The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 47-55.1 Please critique my brake line plumbing......

dsraven · 11-13-2018, 12:41 PM

I admire your nice clean work area and tidy build with attention to detail. one thing I would mention, and I assume it is just not completed yet, is the fuel line support above the rear axle. it may be chaffing on the frame there over time without some sort of clamp to hold it tight.

by "good pedal" what do you mean, exactly.

-pedal has a lot of movement/travel before any resistance is felt
-pedal slowly goes to the floor with a light pressure applied
-pedal movement seems normal to feel some resistance, like the master cylinder is being pushed, but then still goes to the floor with little or no brake application and no real change in pedal effort. drums and rotors can still be rotated by hand by a helper while brakes are applied
-pedal feels spongy
-pedal doesn't get hard on the first application but will get better with a second or third "pump" of the pedal

not sure if the pics are the most recent, showing everything connected, but I don't see any park brake cables. without them the rear brakes will take considerably more fluid to push the wheel cylinders out far enough to take up the slack where the park brake mechanisms hold the brake shoes away from their anchor posts. could this be part of the issue?

things to check, assuming the lines are all in place correctly on the prop valve:

-check to ensure the master cylinder is for your application, disc front drum rear I assume. if the master was originally for a drum/drum set up it may have residual valves in both ports. if it was originally for a disc/drum set up it may have a residual valve in the rear brake port. if disc/disc there should be no residual valves in the master cyl outlet ports. these res valves would hold up to 10 lbs in the lines of the drum brake applications and may mess up a disc/drum set up, especially with the master mounted low on the frame. a paper clip sized wire can be used, inserted into the port where the brake lines connect to the master cyl, to see if a residual valve is installed in the master cyl. if there is one, a spring pressure will be felt on the wire when pushed into the port. just don't push the wire in too far. a paper clip works well because it is not sharp on the end like a cut off piece of tie wire would be

-check the brake pedal pivots and linkage points for any slack that may be gobbling up pedal travel. also ensure there is a pedal return spring of some sort to bring the pedal all the way back up. sometimes this step gets lost when there is no cab in place and guys are mocking up. with the pedal at the top of it's travel there should be some play at the booster/master cylinder input end of the linkage. I assume you have the pedal and master cylinder attached to the frame but that would also be some good info for us to know. frame mounted boosters may need a different residual valve set up

-check the movement and adjustment at the master cylinder to booster, especially if the master and the booster were not a matched pair. sometimes the push rod on the booster is not long enough or is out of adjustment so pedal travel is used up before the master cyl piston is actually contacted or the push rod is too long/out of adjustment so the master cylinder doesn't get to return fully and so the system becomes hard/impossible to bleed correctly. below is a link explaining that in detail and shows a handy little tool for the job. I think a lot of the frame mounted boosters are a copy of the system he is demonstrating the adjustment on. a quick check of this canbe done by having some one step on the pedal while you look into the reservoir. when the pedal is initially activated a small fountain of fluid should be seen in the reservoir. this is because the piston sits behind the fluid holes in the bore and then as the piston is pushed down the bore some fluid is displaced and comes back up the holes. this is normal. it allows fluid to be "topped up" in the bore of the master cylinder as the brakes wear and require a bit more fluid in the wheel cylinders or calipers plus it allows excess fluid to return to the reservoir when the brakes heat up and the fluid expands. a booster with a push rod that is too long or a pedal/linkage system that doesn't allow the pushrod to return fully will not allow the piston to "uncover" these holes and can cause lots of issues

https://www.youtube.com/watch?v=qc6MgNNMQts

-check to ensure the drum brakes are assembled and adjusted correctly. below is a quick link to POL's diagram. it is important to have the park brake set up as well, after the basic drum brake adjustment, because that is what "adjusts" the wheel cylinder end of the shoes out to fit the drum and allows the shoes to center themselves at the anchor end of the shoe. there should be a flat bar that fits between the shoes and it has a stepped slot on one end that can sometimes give trouble if it is tight fit between the bar and the shoe/park brake actuator lever. also, if you are using a second hand set up, check the backing plates for wear in the area where the shoes contact the backing plate. I have seen grooves worn there that cause the shoes to "hang up" and not center or return correctly because the shoe drops into the groove and can't be returned by the shoe return spring tension. this can make it harder to adjust the brakes. better to replace the backing plates now than later
to recap, adjust the park brake to have lots of slack, then adjust the star wheel adjusters, then adjust the park brake

