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Discussion Starter · #1 ·
I've read somewhere that by removing the valve spring from the YJ proportioning/combo valve I can get full pressure to the rear disc on my swapped Ford 8.8. Anybody has done this and if so what do I have to look out for? I'm supposed to remove the bolt on the front of the combo valve just under the master cyl. Will fluid gush out? Do I need to drain the system first?
 

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You can bypass you proportioning valve if you want to, just run the lines direct. With 4 wheel discs you don't really need one.
 

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Discussion Starter · #3 ·
I don't want to rip it all out just want to disable the valve in it. I just need to know if the fluid will gush out or is it in a sealed separate circuit inside the valve body.
 

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you pull the rubber cap off the one end, then unscrew that thing the cap is on, there is a spring, and then a plunger type thing with an o-ring on the plunger, take that o-ring off and put it back together. I'm not sure where the page is either, but that is what it sais with some picks.
 

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Hey Kutyafal,

Let me know if it works I need to do mine also.
Can you e-mail me direct [email protected]


BlueYJ <IMG SRC="smilies/glasses.gif" border="0">
 

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I'm considering doing this on my setup as well. I do not have rear disks, but I have the large Scout drums on the back and my stock MC is just barely up to the task of stopping my Jeep.

If I do this mod, will it increase the line pressure to the rear to bias the rear brakes more, or will I be doing more harm than good?

Also, is this a permanent mod (i.e. the o-ring is destroyed as a result of taking it out, thus making the prop valve useless), or if I don't like it, can I put it back to stock by putting the o-ring back in?

I know that's a lot of questions, but I know very little about brake systems and I really don't want to damage anything that I can't fix.

Thanks in advance!
 

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Discussion Starter · #9 ·
OK, I'm confused. Some says to remove the O-ring, elsewhere I read to remove the spring. Do both have the same effect? I guess the spring removal would be more easily reversed if needed. ???
 

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Here's the deal.

First, the stock valve is not just a proportioning valve, it's a "combination" valve.

I'm too lazy to write all about it, but you can read about it at:
http://www.mpbrakes.com/valving.htm

and
http://www.howstuffworks.com/master-brake.htm

The mod being discussed, will help a bit (but not give you full disc ability, as explained in above links)

here's how you do it:
http://www.bigoffroad.com/pages/bigpages/bigtech/proportioning_valve.htm


You can't just remove the spring, as the nut on the front is vented, and the spring holds the piston back against the cap to seal it.

You can remove the whole spring, piston, and o-ring, but only if you have a solid fitting to replace the vented cap bolt, as described at:
http://www.b-body.net/Technical/Brakes/index.html
 

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Discussion Starter · #11 ·
Originally posted by BillaVista:
<STRONG>
You can remove the whole spring, piston, and o-ring, but only if you have a solid fitting to replace the vented cap bolt, as described at:
http://www.b-body.net/Technical/Brakes/index.html</STRONG>
Great stuff Bill, thanks. Unfortunately, the last (and maybe most important) link doesn't work. Would you care to describe what kind of solid fitting can be used and how?
Thanks.
 

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I just removed the o-ring in the valve tonight, it did seem to make a difference. The o-ring is very easily removed and you wont destroy it. However it is a real pain in the ass getting it buttoned back up because of the spring. I was told that the o-ring is all that was needed, havent read the links yet though, and havent crashed into any walls.

BlueYJ <IMG SRC="smilies/glasses.gif" border="0">
 

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Originally posted by BlueYJ:
<STRONG>I just removed the o-ring in the valve tonight, it did seem to make a difference. The o-ring is very easily removed and you wont destroy it. However it is a real pain in the ass getting it buttoned back up because of the spring. I was told that the o-ring is all that was needed, havent read the links yet though, and havent crashed into any walls.

BlueYJ <IMG SRC="smilies/glasses.gif" border="0"></STRONG>
Did you have to re-bleed the whole system?

I'm still debating this mod even though I don't have rear discs. My brake pedal just doesn't feel very firm. I usually pump the brakes a little anyway just to get the pedal firmer. It feels as though there is air in the lines, but I've bled them like 4 times and get no air out. I'd hate to do the mod, and then find that I'm locking up the rear brakes, but, since you said that I can always put it back to stock the same way I removed it, I may just try it. I hate bleeding brakes, though... LOL <IMG SRC="smilies/maggie.gif" border="0">

Is there a way to bleed the combonation valve itself?

<IMG SRC="smilies/blender.gif" border="0"> <IMG SRC="smilies/blender.gif" border="0">
 

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When I did mine, I pulled the piston out removed the spring and the litte rubber plunger and shoved the plunger bak in with the o-ring. worked perfect fronts and rears lock up at the same time. If you don't have disks the cylinders in your drums will probably explode. if they dont, your rears will lockup under minimal braking.
 

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I stood on the brakes pretty hard with very minimal lock up, I mean minimal and let me tell you it stops on a dime now.

I did NOT have to rebleed the brakes. They where a little mushy the brake light came on drove it and kept hitting the brakes the brake light has stayed off and the peddle is firm.

BlueYJ <IMG SRC="smilies/glasses.gif" border="0">
 

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In the last link (from the GM B-body page - I guess limited numbers of Impalla's were made with discs but GM used the same combi valve as used on higher production volume cars with disc/drum)

What they describe, is either finding a soloid bolt to replace the vented one with (I guess the GM combi valve has a vented bolt on the front, and a solid one on the back....I *think* the Jeep one has 2 vented bolts, and I'm not sure if a GM solid bolt fits?)

or, modifying the vented bolt by drilling out and tapping the vent hole, and installing a small stainles cap screw (allen head bolt) from the inside.

They describe it like this (dimensions may vary for us)

Remove rubber vent cap by squeezing it between thumb and forefinger. .
Remove vented bolt from front of combi valve with a 19mm 6-point socket. Drill vent hole out to 7/64".
Tap with a course 6-32 tap.
Blow any metal filings off with compressed air.
Install a 6-32 x 5/16" stainless steel socket head cap screw from the inside using red LockTite or the equivalent thread locking compound. Tighten firmly with an allen wrench. The screw may be purchased from Totally Stainless as p/n 2-0911. Call 1-800-767-4781 to order.
 

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man dont go through all that, just take the 0-ring out. it was that simple, just dont spill the <IMG SRC="smilies/beer.gif" border="0"> after hitting the brakes.

BlueYJ <IMG SRC="smilies/glasses.gif" border="0">
 

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Discussion Starter · #19 ·
OK, finally I had time to try this out. I took the nut off and pulled the spring but no plunger came with it. I guess it's still in there? I couldn't see in there to pull it out so I just removed the spring and put the nut back on. Can't say there is much difference. I'll go back and try to pull that plunger out somehow. I guess needle nose pliers or a tweezer should do. I'll let you know. I'm also thinking about upgrading my pads and have my rotors checked. It could never hurt. Btw, I love the new board software.
 

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For you guys that have done this:

I pulled the o ring off today AND installed my cadi calipers to the rear. Now my brakes go to the floor. Is that common with the disc setup? I may still have air in the line, but I doubt it. I am suppose to be going up to Clayton, OK for a run and would hate to test the sucker the hard way on a steep incline with only one way to stop.
 
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