Proportioning valve failure?

[The (LJ) Dude]

At a loss on this one. 06 Unlimited (ie, 4 wheel disk brakes)

1) Press the brake pedal...have pretty good brakes. But if you press further for a hard stop...you get way less brake...vehicle just keeps gliding forward
2) After vehicle has been sitting a day or two - brake pedal is initially stiff/stuck with what feels/sounds like back-pressure. Press a little harder, and it suddenly/stickily moves through that stuck position with a release of back-pressure on pedal...and does not stick again that way until it sits for say 24+ hours.

system has been bled multiple times - no air
fluid level not dropping/leaking
master cylinder replaced
had an intermittently sticking front caliper, so replaced both and one hose yesterday. No change to problem, as expected
black magic pads still wearing well
*not seeing any blisters on remaining hoses
no light on dash for brake

I don't know enough about the proportioning valve to diagnose - only going by that it 'feels' like a valve/pressure bypass issue. Any expert advice appreciated please!

The 5083808AA valve that fits my VIN is NLA, and I did not find anything searching @mrblaine 's web site.

https://www.moparpartsgiant.com/page_product/pd?vin=1J4FA44S56P726165&make=Jeep&model=Wrangler&year=2006&submodel=&extra1=&extra2=&filter=()&pd=Brake Proportioning Valve&pdUrl=brake_proportioning_valve

 

[mrblaine]

At a loss on this one. 06 Unlimited (ie, 4 wheel disk brakes)

1) Press the brake pedal...have pretty good brakes. But if you press further for a hard stop...you get way less brake...vehicle just keeps gliding forward
2) After vehicle has been sitting a day or two - brake pedal is initially stiff/stuck with what feels/sounds like back-pressure. Press a little harder, and it stickily moves through that stuck position...and does not stick again that way until it sits for say 24+ hours.

system has been bled multiple times - no air
master cylinder replaced
had an intermittently sticking front caliper, so replaced both and one hose yesterday. No change to problem, as expected
black magic pads still wearing well
*not seeing any blisters on remaining hoses
no light on dash for brake

I don't know enough about the proportioning valve to diagnose - only going by that it 'feels' like a valve/pressure bypass issue. Any expert advice appreciated please!

The 5083808AA valve that fits my VIN is NLA, and I did not find anything searching @mrblaine 's web site.

https://www.moparpartsgiant.com/page_product/pd?vin=1J4FA44S56P726165&make=Jeep&model=Wrangler&year=2006&submodel=&extra1=&extra2=&filter=()&pd=Brake Proportioning Valve&pdUrl=brake_proportioning_valve

No dash light but does it work when you apply the parking brake? If so, then we need to verify that it is working at the combo valve switch. Pull the connector off of the switch and short the terminals in the connector to ground and see if the dash light trips.

Send me an address to the BMB email address and I'll send you a lock out tool to use for diagnostics. Replace the switch with it and see if that changes any of the symptoms. I wouldn't leave it there too long since you are in effect bypassing a safety feature, but it will tell you if the shuttle shifting is causing your problems.

 

[The (LJ) Dude]

No dash light but does it work when you apply the parking brake? If so, then we need to verify that it is working at the combo valve switch. Pull the connector off of the switch and short the terminals in the connector to ground and see if the dash light trips.

Send me an address to the BMB email address and I'll send you a lock out tool to use for diagnostics. Replace the switch with it and see if that changes any of the symptoms. I wouldn't leave it there too long since you are in effect bypassing a safety feature, but it will tell you if the shuttle shifting is causing your problems.

The dash light does come on with the parking brake, yes.

Will go jump sensor terminals and see what happens…

Just ordered tool on your site, thank you!

 

[macleanflood]

The dash light does come on with the parking brake, yes.

That's a different electrical circuit than the proportioning valve but at least confirms the dash light works.

-Mac

 

[mrblaine]

That's a different electrical circuit than the proportioning valve but at least confirms the dash light works.

-Mac

Nope, it is the same circuit. The terminal"s" is/are jumpered between the 2 pins in the switch so it is a series circuit with the parking brake handle switch and the brake light switch at the combo valve both closing the circuit to ground. The ground is picked up via the hard lines to the combo block and then the side of the parking brake handle to the tub.

 

[The (LJ) Dude]

Whelp - confirmed operation of the switch on proportioning valve....when grounded out, the dash light does indeed come on. Tested via jumper line to a nut on master cylinder...so that ground has confirmed continuity.

@mrblaine does this sound fishy to you at full pedal here in this short vid? Hydraulic brakes are not my area of expertise beyond parts changing. I work on and drive air brakes by day.

https://www.dropbox.com/scl/fi/8ezo...ey=juj2z12236kaoks4obb4oonrw&st=fxzzmv6k&dl=0

 

[mrblaine]

Whelp - confirmed operation of the switch on proportioning valve....when grounded out, the dash light does indeed come on. Tested via jumper line to a nut on master cylinder...so that ground has confirmed continuity.

@mrblaine does this sound fishy to you at full pedal here in this short vid? Hydraulic brakes are not my area of expertise beyond parts changing. I work on and drive air brakes by day.

https://www.dropbox.com/scl/fi/8ezo...ey=juj2z12236kaoks4obb4oonrw&st=fxzzmv6k&dl=0

Doesn't sound fishy, sounds like a big vacuum leak in the booster. You need to pull the master and see if there is fluid in the booster. If there is, time for a new booster and master.

 

[The (LJ) Dude]

Ironically…both are new aftermarket, replaced within the past year at differing times.

Replacing Master made no difference to symptoms…guess I’ll start with the booster and report back!

 

[macleanflood]

Ironically…both are new aftermarket, replaced within the past year at differing times.

Replacing Master made no difference to symptoms…guess I’ll start with the booster and report back!

No real surprise. New parts are all crap these days.

-Mac

 

[The (LJ) Dude]

Ordered a reman Cardone booster last night...maybe this one will last longer than the 3 months the "SKP" did.