https://www.performanceonline.com/19...ET-OF-4-18537/

What works for me is to install a couple of nuts/washers to hold the drums up tight on the axle flanges. this eliminates a drum being a little off and causing some drag that wouldn't normally be there. then loosen off the park brake to ensure there is no drag from that end of the brake shoe. then adjust the shoes up right tight with the star wheels. this will center the shoes against the drums. then back the star wheels off until the drums can be turned. you need a long skinny tool to hold the star wheel "ratchet" mechanism away from the wheel so it can be turned backwards to slack the brakes off some. do the same number of "clicks" on the star adjuster wheel for each side. this is adjusting the bottom end of the brake shoes to fit the drum. then apply the brakes a few times and go back to check again to ensure nothing is dragging. then adjust the park brake. this will adjust the anchor/wheel cylinder end of the shoes to fit the drum. a lot of guys don't do the park brake adjustment or simply leave the park brakes disconnected because they "never use it anyway". these are usually the guys that have a low pedal because the wheel cylinder pistons are returned fully into the cylinders and require a bunch more fluid to be displaced in order to bring that end of the brake shoes out against the drums.

-bleed the brakes, start with the wheel that has the longest run from the master cylinder, bleed that one first, then go to the next longest run and so on. usually the right rear first, then left rear then right front and finally left front. when you bleed the brakes, if using a one man bleeder or a vacuum system, ensure you don't open the bleeder screw too far because it can draw air in from around the threads of the bleeder screw and fool you into thinking the system is still full of air bubbles. the same goes for the rubber fitting or tubing used to fit over the bleeder screw. just make sure to have the best fit you can so you are not drawing air in around the connection. if bleeding the system using the buddy method, where someone steps on the pedal while a buddy opens and closes the bleeder screw, just ensure the pedal man holds the pedal all the way down and keeps it there until the bleeder screw is tightened back up. make sure to check the master cylinder fluid level often as well.

-try the pedal again to see if you have a good pedal now. don't rule out the possibility that a new part may be defective

here is a link to show a backyard cutaway of how a brake booster works

https://www.youtube.com/watch?v=I4Ka4__ws1E

here is a link to show the master cylinder residual valve in the port, also an explanation of how it works

http://www.underhoodservice.com/diag...der-diagnosis/

sorry for the long winded response, hopefully you get it sorted out.
post up some more pics, nice looking build you have there.

