71 F100 brake issues, Help

[SublimeSam]

Hello All,

First I appreciate any help given.

after digging around these threads and others I have some questions and need some advice.

What I have:
71 F100 with what I'm told has brakes from a 81 F150. Got it from a guy who had it for 3 months then had financial difficulties. he bought it from the guy who supposedly installed the motor, trans, and front disc brakes from a junk yard F150.

Issue/Problems:
The brakes are almost non existent and the petal goes all the way to the floor. feels mushy and scary

What I have done (before I started reading through the threads):
I have replaced all the Rear Drum brake components, drum, pads, springs. I have replaced the booster and master. Flushed the lines and bled the brake lines. Had Help and did it 3 times until I saw nothing but fluid come out.

Questions:
with everything replaced would this issue be because he did not install the Master and P-Valve from the F150?
May there still be some air in there?

This Truck is "New" to me and I would love to drive it but cant until I have this dangerous problem resolved.

Thanks again everyone!

[hillcountryflt]

Start with the basics. How is your truck setup. If the brakes were pulled from a newer model truck does that mean you have front disc brakes. Is the p-valve a really small, like fits in the palm of your hands size and has no brass "tit" on the front of it. If so that would indicate it has the original p-valve. If your truck has disc brakes, it would need a different p-valve. You started bleeding from the right-rear, then left rear, then right-front finishing up on left front. Are you sure your master cylinder is good and if so are your sure it is the correct one. However, even an incorrect one should probably be able to provide "pedal" if installed and bled correctly.
and of course, no leaks are obvious. You don't want to see any bubbles in the master cylinder. And yes, it still sounds like you have air in your lines.
Can you get pedal by pumping the brake pedal.

[SublimeSam]

Only the disc brakes where installed from an 81 F150, the booster and master are from 71 so no p-valve. From what I have read the master should be a disk/drum master. Since it's the original to 71 style (new re-pop master from advanced auto) it is the Drum/drum master.

I did bleed in that order 4 times now. And yes it does have pedal if I pump.

Do I need a master and p-valve off a 73+?
Could I order a 73 master from Advanced/auto Zone with a p-valve and solve some issues?

Thank!

[ultraranger]

I think there's possibly been some misinformation given on the brake parts. For a disc brake conversion on '67-'72 model trucks, using donor parts from later model pickups, 1979 is the cutoff for swapping disc brake components/I-beams (1973-1979).

In 1980, Ford no longer used king pins in the spindles. They went to ball joints. The spindles aren't the same as the '73-'79 spindles and the caliper anchor bracket mounting points are different on '80-86 than the '73-'79 models.

A 4 wheel drum brake system will have a pressure differential valve.

A disc/drum system will have a combination valve. On a Ford truck, the disc/drum combination valve will have 3 functions contained within one valve body assembly: a metering valve for the front disc circuit, a pressure differential valve (like the drum/drum valve) and a proportioning valve to control the rear brakes in a panic stop situation.

It is possible to use a drum/drum MC in a disc/drum application but it's not recommended. You have to make sure that a drum/drum MC does not have a residual pressure valve (RPV) under the seat of the primary MC port that supplies fluid to the front (disc) brakes. If it is present, it will keep a constant amount of pressure applied on the caliper pistons which will cause the pads to drag on the rotors --even when you aren't pressing down on the brake pedal.

If the RPV isn't present, or, is but has been removed, the next potential problem is brake fluid volume in the MC primary reservoir to the from brake circuit. An actual disc/drum MC will have a higher fluid capacity than a drum/drum MC. A drum/drum MC used in a disc/drum application may initially have plenty of brake fluid to supply the brakes with but as the brake linings wear down, the fluid level inside the MC will also drop. Disc brake pads are generally much thicker than drum brake shoe linings.

The disc brake pads can wear down to the point that the drum/drum MC runs out of reserve to supply fluid to the front discs. If the drum/drum MC runs out of reserve, you run out of brakes.

Most parts stores OEM replacement MCs no longer come with an RPV installed in the port (s) that supply fluid to a drum brake circuit (s) but, sometimes they are present. --it's always best to check before installing a MC. RPVs installed in the MC have pretty much been made obsolete by the installation of cup expanders inside the drum brake wheel cylinders. This is why many parts stores OEM replacement MCs no longer come with RPVs installed, even though it may have been present in its original factory installation.

If you are having problems getting a firm brake pedal, the two most likely cause are air in the system or the pressure differential valve spool has shifted off center. If your brake warning light is hooked up and the bulb is lit (assuming the bulb isn't burned out), you'll first have to recenter the valve and then complete bleeding the brake system out.

