I have a 1987 Ford F150, and after the engine (5.0 windsor V8 with 96,000 miles) has gotten sufficiently warm in a day, the cab and the steering column start to shake.
It shakes whenever I get up to about 30-35 MPH, and whenever i hit the brakes. After the truck has had several hours to cool, it starts perfectly fine and runs just as smooth.
does anyone know what's going on?

 

I'm not entirely sure I understand what's going on here...but if it is what I think it is, try the cab mounts and their bushings. How many miles are on the truck itself, and how's the cab floor?

 

So the truck shakes in the 30-35mph range and also when braking?

Does the shake occur in the steering wheel or more under your butt? If you can feel it in the steering wheel then you have a problem in the steering components; possibly a bad alignment, bad tie rod ends, ball joints, etc.

When you feel the shake during braking, can you feel the shake in the brake pedal? If so, warped brake rotors most likely.

Other than that, I've got my money on out-of-balance or out-of-round tires. Took my local tire shop 3 visits before they finally found that 3 of my 4 tires were WAY out of round, and it was giving me a pretty good shake. Good luck!

 

the engine is original, the truck is the same age. 1987
and basically, after i've driven like 30 miles or so in a day, and gotten the engine nice and hot, when i get the truck up to 35 MPH the cab and the steering column will both start to shake, and when i apply pressure to the brake pedal, until the speed is under 35 again..

 

it's both in the steering wheel and under my butt. and the brake pedal doesn't shake.

 

Only when the truck is hot... Very strange... How about if you run it up to speed when it starts shaking, get on a straight, long, empty road, put the tranny in neutral, and turn the engine off. Does the shake continue?

 

Maybe it isn't what I figured it to be...now that I think about it, you might want to get the tires balanced, just in case. My truck had the tires balanced before I bought it, and it doesn't shake...I just feel every imperfection in the road due to a very stiff suspension. And check the engine mounts, too!

 

while i'm driving if i take my foot off the gas it'll stop shaking, it's only when i give it gas, or when i brake up until i stop.

 

Only when you give it gas... Yeah I would suspect engine mounts first... Check those.

Someone posted the other day that you can put the truck in reverse, and have someone hold the brake (and parking brake) REAL TIGHT and give it some juice while you look at the motor mounts. If the engine lifts up off of the mounts at all then they are bad. Unfortunately if it DOESN'T move you can't be sure that they are good, at that point you would have to lift the engine a bit to check them. Good luck.