11-13-2018, 12:41 PM	#17
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 7,864	Re: Please critique my brake line plumbing...... I admire your nice clean work area and tidy build with attention to detail. one thing I would mention, and I assume it is just not completed yet, is the fuel line support above the rear axle. it may be chaffing on the frame there over time without some sort of clamp to hold it tight. by "good pedal" what do you mean, exactly. -pedal has a lot of movement/travel before any resistance is felt -pedal slowly goes to the floor with a light pressure applied -pedal movement seems normal to feel some resistance, like the master cylinder is being pushed, but then still goes to the floor with little or no brake application and no real change in pedal effort. drums and rotors can still be rotated by hand by a helper while brakes are applied -pedal feels spongy -pedal doesn't get hard on the first application but will get better with a second or third "pump" of the pedal not sure if the pics are the most recent, showing everything connected, but I don't see any park brake cables. without them the rear brakes will take considerably more fluid to push the wheel cylinders out far enough to take up the slack where the park brake mechanisms hold the brake shoes away from their anchor posts. could this be part of the issue? things to check, assuming the lines are all in place correctly on the prop valve: -check to ensure the master cylinder is for your application, disc front drum rear I assume. if the master was originally for a drum/drum set up it may have residual valves in both ports. if it was originally for a disc/drum set up it may have a residual valve in the rear brake port. if disc/disc there should be no residual valves in the master cyl outlet ports. these res valves would hold up to 10 lbs in the lines of the drum brake applications and may mess up a disc/drum set up, especially with the master mounted low on the frame. a paper clip sized wire can be used, inserted into the port where the brake lines connect to the master cyl, to see if a residual valve is installed in the master cyl. if there is one, a spring pressure will be felt on the wire when pushed into the port. just don't push the wire in too far. a paper clip works well because it is not sharp on the end like a cut off piece of tie wire would be -check the brake pedal pivots and linkage points for any slack that may be gobbling up pedal travel. also ensure there is a pedal return spring of some sort to bring the pedal all the way back up. sometimes this step gets lost when there is no cab in place and guys are mocking up. with the pedal at the top of it's travel there should be some play at the booster/master cylinder input end of the linkage. I assume you have the pedal and master cylinder attached to the frame but that would also be some good info for us to know. frame mounted boosters may need a different residual valve set up -check the movement and adjustment at the master cylinder to booster, especially if the master and the booster were not a matched pair. sometimes the push rod on the booster is not long enough or is out of adjustment so pedal travel is used up before the master cyl piston is actually contacted or the push rod is too long/out of adjustment so the master cylinder doesn't get to return fully and so the system becomes hard/impossible to bleed correctly. below is a link explaining that in detail and shows a handy little tool for the job. I think a lot of the frame mounted boosters are a copy of the system he is demonstrating the adjustment on. a quick check of this canbe done by having some one step on the pedal while you look into the reservoir. when the pedal is initially activated a small fountain of fluid should be seen in the reservoir. this is because the piston sits behind the fluid holes in the bore and then as the piston is pushed down the bore some fluid is displaced and comes back up the holes. this is normal. it allows fluid to be "topped up" in the bore of the master cylinder as the brakes wear and require a bit more fluid in the wheel cylinders or calipers plus it allows excess fluid to return to the reservoir when the brakes heat up and the fluid expands. a booster with a push rod that is too long or a pedal/linkage system that doesn't allow the pushrod to return fully will not allow the piston to "uncover" these holes and can cause lots of issues https://www.youtube.com/watch?v=qc6MgNNMQts -check to ensure the drum brakes are assembled and adjusted correctly. below is a quick link to POL's diagram. it is important to have the park brake set up as well, after the basic drum brake adjustment, because that is what "adjusts" the wheel cylinder end of the shoes out to fit the drum and allows the shoes to center themselves at the anchor end of the shoe. there should be a flat bar that fits between the shoes and it has a stepped slot on one end that can sometimes give trouble if it is tight fit between the bar and the shoe/park brake actuator lever. also, if you are using a second hand set up, check the backing plates for wear in the area where the shoes contact the backing plate. I have seen grooves worn there that cause the shoes to "hang up" and not center or return correctly because the shoe drops into the groove and can't be returned by the shoe return spring tension. this can make it harder to adjust the brakes. better to replace the backing plates now than later to recap, adjust the park brake to have lots of slack, then adjust the star wheel adjusters, then adjust the park brake https://www.performanceonline.com/19...ET-OF-4-18537/ What works for me is to install a couple of nuts/washers to hold the drums up tight on the axle flanges. this eliminates a drum being a little off and causing some drag that wouldn't normally be there. then loosen off the park brake to ensure there is no drag from that end of the brake shoe. then adjust the shoes up right tight with the star wheels. this will center the shoes against the drums. then back the star wheels off until the drums can be turned. you need a long skinny tool to hold the star wheel "ratchet" mechanism away from the wheel so it can be turned backwards to slack the brakes off some. do the same number of "clicks" on the star adjuster wheel for each side. this is adjusting the bottom end of the brake shoes to fit the drum. then apply the brakes a few times and go back to check again to ensure nothing is dragging. then adjust the park brake. this will adjust the anchor/wheel cylinder end of the shoes to fit the drum. a lot of guys don't do the park brake adjustment or simply leave the park brakes disconnected because they "never use it anyway". these are usually the guys that have a low pedal because the wheel cylinder pistons are returned fully into the cylinders and require a bunch more fluid to be displaced in order to bring that end of the brake shoes out against the drums. -bleed the brakes, start with the wheel that has the longest run from the master cylinder, bleed that one first, then go to the next longest run and so on. usually the right rear first, then left rear then right front and finally left front. when you bleed the brakes, if using a one man bleeder or a vacuum system, ensure you don't open the bleeder screw too far because it can draw air in from around the threads of the bleeder screw and fool you into thinking the system is still full of air bubbles. the same goes for the rubber fitting or tubing used to fit over the bleeder screw. just make sure to have the best fit you can so you are not drawing air in around the connection. if bleeding the system using the buddy method, where someone steps on the pedal while a buddy opens and closes the bleeder screw, just ensure the pedal man holds the pedal all the way down and keeps it there until the bleeder screw is tightened back up. make sure to check the master cylinder fluid level often as well. -try the pedal again to see if you have a good pedal now. don't rule out the possibility that a new part may be defective here is a link to show a backyard cutaway of how a brake booster works https://www.youtube.com/watch?v=I4Ka4__ws1E here is a link to show the master cylinder residual valve in the port, also an explanation of how it works http://www.underhoodservice.com/diag...der-diagnosis/ sorry for the long winded response, hopefully you get it sorted out. post up some more pics, nice looking build you have there.