Here is the setup: I use a Mustang master cylinder. I can't remember all the details but it is the second one I've installed in the car. The first one wore out the seal but it had never fully activated the rear brakes. I replaced the master cylinder with another and still no workee. I have 11,000 miles on the car and have never been able to lock the rear wheels on gravel. with the drums off you can see the shoes moving freely when depressing the brake. With the wheels off the ground and assembled you can not rotate the rear wheels by hand with brake applied but when driving it has virtually no effect. Last season I replaced the rear wheel cylinders, brake lines and hose. I replaced the brake shoes and am now stumped. I tried switching the lines front to back - no change. I do not have a proportioning valve as I obviously have no need to reduce pressure to the rear. Nor is there a residual valve on the rear line. I did have one but removed it. If I have someone push the pedal down I get a good amount of fluid out of the rear lines. they are clear and not clogged. I am hoping someone reading this can help clear up the problem. I don't want to drive another summer with no rear brakes. I have no problem stopping. I even tow a utilty trailer from time to time (you gotta see the looks on the guys faces at the garbage dump when I back her in. Please don't waste time telling me I'm wacked for towing a trailer. If you've seen my videos on Youtube then you have seen me racing at the track too. - I am already aware of my reckless ways (heh). My guess is that I will be advised to replace the master again. If so, should it be from a manual brake car or power? I think I have always used manual but can't remember. Thanks guys - The sun is going to be coming out in Seattle in few more months! Spooky
Rear brakes
- Thread starter spooky
- Start date
The rear drum is 68 F100 11" shoes. I was careful to install them in the proper configuration (front to back) when I replaced them. rims are 15 inch with 11 inch wide Hoosier racing tires. These are a late addition - I had similar width N50 tires before with normal tread. The bore of the wheel cylinders is the smaller size (1 X 1 1/8"). The front brakes are 14 inch 77 Monza calipers and 77 Aspen rotors adapted to ford spindles. I adjusted the rear brakes the usual way by tightening them til I can hear them drag. I have had several mechanics go over the car visually and that led to me switching the the brake lines to the rear calipers to the fitting located at the piston end of the master cylinder. I had them backwards. This actually made a small improvement in the braking on the street however I still cannot lock the rear wheels up on gravel. So far I have complied with all the "experts" advice to no avail. I discovered my mistake in connecting them in the wrong configuration because I was using a diagram from a web page as a reference. Plus I forgot to consider that in a T-bucket the master cylinder is usually installed 180 degrees from a normal car. Later I compared it to a Speedway diagram in my catalog and discovered the discrepancy (nobody spotted this). I checked other photos etc and know that it is now connected correctly. How am I doing so far?
Hotrod46
Member
Sounds like you have covered a lot of bases. With 11" diameter drums. you should have plenty of brake.
I checked a couple of online parts houses and both listed a 68 F100 as having 7/8" bore rear wheel cylinders. 1 1/8" in the front.
I know you said 1-1 1/8, but you also mentioned they were the small size. I'm pretty sure that your MC has a 1" bore. If you have the 7/8" bore wheel cylinders, then you are loosing a lot of mechanical advantage.
Given the smaller front tire size and discs, the front brakes are simply overpowering the the rears. The front brakes are getting up to operating pressure before the rears do.
I think you should verify the bores of the rear WC's and if they are 7/8", then you should look for larger bore pieces. The front WC's on the same 68 F100 were listed as 1 1/8" bore. There are probably a lot of wheel cylinders that will interchange with yours that have larger bores.
Also, there is a valve available that goes in the front brake line that prevents the fronts from operating until about 100 PSI has built up in the system. This allows the drums on the rear to overcome the shoe return springs and actually get the shoes against the drums before the discs start operating. I have one on my car (even though I have drums front and rear), and I can actually feel the rears working before the fronts. The valve is called a "hold-off valve". Here's a link to the valve:
http://www.speedwaym...-Hold-Off-Valve,8904.html
One other thing. Some modern high end brake shoes are metallic linings. These will need a lot of heat and brake pressure to operate properly. That's not a problem on a modern vehicle with power brakes, but could be an issue with manual brakes. The cheaper grades of shoes are more often organic linings. These will have a lot more friction at lower pressure, but will wear out faster.
Hope some of this this helps.
Mike
I checked a couple of online parts houses and both listed a 68 F100 as having 7/8" bore rear wheel cylinders. 1 1/8" in the front.
I know you said 1-1 1/8, but you also mentioned they were the small size. I'm pretty sure that your MC has a 1" bore. If you have the 7/8" bore wheel cylinders, then you are loosing a lot of mechanical advantage.
