Gentlemen,

I recently got my '79 f250 on the road ( a couple of months ago now), and it has developed a vibration when braking. Single piston calipers, 2 wheel drive, automatic.

In the restoration, it got:
- in the front - new pads, rotors turned, new flex lines and steel lines, new bearings; I carefully used hi-temp brake grease on the caliper slider.
- in the rear - everything, every single part except the backing plates, new.

The vibration seems to be in the front. At first it occurred only during heavy braking, but is progressively occuring during lighter and lighter braking.

When I say 'vibration', I mean a variable braking power that seems to vary with wheel speed. The vehicle doesn't shake - it's as if one section of the rotors have less grip than others, so you feel a jerky kind of braking.

I've had the wheels off and inspected - can find nothing loose. Although when rotating the rotors by hand, I do note the pads will shift ever so slightly forward or backward as they are dragged by light contact with the rotor. This contact is very light - rotor will turn easily with a couple of fingers.

I've been hauling loads ~1,400lbs, mostly highway driving, but less than 1,000 miles on them so far. I have had a few relatively heavy brakings because of the loads at speed, but nothing out of the ordinary - I haven't had to stand on the brakes or lock up wheels or anything.

So, I'm looking for the most likely ideas so as not to replace things needlessly - if at all. Optimism hopes it's just a passing phase of break-in. Realism suspects warped rotors.

 

Apply your parking brake only while slowing down. This will let you know if it is a rear brake problem. ALso, some people set a rotor up differently on a lathe and could have caused it to be turned untrue.
Just thoughts.

 

It sounds as if the rotors are warped. I would also recheck the rears, If they are not properly adjusted you will actually overwork and consequently overheat the fronts wich causes the warpage.

Be sure the self adjusters on the rear are working properly...and installed on the correct side.

The self adjusters are designed to automatically adjust to shoe wear, This action happens when you are backing up and apply the brakes......and let the vehicle come to a complete stop.

Too often people just shift into drive from an "almost stopped" speed, And, after a while, the brakes are out of adjustment.

 

True, true,
You are describing a classic front rotor warping.
This is usually caused by rear brakes not being adjusted tightly enough.
Get busy and have the rotors turned. Adjust the rear shoes out until they drag on the drums. They will adjust rapidly from there.
KingFisher

 

I would take it back and stick it their nose and demand them do it right or a new one.

 

Maybe rotors were machined too thin,won't take much heat to warp again.But your description sounds more like a drum out of round or even a rear shoe problem,NEW doesn't mean GOOD.

 

Thanks everyone. Five opinions for warped rotors - I'll have to face reality.

But misadjusted rear drums as one possible cause I hadn't thought of. I'll double check them. Was very careful about putting the right adjusters on the right side - but you never know, we're not infallible. What I didn't have was first hand knowledge of just how snug to the drums the shoes should be. I adjustesd them so they were just barely touching, ust beginning to drag a tiny bit, and figured the self-adjusters would take it from there the first few times I put on the brakes - but I'll double check.

As for the rotors themselves - they're the ones that were on the truck when I pulled it from a farmer's field, and my local machine shop - a good guy who's always willing to try things to save me money - warned me they were at the bare minimum they could possibly agree to turn them at. Guess I got taught a lesson.

 

One thing about self adjusters, they appear to work the best when backing up. If you got the brakes close, but have not done much backing up and stop it might take quite a while for them get tight.

As for the front, have a reputable machine shop measure them and see if they are too thin. If not, ask them to dress them, taking off just enough to make sure you have a true surface. I actually had to do this on a brand new rotor one time to get it to quit grabbing.

My .02