Brake problems

[hogfarm]

I have been working on my 58 Fleet
I am getting close to taking it to the glass shop,but ran into a problem,I cant bleed the brakes.My master cylinder is under the cab.I put the vacuum pump on the lines and have semi clear fluid at all 4 wheels,but when I try to pump pedal I get nothing,no pressure.I made the brake push rod measuring from power brake booster to the pedal,I'm thinking the rod is not long enough.How much longer should the rod be?am I on right track?

[nvrdone]

do you have a booster or just the m/c? either way the push rod should go into the booster or m/c about 1" and seat on the diaphragm or m/c piston. i'd disconnect the push rod from the pedal & push it all the way in until it wont go any further. then you can see if the push rod is too short. good luck.

[mr48chev]

If you reach up and pull on the pedal arm how far does the arm that pushes the push rod move before you feel it push against the piston or push the piston against the fluid?

[hogfarm]

Originally Posted by mr48chev

If you reach up and pull on the pedal arm how far does the arm that pushes the push rod move before you feel it push against the piston or push the piston against the fluid?

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[hogfarm]

Originally Posted by hogfarm

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I can move the peddle about an inch. Then it tight against the booster no fluid moves
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[mr48chev]

An inch at the top isn't bad, an inch at the bottom would be a lot.

[nvrdone]

also, if you have drum brakes & they are not adjusted properly you can have excess pedal travel.

[hogfarm]

4 wheel disc

[mr48chev]

You may have to fab up a pressure bleeder and pressure bleed them.

Something on this concept but you would have to make a cap that fit your master cylinder. http://faculty.ccp.edu/faculty/dreed...eder/index.htm

A google search for DIY pressure brake bleeder brings up a bunch of ideas. Some you have to view with a grain of salt and some are pretty good but the idea is the same. Small pump up garden sprayer, hose and a cap set up to connect to the master cylinder and seal on it. One shows using a piece of pvc hose and a catch bottle to catch the fluid when you bleed the caliper but I figure you would do that anyhow.

[Black_Sheep]

do you have residual pressure valves in the system?

[hogfarm]

I'm going to try and put longer push rod in,bought a left hand tap and some 9/16" hex stock.or maybe my pedal need more throw

[gbooth]

I installed a under floor brake system and where the master cyl bolts to the booster there was a small 1 inch long rod that went between pedel and master cyl you may or may need that Greg

[hogfarm]

Originally Posted by gbooth

I installed a under floor brake system and where the master cyl bolts to the booster there was a small 1 inch long rod that went between pedel and master cyl you may or may need that Greg

Yes,I have though about that little rod,but I do hope it is in there.that would be my next step,it's just hard to take the booster out,truck is low and I'm old

[dsraven]

1-there should be free play at the top of the pedal so the master cyl has room to return fully. check this by removing the master cover, have a buddy lightly step on the pedal while watching the fluid in the res. when the pedal is first pushed there should be a little fluid pushed back into the res creating a small fountain. that happens because the piston, at rest, is behind the little holes in the cyl that allow fluid to enter the bore or return to the res. there should be a little fountain of fluid, then as the pedal is pushed a little further the fountain goes away and fluid is moved down the brake lines. if no fountain appears then maybe the adjustment on the small pushrod from the booster to the master is made too long, so the little holes don't get uncovered all the way, or else the pedal pushrod is too long and is keeping the piston from returning all the way.
2-the pedal should push the master cyl all the way to the end of it's travel. check this by lossening a bleeder, front and rear, so the pedal will move easily and fully, then remove the pedal pushrod and use another method to push the master all the way to the end of it's travel. compare that to how much the pedal would move the master if it was pushed all the way to the floor
3-check to ensure you have a master that is made for disc front and rear. some with drum rear would have a residual valve built into the line connection in the master.


it kinda sounds like your master cyl is not fully retracting. if you are getting no fluid at the bleeder unless you vacuum bleed. vacuum bleeding can "pull" fluid past the cups on the piston so that part would make sense sorta, if you get fluid when vac bleeding but nothing really if pushing the pedal. the piston is not coming all the way back into the master to allow fresh fluid to enter the bore so all you have to work with is what is already in front of the piston when you start.this will lead to issues as the brakes heat up from use because the fluid expands and applies the brakes for you without you pressing on the pedal. try loosening the master mounting nuts a bit so there is some play there and see if that helps.if is does then that could be the problem. does the pedal feel firm, sloppy, like it is just moving but not making pressure? does it get firm before bottoming out? some systems that get modified don't have a full travel for the master cyl because the attachment point for the pushrod is closer to the pivot point for the pedal arm. ensure you have a full stroke for the master-step 2.

