Okay I should have done more research before starting this project.
I swapped front ends droped the old and installed a 91 straight axle out of a F350 into a 1990 F250. probably screwed up I did not change the springs. The track bar mounts were diffirent so I cut and modified it to work with F250 mounting bracket. I am using the original steering arm from F250 should I have changed that as well. I have the F350 so any parts I need can be gotten. Drives okay however hitting a small bump sends it into the wabble.
Any and all help
Truck the straight axle was put into is a 1990 F250 4x4.
So tell me what I did wrong so I can get my old truck back to being safe to drive.
Thanks
Tim

 

Need to change the springs probably. My guess is the caster is out of whack causing the wobble. you can ship the kingpins, but that is only a bandaid. If you have the donor truck... why didnt you just do it right the first time?

 

F250 springs are much more rigid than the F350 springs; with the 250's TTB they're responsible for locating the axle, which is done by the track bar in the 350s. (not a problem, just information)

Did you say you used the steering linkage from the 250? That would cause heaps of trouble; it's designed to change angle with the moving TTB arms and on the straight axle it would just cause wacky steering every time the suspension cycles!

Use the drag link and tie rod from the 350 (the drag link runs horizontal between the two steering arms, and the tie rod from the drag link up to the pitman arm on the steering box). Or buy new ones, budget providing. They're usually cheap and new adjustment sleeves are much more easily adjusted, which you'll want when you get (or DIY) an alignment (which you should after the swap)

Once you have the proper linkage in the truck, check the angles of the tie rod (drag link to pitman) and the track bar. Ideally, they should be as close to parallel as possible and the more horizontal the better. Your modified track bar mount may need to be modified again, depending. The idea here is that with the tie rod and track bar at similar angles, the movement of the axle and steering changes the same way at the same point in the suspension's cycle.

This may not be totally achievable, but closer is better. My track bar is horizontal at ride height, and my tie rod is a bit sloped, but it rides great. The springs I got gave me a bit extra (~3") height but my track bar bracket is for a 4" lift and lines up perfectly. Rides like a beaut.

 

Spring bushings.
Makes sure the wheel bearings are tight.
Check the king pins to make sure they are right and not rusted out, especially the bottom bearing.

I was under the understanding that the 350 springs needed to be used to clear, but over all the different spring aren't going to matter.

 

From reading and searching I have figured out a couple things I did not do.
I did not change the pitman arm one thing from I still have to change the track bar mounting bracket. as for springs one person who has changed a couple on this sight said springs are fine no need to change.
I did screw up the track bar and have ordered a new one.
The king pins and wheel bearings are good have no play or movement in either. I figure once I get the track bar and all mounted properly and change the pitman arm and have it properly lined up all should be good.
Thanks
Tim
I welcome all insight and helpful ideas from all members

 

Yea, the 250 springs are just stiffer, doesn't hurt anything. Should be better ride quality with 350 springs but personally I think the whole concept of "ride quality" on a leaf-sprung straight axle 3/4-1 ton truck is a bit rediculous.

Hope by Pitman arm you're including the whole linkage... definitely needs to be changed to the 350 style.

With fixed linkage and track bar + alignment you'll be in good shape.

 

I miss typed when stating what I had not changed the linkage is the original from the F350 however the pitman arm is not it is the original from the F250 and I have to pull the track bar hanger off of the F350 and mount it on the F250. Then hopefully a good alignment and all will be good to go.
Thanks
Tim