Anyone run an adjustable brake proportioning valve?

[Xposure]

Since my Jeep has rear disk brakes I've been wondering about the stock proportioning valve that sets the braking bias. From my experience with road race car setups whenever upgrading the rear brakes we typically replaced the oem proportioning valve with an adjustable one to provide more pressure to the rear brakes. We would do a series of hard stops and get it dialed it and it made a significant increase in stopping ability since the bigger rear brakes were being utilized better. It also stopped the car more evenly. I'd imagine going from drums to disks would give the ability for much better stopping, but with the stock proportioning valve they probably don't see near enough pressure to take advantage. Do the later model Jeeps with rear disks have a different proportioning valve? Also, since my rear brakes are from a mid 90's Explorer how do these brakes compare in size to the stock disks in later model Wranglers?

Anyone doing stuff like this after swapping the rear brakes?

 

[Jerry Bransford]

The TJ uses the same proportioning valve for rear disk or drum brakes. It works well for either. Adding more pressure to the rear brakes will likely result in making it too easy to lock up the rear brakes under hard braking since weight transfer during hard braking puts most of the weight on the front tires/brakes.

 

[Xposure]

You would think though that going to a much bigger heavier tire as compared to stock would be able to allow for much more stopping power in back without locking up. The stock tires would be much easier to lock up than say 33’s. Shouldn’t this give us much more room for additional braking power without locking up, over what stock was designed for?

 

[tworley]

What is the balance with stock...80/20? I think most (myself included) will or are happy with upgraded calipers/pads/rotors from black magic brakes

 

[Xposure]

Typically the front has a pass through and gets full pressure. You install a proportioning valve on the rear and it has no affect on the front. The front will still see the same stopping force as it always did. A typical OEM rear proportioning valve just allows for the rear pressure to be reduced so that they see less than the front and don’t lock up, especially because the weight transfers to the front making it easier for the rear to lock up. BUT once you start doing things like much heavier tires that are harder for the brakes to stop (and lock up) it makes sense to give them a little more pressure to help will stopping ability....you just want to run a series of emergency stops at slow then higher speeds to make sure the tires don’t lock up. Ultimately the goal is to get as much rear braking ability without locking up the tires....it’s also good to test it on wet pavement too.

I’m surprised with people running bigger brakes and far far heavier tires that no one really seems to adjust the rear brake pressure. The adjustable proportioning valves are only $100 or so.

It SEEMS like it would be very beneficial, but I don’t have much experience with Jeeps yet so maybe I’m barking up the wrong tree.

 

[Jerry Bransford]

Typically the front has a pass through and gets full pressure.

Not usually and not in the TJ's case. It is proportion bias is something like 70-30 or 75-25, I forget exactly but it's very close to that.

 

[Xposure]

In doing a little research the Jeep has a combination valve. It has a metering section which manages how fast the front and rear see their pressure. In the middle is a pressure switch that alerts if there is unequal pressure throughout the valve (where the sensor is). Then out on front is the proportioning valve section where only the rear brakes are connected, lowering pressure to the rear. What I was thinking of doing is removing the proportioning valve stem and blocking off the hole with a bolt essentially disabling it. This way the metering side and pressure switch would still work correctly. Then I can install an adjustable proportioning valve in the line that goes to the rear, effectively replacing the oem porportining valve with my adjustable valve. It won’t have any affect on the front at all, it will only allow the rear to receive more pressure to compensate for the much heavier tires as compared to stock and since I now have rear disks they should be up to the task no problem. The tires are like a huge heavy flywheel, I’m sure they have allowed for a large amount of additional braking force to be able to be applied without issues of the rear tires locking up.

Here is a good read on combination valves if anyone wants to rear about how they operate. https://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake2.htm

 

[Jerry Bransford]

Why? The OE brake proportioning system works extremely well as is. This reminds me of those who think they can modify the OE cooling system to work better with electric fans, store brand 3-row radiators etc. and then wonder why their beloved Jeep now runs hotter, the fan stops working, etc. My personal opinion is you're screwing with a part of the braking system that should be left alone.

If you truly want better braking, upgrade your front brakes to something known to help dramatically... the dual piston Big Brake Kit from. www.blackmagicbrakes.com (AKA Vanco) designed by someone who knows Jeep brakes better than anyone. I've had that kit on both of my TJs and it works superbly. Bolt-on and makes use of the OE combination valve/proportioning valve.

