What am I doing wrong? (Brake Question)

I hate to post another thread on brakes, but after going through numerous other threads about brakes, my head is spinning...

I'm trying to figure out where I went wrong with the brake system on my '33 Ford that was an old stock car..

Has '42-'48 Ford brakes all around (new wheel cylinders, shoes, drums turned, lines, and hoses).

The master cylinder on the car was a single pot GM style. When I ran the part number cast on the bottom, it came up with either a single or double. I thought I'd make a smart move and go with the dual resevoir master cylinder. This MC was used on a variety of (mostly) GM vehicles and the late 60's early 70's, so I assume that it is set-up for drum/drum applications. Here is a link to it: http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NMAM2040_0332904800 It has a 1" bore. It is mounted in the firewall and higher then the everything else.

I plumbed everything with 1/4" brake line. No visible leaks. Bench bled the MC, installed it, and then vacuum bled the lines. Had problems with soft pedal, so I had someone else help me bleed the brakes today. Got a little bit of air, but even after bleeding them again I have little pedal.

The brakes are all adjusted, maybe even dragging a little too much (to be sure that wasn't the problem).

I've tried adjusting the pushrod quite a bit in and out, but I'm not sure how much freeplay there should be? I've heard 1/16"...

Seems like everyone had their own opinions on residual valves, but seeing as how this MC was used on drum/drum cars, I assume they're built right into it? I did not plumb in any external ones residual valves.

Could it be a defective MC?

Appreciate any advice you guys can give... The rest of the car is pretty much done, but the brakes are haunting me!

 

You can block (fab some plugs) off the master cylinder where the lines attach, and, with no air in the cylinder the pedal should be rock hard and high. Also make certain that you have free play in the actuator rod to the cylinder. The piston must return to the base of its bore or you will trap air. Depending on how you are bleeding the system: If the system was empty(assumption) and you pump the pedal fast as some people insist on doing, you will make large air bubbles into millions of small air bubbles therefore requiring a lengthy bleeding session. Anyone with a power bleeder is your area? These are just basics to think about. When something is kicking my a$$ I generally return to basics and fix the problem.

 

Forgot to explain : blocking off the cylinder with plugs will prove or disprove your question on a bad cylinder.

 

I had a similiar situation on my '55 Willys. Same situation, all new everything and converted the fronts to disc brakes, so everything was new. I bled those things for 30 minutes and still had a soft pedal. I gave up, came back the next day and bled again, and on the first bleeder I popped open, I had air. Bled thoroughly again and finally the pedal was good. Sometimes air just manages to hang in there somewhere. Even sometimes when I use a power bleeder is still doesn't help. Some people crack the lines open and gravity bleed it all day, adding fluid slowly...sometimes the walking away and come back tomorrow works (worked for me).

 

more than good chance it does NOT have residual checks in it. 1" is alittle small as stock Ford was 1-1/16" but should work. Will your pedal stroke the MC full travel? If not that may also be some of the problem as pedal ratio is wrong. Manual brakes need 2 things pedal wise right ratio[5-6 to1] and enough travel to fully stroke the MC.

 

Drum drum will have the same size resivor,disc drum one is larger

 

Your lines are too big....go to 3/16

 

Thanks for the advice guys

Worked a little more on it today... I re-adjusted the push rod and made sure that the piston returns fully- no improvement.

Found the fitting for the front brakes was a little loose, fixed that, secured the line better, and then bled all the lines agin- got quite a bit of air out of the front, but still have to pump pedal, and it'll still go to the floor if I push it enough.

The push rod will bottom the piston out, so I think that's alright. Will have to try to check the ratio??

Weren't all Ford brake lines 1/4"? I realize my MC is a tad smaller, but can't see where that would make a huge difference...

 

Yes, the older Fords used a larger brake line diameter. If part of your new line goes up, air will trap at the top.

 

I agree with "going back to basics" thing.. Always start bleeding with brake farthest from MC and work your way up. My bet would be air in the system.. Make sure you're bleeding in proper sequence.. (Although rarely do I follow my own advice).

 

As above...block off the MC to prove or disprove the Integrity of the unit. When you completely block off the MC it will be rock hard, if not thats your problem. My guess is you still have air trapped in the system...

 

Did you adjust the front brake shoes? I ask because I had the same issue. As soon as I adjusted the shoes, I got a wicked firm pedal.

 

???

 

Line size has NO bearing/efect on brake operation !

