55.2-59 2 front brake lines

[popeyestruck]

Running the brake lines on my truck (disc/drum) the proportioning valve has one front port plugged but I plan on running both front lines separate. Is that going to be a problem?

[leegreen]

Originally Posted by popeyestruck

Running the brake lines on my truck (disc/drum) the proportioning valve has one front port plugged but I plan on running both front lines separate. Is that going to be a problem?

I'd check the manufacturer's specs or call them to make sure both ports are valved correctly.

[dsraven]

just google the brand of prop valve you have and check the images. usually they pics of how the lines connect, just to be sure you have front to front and rear to rear. after that is good to go I think you can simply take the plug out, ensure the threads are what you need, and connect the other line.
otherwise, ensure it is plumbed correctly, install a T close to the prop valve

[Rickysnickers]

No questioning your reasoning as why you want two lines, I'm curious as to why you would want to double your work.

[leegreen]

With a T in the line you have 7 threaded connections / potential leak points. With two lines you only have 4. That is one reason. Potentially easier to bleed is another.

But those connections don't usually leak, I have never seen a system I could not bleed to my satisfaction and by using a T I only had to struggle to make a strain relief coil that did not look like a dog's breakfast for one line.

The Proportioning valve I used also had a plugged port and the instructions said you could use it. Not knowing what valve OP has and with all the offshore stuff sold cheap these days, I suggest finding out for sure there is a check valve on both ports before I hooked disks up using both.

[dsraven]

popeye, are you runnig frame mounted or firewall mounted system? some different valving may be required between the two types due to height of the master cyl in comparison to the calipers and wheel cylinders.

[popeyestruck]

Originally Posted by dsraven

popeye, are you runnig frame mounted or firewall mounted system? some different valving may be required between the two types due to height of the master cyl in comparison to the calipers and wheel cylinders.

I am running frame mounted but it is stock height and above the calipers so I figured I'll be OK. I decided to also just use one line and a T to the front brakes

[leegreen]

It is the drums you have to worry about, masters designed for disk will have residual pressure valves for the disks. If the drum wheel cylinders will be higher than the master, they need a low pressure residual check valve added to prevent drain back.

If you are running stock height suspension you should be OK without.

[mick53]

I plan on using the second front brake line hole for a brake pressure gauge on the line lock.

[leegreen]

Get a quality gauge for that!
I'd be too paranoid of a gauge failure while driving to leave one installed

[dsraven]

Yeah, me too. No gauge for me except for possibly troubleshooting a problem. For me the brakes work or dont work. If they dont work and you cant gind the problem then the gauges come out. Not too often a gauge is needed from my perspective. It would be one more possible trouble spot. Also, you may wanna check local laws to see if it is legal to keep a gauge in the system other than for testing and repair.
Just my thoughts, it's your truck. Be safe though.

[dsraven]

Drum brakes master cylinders usually have a residual valve in the master cylinder outlet port. That can be an issue with rebuilt masters that originally were for drum/drum and are sold as disc/drum. Sometimes that valve doesnt get taken out of the disc section of the rebuilt master. Drum brakes need to keep a residual pressure in the wheel cylinders to keep the rubber cups pressed against the cylinder bores so they dont leak. Calipers dont need that residual valve unless the master is lower or at the same height as the calipers, where there could be a problem with calipers draining fluid back into the master.
Summit has a little blurb written about that scenario as well as a few other brake suppliers. Worth a read if you dont understand how it all works or if you end up with problems.

[leegreen]

I did not find that Summit write up. Link?

I did find this Wilwood document about when to use the valves they sell
https://www.wilwood.com/PDF/DataSheets/new_rpv.pdf
A residual pressure valve is used when a master cylinder is mounted equal to or below the horizontal plane of the calipers or drum brake wheel cylinders. This valve prevents fluid flow-back to the master cylinder reservoir which can cause excessive brake travel or “pumping” of the pedal to engage brakes.

when a wheel cylinder is higher than master flow back can happen as air leaks past the seal, pulled by the weight of the fluid in the line. Often there is a cone washer and spring between the wheel cylinder cups to help keep the seal lip pushed out. Eventually the cups wear and leak, if the master is higher they leak fluid out until master is empty. If the master is lower they leak air into the system and you lose brakes.
A properly setup and adjusted drum brake of an firewall mounted master should not need residual pressure valve to reduce pedal travel. If a residual pressure valve is fitted you want to make sure the shoe return springs can still overcome it and push the pistons back into the cylinders. Drum brakes are not designed for continuous friction surface contact.

Caliper piston seals shape tends to pull the piston back when pressure is released and since the caliper pistons have a large displacement a little movement shows up as increased pedal travel, so residual check valves are usually built into factory disc masters, but often left out of cheap aftermarket parts. Disk brakes are designed for continuous light friction surface contact. Disk calipers typically lock up with corrosion before they leak, unless someone drives the piston back into a corrosion pitted cylinder to put new pads on.

I did brakes for a living back in the 80s when most things were still disk/drum and there was lots of drum/drum still on the road. The Internet collective mind does not understand drum brakes that well. But don't listen to me, do your own research and make your build safe.

[mick53]

Originally Posted by leegreen

Get a quality gauge for that!
I'd be too paranoid of a gauge failure while driving to leave one installed

The ones I'm looking at are electronic with a sending unit that screws in where the line goes into the master. You can put them in a tee but it seems nicer to just use the other outlet. It's as safe as a plug.

[leegreen]

I agree with everything dsraven said except a nuance of adjusting the brakes, that might just be wording.

" then I adjust the park brake so that end of the shoes are also adjusted correctly,"

The parking brake mechanism used by GM for rear drive axles fitted with drum brakes from mid 60s to present should not lift either shoe off the anchor when it is not pulled on, if it does it is over tightened or there is something wrong with shoe assembly.
If you get a better brake pedal with the parking brake on or by tightening the cables the brakes are not properly adjusted.
If the parking brake pulls all the way AND the brakes are properly adjusted then you need to tighten parking brake cables.

for GM drums, the parking brake itself should not need adjustment for the life of the brakes - if the brakes are adjusting properly.
The parking brake does not normally need to be adjusted to do a rear brake job either.

Most of the time when people say they need to adjust their parking brake the real problem is the rear brakes are not self adjusting themselves and usually by the time the parking brake is not working the shoes are worn out at the top ends and need to be replaced. The pedal is probably also low, but people will put up with that 'the brakes work fine'.

[dsraven]

hey, sorry man. I got going and didn't realize that was a small book.

[Phungki]

Originally Posted by popeyestruck

Running the brake lines on my truck (disc/drum) the proportioning valve has one front port plugged but I plan on running both front lines separate. Is that going to be a problem?

I ran 2 lines in the front. No issues with it. Used a 25’, ran 2 front lines and one to the back. Had a couple feet left over. I didn’t consider it work. Supposed to be fun right?
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