Truck is a '69 Ranchero 302 C-4 power front disc-brakes. The issue has been present since I bought it. The brake pedal has a lot of travel before any brake engagement actually happens, and once it gets to a certain point that the brakes are actuated, it's like 100% full power assist and wants to throw you through the windshield. If the brake pedal is absolutely babied, you can get it to stop normally if you push through all the sloppy travel extremely slowly. Here's what I've done to solve it. New master cylinder, new rebuilt booster, new calipers, new pads, new front hoses, new rear wheel cylinders, rear brake adjustment. I had the wheels off the other day and I noticed the RF rotor didn't spin easily. I pulled the caliper apart and greased the slide pins. Test drove it, and it felt pretty good. However, it got worse and worse until returning to the previous condition. I have also noticed that the RF rotor is much hotter after driving. I'm thinking at this point, either I replace the RF caliper or I take a look at brake pushrod and master cylinder as I've been told a drum brake master cylinder could be causing my issues. Anyone have any bright ideas?
A) Brake booster pushrod may have too much clearance between the brake booster and master cylinder bore. B) Brake fluid steel lines may be corroded internally, causing a reduction in fluid pressure and volume as well as a possible blockage. As far as one caliper/front brake rotor being hotter, this usually indicates a caliper piston that isn't retracting fully, could also be an internally ruptured flex hose(between the brake line and caliper). If possible you can do a pressure check at each corner with brake fluid pressure gauges/plumbing, this will also show that there is very little residual brake fluid pressure once the brake pedal is released(if residual pressure exists on the pressure gauge, the flex line is a very likely culprit). Good luck, Todd
With the engine off, move the brake pedal downward by hand. You will be able to feel when the rod engages the master cylinder. That distance should be around 3/8" at the bar maximum. If engaging the parking brake partially makes the brakes operate better, you have a rear brake adjustment issue. Check the rotors to make sure they run true and have no warpage. I have seen new (Chinese) rotors that were more than 1/8th inch out of true right out of the box. That causes the brake pads to sit too far from the rotor, and will lead to rubbing on one side.
There is no shaking the steering wheel at all, but the truck does dive to the right if I brake hard and take my hands off the wheel.
I don't understand your point. I would imagine that if a rotor issue was so extreme that it caused the steering to shake, you would have resolved it rather than creating this thread.
Yes, I am stating that I don't think rotor runout is my issue here. EDIT: Are you saying really really small amounts of runout could be my issue or contributing to it? I don't have a dial indicator to check it.
Small is a very subjective term. You can look at the rotor and pad position. If there is an obvious gap on either side you have a rotor or stuck caliper issue. (at this point I am leaving the master cylinder out of the equation, not because it can't be the source of the problem, but because other things point elsewhere)
Will a 70 or 71 Torino booster and master cylinder work in my application? Also off a power-disc car.
Updates aplenty. Still haven't 100% nailed down the brake issue and it's driving me nuts. I realized that as I was driving the truck after switching to the Bendix system, that my brake pedal would get higher and higher and I would lose power. Holy schnikes were the brakes dragging badly. Jack the wheels up it was nearly impossible to turn the wheels with two hands. Obviously, it gets progressively worse as the truck is driven more. Seemed like a master cylinder problem, so I get an actual NEW master cylinder from NAPA that is for power front disc brakes. I drove it on Friday night and it's still dragging the brakes but not as badly. Jack up the front end and the wheels are still tough as heck to spin by hand. What gives?! I'm losing my mind over here. My Dad has a 390 GT Torino parts car that was power front discs and I'm thinking about taking the proportioning valve off that car and rebuilding it and seeing if that makes a differnce Here's what I'm working with now. O'Reilly's rebuilt Bendix Booster NAPA NEW master cylinder Proportioning valve rebuilt by myself with kit from West Coast Classic Cougar Disregard edit if you saw it.
