I have a 79 ford f-150 4x4 disc up front drum on back.my question is that my brakes seem fine until i really got to stop.i cant lock up the brakes i really got stand on them.i replaced everthing but no luck. I have 35" tall tires but i had trucks like that before and never had a problem.just seems like i dont have the pressure to clamp down good. need some help thanks.

 

you probably need to adjust the rear brakes and might need to change the front pads and machine the rotors, more than likely the rotor's and the drum's are glazed up

 

I put new drums on and had rotors turned. i got the rear brakes adjusted up and tried different brake pads up front.

 

if you did all that it is probably going to be a bad master cyl, could also be a weak booster. check the check valve in the power booster to make sure it is not leaking vaccum. it should only allow air flow 1 way

 

yea, i put two different mastercylinders on too.new ones. Could it be wrong calipers maybe.

 

I have a '77 F150 4x4 and I have never been impressed with the breaks, even with stock tires. I currently run a 30x9:50-15 tire wihich is only about 1" over stock and I cannot get the front to lock up. I have replace everything but the brake booster and there is nothing leaking. In another thread somewhere I read where the fix was to aquire a booster and master cyl. assy. from a like year F350 and this would cure the problem. If I remember my hydraulics right, if you have a slightly smaller dia. piston in the master cylinder you'll obtain a higher pressure at the calipers but you have to be careful because a smaller dia. piston will displace less fluid per stroke. ANYBODY ELSE GOT ANY GOOD IDEAS? (And I'm not yelling.)

 

I thank i heard that to but i think the calipers would need to be changed also.

 

My truck is undergoing a staged restoration. Last winter I completely rebuild the brake system. I installed new stainless steel lines, new rear cylinders, new master cylinder and new front calipers. I still have the same problem as before. Looks pretty but still doesn't lock up the front end. I can lock the rear's with no problem.

 

Think of it as a poor mans ABS. If they do lock up, you won't be doing any steering!!! Being as a truck has most of it's weight on the front when the bed is empty, it is going to be hard to lock up the front's anyway.
Jimmy

 

That would be your problem.

I have never had a problem with my brakes, Ford brakes are usually never complained about.

You really shouldn't be able to lock up the front brakes.

 

they do not offer a different caliper for the front of the 1/2 ton truck's. they were all a single piston caliper. the majority of the braking is done with the front disc brakes, should not be impossible to lock them up but those 35's definetly don't help.

what kind of pads did you put on it? metallic, semi metallic or just plain organic? that will make a difference also

 

The F350 upgrade is discussed step by step in a tech article about upgrading 78-79 Bronco brakes. The upgrade will work identically on any 73-79 F100/F150 2wd/4x4 with front discs.

Do a search, several users have posted how they liked the upgrade.

Marty

 

quote: "they do not offer a different caliper for the front of the 1/2 ton truck's. They were all a single piston caliper. the majority of the braking is done with the front disc brakes"

One question on this... I have a 78 F-250 supercab (disk front and drum rear) and the brake pedal started dropping to the floor. I can stop, but not nearly well enough to trust, especially since the pedal drops enough to make the brake light come on.

I don't appear to have a vacuum leak. When I take the check valve off and plug it, the brakes give me more difficulty pressing (no assist) but the pedal still seems to drop too low (I havn't driven it like this for safety/scaredy cat reasons).

Anyway, I'm assuming that the M/C has blown. I havn't pulled any wheels yet since it's really cold out, but I will if I need to.

Finally, my question: My auto parts guy just asked if the M/C is a single or twin piston. I guess from the quote above that it has to be a single? Otherwise, I'll go out and pull a tire... brrrrrrrrrrrrr.

Also, anyone see anything wrong with my troubleshooting before I replace a working M/C. I'm just a weekend warrier with the truck, so I'm not the best diagnoser.

thanks and cheers,
Stanky (Aaron).

 

Did you bleed the proportioning valve by pullin the pin ......to bleed the fronts properly?

 

Your auto part's guy is asking you if the M/C is a single or dual piston??

I am reffering to the caliper on the front wheel, all 1/2 ton trucks are a single piston caliper, 3/4 ton and up are a dual piston caliper, maybe I should rephrase that. I am almost certain all 3/4 ton are a dual piston. There is no need to pull the wheel to check, just look at the caliper. It should be pretty easy to determine if there is a single bore or dual bore on your caliper

the M/C is a dual reservoir, the single reservoir went out a long time ago



When you take the check valve off after having the truck running did a bunch of air escape from the booster? If so then there is no leak. Pulling and plugging the check valve will do exactly what you said, make the pedal harder

Did this problem out of the blue just start or was there work done on the brakes prior?
Did you look for puddles of brake fluid on the ground for a bad rusted brake line?
Is there brake fluid leaking between the booster and the M/C?

If it has just started to do this for no reason it is more than likely a bad M/C