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.

[dsraven]

popeye, sorry, I don't mean to hi-jack the thread but since there was a question, and there are usually lurkers with questions they don't ask, here are a few links that explain a bit about the differences of drum and disc master cylinders, different valves, one on bleeding through the combo/prop valve and some info on drum brake adjustment etc. hope they help somebody.
understand that there is a difference between the firewall master cylinder and the frame mount master cylinder requirements. this is because of the difference in height and the related pressure difference in the lines due to the weight of the column of fluid. the "through the floor" pedal assemblies also weigh more than the suspended pedals do in so they require a proper pedal return spring and fairly hard bump stop so that the pedal returns easily and quickly and also stops at the same place each time it returns. otherwise the pushrod adjustment at the master cylinder is never the same twice and this can cause problems with fluid returning to the master cylinder reservoir each time the pedal is released. this part is easily checked by looking down into the master cylinder reservoir while someone steps on the brake pedal. if the pushrod is adjusted properly you will see a little ripple or fountain appear in the fluid, then it will stop as the pedal is depressed further. it is because of the compensating port hole that is forward of the cup on the master cylinder piston. this allows the return of excess fluid to come back into the reservoir but also causes the fountain through the port as a slight pressure builds inside the bore as the piston moves forward. below is a link with a pic.

http://4mechtech.blogspot.com/2014/1...-cylinder.html


I have seen some where the driver/owner complains of the brakes getting tight once they warm up. it was because the fluid couldn't get back to the reservoir to release pressure in the lines and when it got hot the fluid expanded enough to make the brakes drag.

some will say that the rear drum brakes need the pressure to keep the shoes pushed against the drums so the pedal doesn't need to be pumped up. well, if you have done drum brakes before you would probably understand that the brake shoe return springs far outweigh the 10 psi against the cups in the wheel cylinders, thats why we have those fancy brake spring tools. the pressure is there to keep the cups pressed against the bores in the wheel cylinders so contaminants can't get in the system. if you need to pump up the brakes it is usually because they need to be adjusted so they take more fluid to get the shoes out against the drums. the adjustment is set up so that the star wheel adjusts that end of the shoes opposite the wheel cylinder, the other end of the shoes butt up against the anchor by the wheel cylinder BUT that end of the shoes also has the park brake adjuster incorporated into the system, with a cross bar that connects the shoes so that when the park brake is applied both shoes move out to the drums. if you don't have the park brake set up properly then it still takes extra fluid to push the shoes out against the drums even though the star wheels have been adjusted. when I adjust drum brakes I always release the park brake (with wheels blocked of course-safety first) then adjust the park brake to be loose. this is so the shoes will return all the way back so they are against the anchor and the wheel cylinder pistons are fully retracted by the brake shoe return springs. then I adjust the star wheel so that end of the shoes are adjusted correctly and step on the brakes a few times to make sure things are all centered up. sometimes I will adjust the star wheel until the brakes lock up, then back the star wheel off a number of turn to allow the wheels to rotate. depending on how course the star wheel is that can be about 6 or 8 "clicks" on the star.then spin the wheel to ensure it isn't dragging. then I adjust the park brake so that end of the shoes are also adjusted correctly, stepping on the brake to ensure the wheel cylinders follow the shoes out. when doing the adjustment both star wheels should be about the same number of "clicks" backed off from tight. if not then start looking to see why. it could be a different star wheel has been installed that has a courser or finer "star", so less or more clicks to achieve a full turn of the star wheel.
one thing to watch for on older drum brakes, if the backing plates are also old, is that the contact area where the shoes rub the backing plate can get a groove worn in it over time and the brake shoe will fall into that groove which then doesn't allow the shoes to centre properly. this is usually a problem when the old shoes have been replaced and the new shoes need to sit a little differently on the backing plate. there is also a brake lube that should be applied sparingly to that contact area to help prevent the wear of the backing plate.

here is the summit residual valve blurb

https://help.summitracing.com/app/an...idual-valve%3F

here is a summit link that shows a cutaway of the inline residual valve

https://help.summitracing.com/app/an.../546/related/1

here is a link to show a cutaway of the master cylinder res valve

http://4mechtech.blogspot.com/2014/1...re-valves.html

https://www.onallcylinders.com/2013/...%20all%20times.

here is a summit blurb on combination valves that also includes a cutaway pic. the combo valve will sense pressure differences between the front and rear so they will need to be kept centered when bleeding. a special tool is made for that. some guys have had trouble with no front or rear brakes after a bleed job because the valve wasn't kept centered so the one circuit was closed like it would be if you blew a brake hose or whatever.

https://help.summitracing.com/app/an...5144/related/1

here is a summit blurb explaining the metering valve with a diagram of what it looks like from a cutaway view. this valve can also be incorporated into a combination valve, hence the name.

https://help.summitracing.com/app/an...5159/related/1

here is a summit blurb on centering a combo/proportioning valve with the special tool. the tool goes in where the brake failure switch would normally thread in

https://help.summitracing.com/app/an...5159/related/1

[dsraven]

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

[dsraven]

ok, one more item.
caliper piston seals are not circular in a cross section view. they are square shaped and grip the piston until the piston moves far enough so the seal has deformed to it's max and then the piston will slip on the seal as it travels further out. this happens on a brand new caliper or when the piston has been pushed back into the caliper as in a new brake job. when the brakes are applied the piston is moved outward and this causes the seal to roll because it is gripping the piston. when the brakes are released the seal will pull the piston back into the bore slightly as the seal rolls itself back to being the square shape. this allows for a small gap between the brake lining and the rotor. if you are doing a brake job and find the piston side of the caliper has linings that are worn considerably more that the other side then that is a reason to look closely at the caliper to ensure the piston is not starting to get siezed up in the caliper bore. if the opposite side lining is worn more than the piston side then that is an indicator that the caliper is not sliding on it's mounts well. if the lining is worn in a wedge shape it usually means the caliper mounting slide mechansim is tighter or siezed up on one end, the smaller end of the wedge shape.

ok. done
shouldda started a differwent thread there. again, sorry popeye.

[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'.

[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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