Slick 60's

The truck pulls to the left (badly) on panic stops. I have manually adjusted all brakes. PO claims full out brake job 1 year ago. Upon examination, I have no reason to doubt him. Even lines were replaced. I tried to over adjust the right front and under adjust the left for grins. This made only a little difference. The left front locks up before any other wheels.

If I stop nomally all is good. The truck does veer to the left as well. Could this be a suspension issue?

guess the first question i need to ask is do you have the single mc or has it been converted to dual?
the left front wheel cylinder is closest to the mc, therefore if any air is in the line it will likely be on the right front, and the left would lock up.

as to the steering and suspension components yes, things out of whack can cause this, in a 4x4 it can be the knuckle bearings, wheel bearings, spring eye bushings, loose tie rod ends or even the steering gearbox.
when you jam on the brake, the action of the sudden stop can move the loose component -for ex. -loose wheel bearing causes drum to roll unevenly around the shoes, you jam on brake and it gets tight, locking up.
veering to the left does indicate that the front end needs examination. jack it up so both sides are off the ground and see what moves that should not.

Could be, more likely it is mismatched wheel cylinders or improperly fit shoes and drums.

You can rule out alignment if the truck drives straight and does not pull when you are not braking. That is of course unless you have worn suspension components or possibly broken leafs in your spring pack.

In the old days brake shops would turn (machine) your drums then re-arch your brake shoes to match. Now with the fear of asbestos no one does this. Without proper contact braking performace is diminished dramatically! You can however reshape the shoes for better fitment with an arbor press and some creativity.

The other thing to look for is the wheel cylinders themselves. They should always be replaced in pairs and checked to make shure the bore size is the same. For example if your left side wheel cylinder is 7/8 and your right is 1" the truck will pull to the right under braking.

There are always silly mistakes like a wheel cylinder installed upside down, the bleeder needs to be at the top. Or putting the brake shoes on backwards, the longer friction surface goes to the rear by the way.

If you've checked the master cylinder and it's o.k. then it sounds like you need to take the front rubber brake hoses off and replace them. If they're the originals, the rubber has most surely swelled shut, keeping pressure on and causing on of the cylinders to be tighter than the other.
When you get them off, cut them in half and take a look. I think you'll be shocked at what you find.
U@ss

Make sure the wheel cylinder on the right side hasn't frozen with rust & gunk. My Son's truck was like that when he first got it, the pistons were frozen in the cylinder, making only the one wheel grab.

The easy way to check would be to pull both drums (one at a time) & have a helper lightly press the brake pedal (not more than halfway). You should see the shoes spread at the cylinder, when the pedal is pressed.

I'm with Steve, another problem is "Bell Mouthed" drums.

A result of overheating during heavy or hard usage over time, it's not wear it's distortion. Especially if drums were on the margin when last turned or trued.

FBp

It is a power assist dual MS. I will check for air in the lines. All cylinders, bearings, hoses and shoes were replaced and look good. The drums were turned, but who knows if they are true.

As for the front-end, I am not sure what needs to be done. The ball joints on the drag line rotate real easy and probaly need replacement. The steering seems to have too much play, but I am not sure if this is normal for this truck or not. It steers god and easy. Shocks are dead and getting replaced next week. A metal clunk is heard when executing a sharp turn. It was suggested I check the king pins. How do I do this? I have a 70 f-150 2WD and the front end in not even close to a staight axle 4X4!

Thanks to all for the replies

There are king pins in the Twin I beam to Spindle connection.
Also check inner pivot bushings of the Twin I Beams, radius arm bushings at mounting point back where radius arms meet frame rails. I'd take a look at the centerlink ( piece that strings steering together with pitman arm).


FBp

To check the king pins you need to jack up axle so the tires are of the ground and push in at the top of the tire if it moves in the king pin is worn but you need someone to look and see if that is where its moving and not the wheel bearings. You should also check the springs on the front axle but you have to jack up the frame and not the axle jackup the frame so most of the weight is off the axle you can tell this because at the front of the spring will not be touching the spring hanger bracket but not touching the spring retaining bolt. Then you can push back and pull forward on the axle and see if the spring pins are worn you should have no loose moition in the spring pins.

Paul,
He's not talking about a 4X4, or a 64 with single I beam. He's talking about his '70, F-150, 4X2wd. There aren't any front spring bolts in a 70 F-150 4X2Wd, twin I beam front spring system. Coil springs are simply clamped down and that's all there is to it.

Only vehicles with semi eliptical front leaf springs, like those in the rear of a 70 F-150 4X2Wd or rear of any 65-79 for that matter have.

FBp

MY BAD

me too.

Don't laugh at this, but when I was a youngster, working at a service station in high school, I was cautioned to not get grease on the flexible brake lines because it would cause the brakes to "grab". We tried it to see if it did, and it was true!! When a glob of grease was on the flexible line, the brake grabbed. When we cleaned it off, the brake no longer grabbed. So, if everything that has been suggested here does not correct the problem, check for grease on the lines.