Technical Brake issues on a 42 ford

I'd say, for giggles, adjust the rear pads out so there's no travel and see if the brakes improve. I've had it where the rear take just a little too much pedal travel due to not being quite matched to the front brakes; pumping them would make them move in (due to the parking brake design they were a little slow to return) and then decent pedal was achieved.

Phil

 

I bleed my brakes by myself. I use 4 bottles, and 4 rubber hoses. I put a rubber hose on each bleeder valve, then I put an inch or two of brake fluid in each bottle. I put a bottle at each wheel, and put the hose in the bottle so it's submerged in the brake fluid that I've put in the bottle. I then open all four bleeder valves and start pumping the pedal. Keep an eye on the fluid level in the master cylinder so it doesn't go dry. Which ever bottle fills up about an inch more than what I started with is the bleeder valve I close first. The next bottle to fill up with more fluid than I started with is the next one I close. I do this until all four bottles have about an inch or more fluid than I started with. I've done it this way for a lot of years and it's never failed me. I learned this from an old friend of mine when we were working on Ferrari's probably 45 years ago. Good enough for a Ferrari, good enough for a Hotrod.

 

Does the new m/c have one or two outlets for the front discs?.
The reason I ask, my friend had a m/c of unknown origin, single pipe forward, and single pipe to the rear.. and replaced it with a Ford Falcon tandem m/c, which had two pipes forward, and one to the rear..
As his old m/c only had one pipe forward, he blocked off one outlet on the new m/c, and ran the other outlet to both front calipers, thinking this would be ok..
We bled the system many times, but the pedal wouldn't come up..
Fitted the second pipe (one each side now) and got a full pedal first bleed..

 

I’m going to point out a couple things, V8 Bob pretty much has it under control as per usual however line size has nothing to do with anything here, 3/16 or 1/4 will make zero difference in brake performance, many misunderstand there is almost zero fluid flow in a brake application, once the air is gone the fluid acts as a solid. Same as having two outlets from one circuit on a master, have a look at pascals law, again zero difference. Sounds an awful lot like air trapped somewhere. When you pump the brakes a couple times do you get a good pedal? If so, what happens when you hold steady pressure on the pedal?


Just re read and saw my questions answered, did you bench bleed the master? As far as brake performance what size is the master bore? Caliper bores?

Disc brakes have no self energization so they rely on force to work, a mis-match in hydraulic parts will not work well.

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So 3/16" or 1/4" does not change the available amount of fluid that is now serving as the "solid" in the hydraulic system? I thought that it allowed more volume in the system over a long span, and through fluid dynamics, a 1/4" x 3/16 x 3/16 T on the rear axle increased pressure as it was forced through the orifice that is the smaller line? My bad. I still say you've done everything right. You can only skin a squirrel, and bleed brakes so many ways. Solid fluid is solid fluid. You have a defective component in your system. But if I'm wrong im all about learning.

 

No need for more fluid, there is so little flow that the smaller line is not raising pressure, the only reason we need a reservoir is for fluid to fill behind the caliper piston as the pads wear. In a hydraulic system with actual flow you are correct that the pressure is from resistance to flow. In our brake system that pressure builds because our system is a dead end or closed system, fluid has nowhere to flow once the pads touch the rotors, almost instantly, there the pressure builds and generate more force to apply the brakes. That all depends on input piston size, force applying the input and output piston size. Brake systems basically convert mechanical force (our foot) into hydraulic pressure and back to mechanical force at the caliper.


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Have you checked to see that the calipers are mounted square to the rotors in both planes. Maybe something out of whack since it loses pedal after sitting.

 

Has he done this successfully before?

I ask, because I found that there was still air in my system when bleeding by myself. I was pushing the pedal down too slowly. Increasing the force applied to the pedal, pushed out the last bubble.



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I doubt it. They gave me a much better pedal. I was going to call ssbc to see if they could offer advice. Looks like they closed for good. They are still taking orders but not sending out parts. A lot of people got screwed.

 

Well here's my thoughts, and i sincerely hope you get it figured out, but my whole life, air in a brake system was defined as "spongy", I've not heard you mention that your brake pedal felt spongy. You said that you can build pressure with a few pumps of the pedal, and left alone it disappears. Pumping your pedal is pushing the calipers against the rotors, giving you the solid pedal, the rpv's should be maintaining the close relation of the caliper pistons to the rotors, so in turn when you lose pedal pressure, that means it's in the master cylinder. If you pump up your brakes until you have a pedal, and walk away for an hour, the rpv should be holding 2psi of pressure against your caliper, leaving that even though you have no pedal, you could still open the bleeder and see that 2psi coming out. If that happens then I'd try another mc, if not I'd verify my rear rpv is operating.

 

Don't know why I let myself get involved in these brake problem threads, I have just as much trouble as the guy asking. I have learned that Bob & Fargo know their **** when you need advice. The only thing I can add is you "think" you have a high spot in the line or lines where the air could be trapped, maybe raise the front or back of the pickup and bleed again?

 

Thanks brigrat, all I’ll say is all of my junk stops well, whether it’s disc or drum....