 

Line size makes no difference.

 

What this guy says.

 

OK, didn't think the line size would make any difference...

Went through the bleeding process yet again... Bleeding from the farthest wheel from the MC first, etc.

Got some air out of the driver's rear, a little on the other wheels, but not much.

Funny thing is, after bleeding the rears I had some pedal, but when we went to the front, I lost ALL of my pedal after we bled a wheel. Would not pump up at all...

After I had someone take the top off of the MC, I got my pedal back. Actually, I seemed to get a little more pedal with the cap off of the MC... Does this make any sense?? It happened each time bleeding the front wheels... No matter how much we bled them, I lost all pedal, until the top was taken off of the master. Could it be sucking air in somewheres??

I also forgot to mention, I plumbed the rear brakes to the rear resevoir (closest to the pedal), and the front to the front resevoir. The guy that helped me seemed to think I should switch them around, would this make any difference?

 

^^what he said. 1/4 is just too much volume. The master cylinder will only push so much volume, yours is likely designed for smaller lines.

 

Sigh.....wrong wrong wrong. And oh yeah. Wrong.

Unless you have invented a way to compress liquid with a measly 1200 or so psi.....

 

The piston must return to the base of its bore or you will trap air.

 

Yep, it's returning all the way..

 

I'm out...

 

I'm in.

I don't want to start anything but folks come here for answers and advice. So, Seriously, pressure is pressure. The line size has nothing to do with it. The only thing that the line size will change is the velocity of the fluid moving from one cylinder to another. The piston size will affect the EDIT:velocity too. In this application the difference between 1/4" and 3/16" is nothing. This is why my Model A with 40 ford brakes, a 1" bore master, and 3/16" lines stops fine.

 

I might as well through in my suggestion too. Jack the car up and readjust the brakes again. I have had situations in the past where, the shoes take a bit to center in the drums, and take a couple times of adjustment to get them correct, Then bleed them again. To adjust them correctly, there should be a very slight drag when spinning the wheel that you are adjusting (not even a drag really, more of just a dragging noise), and remember if they have individual adjusters for each shoe like early Ford brakes (others as well) that you need to adjust both shoes separately.

I know it's been stated, but make sure you have a very small amount of free play when the brake pedal is released.... This actually causes a hard pedal buildup, as the fluid can't return to the Master cylinder properly, and the next time you apply the brakes you are "jamming" more fluid into the lines and cylinders, and the cycle repeats.

 

^^^he's right ^^^ line size is volume not pressure

 

Just a thought... Two things Nobody has asked if the master was bench bled, and secondly,are the bleeders all at the top? In other words maybe the backing plates are crooked and the cylinders are trapping air cuz the bleeder is not the highest point...

 

Thanks again guys for the advice

I re-adjusted the front and rear brakes again yesterday- the front brakes did need a little adjusting, but it didn't help my pedal at all... I've rechecked the push rod, and it does return all the way

Yes, it was bench bled. As far as I know none of the backing plates are bent/crooked, but I will be sure to look into that today...

What I don't understand is why I lose ALL of my brakes when the front ones are bled- and then I regain pedal when the master cylinder top is taken off?? I've never heard of this happening before....

 

Lots of these lately. I had same issues. Read through these below, lots of good info.

I ultimately went with a larger boare MC, 1 1/8" performing better, but still not perfect.

http://www.jalopyjournal.com/forum/showthread.php?t=804271

http://www.jalopyjournal.com/forum/showthread.php?t=804596

http://www.jalopyjournal.com/forum/showthread.php?t=793651

 

Two things come to mind. first, where did the mc come from? Is it new or, a re-man? Imported crap or, made by a known good mfg? The part about it woking better with the lid off the mc could be that the lid is not venting. It should not be 100% sealed as you need atmospheric pressure to allow th mc to pull fluid from the reservoir into the bore. If all your fittings/lines are tight and there are no leaks, the problem has to lie with themaster cylinder.

 

"What I don't understand is why I lose ALL of my brakes when the front ones are bled- and then I regain pedal when the master cylinder top is taken off?? "

Does the cover gasket have "accordions" built in?
http://i.ebayimg.com/t/Master-Cylinder-Cap-Gasket-1967-1968-1969-1970-1971-1972-Mustang-Drum-Brakes-/00/s/MTA2M1g5ODA=/$(KGrHqJHJEEE-njyti9OBPs8nEF+Zg~~60_35.JPG