The set-up: 65 Ford Econoline with D&D disk brake conversion (uses GM metric calipers) 77 Ford Maverick dual MC for manual brakes (A-1 CARDONE Part # 101614) Stock brake pedal in stock location Blue 2psi residual valve in front Red 7psi residual valve in rear Combination valve, too The Problem: The pedal goes nearly to the floor before doing anything. The pedal is hard, but barely stops the truck. The pushrod is touching the MC and engages it immediately What I've tried: Manually bled the brakes, then bled them with speed bleeders. Bench bled the MC. I can hear the rear brake shoes drag on the drum, so they're adjusted. The disk pads look close to resting on the disks. I know they actually engaged because they cleaned the rust off the rotors. Observations: When bleeding with the speed bleeders on the REARS I noticed that the pedal goes nearly to the floor, then it's hard. BUT when I bleed the fronts, the pedal goes all the way to the floor with little to no resistance. I guess that means I'm mainly stopping with the rear drums. SO, what the heck? If I had a MC intended for drum-drum, would that cause this situation? I got the MC from RockAuto and their catalog says it's for manual brakes. The other MCs for the 77 Maverick are listed as power disk. I don't have a booster. Could it be a problem with the Combination Valve? I'm getting fluid at all 4 corners, so I know it's not stuck.
You don't say which exact calipers you have, but certain year midsize GM metric calipers required a "quick take up" (QTU) master cylinder as the GM engineers modified the calipers to pull back much farther from the rotors to lessen the brake drag and thus increase the fuel mileage. Fitzee went thru this last year using metrics and a Ford master cylinder. The cure was to replace the Ford master with a GM aluminum QTU master cylinder. Can't be sure its your problem...but you need to check the year calipers you have. Heres a link that explains the potential issue. http://www.mpbrakes.com/uploads/documents/lowdrag.pdf
I don't remember which ones I bought, but here's a list of the ones that go with the kit. I think I got the Monte Carlo or Malbu, but maybe the Camaro. Is there any way to tell which ones I have and if they're QTU? FWIW, the pads look like their pretty much touching the rotors. 78-88 Monte Carlo, Cutlass 78-83 Chevelle, El Camino, Malibu, F85 82-87 Camaro, Z28 78-87 Grand Prix 78-81 Le Mans, Tempest, Grand Am 82-86 Bonneville
D&D, isn't that the guy that was extremely critical of my master cylinder design, because I didn't include a push-rod or have a grease zerk on it? I'm sure he could answer your question, being the expert he is Hackerbuilt already covered my initial suggestion. Anything newer than the very early 80s I would suspect of being quick take up calipers.
Don't know what you mean, Shiny. That's what it's doing. The large chamber of the MC is plumbed to the fronts and the smaller chamber is plumbed to the rear, in case that was your next question. Polacko - I doubt the D&D guy is on the HAMB, but I don't know
According to my brake info, your '65 Econoline used a 1" master, while the '76-'77 disc/drum Maverick ('75 was the last year for drum/drum Mavericks) used a 15/16" for both power and non-power. Many/most power masters have a deeper push rod bore than non power masters, making them safer to use on non powered non stock systems by allowing un-retained push rods to stay in the bore and not fall out. With the pedal fully retracted, check to be sure the push rod has about 1/16th" (.040"-'060") clearance in the primary master piston. The first thing I would check is to make sure you are not running out of pedal travel. The master has to bottom before the pedal comes in contact with the floor. The smaller bore master will generally require more pedal travel. Switching to a 1" master will help reduce travel at the expense of slightly higher pedal effort. But you have to check pedal travel on any non-stock system, as even masters with the same bore do not all have the same piston stroke. Open a front and rear bleeder to perform this check. Running 3/16" clear Tygon tubing from the bleeders to a waste container keeps the mess to a minimum, and is a good way to check for air while bleeding. Bleeding the rears and having the pedal get hard before hitting the floor means you are developing pressure to the fronts. Make sure the rears are adjusted correctly, usually about 10-12 "clicks" off from a very tight drum. This will generally give you 025"-.030" shoe-to-drum clearance. I am not that familiar with the GM metric calipers mentioned, but using the matching GM master might be the answer, as some have suggested. I would ditch the "combo" valve and simply use an adjustable proportioning valve because, 1-you have no idea what the "crack" pressure or percentage is on a generic combo (prop) valve. 2-many combo valves include a "metering valve" which can cause balance or aggressive rear problems in vehicles not designed for them. 3- most people do not wire up (and take advantage of) the differential pressure switch, so what you end up with is a big block of crap that 99% of the time will not perform as good as a simple adjustable prop valve. Hopefully this will help you get the brakes working like they should.