[hogfarm]

Originally Posted by dsraven

1-there should be free play at the top of the pedal so the master cyl has room to return fully. check this by removing the master cover, have a buddy lightly step on the pedal while watching the fluid in the res. when the pedal is first pushed there should be a little fluid pushed back into the res creating a small fountain. that happens because the piston, at rest, is behind the little holes in the cyl that allow fluid to enter the bore or return to the res. there should be a little fountain of fluid, then as the pedal is pushed a little further the fountain goes away and fluid is moved down the brake lines. if no fountain appears then maybe the adjustment on the small pushrod from the booster to the master is made too long, so the little holes don't get uncovered all the way, or else the pedal pushrod is too long and is keeping the piston from returning all the way.
2-the pedal should push the master cyl all the way to the end of it's travel. check this by lossening a bleeder, front and rear, so the pedal will move easily and fully, then remove the pedal pushrod and use another method to push the master all the way to the end of it's travel. compare that to how much the pedal would move the master if it was pushed all the way to the floor
3-check to ensure you have a master that is made for disc front and rear. some with drum rear would have a residual valve built into the line connection in the master.


it kinda sounds like your master cyl is not fully retracting. if you are getting no fluid at the bleeder unless you vacuum bleed. vacuum bleeding can "pull" fluid past the cups on the piston so that part would make sense sorta, if you get fluid when vac bleeding but nothing really if pushing the pedal. the piston is not coming all the way back into the master to allow fresh fluid to enter the bore so all you have to work with is what is already in front of the piston when you start.this will lead to issues as the brakes heat up from use because the fluid expands and applies the brakes for you without you pressing on the pedal. try loosening the master mounting nuts a bit so there is some play there and see if that helps.if is does then that could be the problem. does the pedal feel firm, sloppy, like it is just moving but not making pressure? does it get firm before bottoming out? some systems that get modified don't have a full travel for the master cyl because the attachment point for the pushrod is closer to the pivot point for the pedal arm. ensure you have a full stroke for the master-step 2.

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[hogfarm]

As you may be able to see the bore in the master cylinder is to big for the push rod on the booster. Am I missing a part? Wrong booster? Can I machine a bushing to put in M/C ?
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[Steve-W]

Originally Posted by hogfarm

As you may be able to see the bore in the master cylinder is to big for the push rod on the booster. Am I missing a part? Wrong booster? Can I machine a bushing to put in M/C ?
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I had the same problem, no pressure..was bleeding brakes like crazy, adjusting rear drums over and over again..nothing. until I lengthened the push rod with 1 inch. Now it brakes like a other pucker!

[mr48chev]

I'd say miss matched. You could either do as Steve-W said he did and lengthen the pushrod to fit. A bit of diligent measuring needed there to get the right length without being too long.

Looking at the photo of the booster it looks like the push rod has a hex end on it. Is it by chance adjustable? or is that just part of the design to center it in the mc.

Still I'd be figuring out what the difference is between the two and what course of action to take.

[hogfarm]

I'm pretty sure these parts don't match. Sad part is I bought kit from same vendor. So I made the little sleeve. I'm pushing fluid now. Still need to make the adjustable push rod
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[dsraven]

if fabbing up a spacer or filler to fit into the master's bore to make up the difference I would measure the required length then have one made from solid stock to fit the bore snug. bullet nosed on the inner end and with a depression to center the booster push rod on the outboard end. not a hollow affair that may have a chance of the booster push rod forcing itself through the end and into the hollow area, or wearing the end of the push rod to fit into the hollow bore.
just me though, overthinking things.it is a safety item though.
does the booster push rod adjust at all?
check the stroke on the master while it is accessible and then make sure your booster stroke will go at least that far when the pedal is pushed to the floor. this will ensure a full stroke with a full pedal travel. I know, disc brakes need less fluid for an application but if you have ever had a brake problem, like a blown brake flex line that uses a lot of fluid per stroke until the master is empty on that circuit, you will know what I mean. these things don't usually happen in the driveway.
good luck, keep the pics coming with what your fix looks like. great job troubleshooting.

[Richard2112]

Probably one of the most detailed articles I have seen posted on the brake system. http://www.pirate4x4.com/tech/billavista/Brakes/

[hogfarm]

Originally Posted by dsraven

if fabbing up a spacer or filler to fit into the master's bore to make up the difference I would measure the required length then have one made from solid stock to fit the bore snug. bullet nosed on the inner end and with a depression to center the booster push rod on the outboard end. not a hollow affair that may have a chance of the booster push rod forcing itself through the end and into the hollow area, or wearing the end of the push rod to fit into the hollow bore.
just me though, overthinking things.it is a safety item though.
does the booster push rod adjust at all?
check the stroke on the master while it is accessible and then make sure your booster stroke will go at least that far when the pedal is pushed to the floor. this will ensure a full stroke with a full pedal travel. I know, disc brakes need less fluid for an application but if you have ever had a brake problem, like a blown brake flex line that uses a lot of fluid per stroke until the master is empty on that circuit, you will know what I mean. these things don't usually happen in the driveway.
good luck, keep the pics coming with what your fix looks like. great job troubleshooting.

Thanks Dsraven
yes it took a lot of measurement to get this thing right,the spacer is not hollow the hole in the end is .300" deep and I used a ball mill in my lathe to cut the bottom,hope this takes care of the problem.I need to make an adjustable push rod,I ordered a 3/8"-24 left hand tap,an left hand heim joint and a piece of 9/16" hex stock,amazon prime is taking a long time for the hex stock to get here

[Black_Sheep]

Originally Posted by hogfarm

I'm pretty sure these parts don't match. Sad part is I bought kit from same vendor. So I made the little sleeve. I'm pushing fluid now. Still need to make the adjustable push rod
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I did the same thing. There are 2 different pushrod depth GM master cylinders, I had the short rod in the booster and the deep mc. I measured carefully and came up with a 1.10 OAL for the filler plug, then it worked like a charm.