Given the smaller front tire size and discs, the front brakes are simply overpowering the the rears. The front brakes are getting up to operating pressure before the rears do.
I think you should verify the bores of the rear WC's and if they are 7/8", then you should look for larger bore pieces. The front WC's on the same 68 F100 were listed as 1 1/8" bore. There are probably a lot of wheel cylinders that will interchange with yours that have larger bores.
Also, there is a valve available that goes in the front brake line that prevents the fronts from operating until about 100 PSI has built up in the system. This allows the drums on the rear to overcome the shoe return springs and actually get the shoes against the drums before the discs start operating. I have one on my car (even though I have drums front and rear), and I can actually feel the rears working before the fronts. The valve is called a "hold-off valve". Here's a link to the valve:
http://www.speedwaym...-Hold-Off-Valve,8904.html
One other thing. Some modern high end brake shoes are metallic linings. These will need a lot of heat and brake pressure to operate properly. That's not a problem on a modern vehicle with power brakes, but could be an issue with manual brakes. The cheaper grades of shoes are more often organic linings. These will have a lot more friction at lower pressure, but will wear out faster.
Hope some of this this helps.
Mike
Ma_n_Pa T
Member
Little more info,
Does your front brakes lock up?
What is the bore size of the Master?
Have the drums been turned?
About how much pressure are you applying to the pedal?
There is a Brake pedal Ratio Chart in the Tech section under brakes, figuer your ratio and let us know. If you are less then 6:1 ratio you must run a 7/8" or even a 3/4" piston master.
The master has a primary port (next to the plunger) and seconary port, which one do you have the rear brakes to?
Jerry
Does your front brakes lock up?
What is the bore size of the Master?
Have the drums been turned?
About how much pressure are you applying to the pedal?
There is a Brake pedal Ratio Chart in the Tech section under brakes, figuer your ratio and let us know. If you are less then 6:1 ratio you must run a 7/8" or even a 3/4" piston master.
The master has a primary port (next to the plunger) and seconary port, which one do you have the rear brakes to?
Jerry
I was having a problem with a SSB rear disc kit. To be able to actually see where you are on
pressure and what changes cylinder sizes can do, you need a pressure gauge. I bought one, I think for
about $50 from Summit Racing. A very good tool for solving problems and balancing your brakes. I think
you have gotten some very good advise, but you will love seeing the results of your changes with this set-up.
The gauge comes with adapters that fit in the bleeder vavle holes. You may improve the drum brakes by having the shoes re-arc ed. I do not know if this is the correct term, I forget more each day, but it shapes the shoes to increase the contact area by making the arc of the shoe lining match that of the drum.
Most people, just let the wearing of the lining conform with time.
good luck,
pressure and what changes cylinder sizes can do, you need a pressure gauge. I bought one, I think for
about $50 from Summit Racing. A very good tool for solving problems and balancing your brakes. I think
you have gotten some very good advise, but you will love seeing the results of your changes with this set-up.
The gauge comes with adapters that fit in the bleeder vavle holes. You may improve the drum brakes by having the shoes re-arc ed. I do not know if this is the correct term, I forget more each day, but it shapes the shoes to increase the contact area by making the arc of the shoe lining match that of the drum.
Most people, just let the wearing of the lining conform with time.
good luck,
I have, somewhat, the same issue. I am tearing up front solid disc rotors ... really tearing them up. I have 4 piston calibers and disc brakes on all four wheels. I have talked to Wilwood until I am blue in the face and get no where with them. At Good Guys I was talking to Scott's and they suggested a propotional valve, but in a reverse type installation. Usually the valve is placed in the rear line to keep the rear brakes from locking up first and making the car swap ends. The valve allows you to adjust the pressure going to the caliber pistons.
I am going to put the valve in the front line to make the rear brakes work harder (more) than the front. I have not done this as yet. I am currently tore down for body work and paint and address some other, minor, mechanical issues, but the valve is getting close to the top of my to do list.
The valve cost me $45 at Good Guys and if it works, I avoid a $700 change out from solid rotors to vented ones ... rotors, hubs, etc.
I am going to put the valve in the front line to make the rear brakes work harder (more) than the front. I have not done this as yet. I am currently tore down for body work and paint and address some other, minor, mechanical issues, but the valve is getting close to the top of my to do list.
The valve cost me $45 at Good Guys and if it works, I avoid a $700 change out from solid rotors to vented ones ... rotors, hubs, etc.
Thanks gang! In response to the many questions I say:
Rear wheel cylinder size - I actually can't recall if I bought the largest or the smallest diameter. I believe I was advised to use the larger size for more power. I guess I misspoke. I believe I did install the large diameter.
