher to adjust.

Additional thoughts?

B
 
When you bleed the rear brakes, do you move fluid thru the rear calipers?

You will only need to adjust the PV once. Mount it on the frame or near the master cylinder.
 
Yes, i get great fluid to the rears when bleeding, just not sure its enough. Ok, found plugs that should fit the PV. I can plug it rather than loop a line between the two.

Since doing the other work I took it out for a cruise, brakes are the same as they were before. Not surprising since I believe it's the PV now and the volume of fluid is the same as before.

On sandy roads the front driver locks up, but otherwise all the same as before. Going to let it cool down then bypass the rear line from the PV and plug it...then I'll have fluid directly from the mc through the adj PV...see how the rears close then.

Bottom line, I can still stop, just think I should be able to stop better. Either way, I'm hitting Easter Jeep in a few weeks and this is going to make it!

B
 
OK,

I have a pedal,but it's rock hard and it's not pulling up in time! Any ideas? New Booster?
 
Cobound said:
Yes, i get great fluid to the rears when bleeding, just not sure its enough. Ok, found plugs that should fit the PV. I can plug it rather than loop a line between the two.

Since doing the other work I took it out for a cruise, brakes are the same as they were before. Not surprising since I believe it's the PV now and the volume of fluid is the same as before.

On sandy roads the front driver locks up, but otherwise all the same as before. Going to let it cool down then bypass the rear line from the PV and plug it...then I'll have fluid directly from the mc through the adj PV...see how the rears close then.

Bottom line, I can still stop, just think I should be able to stop better. Either way, I'm hitting Easter Jeep in a few weeks and this is going to make it!

B
Click to expand...

I think if you plug the rear fittings on the PV it will leave your brake warning light on, and the PV becomes just a junction block in that case. I'd just bypass it all together or try the valve I linked in the earlier post.
 
Bogged said:
OK,

I have a pedal,but it's rock hard and it's not pulling up in time! Any ideas? New Booster?
Click to expand...

Make sure that the linkage pivot points don't bind, either.
 
get completely rid of the stock PV. T the line out of the MC for the fronts and run direct pressure to the fronts. Put the adjustable PV in the rear line and you are set. I mounted my adjustible line in the dash by the head light switch, so i can actually adjust from the drivers seat. I repeat Get rid of the stock PV
 
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