Thread: Brake troubles

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Navy, Yes not all GM metric use the same volume as some aftermarkets (including numerous from speedway) have different bore and pistons so look at your order ticket and confirm they are the same bore. Jerry is also right many contain the RPV already however it does not hurt if you use two inline if I remember so shouldn't be a issue on that part, the rpv's simply hold pressure on the line so the pads or shoes are near the drum or rotor and don't suck back fluid on under floor MC's or where the MC is lower than the calipers. The solution they had for me was get the same size pistons on the calipers front and rear. I guarantee you there are hundreds of rods running around without rear brakes because of this, the mistake is made all the time I have seen it at alot of rod shows but I am not sure its your problem yet, just something to check. On a disc/disc setup you should have 2 lb rpv's front & rear if you have a drum rpv its 10 lb and would drag the disc brakes it was put on.

Todays brake trouble shooting results.

1. Bled the piss out of the brakes.

2. Check vacuum to the booster 20 at idle.

3. turned proportioning valve full both ways no noticeable change at rear brakes.

4. cracked open front line at master cyl. and applied brakes, results fluid running down on pile of old rags no real change to rear brakes. ????????

5. Pads are as close to the disc as they can get. They are held off the pads a very small amt. .040" by a rubber bumper of sorts that is centered in the piston. this gives very easily when brakes are applied.

6. Even with the rpv's I can see the caliper pull/pushed back when the peddle is released, I'm guessing it's that rubber bumper in the center of the caliper.

7. Next try will be putting my old parts back on and see what happens, 7" booster and a leaky master cyl.
If that does show any results I'll head to the store for a case of Corona !
Thanks for the inputs Guys, keep them coming and we'll get this truck on the road by next summer.

Originally Posted by DennyW

Looking at their diagram, you have the master cylinder lines possibly incorrect. http://static.speedwaymotors.com/ima...ake_System.jpg
They show the rear port going to the front brakes.

Thanks for the input but the trouble is is that the diagram doesn't which way the cyl is facing.. Mine faces backwards plus the cyl have same size reservoirs which leads me to believe that all is equal with master cyl.

Originally Posted by DennyW

Think about that for a minute. The booster is still where it should be, in the rear of the master cylinder. Therefor the lines would still hook up like the diagram. Secondly, the diagram is showing disc on front, and drum on rear. Still the line from the master to the front, is located on the rear side of the master as it is mounted to the booster. See what I mean. The only effect would be if you were running the size of caliper pistons way different in size. That would make one brake much sooner than the other.
Next, you only need a 2 psi residual valve in line running 4 wheel disc. It looks like you have more than that by the picture. The last thing if you have a gauge, you can connect that to the master cylinder to check to make sure the master cylinder itself is not faulty. I asume you have the booster and master mounted on the firewall by your picture ?
If you were running rear brake shoes, the springs hold them off of the drum. And the travel is controlled by the adjustment of the rear shoes. I'm sure you know that, but thought I would throw that in as well. hahaha.

DennyW: the diagram from speedway shows no booster it could be on either end . This is what I found at CPP co.
http://www.classicperform.com/Instru...structions.pdf

note the front and rear markings. Is it correct who knows but I'm thinking these folks sure should.

Originally Posted by DennyW

Maybe, But I really don't think they would show a master cylinder like that diagram with the fronts being drum, and the rear being disc. But, who knows...Remember, just because a part says new, doesn't mean it works like new...hahaha

There not showing fronts as drums but as disc with rear drums being converted to disc.

Did you bench bleed the master?
What are the calipers from front and rear?
Rears have BUILT in parking function?
Diameter and number of pistons? floating or solid mount calipers?
Are calipers single or dual side?(pistons on both sides of disc?)
thickness of discs
diameter of discs
bleeder screws top mounted?
master higher or lower than calipers?
loops in brake lines that could trap air in upper part?
leverage of pedal
proper geometry of pedal for correct amount of master cylinder travel?

better pictures!!!!!!!