The brakes take a lot of force to rapidly stop the car and to "lock up" however not alarmingly so. I am hesitant to use a "hold-off valve" on the front lines as this will surely increase the pressure needed to aply the brakes. The pedal is about like any car without power assist.
I can't remember if I bought organic shoes. I will try to find the reciept.
I have not turned the drums myself but they came with the rearend housing I bought at a yard-sale and are not worn to any degree. They are in perfent shape with no visible wear or grooving. I roughed them up with sand paper. Even the original shoes were not worn. I replaced them anyway just in case.
On the master cylinder I now have the primary port connected to the rear brakes. I'm pretty sure it is 3/4 " bore.
After 11,000 miles I see virtually no wear on the front pads.
Thanks for jumping in so fast. There is a lot things I have to verify regarding bore sizes, etc. At the moment I am unable to dismantle the car.
The brake pedal ratio is 5 to 1. I have not been too concerned about this as the front and rear brake hydrolic pressure is initiated by the master cylinder - regardless of the force required to depress the pedal.
One more thing I might add is that when I replaced the master cylinder in an effert to get the rear brakes to function - I discovered that the seal to the rear brakes was destroyed. I figured then that a new master cylinder would fix the problem, but alas, it did not.
Rear wheel cylinder size - I actually can't recall if I bought the largest or the smallest diameter. I believe I was advised to use the larger size for more power. I guess I misspoke. I believe I did install the large diameter.
The brakes take a lot of force to rapidly stop the car and to "lock up" however not alarmingly so. I am hesitant to use a "hold-off valve" on the front lines as this will surely increase the pressure needed to aply the brakes. The pedal is about like any car without power assist.
I can't remember if I bought organic shoes. I will try to find the reciept.
I have not turned the drums myself but they came with the rearend housing I bought at a yard-sale and are not worn to any degree. They are in perfent shape with no visible wear or grooving. I roughed them up with sand paper. Even the original shoes were not worn. I replaced them anyway just in case.
On the master cylinder I now have the primary port connected to the rear brakes. I'm pretty sure it is 3/4 " bore.
After 11,000 miles I see virtually no wear on the front pads.
Thanks for jumping in so fast. There is a lot things I have to verify regarding bore sizes, etc. At the moment I am unable to dismantle the car.
The brake pedal ratio is 5 to 1. I have not been too concerned about this as the front and rear brake hydrolic pressure is initiated by the master cylinder - regardless of the force required to depress the pedal.
One more thing I might add is that when I replaced the master cylinder in an effert to get the rear brakes to function - I discovered that the seal to the rear brakes was destroyed. I figured then that a new master cylinder would fix the problem, but alas, it did not.
WEDRVIT
New Member
WEDRVIT
New Member
Your master is bottoming out on the rear wheel section and only applying the front calipers, due to the displaced fluid area in the rear is larger than the front. The pressure gauge will reveal the problem, but the cure is going to be tough. Remember 31" tall tires take more force from an 11" drum or rotor than a 26" tire. I'm running a 3/4 master with two Harley 4 piston calipers on 11" rotors up front and four 86 vette calipers on 11" rotors on the rear. A lot of trial and error went into this setup, but when you stand on the brakes the 18-31 Mickey radials know it's time to go to work, I also pull a cargo trailer for my show supplies total loaded weight approx. 2500. Due the math. for fluid displacement and you'll have the answer.
GOOD LUCK. Harley
GOOD LUCK. Harley
rooster57
Member
WEDRVIT
New Member
Wild Mango
Member
Harley is right on the money. This is a great forum for advice. Just one thing got missed, pedal ratio has everything to do with the hydraulic pressure especially in a non booster system. Most people agree 5:1 is a minimum for a non booster system.
putz
Member
You should deal with ABS on a daily basis it is just a joy. So are tire pressure monitors gm has 27 different ways to recalibrate them after rotating tires..Toyota has 2ways.
Wild Mango
Member
Lesson here is, if you mixing components like wheel cylinders and master cylinders make sure the master cylinder displaces enough fluid to operate the wheel cylinders fully. In the case just discussed, going from the stock 7/8" wheel cylinder to the 1 1/8" means a whopping 40% more area. Drum cylinders typically need a lot more displacement than disc calipers, so a tandem master cylinder tends to come up firm when the discs contact and the drum shoes are still a ways off. This is one of the problems RP check valves were intended to solve. This is why knowledgeable guys like Ted recommend two master cylinders connected by an adjustable balance bar, and that, girls and boys, is the definitive way to approach it.