Dragging front wheels is a 'stuck piston' issue. You need either calipers or flex hoses, and you should replace both. Are the rear brakes also having a drag issue?
I've actually put new hoses and calipers on both sides. Even fairly recently greased both slide pins of both sides. And by "new" I mean just the stuff you buy from O'Reilly's, and I'm starting to lose faith in them. Yes, I'm fairly sure I have all 4 brakes dragging. I haven't spent a lot of time investigating the rears, however.
Yeezus, I've been helping a friend off Fullsizebronco.com with the major brake issues he had on his '72 F350 CC all weekend long! Full Moon Fever, I suppose....
A lot to ask Mike but something to check if the hoses and calipers check good. On that Bendix booster did you happen to notice if the master cylinder push-rod was adjustable ? It may be adjusted too long and be holding residual pressure on the master cylinder piston. Means that it isn't letting the master cylinder piston fully retract. With everything hot and dragging , try backing off the two master cylinder mounting nuts enough that you can move the master cylinder forward away from the booster. If then the brakes release you have found your problem. Most I find are adjusted too short giving a too close to the floor pedal but now and then I find one set too long causing the brakes to drag. Ever run into that Andy ? Another potential problem spot is the belcrank linkage in the booster mounting bracket on the firewall. It has to move freely without any sticking. Got any freeplay in the brake pedal before you feel the booster start working ? There has to be a tiny amount of play there or the booster will be activated constantly. Brake pedal needs enough play to operate the brake light switch before activating the booster. Some Fords need shims between the booster and mounting bracket to get enough play that the booster fully releases. Hope you find the problem easily.
Also easy way to check and see if it's holding pressure (and keeping brakes applied) is to crack a bleeder open and then see if the wheel is still hard to turn.
No, I've only had ones that were too short. But I do know about the too-long rod--that was common when MCs were remanned and the mechanics would not check the adjustment.
I replaced a rubber brake line on an old VW VAN i HAD A FEW YEARS AGO. Was putting disc brakes on it (A 69) from a 74 or so van. About 5 or 6 months later I stared having a dragging brake problem. I finally tracked it down to the new brake hose. The rubber inside had swollen to where it would pass fluid to the brake cylinder but it would not release the pressure on the shoes until it sat for a while. Cheap parts from somewhere but I paid premium prices for them. Finally bought some genuine VW brake hoses to fix it. Worked fine until I sold it some tears later. By the way I tried to drive that one with out putting the proportioning valve from the donor on it. Back brakes would lock up trying to stop it, even a gentle stop and it had a too sensitve pedal. Had to put that donor valve on the 69 to get it to work right. I also had a vacuum leak on my brake booster recently on my 78 Ranchero. I managed to find one on E-bay rebuilt. It actually came from Summit Racing's e-bay sight where they sell outdated stuff. Anyway I put that on and now the brakes will throw you through the windshield if you push them to quick. They're way to sensitive. I guess the old proportioning valve is bad and worked okay with the old worn out brake booster. I can't find a new prop valve so I'm fixing to take the old one out and clean it up and see if I can find some new parts for it. That prop valve works by sending fluid to the back brakes first until enough pedal pressure is built up send fluid to the front discs. It smooths out the brake pedal so it's not so sensitive. Wish me luck, information's important!
What ended up completely fixing my problem was replacing all the hard lines in the braking system, minus the one that goes to the rear distribution block. I also replaced that rear rubber hose at the rear block at the same time and that large fix solved all my braking issues. So, basically I replaced the entire braking system piece by piece.
Unfortunately, that happens sometimes. But the upside is that you should have trouble-free braking for a long time. Of course, go easy when you first drive it until you've verified all the bugs are worked out.
glad you solved the problem. though sounds expensive. my buddy had issues with the pushrod/master/booster in his galaxie. it was recommended to replace both as a unit to eliminate the hassles of pushrod length checking and mating etc etc. esp with reman units from O reillys and the like.
