Brake Metering Valve

I am collecting parts and working on the design of a disc/drum upgrade to my CJ5. Knowing that the internet is rife with mis-information I am still surprised how many out there seem to have overlooked the need for a metering valve (hold-off valve) in a disc/drum system. I plan on an adjustable proportioning valve so will not be using a combo valve.

So what experiences have others had with or without a metering valve?

 

I put proportioning valve on mine that I got from jegs. I backed off the pressure on my rear drums to make sure my jeep stays pointed in the right direction with heavy braking in wet weather.

I never drove the disk brake setup without it except when I was testing & breaking in the new setup. The proportioning valve does make a difference.

 

I'm not talking about a proportioning valve nor a residual pressure valve. A metering valve is used only on disc/drum systems. You could say it retards the front calipers until the drums have taken up all slack. It is installed on the front disc circuit. It does not allow fluid flow until pressure has reached 75-125 PSI. By this point the rear drums are just beginning to engage. Without it the front disc caliper would engage immediately causing the nose to dive. Don't confuse it with the proportioning valve which limits the top end rear wheel cylinder pressure. The metering valve's work is done at the beginning of the brake application cycle while line pressure is just starting to increase.

 

After checking the articles I have saved for performing disk brake conversions on jeeps. I noticed something; only one article mentioned a metering valve. That article talked about needing to remove the metering valve when switching from all drum to disk. This probably explains the lack of information. It is also interesting that brake part manufactures seem to ignore this subject on metering valves as well.

On the Wilwood site, only one of their products has a metering valve. This was there newer gm style proportioning block. This had a brake force delay of 30 psi. Tech Center - GM Classic Car Valve Configurations

Right stuff also has a short article on identification of brake valves, and of course sells a standalone metering valve that is made for gm vehicles. Tech Center - GM Classic Car Valve Configurations

This site had a great write up on metering valves, also addresses common failures for stock type of metering valves. Brake Valves: Operation and Service

I’m thinking that people who have been doing disk brake conversion haven’t been running into problems due to the fact they normally have a residual pressure valve on their back brakes. This would allow the rear drums to be pressurized so the brake dive would be minimal if not non-existent. That is my thought process. I don’t see how a metering valve could hurt in your application and would love to see some of the others opinions and or facts on this matter.

I would think a pressure sensor, would be more important feature to add as well.

 

It seems they are not very common. Not a critical item and I would think depending on the type of driving may not even be missed. I can see that with a RPV there would be little to no "slack" in the drums but there would be no braking action until the shoe return springs are overcome. I find the Tech Center link above notes that "This results in better front to rear brake balance at low pressure". That would be advantageous on a steep downhill trail with loose material where braking needs to be light and equal on all wheels.

 

Most modern Combination brake valves that are spec'd correctly for the brake components used ( Master , calipers and wheel cylinders ) offer ( Proportioning , metering , and residual ) in one valve and that is what you want.............

 

Focker, yes I have a dual MC. The PO put it in. Looks like Herm's bracket. And there is a combo valve on the inner frame rail. I'll be replacing everything.

 

When I did mine. I used parts from a 1985 CJ. I got the calipers, discs, and combo valve.
You can kind of see it here.

 

I initially installed one of these:

Brake Metering-Hold-Off Valve

I also put in the Wilwood adjustable prop valve.

I could not for the life of me get much pressure to the front brakes. I made sure the back brakes were bled well and adjusted. I actually bent one of the brake pedals pushing trying to get the fronts bled. I finally gave up and removed the valve from the system The front brakes seem to work fine now.

I'm still in rebuilding mode, so I haven't tested anything on road as of yet.

 

That's a concern I have. Some of the parts house reviews of the item indicate some people have had problems with them. I'd like a brake system that isn't overly complicated and is reliable as this is for a trail rig. We'll see, I'm still on the fence with this.

 

It being a trail rig, and assuming it's going to spend most of its life locked in 4wd, I'd think you wouldn't notice it one way or another. The t-case will prevent any difference in front-to-rear wheel speed when in 4wd. (Okay, ring gear speed, not necessarily wheel speed before I get corrected.)

I guess conventional ratchet-type lockers could allow a tire to spin faster than the ring gear, but still, I doubt in that one instance you'd notice - if everything in your braking system is in good working order.

 

When you make the change in your system, are you going to install swing pedals? With the swing pedals you have a multitude of options that don't, to me anyway, seem available with the frame mounted master cylinder. Swing pedals for example, make power brakes an easy install. Step bore master cylinders can be selected to help dial in front/rear braking ratios and well as wheel cylinder bore size selection.

In my case, I used a 1984 S10 power brake system (power brake booster/ step bore master cylinder/ combination valve) with 11" rear drums (Jeep 15/16" wheel cylinders) and the GM K10 front disc calipers. With this, the brake system appears to be well balanced. And, I agree whole heartedly with Tarry99 in that a combination valve is needed in a disc/drum system. I believe it is the one major component the is aiding to the balance of my system.

 

I just put in a wrangler booster/master with swing pedals. I used no proportioning vales and no residual valves. I have GM calipers on all 4 corners. My brakes are now amazing. I drive it in city traffic and it responds like a modern braking system does. I am extremely happy with it.