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Unread 02-05-2015, 05:59 PM   #1
yj-dax
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proportioning/combination valve question

Hey guys,

I'm looking to get a little better braking power out of my 8.8. I would like to find a proportioning valve from a ZJ or do the o ring mod I hear about.

If I find the whole valve at a wreckers, do I need to swap out the whole distribution block or can I just pull the spring loaded valve out of the front and replace it in my existing distribution block?

Thanks

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Unread 02-06-2015, 04:07 AM   #2
Mike Romain
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A proportioning valve is a safety to stop you from locking the rear brakes up too soon. Saves you doing 360's down the road...

I find the best braking power increase to be the softest cheapest pads and shoes that still use rivets to hold them on. (Glued on pads can water shock off) The soft pad wears faster, but it grabs Way better. I tried semi- metallic pads and changed them out within a week. Had no stopping power at all.
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Unread 02-06-2015, 08:08 AM   #3
fishadventure
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Quote:
Originally Posted by yj-dax
....looking to get a little better braking power out of my 8.8. I would like to find a proportioning valve from a ZJ...
Quote:
Originally Posted by Mike Romain
....braking power increase to be the softest cheapest pads...The soft pad wears faster, but it grabs Way better...
Agreed on soft pads. I always buy the cheapest if there's two selections of grade; if three or four grades I might buy grade two...

As far as proportioning valve- what happens now when you lock the brakes? You might not need it...
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Unread 02-06-2015, 09:09 AM   #4
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80% of the braking on any vehicle comes from the fronts. Personally I see no reason to mess with the proportioning valve unless it's clogged or damaged.

In my experience the main benefit from rear disks is not so much about stopping power as it is about better braking control. Meaning, going downhill slowly they are les likely to be grabby or lock like drums do sometimes.

I have a TJ booster and master with the original prop valve and EBC pads in front. The read pads came with the 8.8 from the junkyard. I can lock all 4 wheels easily.
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Unread 02-06-2015, 09:29 AM   #5
Morris4x4Center
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If the valve isn't adjustable, I'm not sure how you will know if it works the way you want it to, better or worse?. The other poster is correct, an average braking would be 80% front, 20% rear, but the actual numbers can vary depending on the vehicle.

Some companies make adjustable ones so you can narrow down exactly what you want, if that helps -
http://www.jeep4x4center.com/prop-block-ssbc-a0730.html
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Unread 02-07-2015, 12:38 AM   #6
Nickabis
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I'd grab the block with the valve. I was going to get an adjustable but may stay with a valve from a 4 disc brake system instead of my original one.
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Unread 02-07-2015, 01:09 AM   #7
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Originally Posted by jbolty View Post
In my experience the main benefit from rear disks is not so much about stopping power as it is about better braking control..
Total BS Its about the next brake job you do.

I use 8.8 disks in the rear and never messed with the o-ring removal. Stops totally fine.
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Unread 02-07-2015, 10:37 AM   #8
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Quote:
Originally Posted by Mike Romain View Post
A proportioning valve is a safety to stop you from locking the rear brakes up too soon. Saves you doing 360's down the road...
^^^ this.

The click style prop valve on the race car was adjusted to prevent the rear from stepping out under threshold breaking by decreasing the amount of braking power in the rear. If the rears locked up first you would back off the rear brakes. If the fronts lock first you would dial in more rear.

Have you had someone observe the wheels while you stood on the brakes at speed? Put some chalk marks on the sidewalls to help see when one wheel is spinning slower than the other.

If you want more braking power, change pads.
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Unread 02-07-2015, 10:59 AM   #9
mike134
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I wouldn't bother trying to increase rear brake power.

I think your 95 already came with the larger brake booster model. I'm not sure what else you could do to increase braking power. Are you sure all of the air is out of the lines?
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Unread 02-07-2015, 12:21 PM   #10
yj-dax
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Thanks guys, some good advice there.

Yes I do have the 95 with the upgraded braking system on it. As of now my rear brakes are only engaging minimally. We have bled and re-bled and still getting very little power out of them. The brakes on all four corners and all hard lines were completely replaced last year, new rotors pads and calipers. After a year the rears look like the rotors are still brand new with the cross hatching machine marks still visible. On full brake on a gravel road the rears do not lock up at all.

At this point is less about getting more braking from the rear as getting some.

I was hoping that the valve out of a 4disc Cherokee might help.
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Unread 02-07-2015, 12:29 PM   #11
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Have you done a fluid change? Before I did my axle swap or brake upgrade I had a rusted out brake line. I swapped all the hard and soft lines and obviously all new fluid. Just that, and changing noting else made a noticeable difference in braking

Unless you've don't the same you fluid is over 20 years old.
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Unread 02-07-2015, 12:45 PM   #12
mike134
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Quote:
Originally Posted by yj-dax View Post
Thanks guys, some good advice there.

Yes I do have the 95 with the upgraded braking system on it. As of now my rear brakes are only engaging minimally. We have bled and re-bled and still getting very little power out of them. The brakes on all four corners and all hard lines were completely replaced last year, new rotors pads and calipers. After a year the rears look like the rotors are still brand new with the cross hatching machine marks still visible. On full brake on a gravel road the rears do not lock up at all.

At this point is less about getting more braking from the rear as getting some.

I was hoping that the valve out of a 4disc Cherokee might help.


This makes me think the wheel cylinders on your particular 8.8 are just not the correct size for the rest of your braking system. After all, they weren't designed for the wrangler. You might try changing to a different wheel cylinder. (I suppose the end result could be pretty similar to your original solution of changing the proportioning valve. But proportioning valves are relatively expensive and harder to change so I wouldn't mess with it if I didn't have to).

what vehicle did the 8.8 come from?

I'd also double check the star wheel positions since it could be causing your problem and would be the easiest solution. They may not automatically adjust if they are too loose to begin with.

If you really really wanted to go the proportioning valve route for some reason, a universal adjustable valve should be available for around $150 from Summit Racing. It could be dangerous to adjust it unless you have a closed track available. When tinkering, remember that the disc brakes need much much more pressure than a drum brakes since drums have an intrinsic power assist.
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Unread 02-07-2015, 01:46 PM   #13
tom_sprecher
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If you are not getting any wear on the back then change the prop valve and see what happens. You are getting fluid back there since they bleed but maybe not enough pressure.
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Unread 02-08-2015, 07:36 AM   #14
Mike Romain
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Quote:
Originally Posted by yj-dax View Post
Thanks guys, some good advice there.

Yes I do have the 95 with the upgraded braking system on it. As of now my rear brakes are only engaging minimally. We have bled and re-bled and still getting very little power out of them. The brakes on all four corners and all hard lines were completely replaced last year, new rotors pads and calipers. After a year the rears look like the rotors are still brand new with the cross hatching machine marks still visible. On full brake on a gravel road the rears do not lock up at all.

At this point is less about getting more braking from the rear as getting some.

I was hoping that the valve out of a 4disc Cherokee might help.
Were the hard lines replaced with factory style lines that change size when they split from the flex line at the back axle? I see folks just going with all one size steel lines, then having reduced rear grab because of basic hydraulics. Mine was like that, went through 3 or more front sets for one rear. I bought a stainless set and now the rears show better wear.
The disk disk combo valve might be a good thing to have too, but I read of lots of folks that don't need it.
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89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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