1966 brake issues

[jaythejug]

Hey all!
I have a 66 2wd long bed. I drove it daily for the past 2 years.i parked it for the winter and decided to restore the engine and engine compartment. I finished everything i wanted so i can start driving it again and the brake pedal hit the floor. i saw some fluid leaking out the back of the master cylinder. pretty straight forward so far... instead of rebuilding it myself it was cheap enough to get a reman. so i did. installed in minutes, bleed the system and had brakes. a nice hard pedal just like before. i pulled it out of the garage and notice the front brakes were dragging badly. so i broke the bleeder on both brakes and they released. pumped up the pedal agin and they locked. its like the pressure never returns to the master cylinder. pumped it up and loosened the line directly on master cyl. brakes released. so, this tells me its the master cyl. thats the culprit. did some research and found that people will remove the residual pressure valve. i makes complete sense that i do this. so, remove master disassemble and dont find what im looking for. im the second owner with no info and its frustrating as hell.

single master cylinder - distribution block - front calipers - rear drums.

What confuses me is that the master cylinder that i had is no different than the one i bought. i know from what i have been reading that calipers and drums require different pressures and i beleive thats why they remove the residual pressure valve so the calipers can pull back. i really didnt want to replace my whole system right now. i know a dual master is safer! i just want to drive my truck!!

thanks

[Paul Merrell]

It sounds like the brake rod needs to be adjusted. On the brake pedal the bolt that goes thru the rod has a cam and it can be adjusted. I would check that first before returning the master cylinder

[Lowell]

I agree with Paul, If the rod is too long it wont let the piston return all the way and pressure will build up

[bruceandersson]

The font calipers did not come with the truck and are designed to run with a dual master cylinder. I'd try to figure out where the front calipers came from and get the appropriate dual master and install the proportioning valve as well.

[jaythejug]

bruce I agree
I really want to figure out how the previous owner made this happen. the front calipers look like a new after market set up like you would see in a lmc catalogue. I had no issues before. the crappy thing is i returned the old master cy. for the core. so i cant compare the two. im a little reluctant to re-doo the brakes right now. ive been spending a lotof money and time and all i want to do is get back behind the wheel!! Im sure all know what im going through! HA!

bottom line it looks like i have to start from scratch and run a new dual set up. Argh!! I know its safer!

[banjopicker66]

My first suspicion is that the flexible brake lines are swollen internally, but you cannot discern this from the outside. As the old rubber lining inside deteriorates with age, it swells up and blocks the line. Braking pressure will easily force the brake fluid through the line one way into the wheel cylinders/calipers, but but the lines are too swollen to allow the fluid to return for them to release.
We can help better if you can tell us if you have a single or dual master cylinder, and if you know anything about the front brakes.
If you can post some pictures of the discs and calipers, we may be able to identify what you have, and prevent you from spending too much money or time on it.
Many of us have made the front disc upgrade, and are familiar with the possible issues, so don't hesitate to post back.

[jaythejug]

Ive been running with a single master cylinder, front disc and rear drums. I know that technically this set up should not work. but this is how i purchased the treuck and i cant stop thinking about how they made this work so well.
So, I will get pics of what i have this evening. and maybe show off the work i just completed. Ha!

[banjopicker66]

Since it is the incorrect master cylinder, I suspect the previous owner may not have changed the front rubber brake lines (or the rear one for that matter).
If we can figure out which calipers you have first, that will give us all the best indicator of where to start.
Fortunately, the hardest work has been done for you already!

[packrat54]

The master cyl. used on drum brakes has a check valve in it. Disk brakes do not. This valve will hold pressure on the calp.
May be rod length also.

[DanH]

I am not a mechanic as the guys on this forum, and those who attended last slickstock, can attest. But I post this because of my recent 66 brake issue. I had the same issue with the brakes having almost no pedal and then, bam, locking up. After noodling every conceivable issue and fix, it turned out I had a frozen front caliper. Before you tear into a lot, or start parts swapping, jack up the front and make sure you don't have a caliper that's stuck or almost stuck.

[charliemccraney]

I don't believe those single pot mc's have any kind of residual valve or check valve in them. I'm going of memory and recall a pipe thread at the front and you can see straight through to the piston with a flashlight.

[Toyz]

Jay, once again, Google is your friend!
http://www.thebrakeman.com/valvetechi
Charlie, actually, there are two valves in the OEM m/c, one is riveted to the piston, the other is what can be seen thru the discharge port.
This check valve evidently had been removed by the PO to facilitate the discs. Not a very good solution IMO; do yourself and other drivers a big favor and get a dual m/c and proportioning valve, or combo valve.
Paul

[William-in-St George]

Are these brakes boosted? The end of the shaft that is exposed when you pull the master off the booster is adjustable. Turn it in about three turns and try again.

[Toyz]

This is an early Mustang cylinder, parts arrangement is the same. The original F100 front brakes were single piston; I would have some concerns about depending on the single master cylinder even if removing the check valve did not result in failure.

http://www.mustangmonthly.com/techartic ... to_02.html

I'm sure you don't need to be reminded that with a single pot, any loss of pressure will result in NO hydraulic brakes. Good luck stopping it with the hand brake!
Paul