 

[05 Blue Unlimited]

In doing a little research the Jeep has a combination valve. It has a metering section which manages how fast the front and rear see their pressure. In the middle is a pressure switch that alerts if there is unequal pressure throughout the valve (where the sensor is). Then out on front is the proportioning valve section where only the rear brakes are connected, lowering pressure to the rear. What I was thinking of doing is removing the proportioning valve stem and blocking off the hole with a bolt essentially disabling it. This way the metering side and pressure switch would still work correctly. Then I can install an adjustable proportioning valve in the line that goes to the rear, effectively replacing the oem porportining valve with my adjustable valve. It won’t have any affect on the front at all, it will only allow the rear to receive more pressure to compensate for the much heavier tires as compared to stock and since I now have rear disks they should be up to the task no problem. The tires are like a huge heavy flywheel, I’m sure they have allowed for a large amount of additional braking force to be able to be applied without issues of the rear tires locking up.

Here is a good read on combination valves if anyone wants to rear about how they operate. https://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake2.htm

IDK...sounds like a recipe

 

[BendLarry]

I believe my Jeep has what you are describing. There is an adjustable knob on my master cylinder.


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[Xposure]

Why? The OE system works extremely well as is. This reminds me of those who think they can modify the OE cooling system to work better with electric fans, store brand 3-row radiators etc. and then wonder why their beloved Jeep now runs hotter, the fan stops working, etc. My personal opinion is you're screwing with a part of the braking system that should be left alone.

If you truly want better braking, upgrade your front brakes to something known to help dramatically... the dual piston Big Brake Kit from. www.blackmagicbrakes.com (AKA Vanco) designed by someone who knows Jeep brakes better than anyone. I've had that kit on both of my TJs and it works superbly. Bolt-on and makes use of the OE combination valve/proportioning valve.

It doesn’t really remind me of that at all...the cooling system was designed for the engine and most people are running the stock engine with very little if any power increase over stock....I don’t see any need to upgrade it. Maybe if there are some quality parts that work great and you have to replace parts anyway....but no one changes anything that requires more cooling ability.

The brake system design on the other hand seems to be drastically compromised by everyone (including me) who runs tires bigger than what the system was designed for. Especially with low pressure stock drums, they weren’t designed for the momentum of 33, 35, 37, and so on inch tires.

To me it seems like what everyone is doing with the rear brakes is the same as mounting a 35” tire on a swing out arm attached to the stock back bumper.

 

[Jerry Bransford]

Ok I can see I'm shouting into the wind so go for it.

 

[Xposure]

IDK...sounds like a recipe

Yeah, I might test it out and see how it goes. A quality adjustable valve is around $100 and it would take less than a hour to put it back to stock if it doesn’t work well or if it doesn’t help things. These valves are very very common in cars set up for road racing with large customer or aftermarket brake kits. As a matter of fact, I haven’t looked but I bet some of the big brake kits for Jeeps come with a proportion valve.

 

[Xposure]

I believe my Jeep has what you are describing. There is an adjustable knob on my master cylinder.


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If you get a minute poking around under the hood and think about it, I’d love for you to post a picture of it hereto see how it’s hooked up

 

[Xposure]

Ok I can see I'm shouting into the wind so go for it.

Well I don’t know if I’d go that far....I do appreciate your feedback....I just feel like for the cost of $100 valve I’d like to test it out and see how it does. Based on some nonJeep related experience I have a feeling it may make a big difference. If not, I can easily put it back to stock and not be out much.

But hey, shouting in the wind is better than peeing in the wind.

 

[BendLarry]

If you get a minute poking around under the hood and think about it, I’d love for you to post a picture of it hereto see how it’s hooked up

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[Xposure]

View attachment 50528



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Hey man, thanks! I appreciate that....looks like it was installed directly into a combination block...or that the entire combination block was replaced with one that has a adjustable proportioning section. What year and engine is your Jeep?

 

[BendLarry]

Hey man, thanks! I appreciate that....looks like it was installed directly into a combination block...or that the entire combination block was replaced with one that has a adjustable proportioning section. What year and engine is your Jeep?

2006 Rubicon 4.0 auto.


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[BendLarry]

Im glad to see this thread. About a year ago I posted a question about this brake option. All I got was crickets.


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[Xposure]

2006 Rubicon 4.0 auto.


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Update....you have Wilwood combination valve...this one https://www.wilwood.com/MasterCylinders/MasterCylinderProd?itemno=260-11179

Pretty nice....how do your brakes feel? Did you or a PO install it?