Thread: Brake troubles

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I'm not getting the brakes to work on my 40 Ford p/u.
Have I hooked the lines up wrong from the master cyl. to the proportioning valve ?
I have turned the valve both ways and I can't get the brakes to lock up on the rear.
Never had any trouble bleeding brakes in 45 years of working on cars and this thing is kicking my butt. Rear has disc with emergency brake calipers . I have followed the instructions to the letter from the supplier (speedway). The master cyl faces towards the rear of the truck. Both reservoirs are the same size.

Only a guess here, Maybe the rear disc calipers are not the same size as the front calipers? I beliieve your master cylinder (assuming this is a disc MC and not a drum as you have equal sized reseivors) only can and will move a given amount of fluid to the front and rear, your metering valve and your porportioning valve limit pressure or hold off the timing not volume, if it was to limit volume the fluid would have to be displaced somewhere and its not as the pedal travel remains the same. So if your front calipers are a Wilwood or small volume caliper and your rears are a GM metric or corvette as an example you will never move enough fluid to collapse the GM's as the wilwoods collapse with less volume and once collapsed the pedal can no longer travel anymore to move more volume. This is only true on disc setups as a drum master cylinder moves a different volume for the front and rear. Sorry for the long answer and I hope I explained it enough to either solve or eliminate this as the problem, but I could also tell you how I know this but I am sure you know why! Best of luck

Originally Posted by Matthyj

Only a guess here, Maybe the rear disc calipers are not the same size as the front calipers? I beliieve your master cylinder (assuming this is a disc MC and not a drum as you have equal sized reseivors) only can and will move a given amount of fluid to the front and rear, your metering valve and your porportioning valve limit pressure or hold off the timing not volume, if it was to limit volume the fluid would have to be displaced somewhere and its not as the pedal travel remains the same. So if your front calipers are a Wilwood or small volume caliper and your rears are a GM metric or corvette as an example you will never move enough fluid to collapse the GM's as the wilwoods collapse with less volume and once collapsed the pedal can no longer travel anymore to move more volume. This is only true on disc setups as a drum master cylinder moves a different volume for the front and rear. Sorry for the long answer and I hope I explained it enough to either solve or eliminate this as the problem, but I could also tell you how I know this but I am sure you know why! Best of luck

You may have the answer to my problem, not sure. The calipers on the rear are 1978 to 1988 GM.
The fronts are also GM but maybe different volume is used to operate.
Matthyj: what was your fix ?

Navy, just a question - I see a purple (appears to be) residual valve in the rear line to the proportioning valve block, and then what appears to be two blue residual valves in the lines from the proportioning valve block to the front & rear brakes? Can you explain your hardware as installed?

Originally Posted by rspears

Navy, just a question - I see a purple (appears to be) residual valve in the rear line to the proportioning valve block, and then what appears to be two blue residual valves in the lines from the proportioning valve block to the front & rear brakes? Can you explain your hardware as installed?

The 2 blue residual valves go to the front brakes and the purple one is for the rear. Should have just put one for the front line near the master but I put one for each line.

Why are they different front to rear if you have disc's all around? The purple one is a 10# valve meant for drum brakes, right?

I had a similar problem on my 46 coupe. In my case it turned out to be air trapped in the rear line. I could not get it out by the traditional pump and bleed method. I finally built a pressure bleeder and that was able to move enough fluid in a steady flow and get all the air out. This might not be your problem, though. Just a thought. Like you, this was the first car I couldn't get to bleed in the normal way

I would have plumbed the residual valves closer to the MC and used only 1 for the front. Also, I have a prop valve in my rear brakes and it is not needed. It is set to max pressure. I have Ford Explorer disc brakes on the rear. Between the smaller disc size than the front, smaller caliper bore and difference in tire size, the bias is built in. As has been said, you may have built in brake bias that simply won't allow the rears to lock. In my case, I know the rears are working because the rotors show wear and the pads appear to be wearing.

there is an issue adjusting those rear disc parking brakes-check an OEM manual, not Speedway--------
get the eze bleeder screws-------you can bleed a whole system by yourself in less than 10 minutes

Here is the absolute best source for factory manuals on the planet....
Faxon | Shop Manuals for Car & Truck Owners | DIY Service, Repair or Maintenance

.

ALSO_---lots of OEM type master cylinders contain the residual pressure valves where/as aftermarket (Wildwood?etc) do not-and, the valves that have been used in all vehicles since dual brake systems (1960s) have some delay, proportion,etc funstions so I would suggest that you eliminate those parts out of yours

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.

Originally Posted by jerry clayton

there is an issue adjusting those rear disc parking brakes-check an OEM manual, not Speedway--------
get the eze bleeder screws-------you can bleed a whole system by yourself in less than 10 minutes

Yup I got the eze bleed screws and have bled the piss out out of them, work great but I still have problems .

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.

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

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.