I seem to have a problem with the front brakes on my 78 F150. The disc brakes on the front seem to be way too tight. If you jack up a wheel it takes quite a bit of effort to roll a wheel.

I have replaced both front rotors, calipers and brake pads and it doesn't seem to help.

Is it possible that the proportioning valve may be sticking and holding pressure on the front brakes? Is there a check valve or something that I don't know about?

When I first got the truck I noticed that there had been water in the brake system. When I rebuilt the back wheel cylinders they were corroded from water contamination.

Is it possible that the proportioning valve may be corroded too?

 

[updated:LAST EDITED ON 11-Aug-02 AT 01:22 AM (EST)]yes it is possiable but highly unlikely, sounds like the seals in the brake master have swollen. Was there extra effort needed to bleeb the brakes?? Did the pedal return back properly or was it slow to rise? Also take a look at the hoses and make sure they are in good condition, if they are cracked replace them.

Don't quote me on this but i don't think there shold be a check valve in the lines for disk barkes

jeremy

 

could be the master cylinder. An easy way to see is to jack up the front. See how tight the wheel is, then loosen the rear line on the master cyl. until fluid runs out for a second. Tighten it back up and check the wheel again, if it is free, then it is the master cyl. If not, well, I have seen some snug fits with new rotors, pads, and such. Have you drove it since you installed the brakes? Do both sides feel the same?

 

Could it be the wheel bearings being too tight? Just a thought.

 

Hmmmmm.... I've double checked the wheel bearings, they seem to be OK. I'm not sure about the brake pedal because I had my son pump the pedal when I was bleeding the brakes.

I've driven the truck a couple of hundred miles since I rebuilt the brake system. Some days the truck seems to drive just fine and other days if feels like you are dragging an anchor. That's why I started looking for a brake that was dragging.

Both front wheels seem to have the same resistance.

The rotors haven't seemed to have discolored from excess heat, but there seems to be an excess amount of brake dust.

I'm going to check the master cylinder. That's something I haven't looked at yet.

Thanks guys for all your help. If you have any other ideas let me know. I can't find a check valve in the Haynes manual, but that doesn't mean there isn't one.

 

I am having a similar problem with the left front wheel on a van. The two things I am going to look at when I get the time are:

1- Check the caliper piston for corrosion or swelling. Some calipers use plastic pistons.

2- Check the brake line for a possible collapsed lining. This can make the line act like a one way valve.

 

Open bleeder screw on suspected tight wheel,when you think its tight if there's pressure,keep opening up system back to masterC until you find culprit.

 

I once had a problem with my front brakes dragging and it turned out to be the proportioning valve. There's a pin type thing in there that is supposed to be centered between the front and rear brakes. When I put on a new master cylinder it got shoved to one side. I had to take it apart and recenter the pin then everything worked fine.

 

[updated:LAST EDITED ON 12-Aug-02 AT 09:56 AM (EST)]I've seen the same symptoms you describe, caused by a vacuum booster that is adjusted too tight. Had to remove the master cyl and adjust the rod shorter. It was keeping pressure on the master cyl.

Might want to loosen the master cyl from booster and see if the wheels spin easier, if so then just adjust the rod from booster to master a little shorter (just a little)...

Just a thought.

Marty

 

Had an old dodge with a dragging front brake, turned out to be a bad flexible hose from the frame to caliper.

Bob L

 

I eliminated the master cylinder. I just went ahead and replaced it for grins.

I'm beginning to think it's in the proportioning valve. After the truck sat for two days while I rebuilt the steering box, the wheels freed up.

After I drove it to test the steering box, I came back and the wheels were stiff again. I released a bleed valve and the wheel freed up.

I noticed that the wires had been disconnected from the valve I suppose to turn the warning light off.

Like someone said earlier, I'll just keep moving down the line until I find it.

I need to check brake booster as someone suggested also. I replaced it sometime last year because it was leaking. I also need to check the flex lines too.

I have to find it soon, there isn't much left.:P

 

 

A quick way to see if it is the booster push rod adjusted too long is drive the truck til you get the brake drag. Lift the front wheels of the ground and then back off the master cylinder bolts so it moves forward from the booster. If the wheels now rotate freely the booster push rod is too long and is applying your brakes for you. I've seen some trucks that work fine cold, but when the brake fluid warms up and expands after a few good stops the dragging starts. I think the spec for the push rod length measured from the booster to the rod tip is about 1".