According to the guy who designed the disk kit, most of his customers use the 77 Maverick non-power 15/16" bore MC without problems. 1" seems like a good option after I read a bunch of calculation articles, but if the 15/16 is working for everyone else with these calipers, it must be something else. As soon as I press on the pedal, the brake light pressure switch turns on the lights, and I can see fluid move in the MC chamber. Is that what you meant? The rear shoes are self-adjusters, and the shoes have a light drag on the drums as I rotate the tires
"The pushrod is touching the MC and engages it immediately" This could be the problem, there needs to be a little play between the pushrod and the master to insure that the piston is retracting all the way .....
get a corvette ;master cyliider w/ 1 1/8" bore - gm calipers need a lot of fluid to push the pots out
What year Corvette? FWIW, I've heard that the 15/16 bore works fine with this set up, others have said that I must use a 1" bore and anything bigger or smaller will fail, and now 1 1/8"
Maybe its just me but, I'd match the master cylinder to the calipers (per your list). The rear drum cylinders aren't as touchy (as long as they're near the same diameter/volume as the 'GM metric' rear cylinders.)
Do you really think the 15/16" bore master displacing 6% less than the 1" bore master cylinder piston is causing this? I don't. Likewise, I don't believe the larger 1.125" bore which is going to displace 17% more volume over the 15/16" master cylinder is going to solve this issue either. The reality is, changing the bore size has more to do with the mechanical advantage you have over your system than it does about solving a pedal that goes to the floor. I find this really interesting though, I would really like some further explanation of why you think hooking up a warning light switch is going to make a combination valve work better. Here is a simplified diagram of what is inside of these blocks of mystery. If you have a better picture, please post. As for the rest of these recommendations, I don't see any of these as actually helping solve this issue. Everything you suggest is an alternative way of balancing needed pressures under certain conditions.
I "HEART" Google, check this out for a nice write up on what Don is talking about: http://www.tegger.com/hondafaq/mastercylinderreplace/howworks.html
The rear brakes, if (probably) Bendix, are self adjusting only when applied during rear vehicle movement (backing up), not statically. Have you checked for pedal travel and push rod clearance as I mentioned previuosly? The 15/16" master will work IF the pedal has enough travel-otherwise, you have to change the pedal ratio or master cylinder size. As I previously stated, non power (manual) masters usually have shallow push rod bores because many of the rods are held in the piston bore with metal retainers. Power brake masters generally have mch deeper bores because the booster push rod cannot be retained for obvious reasons. Take the time to read and understand the suggestions you have recieved, and go through the basic check steps, otherwise we all are waisting our time.
One more time for clarity. Please check and see if the calipers are quick take up! http://www.mpbrakes.com/uploads/documents/lowdrag.pdf
What I see there is the possibility of fluid bypassing/leaking by the piston to the front brakes. Sure there's enough pressure to bleed an open system but not enough to activate a caliper piston. It would also explain why he sees fluid moving when applying the pedal.
Please read the link I provided on post #15 It explains why you will see fluid moving inside the master cylinder. Granted, a bad master cylinder could very likely be the cause of all this, but usually if the master cylinder is leaking internally you won't see much fluid coming out of the compensation or pressure equalization ports as the piston just travels through the cylinder not displacing any fluid.
Elpolacko "I would really like some further explanation of why you think hooking up a warning light switch is going to make a combination valve work better". 'Cause that's what makes up most of the "combo" valve. If you're not going to use the diff switch, why use it in the first place? I've tried to explain why fixed prop valves are not the best on a custom system, and that goes also for the metering valves, if included. "Do you really think the 15/16" bore master displacing 6% less than the 1" bore master cylinder piston is causing this? I don't. Likewise, I don't believe the larger 1.125" bore which is going to displace 17% more volume over the 15/16" master cylinder is going to solve this issue either. The reality is, changing the bore size has more to do with the mechanical advantage you have over your system than it does about solving a pedal that goes to the floor." Yes, going from a 1" to 15/16" master can cause excess pedal travel because of the longer strokes smaller masters usually have to maintain needed fluid displacement. It's something ANY good chassis fab expert SHOULD check for when building a custom brake system. "As for the rest of these recommendations, I don't see any of these as actually helping solve this issue. Everything you suggest is an alternative way of balancing needed pressures under certain conditions." Not sure what you don't understand, but it's not because I haven't tried! Be more specific and maybe, just maybe, I can clear things up.