Since the front is converted to disc, the best thing you could do is replace the drum/drum MC with an actual disc/drum MC (best to buy new not rebuilt MC) and install a disc/drum combination brake valve.

Before doing any brake bleeding, this simple tool can save you from a lot of aggravation of the pressure differential spool shifting off center.

https://www.musclecarresearch.com/brake-valve-tool

[SublimeSam]

Thank you very much UltraRanger. you are very informative and your info has helped me very much. what you say is correct I was misinformed the only thing that is an 81 piece is the C6 trans, it was manual. turns out the motor is original and you touched it on the disc brakes.

that's what you get for buying a used vehicle that some one else has tinkered on.

I just found a 77 on Craig's List that is parting out. the guy told me he would pull the brake set up from the combination valve to the MC for $75. Ill replace or rebuild the MC, I'm sure it will not be pristine. So that way I will get all the correctly bent lines, hoses, booster, etc.. you think that is the best rout at this point?

Thanks!

[ultraranger]

Thank you very much UltraRanger. you are very informative and your info has helped me very much. what you say is correct I was misinformed the only thing that is an 81 piece is the C6 trans, it was manual. turns out the motor is original and you touched it on the disc brakes.

that's what you get for buying a used vehicle that some one else has tinkered on.

I just found a 77 on Craig's List that is parting out. the guy told me he would pull the brake set up from the combination valve to the MC for $75. Ill replace or rebuild the MC, I'm sure it will not be pristine. So that way I will get all the correctly bent lines, hoses, booster, etc.. you think that is the best rout at this point?

Thanks!

I would get everything except the MC --or, at least I wouldn't use the donor MC. I would buy a brand new (not rebuilt or used) MC.

I have all the disc brake/I-beam components from a '77 F100 to swap over onto my '69 Ranger.

[elliottboo]

I have a 71 that I just replaced the front drum brakes, and wheel cylinders on. Bleed the brakes starting with the rr, lr, fr, fl. And I still have NO pedal! Checked everything a couple of times and still no pedal. Took it to a shop that original replaced my MC, and they couldnt tell me why it won't build pressure.

Here's the weirdest part, not running it'll build pressure by pumping the pedal. Running it has no pedal. I don't get it. I also don't get why, when bleeding the brakes that my MC WOULD drain the small front reservoir for the back and the large reservoir for the front.

Someone help I'm missing something somewhere.

Also, when bleeding brakes.... Is it with the cap on the reservoir or without it on? Running or not running with a brake booster?

[HIO Silver]

I have a 71 that I just replaced the front drum brakes, and wheel cylinders on. Bleed the brakes starting with the rr, lr, fr, fl. And I still have NO pedal! Checked everything a couple of times and still no pedal. Took it to a shop that original replaced my MC, and they couldnt tell me why it won't build pressure.

Here's the weirdest part, not running it'll build pressure by pumping the pedal. Running it has no pedal. I don't get it. I also don't get why, when bleeding the brakes that my MC WOULD drain the small front reservoir for the back and the large reservoir for the front.

Someone help I'm missing something somewhere.

Also, when bleeding brakes.... Is it with the cap on the reservoir or without it on? Running or not running with a brake booster?

Sounds as if your shop installed the wrong MC. I think on 4 wheel drums that the reservoirs are equally sized.... and the rod between the booster and MC needs to be adjusted.

The cap can be off during bleeding. Just don't stomp on the pedal or you'll end up with a big mess. The engine is off during bleeding.

[ultraranger]

I have a 71 that I just replaced the front drum brakes, and wheel cylinders on. Bleed the brakes starting with the rr, lr, fr, fl. And I still have NO pedal! Checked everything a couple of times and still no pedal. Took it to a shop that original replaced my MC, and they couldnt tell me why it won't build pressure.

Here's the weirdest part, not running it'll build pressure by pumping the pedal. Running it has no pedal. I don't get it. I also don't get why, when bleeding the brakes that my MC WOULD drain the small front reservoir for the back and the large reservoir for the front.

Someone help I'm missing something somewhere.

Also, when bleeding brakes.... Is it with the cap on the reservoir or without it on? Running or not running with a brake booster?

I'm not clear if you have a power brake booster (?). If you do, loosen the two nuts holding the MC to the booster studs (will require a 9/16" end wrench or socket) and slide the MC a little bit forward, away from the booster. Look and see if the back end of the MC is wet with brake fluid.

If it is, the MC is bad and if you have a brake booster, the brake fluid from the MC running over inside it will dammage the rubber diaphragm inside and the booster will soon be bad too. This means the booster will have to be changed out as well.

I don't know if your MC was a rebuilt unit but, if so, I would suggest buying a brand new MC and not a rebuilt one. Rebuilt MCs generally don't last very long and they have a high failure rate.