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I have done a bunch of brake jobs on hot rods over the years and have had a handful of them not to my liking BUT the customers have said they were acceptable and I was expecting to much. My feeling is if you have disk/drum or disk/disk on a light hot rod it should be capable of locking all 4 up if need be...............................

 

can't hurt to try.

 

Everything you are saying makes sense. I have personally built multiple brake systems and repaired hundreds of them over the last 20 years. I have never fought a system this much in my life. The first 2 pumps of the pedal are on the floor board. Then they start to build pressure. Even when the pressure pumps up, It still does not lock the wheels. I changed the master cylinder and got no change in the symptoms. I have been dealing with a winter storm. As soon as I get a chance, I will try to reverse bleed the system. Before I do that, I want to double check every fitting on the truck for tightness. I know the RPVs are doing something because before I put them in the pedal would pump up and drop a lot of pressure when released for just seconds. Now it holds pressure for a longer period of time. I don't even care if I have to pump the brakes up before driving it for the day. I am more concerned with the lack of performance. That performance did improve also with the RPVs. With the master disconnected and plugged the pedal is like a rock and stays that way.

 

one of the issues is that the pedal is bottomed out while he is holding it. Even after it "pumps up" it still does not have a great feel to it. The Master bled fine and still tests fine on the bench. When I say bottomed out, I mean on the master cylinder. The pedal still has an inch before it hits the floor.

 

The pads look straight to the rotors. I will take another look to be sure. At this point, I will check anything. I am almost ready to replace the entire system and move the master up under the hood.

 

Stay with it, it sounds like you isolated the master and its's ok, now keep going along those lines. Plug the rear port at the master and try again, then the front. Double check wheel cylinders for leaks on the end that doesn't hold. Narrow it down one fitting at a time until the problem surfaces.

 

I will give that a shot

 

I did bench bleed the master. I have 2 port out of the master into the combo/adjustable proportioning valve. That has 3 outlets. As per the instructions that came with it, I plugged one outlet. The master cylinder has a 1 inch bore, the front calipers are 2.5 inch bore. I'm not sure about the rear size. They look smaller than 2 inch. I'm not there to measure it now. I tried calling SSBC to find out but they are now out of business. I did give the info to the sales rep at leeds brakes and they told me this was the correct master. If you can trust a salesman....

 

Does the combo unit have a metering valve? When you bleed is there good pressure at the calipers, have you put a gauge on them to see? Also see my above post

 

That looks like the only way to do it. I'm sure I will find something silly and easy to fix in the end.

 

I have not put a guage on them. The valve has an adjustable proportioning valve for rear brakes and a pressure switch for brake lights. I do not believe it has a metering section. It just function as a distribution block.

 

The master has 2 outlets (one front and one rear). But, the proportioning valve has 3.... 2 front. As per their instructions one can be capped. I am considering removing the proportioning valve to see if I get a better pedal.

 

I would try vacuum bleeding first. If the calipers are higher than the master, take them off, block the pads in place with a hunk of 2 x 4. It should bleed better with the calipers being the lowest point. But you will still have the proportioning valve to deal with, should not be as air-bound as the calipers. I would take some free-play out of the master rod, take it down to an 1/8" and see what happens. I would almost like to have them locked up for too-little free play and adjust that out.

 

Helped a friend do a front disk brake conversion on his 72 chevelle. We were having similar problems.
Ok brakes but not even worth the effort of installing the kit. We finally discovered there was a adjustable shaft in the booster in between the MC and the booster. We adjusted the shaft until the m/c was getting a full stroke. Bleed everything again. Buddy went for a test ride came back with big smile and great brakes. I know your system and my buddy's are different but it's food for thought.

We would pump and pump get a little bit of a pedal crack a bleeder and the fluid would come up about 1/2". After we found the problem it bleed like normal.

Mike

 

I had this EXACT same issue with my brakes. Not going thru the whole deal, other than to say that I drove like this for about 2 years, when I experienced a "close encounter" where I barely stopped in time. I had no (as in "0") brakes until I pumped them 2 or 3 times, same as you.
In an emergency you gotta be super fast. I had enough and decided it was time to fix them.
I did the vacuum, pressure, old way, etc, etc for bleeding brakes, always had flow with no air, but same problem.
Ultimately, what it all came down to; my rear calipers were mounted at the 12 o'clock position, higher than my master cylinder. I made new mount, moved calipers to 9 o'clock position (3 o'clock would have been fine too) bled brakes one time pumping the pedal and bleed each wheel ("old way"), and my brakes worked perfectly.
As an aside, I did pull my calipers off, put a piece of wood between the pads, bled with calipers low, lots of fluid again, put back on car (12 o'clock position) and same problem.
Moving those calipers down was the answer for my car.
I have over 50 years working on cars and this one had me stumped for a little bit. Weird until I thought about it.

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Do you know if you have the older "metric" calipers? Read a thread on them never feeling just rite but can't remember the remedy................................

 

Low drag calipers, they require a quick take up master cylinder


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Any updates?