Bob, do you have a background in mechanical engineering or specifically automotive brake hydraulic systems? If you do that would really add to the discussion here, I would really appreciate if you could dig into some minutia on your theory of why a warning light switch is going to make this problem go away. Or conversely how ditching this combo valve in lieu of a single adjustable valve is going to make the pedal suddenly "rise to the occasion". To be perfectly frank, I really don't understand why you think this issue is due to a metering/proportioning or hydro-mechanical problem. Those are all relevant issues to contend with after the system is operating. I don't know how to be more "clear" than that. Can a larger bore master solve this issue? If we determine that he is using low drag, quick take up calipers, absolutely. The proper master cylinder to operate with those calipers will solve the problem. Do I believe that is the case here, no. We haven't determined what the actual issue is. We know for a fact that very similar systems have worked, what we need to determine is what is different on this system from the ones that do work.
Like I said, the designer of the bracket says most of his customers use the 15/16 bore MC with these calipers without issue. A 1" bore MC may work better, but it doesn't seem to be my issue right now. It's worth looking into, but I'll try to eliminate a few other possibilities first. Correction, the brake lights kick on with about 1/4-3/4" of pedal travel, not "immediately" as I stated earlier (inline pressure switch inline to rear brakes) The calipers are set vertically as designed by the kit & GM. That puts the bleeder on top, but the bleeder doesn't face up. In order for it to face up, it would have to be mounted on the bottom of the rotor and I've never seen that. If I'm reading the QTU check correctly, I clamp off the brake hose, step on the pedal, and see if the pedal returns? I just realized that i have a few places where the lines are above the MC by a little bit, like where they enter the combo valve. Embarrassing, but true. The combo valve itself is mounted at the same level as the MC. This hadn't occured to me while plumbing the system (MC is mounted to the frame under the floor) but could I be trapping air despite all me bleeding effort? If so, I think I may be able to unclamp the lines from the frame and drop them down lower and re-bleed.
I have set up this similar system so many times. This is not an uncommon system with the bore size of the master, calipers and assuming stock Econoline rear brakes. If I recall the D&D system reuses the stock brake pedal and does not modify the location of the pushrod on said pedal. Having the lines and combo valve higher or lower will not affect the function, provided the system is bled properly. If you have new rubber brake lines, it is safe to lightly clamp off the hose temporarily. If they are braided stainless, DO NOT clamp them off. You will damage the nylon tube inside. Your caliper installation should look like this regardless whether the caliper is in front of or behind the spindle. The fact that your brake light switch is installed in the rear line AND you are creating enough pressure to engage it makes me further believe the problem is in the front brakes, namely the calipers.
Yeah, I found an article in R&C that shows the MC in line or lower than the combo valve. http://www.rodandcustommagazine.com/techarticles/1001rc_1949_chevy_brake_lines/photo_01.html My calipers do look like that. the D&D kit is designed to keep the stock pedal and MC, but I converted to a dual MC which required an adapter bracket. Fred designed it and he's on here somewhere. That bracket keeps the pedal pivot in the stock location. Anyway, both he and D&D say that their kits work together Yes, new rubber hoses and steel lines. Will test for QTU tonight.
MPBrakes says to use a brake hose clamp. Anything special about that, or can I use any clamp, like vise grips?
I use 3/8" tubing over needle nose Vise Grips for this. You were the first to respond on my thread about the brackets I made. http://www.jalopyjournal.com/forum/showthread.php?p=5273666
Elpolako, I spent 35 years as a brake test technition-that's building, dynamic (driving) testing, data reduction, modifying, etc. Engineer, no, just worked with, for and along side some of the best from every major manufacture. I suggested to ditch the combo valve because it's most probably not going to work as well as a simple adjustable PV. Just more crap to bleed and have problems with. If you want to invest a few thousand bucks to run dynmic tests to see if the combo valve really works on your rod, be my quest, because that's what the factories had to do on every car that came with a combo valve. One size doesn't fit all in this case. Hellfish, Clamping brake hose, any hose, is not a good idea, requardless who says it is. Best to plug the master outlet port or cap off the lines(s) to the calipers or wheel cylinders. The quick take up master refers to the initial stroke while applying the brakes, not release. Have you verified the master bottoms BEFORE the pedal bottoms out? Have you MEASURED the push rod clearance? Have you re-checked the rear brake adjustment? Leave them on the tight side until the system starts to act normally. These things HAVE to be known/corrected before any additional investigation, or you could be just wasting time.
Haven't measured that yet. I started to last night, but needed to remove the belly pan to get to the MC and didn't have time. Hopefully can take a crack at it tonight. Fitzee's pedal situation is not quite the same as mine. He could get pressure.
One comment on the combo valve. I chased a similar problem a few years ago and what had happened was the piston in the combo valve had gone off center. All the bleeding and stomping on the pedal would not re center it. I took it apart and put it back in the center, re bled everything, and the brakes worked perfect! The off center piston was blocking pressure to the front brakes.
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