I am working on my dads 24 Bucket T. It has a 1966 mustang dual bore master cylinder and Speedway front disc brakes kit. The issue is the brakes are sticking closed. They are really heating up and I dont even have to hit the brakes to stop. I jacked it up and the rear wheels move freely and then the front and they are locked up. I loosened one of the bleed screws and fluid came out and they released so I am confident it is not the calipers. Master cylinder? or something else?
First thing to check is that the pedal is fully returning and there is free play in the rod. No pressure or contact in the master, Next is that any residual vales are working correctly, there may be residual valves in tha master already and an additional residual valve may complicate and compound into the proble you have. Start there
Is it all new parts? Possibilities... Front hoses collapsed inside.(on an old system) Residual valve too high of pressure rating. Pedal may not be allowing any freeplay from pushrod to master cylinder. Sent from my Moto G Play using The H.A.M.B. mobile app
Check the front brake hoses , if they can collapse internally and hold pressure and not release, check and see if the master cylinder has a internal check valve , if so is it for drum or disc brakes there is a difference.
This was all on here before I got the car. It looks all new. The front disc brakes and hoses are new. The master cylinder looks new. There is a difference for master cylinders for front drum and front disc for 1967 mustang master cylinders. If it had a drum master cylinder would that be a symptom?
Any drum brake ever made needs a residual valve. Some master cylinders have that residual valve installed in the port, they are removable. The presence of that valve will change the the application and the part number to correspond with drum brake application. Again some, some master cylinders are exactly the same except for that valve. Now your problem may or may not be related to that little fact. Any under floor master needs to have residual valves 2lbs for disc and 10lbs for drums. It's completely plausible that you have the equivalent of 10lb residuals for your front brakes. It's more probable that the pedal is keeping tension /pressure on the master cyl. So check that first. Also, sad to say but in today's parts world, we need to retrain our thinkers than "new" no longer means good. The best way to think about new parts is that they have yet to prove themselves and are still suspect until proven good. Just the way it is.
When calipers were locked up - you check both, right?, and when you cracked a bleeder and pressure shot out you said it freed the wheels, did you check both of them or the wheel you were working on?
I'm with the first person who responded. Check to be sure there is some free play in the pedal at the top of the stroke. The pedal rod between the pedal and the master cylinder may be adjusted to tightly. First thing to check.
Had to look that one up. It looks like the disk brake 66 Mustangs did have dual master cylinders . I sure don't remember many of them though. I'd go along with pedal adjustment and on the T the lack of a return spring on the pedal to pull it back off the piston of the master cylinder. If it is adjusted up too tight it can put pressure on the front brakes or cover the return hole in the master cylinder so the fluid doesn't return back to the reservoir as it should. First thing I'd do is slide under the car and make sure there is some slack in the movement of the push rod before it engages the piston in the master cylinder. You can probably reach up and move the pedal by hand and watch what happens. If there isn't a return spring on the pedal I would be figuring out how to put on on it. The weight of the pedal may be applying pressure to the front brakes without one. The springs on the rear drum brakes will hold the shoes in until you apply pressure but the disk caliper pistons don't take much pressure to cause a drag.
Yes both were locked up. When I released one bleeder screw they both became free. I will check the spacing for the push rod next. So I understand the different pressures between disc and drum so would a drum/drum master cylinder cause this issue?
Make sure the ''byp*** port '' in the master cylinder reservoir isn't blocked with crud (there are two ports in the bottom, the byp*** is the smaller hole) This is also the hole / port which is affected by the push rod being out of adjustment.. With the master cylinder in the released position, and you have a skinny piece of wire, check to see if it's blocked, if clear, you should be able to carefully slide it thru the port a little way till it touches the piston, if it starts and touches the rubber cup, the push rod needs adjusting..
The MC doesn't know the difference between disc & drum, its is a hydraulic pump like the one in your floor jack. ***igning pressure is done in the 'combination valve', that is the gizmo most refer to as the propotioning valve but looks more complicated.
If both wheels free up with cracking one bleeder then the problem is likely located at the input end of master cylinder. What's at the input end of the master ???? The internal piston returning fully that allows the fluid pressure to release .... The push rod from the pedal... And the pedal itself ... If a component fails to produce the designed out put ((( in your case it's allowing the releasing of the brakes))) you need to verify that component is getting the required and designed proper input.
My bucket had set in the barn for a few years when I decided to resurrect it. Had the exact same problem. Goo in the bottom of the master reservoir.
Found the culprit. The rod that is going into the master cylinder is thick and has a slight angle to it which causes one side to be bigger than the other. If the side that has the the holes on the clip is at the top the rod will hit it. So I moved the holes to the bottom. I took a hammer and bent it back to being straight and its working fine. Problem solved. Thanks to everyone who said it had to be at the end of the master cylinder.
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