Hello looking for some help here and thanks for replies.

I have a 68 f100 with the 75 disc brakes. I've been trying to get my brakes perfect. I also have the dual diaphragm power booster set up.

My problem is my brakes work fine but after about 10 minutes of driving the fronts start to drag and get hot. The pedal even gets stiff.

Why would this happen?

Maybe the brakes have air at start up and kinda bleed themselves after a short drive and brakes get tight?

I have bled the brakes and seem to get all the air out.

I will shorten the booster rod for a quick fix so when brakes start to warm up they won't start to drag.

Anyways looking for suggestions and what is causing this.

Thanks
Kenny

 

Kenny, pop a bleeder screw open when you are having the problem. See if you have a pressure squirt before the dribble. Then come on back in and we will brainstorm the issue.

 

My bet is the adjustable output rod between the booster and the MC is adjusted too far out and keeping the brakes partially applied at all times.

 

I agree . Rod is keeping master applied . Or a restriction not returning to the master .

 

You don't say if started with rebuilt calipers or using old ones that have been sitting for some time?.
New or rebuilt master cylinder ??
If using old junk yard parts then that could be your problem.
Orich

 

I had this same issue with the drum brakes on my truck. The cause was the rebuilt master cylinder not releasing all the way. It slowly built up to cause the brakes to drag after going through a couple lights. As the others have stated though it could be bad hoses, calipers, or master cylinder.

 

Thanks for the replies. Info I left out is all new brake lines, new booster, new 2005 Explorer master cylinder.

So it's been a busy work week but I believe I know the problem and I will find out this weekend. I have the rod now adjusted right and no dragging. But like before the brakes start out soft and begin to firm up. The problem has to be a bad hard brake line not sealing, bad flare?. So I will be checking that.

I will get back this weekend.
Thanks again
Kenny

 

Not to say there might not be a leaky flare connection but, a leaky connection would tend to cause the opposite problem of a firm brake pedal. A leak would cause a drop in hydraulic pressure in the brake system. This would make the pedal feel mushy or cause the pedal to travel nearly to the floor. Is the brake warning light on the dash hooked up and is it lit up?

When you put the calipers on, did you lubricate the caliper slides with synthetic caliper slide grease?

What type of line do you have going to the booster? Is it 3/8" rubber fuel hose or, is it actually vacuum hose? There is a difference and a rubber fuel hose can easily suck flat after a few minutes run time and cut the vacuum supply off to the booster.

 

And what about the calipers

A bad flare should be leaking not build up pressure in the system.

Digital inferred temp gun check the temp of the rotors and see how hot their getting after a few minutes driving when you notice the pedal is hard.
This was how, I've found a dragging wheel brake.

Orich

 

Thanks Orich
I have rebuilt calipers but haven't installed yet. I'm planning on that last.
Also what temp did u find on the calipers when they are working properly?
Kenny

 

For my way of driving the rotors oh sorry I had drum at that time I think was like 180 rears, an think 212- 217 fronts drums.. I had check them a number times this is what I seem to remember.

I have not checked disc rotors brake system as have not had any problems since installing.
Orich

 

Ok so I have my brakes pretty close to perfect. I had my new 16 year old driver do the test drive. He thought the brakes felt good. I find that sometimes I ignore the problems.

Anyways thanks again for the help. The problem was actually basic and you guys recommended it.

So first I tried to get the booster/master rod adjusted. If anything make sure no drag. You can almost do this by lifting the truck on stands and making adjustments. When you press the brakes check for drag when you let go, if the wheels are turning should be good. Also when you go on the test drive and you are at a stop see if the car will move at idle. If it don't the front brakes are probably dragging.

Next adjust rear brakes. I kinda thought they would adjust themselves but I found out that you really need to do a minor adjustment. So if your parking brake isn't working it's probably because your rear drums aren't adjusted properly.

My brakes are now working great. My problem this week was I was focused on the booster/master rod adjustment. It would seem fine but after a short drive the brakes would normally heat up and expand and the dragging would get worst to the point that the calipers would smoke. So I kept trying to adjust the rod. This was my mistake. I needed to start with the basic and get the rear drums adjusted first and then focus on the rod.

Anyways most of you guys know this stuff but it really stumped me. So I will drive to work this week and see how they perform. I plan on changing my front calipers and pads and also change out the rubber lines and get maybe some stainless steel braided lines. I just need to find where.

Anyways thanks again
Kenny