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Drum vs disc - Residual pressure?

xj4rocks

NAXJA Forum User
Location
york, pa
ok. so I converted my D44 from drums to ZJ discs and I have good pedal pressure and seemingly good stopping power.

My question is -- I think that the rear pads might be dragging because of a residual pressure setup that used to be for the drums. Is that correct? do drum setups have a residual pressure valve? or do I have it backwards -- are discs supposed to have the vavle? which setup needs the (2lbs was it?) residual pressure.

regardless I think my rears are dragging some and am trying to think of reasons why they would be.

thanks.
 
Drums usually run a 10lb check valve to overcome some of the pedal slop from the return springs - discs often use a 2lb to do the same (no springs but keeps the pads tight to the rotor)

I would say the easiest way to deal with the issue is to go to the junkyard and get the porportioning valve from a ZJ with discs in the rear - that way the whole deal is already set up for you - should be pretty close to plug and play depending what fittings you have... (just grab some of the lines for the fittings) HTH

Matt
 
You don't need a residual pressure check valve. THe only reason a residual check valve is used is to expand the cups in the wheel cylinders, so that air cannot get into the system. All you need to do is take it out and get an adjustable proportioning valve.
 
Matt said:
Drums usually run a 10lb check valve to overcome some of the pedal slop from the return springs - discs often use a 2lb to do the same (no springs but keeps the pads tight to the rotor)

I would say the easiest way to deal with the issue is to go to the junkyard and get the porportioning valve from a ZJ with discs in the rear - that way the whole deal is already set up for you - should be pretty close to plug and play depending what fittings you have... (just grab some of the lines for the fittings) HTH

Matt

That's kind of what I thought. But with that 10lb check valve it could be causing my rear discs to drag slightly right? my rear brakes always seem tight which is a good thing but sometimes it doesn't seem like they're letting up enough when I'm not pushing on the pedal. That's what led me to wonder about the check valve.

I'll see what would be involved and swapping the zj prop valve. Is there anyway to remove the check valve from my XJ's system? or is it too integral to the whole thing? just curious.

Thanks.
 
The check valve is not included in the combo valve. I dont know where the check valve is. but im sure someone on here will know
 
I dont know the exact location of them but they must be in the rear brake lines. I know this doesnt help but maybe you could trace the lines and see. There might be two individual ones. One in each line.
 
I'd bet my lunch money on the residual pressure being built into the XJ combination valve also known as the proportioning valve.
BTW, I picked up a ZJ disc/disc prop. valve for my SVO rear disc setup (almost identical to the ZJ rear discs) at a local bone yard for $6.00.............best solution for your setup, IMO.

XJEEPER
 
so how much money do you spend on lunch that you'll be betting? ;)

anyone else know for sure where it is? I don't feel like swapping the combo valve it it's not going to get me anywhere. I can get one cheap here locally also, but I'm lazy. :D :D no more work than necessary.
 
It is the nut on the back end of the porportioning valve - there should be an o-ring, spring and a little ball - I cannot remember what you do with it (for some reason removing the O-ring sticks in my head - however I am not responsible for any spills or blowouts!!! )

I would get the ZJ one since you are running the ZJ disc - despite running around most of the time with their head up their butts the Jeep engineers did match components to function as needed!

I believe the fittings should match up pretty well - the rear line should have a union that is female IF 3/8" 24 tpi (std 3/16" brake tube) and the two front channels use some metric crap so you cannot cross connect a rear line with a front line (unless you're an idiot with a flaring tool) Enjoy and post up how it goes

Matt
 
Removing the spring is dumping the proportioning between front and rear.

Stu seems to think that the ZJ distribution block will solve the residual pressure prob, so I guess I'll go pick up one. will be 2 weeks or so. I don't want to F' with the brakes, I have a big wheeling trip coming up.
 
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