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Unread 05-29-2009, 05:53 AM   #1
joshs1ofakindxj
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Join Date: Apr 2006
Location: SWPA
Posts: 210
Proportioning Valve

So I'm putting rear disc brakes on the 89 XJ, and therefore putting in a proportioning valve (PV) from the grand cherokee I got the disc brakes from.

The old PV in my NON-ABS 89 XJ has two connections for the front brakes and 1 connection for the rear brakes.

The PV from the ABS 96 ZJ has 1 connection for the front and 1 connection for the rear. Where the 2nd connection for the front is located there is a threaded plug for something but it does not appear to be a place to connect the other front brake line because it doesn't look like a seat for a double-flared connection.

Correct me if I'm wrong.

So do I need to find a PV from a NON-ABS ZJ with disc brakes?

OR

Can I run one brake line front the PV's single front brake connection and then use a "T"-connector to split the line into the two lines needed for the front? Would that be bypassing something in the ABS unit or non-ABS PV that I'm missing?

Thanks.

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Unread 05-29-2009, 12:33 PM   #2
nostaw22
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1998 XJ Cherokee 
 
Join Date: Apr 2009
Location: Hollis, NH
Posts: 400
When I did the conversion I didn't bother changing proportioning valves, and the brakes work fine, so if you do nothing it will be "OK".

I was talking to my mechanic about it and he said there is a spring which helps hold residual pressure, which is different for the drum / disc brakes. He said just pull the spring from the GC proportioning valve rear output line and use it to replace the spring in the XJ proportioning valve's rear output. I haven't done this yet since the brakes don't seem to drag using the stock XJ proportioning valve and I don't have a GC proportioning valve.

Not sure if this helps, but it may save you some hassle.

JW
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Unread 05-29-2009, 02:22 PM   #3
AZ Jeff
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2014 JK Wrangler 
 
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Quote:
Originally Posted by nostaw22 View Post
When I did the conversion I didn't bother changing proportioning valves, and the brakes work fine, so if you do nothing it will be "OK".

I was talking to my mechanic about it and he said there is a spring which helps hold residual pressure, which is different for the drum / disc brakes. He said just pull the spring from the GC proportioning valve rear output line and use it to replace the spring in the XJ proportioning valve's rear output. I haven't done this yet since the brakes don't seem to drag using the stock XJ proportioning valve and I don't have a GC proportioning valve.

Not sure if this helps, but it may save you some hassle.

JW
Your mechanic is correct. Just put the GC spring in the XJ prop. valve.
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Unread 05-29-2009, 06:02 PM   #4
Ed Rico
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1997 XJ Cherokee 
 
Join Date: Jun 2007
Location: Terre Haute, IN
Posts: 526
Quote:
Originally Posted by joshs1ofakindxj View Post
So I'm putting rear disc brakes on the 89 XJ, and therefore putting in a proportioning valve (PV) from the grand cherokee I got the disc brakes from.

The old PV in my NON-ABS 89 XJ has two connections for the front brakes and 1 connection for the rear brakes.

The PV from the ABS 96 ZJ has 1 connection for the front and 1 connection for the rear. Where the 2nd connection for the front is located there is a threaded plug for something but it does not appear to be a place to connect the other front brake line because it doesn't look like a seat for a double-flared connection.

Correct me if I'm wrong.

So do I need to find a PV from a NON-ABS ZJ with disc brakes?

OR

Can I run one brake line front the PV's single front brake connection and then use a "T"-connector to split the line into the two lines needed for the front? Would that be bypassing something in the ABS unit or non-ABS PV that I'm missing?

Thanks.
The ZJ valve will work fine for you. Just remove the threaded plug from the ZJ valve and replace it with the threaded adapter in the same location from the original XJ valve. This will allow you to install all 3 of the XJ lines in the original location if you remount the ZJ valve on the XJ valve bracket. The ZJ valve only has the 2 outputs because it doesn't split the 2 fronts out until after the ABS. I put the ZJ valve on my XJ with the ZJ rear disc conversion and it works fine just as described above. Note that depending on what year ZJ valve you have, you may need to scavenge the electrical connector from the donor vehicle. I still have to do this on my '98 XJ since the switch on the ZJ valve uses a different connector than the original.

-Ed Rico
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Unread 05-29-2009, 10:30 PM   #5
alexrule123
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2001 XJ Cherokee 
 
Join Date: Dec 2005
Location: Jacksonville, Florida
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Quote:
Originally Posted by AZ Jeff View Post
Your mechanic is correct. Just put the GC spring in the XJ prop. valve.
I tried that when I did the conversion and didn't notice any difference in brake performance, after putting in the zj prop valve I noticed a huge difference. Also make sure you get the cap that holds the prop valve in the zj master cylinder since the zj one has a smaller internal diameter and will leak fluid when the brakes are applied.
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