Navy, Don't ever think that there cannot be a problem from the manufacturer here. I built a '65 mustang and added discs and purchased the master cylinder from Master Power brakes, a good ol' american company, the whole "direct fit" unit didn't fit I could tell before monting, I called and read them the part numbers off the instuctions and box (none on the unit itself) and they said its right and something is wrong with my mustang the parts are right and it might take a few extra mounting holes, I drill 'em bolt the thing up and nothing works I call 'em and they insist its right, I look up the pics on the net and call them and let them know they sent a 1968 unit in a 1965 box to me!! Now I have extra drilled holes in a smoothed firewall. Sometimes I think this stuff only happens to me, but reading this forum I can see I am not the only lone wolf out there! Point being make sure the MC is working you might have a seal on the MC piston with a wrinkle in it or something else only giving fluid to the front, like Roger mentioned a gauge would let you know, or take a rear caliper off and swap with the front with a socket in between to simulate the rotor and see if they are working hooked up opposite if you don't want to purchase a gauge. It appears you are dealing with a frame mounted MC and booster. You would not be able to notice the adjustement on a proportioning valve without driving it and cramming on the brakes, it merely limits pressure until the setting adjusted is overcome. I am sure we can keep coming up with something!

I would take the purple residual valve out as it is not needed with 4 whl. disc. Then take one blue residual valve out of the front and put it inline to the rear. I have wheel discs on my car. I have 2 blue 2lb residual valve inline coming from the MC, one to the front and one to the rear.

Used to be that if you built with front disc/ rear drums the master of choice was the Ford Mustang/Toriono/etc and if all 4 disc Corvette master

has a lot to do with how much volume was needed front/rear and area of the wheel cylinders was related to car weights, wheel/tire size ( pre antiskid) so the fronts would lock up before the rears---nobody wants the rears to lock/skid!!!!!!!!!!

Navy, I assume that you used through-the-frame fittings? There were some out there made out of tubing & fittings (as I recall) that trapped air in the tube (I think the hole through the fitting was a lot smaller than the ID of the tube, creating a larger hollow area to trap air on top) that were all but impossible to get the air out of. Just tossing it out as a possibility. The good ones are machined with a constant ID through the whole fitting.

Originally Posted by rspears

Navy, I assume that you used through-the-frame fittings? There were some out there made out of tubing & fittings (as I recall) that trapped air in the tube (I think the hole through the fitting was a lot smaller than the ID of the tube, creating a larger hollow area to trap air on top) that were all but impossible to get the air out of. Just tossing it out as a possibility. The good ones are machined with a constant ID through the whole fitting.

Nope no through frame fittings used. good thinking though.

I'll toss this out there, "just because". For testing purposes only, remove the residual valves and replace with couplers, then bleed and see the results.

Simple, relatively in-expensive, and easy to do.

Roger had a great thought on the trapped air in small id through the frame fittings. Navys rpv's appear ok, he simply is using two rpv's in the front as they are located after the tee splits the lines to the left & right front brakes, since his MC is below the floor the rpv's would be needed. I would think if the rpv's where backwards (check in on RPV) or not working there would be no fluid during bleeding. Like mentioned earlier the rpv's color can vary between manufacturers.
Here is Master powers definition of brake valves.
Metering
The metering or hold off valve is used in the brake system to better balance the front to rear brakes. The valve does not allow the pressure to rise at the front disc brakes until the pressure at the rear drums has risen sufficiently to overcome the brake shoe springs. At this point the valve opens to allow full pressure to build at the front brakes.
Proportioning
The proportioning valve modulates the pressure to the rear brakes. The modulation is necessary to minimize rear wheel lock up found in heavy braking and to compensate for the differences in braking conditions in front disc / rear drum systems. As pressure is applied to the system full pressure is allowed to the rear drums up to a certain point. Beyond that point the pressure to the rear is reduced preventing rear brake lock up.
Residual
There are two different residual valves. A ten pound residual valve will maintain a line pressure to the rear to keep the drum brake shoes out close to the drums giving a higher firmer pedal. Without a ten pound residual pressure to the rear you will experience a spongy pedal. A two pound residual valve is required whenever the master cylinder is lower than the calipers to prevent backflow of fluid from the calipers to the master.
Combination
A combination valve incorporates metering and proportioning into one valve. These are available for disc/drum or drum/drum systems.
Adjustable Prop. Valve
The adjustable proportioning valve is used when you have a special rear condition that requires higher or lower pressure than a normal condition. You sould always use a metering valve to the front when using the adjustable

Navy, had any time to work this problem out yet?

Originally Posted by 40FordDeluxe

Navy, had any time to work this problem out yet?

Last time I worked on it I had High hard pedal no good brake action. Applied emergency brake with all my strength and no good brake action. Too tired to give the details along with the pictures iI took ect. The airplane is wearing me down so there's not much ambition left to work on the truck. This weekend I hope to solve the mystery .