Well, new tie rods, bushings, rotors, shimmy shock and deglazed brake pads-$1000 worth of work and truck still has vibration(gravel road washerboard effect) when I press on the brakes.  Still only when hauling a horse, not when truck is by itself nor when truck is pulling just the trailer.  Does anyone have any insight to what could cause this?

2002 Ford crew cab F350 diesel w/C&C 3 horse slant with 10 foot short wall-24 foot box length.

Is your truck a dually?  The duallys seem to have more brake problems than the SRW trucks.

Did you have new rotors put on the front only and are they aftermarket or Ford Rotors?  Our 2002 truck had the same problem, when we had new aftermarket rotors put on, we tried putting them on the front only but the back rotors were so bad, the shimmy when braking wasn't taken care of until we had new rotors all the way around. 

In addition, to checking your ABS, make sure that your tires are properly balanced.  Tires that are out of balance can cause a shimmy too.

I assume you have disc brakes on front and rear.If it is worse when you pull your trailer, it may be because you put more pressure on the brakes and it picks up on the warpage of the rotor.If you have a dial indicator you can check for run out.

It is also possible the rotors are not machined just right and when you install them you will get a little run out.

It is also important that the hubs be clean and square. Your torque on the lugnuts can cause problems to.

Try just using the trailer brakes,better or worse ?

Try just truck brakes, better or worse ? more front or rear ?

Sometimes the trailer brakes can feel like the truck is to blame. Did it do it before the brake job?

Lots to think about and process of elimination.How are your bearings?

I had a 2001 F250 cc pulled a4 horse slant and when it got dust in the trailer brakes it acted like it was grabbing. Washed the dust out and worked fine again.It was also touchy on where i set my brake to come on.

Good luck and yea try a different horse or have someone ride in the trailer a short distance to see whats goin on there.

It does sound like an anti-lock problem if it occurs when you go over a bump.  You might try posting your problem here:

http://forums.thedieselstop.com/ubbthreads/postlist.php?Cat=0&Board=towing1

There are a lot of knowlegable people there (including Ford techs), they might have an answer for you. 

Thank you so much for suggesting the diesel stop site!!!!!  It was a godsend.  NOW>>>>>>>

Guess what????? I swapped brake boxes on the two vehicles I pull with and BOTH vehicles pull the trailer and horse with NO problem whatsoever now. By the way, never had a problem pulling with the other vehicle(96 Chevy 3500 diesel extended cab with Draw tite brake box), only with the 02 Ford with Tekonsha Voyager brake box. After talking to a trailer dealership in town, I found out some interesting things. Seems the Tekonsha Voyager brakebox combined with the 02 Ford antilock brake system and certain weights(trailer and cargo) have had problems. It is not very common but then again not uncommon I was told. When you hit a bump and are braking, the balance pendulum vibrates in the brake box, thus causing the antilock brake system to come on and off. Rate of on and off depends on vibration of pendulum with is a tiny thing so on and off is at a very fast rate giving a vibration or slight jerking effect. Dealership says it is the Ford braking because they have never had the problem with the Chevys. Seems to me like a glitch Ford needs to fix in the anti lock brake system. Or maybe change the sensitivity of the pendelum in the Tekonsha brake box?????? Anyway, I AM FIXED and so relieved!!!! Happy and safe hauling!!!!!!