Brake pressure problem

This question is actually for my father in law. He has a '64 A100 pick up three window with a 273/3 on the tree. He recently did the scarebird front disc upgrade. Once he put everything back together he cannot get the brake system to hold the pressure. Once he bleeds the system he has to pump the pedal to get pressure but if he lets it sit and presses the pedal it goes straight to the floor. He's tried three different master cylinders which bench bleed fine. He also has a proportioning valve as well. We cannot figure out what the problem is. Anyone have any ideas at all? Anything? We are stuck. Thanks.

Chad

Sounds like a bleed problem, I know from experience these things are difficult to bleed to say the least. I bought a V12 pressure bleed tool to get the job done on mine.

Tom

Sorry I havent followed Scarebird thread all the way. Are you guys running residual valves in the dodge set up? Something else to check on your FILs truck, make sure the calipers are moving freely in the brackets and your not fighting a spring action causing it to take alot to engage and making it return to far. Just an idea.

some calipers -in the way they mount will sometimes need to be removed from the mounts & bled. This is due to placement of the bleeder screw being below the "TOP" of the brake fluid area, allowing some air never to be able to be bled out. Take a look at this area & if ness = remove the caliper -& bleed -one at a time making sure the blead screw is at the "TOP:" of the small resivious area on the caliper. Might also look at any lines having a "High Point" area-that could be retaining air ??pressure bleading is the best way to go alos.

Thanks for the advice. I remember he did have an issue with the calipers at first but he fixed that. He bought some kind of pressure bleeder but I don't know if he's gotten to use it yet. I don't understand about the two line bleeding. He's using a double master cylinder. Does this make a difference?

Chad

he may need a check valve, thats a one way valve that lets brake fluid flow only one way, with the master cylinder mounted lower than the lines the fluid flows back into the MC and then you have to pump the pedal to reload the brake pressure, summit sells them

Not a check valve.. a residual valve,, that bleeds off to 2lbs for the disc stuff

Doesn't the proportioning valve take the place of the residual valve? Maybe I'm mistaken. Where in the system would the residual valve go? There's so much to learn.

Chad

did he try gravity bleed ?? fill the system up fit a tight hose to the bleeder remove the caliper and hang it so the bleeder is the highest point of the caliper and crack the line over night make sure there is fluid in the hose above the bleeder and what mc did he use.???

I do believe he did gravity bleed but I do not remember the outcome of that. But based on the fact that he still has no brakes I'd venture to say that it did not work......at least like it's supposed to.

Someone before him changed the master cylinder to a dual. He used that one first since it worked. I think one came with the kit and he used that one. And he also bought another one because he thought that he ruined the first two.
I'm pretty sure that two out of the three still bench bleed and hold pressure. I think he did damage one.

I have helped him bleed the brakes on two occasions. We did it just like you would do any other system. I didn't think that a vehicle could be "difficult" to bleed. I was under the impression that once air stopped coming out at one wheel the rest of the air would come out elsewhere. I didn't think that it could "hide" in the system.

I'm hoping to do this upgrade to my van in the near future so I am hoping to find what the issue is. Thanks again to everyone helping out.

Chad

No, a proportioning valve controls applied pressure from the M/C. A residual valve will maintain a certain amount of pressure at the caliper or wheel cylinder. I am only familiar with my GM set up so if there is something different about a Dodge , somebody please step in here. On the front disc a 2 lb residual can be used, this keeps the pads out towards the rotors. On the rear a 10 lb valve this keeps the wheel cylinders ready for action. Perhaps a proportioning valve with this stuff built in is available? I don't know. Still to me . the way it is being described it would have to be air in the system or a problem at the calipers. The way Don was saying to do each circuit a little at a time might be a route to go also. a little air in the wrong place can be aggravating.
All these tips and techniques the guys are tossing out are good.

You probably have already been thru this but here's the link to the scarebird stuff
https://vintage-vans.forumotion.com/t31441p15-scarebird-brakes
John mentions something about the rotors clearing some bolts. This would cause that springing action I mentioned if there is any contact. Making sure the rotors are flat against the hub is a must also. For that matter if there was any difficulty getting the drums off the hubs, it is very easy to have warped the hubs. It doesnt take much at the hub to make the outer edges of the rotor out of whack.

I did do a bit of research but I will definitely check this out and pass it along. He did have some issues with the bolts but I believe that he figured that out and corrected it.

Chad

if you did a disc brake conversion and you are still using the stock type m.c. that is the problem he is not done with the conversion you need to get a m.c. from a 1972/1973 dodge van (b100 or b200) it had disc brakes in the front and brums in the rear. an has a larger reservior. you need to cut out some steel to meke it fit http://www.flickr.com/photos/scottie8door/sets/72157619785381907/.

the m.c. from a 72/73 is set up for the correct preasure already. you should not need any other valves .....

No, it was not the stock MC. There was already a double on the truck when he bought it. I'll have to check with him but I believe that his conversion kit came with everything or scarebird told him what to buy and he bought that. This is all good info.

Chad

Here is a very good 2 page article:
http://www.thebrakeman.com/valvetechi

I'm just starting my disc conversion as well. I learned about residual valves on one of the HorsepowerTv shows.

I have the scarebird brakes with the later b van master cylinder. I don't have any other valves at all. It sounds like you have air in the system. Make sure the bleeders are on top of the calipers and all your lines are tight. I've see loose lines hold pressure and still suck air back in.

Are the master cylinders new or rebuilt? The quality of rebuilt stuff is crap any more.

i just finished mine up today and everything works great, he might have the wrong master cylinder,

http://www.ebay.com/itm/280896642857?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
tell him to get one of these, and he wont need any residual valves or anything else, just did mine and everything works great,

Cool. I'm gonna take all of this info to him and we can take it one step at a time. All of the MC's he had were new except for the one that he used that was on the truck. I think he has the wagner one because the clip the holds the lid on looks really familiar.

It's starting to sound like it's just air that he has not gotten out of the system. We will have to check and see if the bleeders are on top. If there's more info keep posting for sure but I think we have a consensus.

Chad

last night i said to remove the calipers and hang them and gravity bleed. try to get the bleeder as high as you can . it doesn't hurt to turn them back and forth to try to get a air pocket to move.

I spoke to him this morning. He does have the wagner MC so that should work. He did say that the bleeders are on the bottom of the caliper so he is going to try removing them and turning them up. He also said that he has removed the front brake lines from the proportioning valve and left the back brakes attached and he has full pressure....so the problem appears to be exclusive to the front.

He also told me that he has a vacuum bleeder. He bled the back brakes with the vac bleeder and it worked fine. He tried the front brakes and he cannot get the fluid to come out of the bleeder. Any ideas on that? I think that he was running it through the proportioning valve when he did that.

His next course of action is to take the prop valve out of the equation and see if that's an issue.

Chad

once he has the calipers on the right side with the bleeders up, that will fix his problem,