Proportioning valve/Combination valve

[PanelDeland]

So to explain. I have a 68 C10. It has been upgraded to discs in front (about 12-14 years ago). I used a McGuaghey's drop spindles and brake kit that uses the factory 68 brake lines. I also added power with a MC, booster and bracket from "Right Stuff" which came with an adjustable proportionng valve. I never felt like the brakes were where they should be but they worked well just had way more pedal travel than I thought they should. Like manual brakes. I'm needing to rebuild the rear brakes and thought while I had the system open I would address that also. I've not had much luck figuring out whether the factory Combination type valves have the residual valve built in. "Right Stuff' Doesn't sell a prop valve for it. POL says theirs is right but doesn't have the residual valves built into the combination valve. It also is a dual outlet to front disc that would require I block off one line or replace the front brake lines (that would mean the brake lines would come out in a different place and require new brake hoses (I think). I know this isn't rocket science, too many on here have done it. but getting the right combination valve doesn't seem to be an easy task. I don't want to have to spend $300 for a new booster MC and Combination valve to get it right.

[siggyfreud]

So to be clear, you're running Disc/Drum, right?

What size MC bore are you running?

Which proportioning valve did they provide? Even with an adjustable you still might need a residual if you have drum rears.

Have you checked the gap between the booster rod and MC to ensure there is engagement immediately with pedal travel?

Been where you are, but my problem was with the rear disc conversion e-brake not being adjusted right.

[PanelDeland]

Yes, I'm running disc front ( from McGuagheys) and Right Stuff MC and Booster.
The brakes work. It just takes a lot of pedal before the fronts start to clamp. The rears are already working by that point so the fronts don't do much. There's not a residual valve in there now. I'm trying to figure out which factory style Combination valve has the proportioning valve, the residual valve and distribution block all in one and where to get a "Kit" with all that in it. The conversion to disc used the original 68 (drum style) hard lines and came with new brake hoses that work with them. But that only uses one line to feed both front brakes. Most of the valves I'm finding, use two. I would like to just buy a Proportioning valve kit and install it to get all the functions in one unit. I know that since I installed the disc, companies have started offering a booster/MC kit with the valve, I'm just unclear on whether they have the valve with residual built in. POL said I would need residual valves along with the prop valve. "Right Stuff" doesn't offer a prop valve kit for that application and none of the other vendors have replied.

[geezer#99]

I don’t think the prop valve had residual valves.
The residual valves were located in the outlets on the master.

[jocko]

In a regular old truck disk/drum setup, generally speaking, you should still run a 10 lb Residual Pressure Valve in the rear brake circuit (only) "somewhere" in order to keep your rear wheel cylinder cups expanded and in contact with the shoe actuation train. Long pedal travel is a key indication of the lack of a residual pressure valve. I've heard that most reman/aftermarket MCs do not have RPVs, but, I've also never had a long pedal travel problem when I've installed one... so, not sure where ground truth lies on that.

So, a couple questions:
- can you confirm you purchased a C10 MC from the Right Stuff? (only asking because a C20/30 is plumbed the opposite of a C10 in a factory disk/drum system)
- assuming that is a yes - is the rear outlet of your mc ultimately connected to the rear brake circuit (thru the the prop valve)? (asking for same reason) - it should be connected to the rear for your C10.

If both are yes, I would ping the Right Stuff again until you get someone who can answer your question - they "should" know if the MC they are selling has a built-in RPV.

If they truly don't know, you can confirm for yourself. If the MC does have one, it will likely be beneath the MC's rear brake outlet tubing seat. It would be a small valve under the tubing seat followed by a small spring. You can (carefully) insert the blunt end of a small drill bit that fits thru the tubing seat in the mc connection and - if you feel spring pressure resistance shortly after pushing it in there, then it probably has an RPV. If the drill bit goes smoothly in relatively deep, without resistance, then it likely does not have an RPV. Be careful and don't use anything that could possibly snap off in there if you sneeze...

Some places will tell you that modern wheel cylinders are sealed (preventing any air from entering) and that RPV is not necessary. This may be true, I honestly don't know, but I've yet to figure out if "modern" means "new vehicle wheel cylinders" or "newly manufactured wheel cylinders for an old vehicle"... Most I've dealt with don't seem to have changed in decades - and therefore I assume the 10 lb RPV is still necessary in any older automotive brake system that has any drum components on it.

If all else fails, you could experiment for <$20 and add an inline 10 lb RPV in your rear lines somewhere before they split to the rear wheels and then (cautiously) see if this solves the pedal travel problem. https://www.performanceonline.com/Re...-Brake-System/

One more note - and not related to your pedal travel issue - but perhaps to "feel" - the stock GM disk/drum setups used 3/16 line on the front circuit. Your stock 68 lines are 1/4" front and rear. Not a huge deal, it may feel slightly different than a 71-72 factory disk/drum setup if that is what you're comparing it to, but it's still safe and acceptable to use 1/4" lines on front disks, lots of folks do this - but just mentioning because GM did not.