Twin I-beam front wheel setback specs

[GPatrick]

1970 F-250 2WD. After installing a Sterling rear axle someone noticed that my truck appears to be crab-walking. Since I installed the rear perches myself, I assumed that I must have made an error there but my measurements show it the axle is square with the frame. However, I have about 1/2" difference between the left and right wheelbase. The 1/2" difference seems to be in the front wheels. The fender gap is closer on the left side and measurements from the rear of the door to the wheel centers also confirms the 1/2". A number of searches indicates that a "setback" is built into the twin I-beams. Here is one quote - "Setback is actually designed into some vehicles, such as old Ford trucks with twin I-beam front axles"

I can find camber, caster, and toe specs but none of my searches finds a setback angle or distance. Some of the chassis drawings show them being in-line. So, do I have an issue with my front axles or is the 1/2" difference normal? Is there a specification for the king pin twins?

In the meantime, I have installed new rear springs since the right rear was sagging. I haven't had a chance to have someone follow me down the road to see if that help with the dog-tailing/crab-walking.

[sargentrs]

At the C/L of the tire tread, the front is about 1-1/4" wider than the rear. http://www.fordification.com/tech/images/bb70/p09.gif Your body sheet metal may be out of alignment, worn cab mount bushings, etc, a number of factors could shift body alignment out of whack over 40 years.

[basketcase0302]

Gary,

Look real hard at the things Randy spoke of above but also...
Take it to a reputable "old school" alignment shop, (no pep boys / advance / oriellys / etc) and have them put it on the rack to check the alignment.
They may find that a PO has hit something real hard and actually bent the I-beam.
And also look real...hard at the radius arm bushings and their mounts for wear or other issues there.
And try using a piece of string, (with a second set of hands) to actually measure from the rear end of the frame rail to the rear of the axle spring mount to see if the new Sterling is truly square with the frame).
Oh yeah LOL...
Excellent choice of axle BTW!

[DuckRyder]

I would also measure the frame diagonally at several points (pick bolts or holes that should be symmetrical and measure in an X pattern).

Also measure from spring/radius arm bolts to rear axle.

[GPatrick]

Thanks for all of your responses. The problem is not side-to-side in front but front-to-back. I need a second pair of hands but essentially the right side wheel base is 131 and the left side is 131.5 center to center. The new Moog radius arm bushings are in good shape but on the "long" side, the washer does not seem to be tight against the shoulder so that may explain some of it. 1/8" at the arm will pull the wheel back about 1/4". The Sterling axle is wider than the old Dana so it does not have a narrower width than the front now. Both the front and rear are both well centered side to side with the body. I have read on 4 different sites (that may be borrowing content from one another, perhaps) that the twin I-beam has a built in setback as part of the design but I cannot find a drawing or spec to support this claim.

At some point in its life something pretty tall back into the front end from the side. It did push the radiator support over (bolts slipped) and damaged the driver's side fender and the hood. I had the whole front end off and it all went together straight but with clearance holes that doesn't ensure that the frame was not tweaked. There is a shop in the area that can do a full frame measurement so I guess that is where it needs to go. But, if the setback is "normal" I may be worried about nothing.

[DuckRyder]

I will try to measure mine today.

The radius rod bushing is a worry, they should be equal...

Should not be too hard to measure the frame in an X in fact if you poke around there may be a frame dimension sheet on the web (maybe even here) with it having had a shot on the front I’s strongly suspect a diamond in the frame, but a few measurements and a thrust angle alignment is going to be far cheaper than a frame rack set up and measure...

[DuckRyder]

Probably going to be the weekend before I get any measuring done, my apologies...

[GPatrick]

I'll try to get motivated to crawl under the truck to see if I can get some cross readings. If it was "diamoned", wheel base readings should be equal on both sides so it appears that I need to focus on the two front corners instead. Either the driver's side is too far forward or the passenger's is too far back.

Let me know what you get on your wheelbase readings when you have a chance.

Gary

[DuckRyder]

I did a quick and dirty from the coil spring bolt to the rear end housing between the U bolts and got 129 on both sides, wheel base is harder as there is no hard reference point.. Keeping in mind my truck is a F100 long bed.(131 WB) considering the bolt head and the diameter of the rear end housing tube 129 sounds about right.

Keep in mind frames are generally considered to be divided in 3 sections, front, center and rear. Frame damage conditions can be present in any of the sections. So if you find for instance that the front measures unequally yet the center section measure equally, look for evidence of a buckle or other repair.

I would focus first on making sure the frame is straight, then that the rear axle is square with the frame... once you do that the thrust angle should be close to zero and eliminate crabbing.

With respect to set back being built into the I beam suspension, the pivot points are clearly not equal and it is possible this is what folks are referring to.

BTW, is the steering wheel straight?

[GPatrick]

Thanks for the dimension. Your equal readings are a lot better than the 1/2" to 5/8" difference I am seeing.

The wheel is straight and it doesn't pull. I had it aligned last summer when I got new tires but I don't think they did a lot to it. It does have a numb straight line feel that requires somewhat constant correction.

I found about a 1/4" difference left to right on the strut arms/radius rod mounts to the I-beams and almost all of this is in the bushings. When you take that 1/4" difference and extend it out to the outside of the tires that can easily be my 1/2". I always wondered and searches seem to prove that I installed the rear washers backwards on the bushings. The Moog washer says "this side toward rubber" but I remembered a TV show recently where they showed that many washers are used in a variety of applications so the markings are not always correct. The Ford diagrams show the rear washer cup facing towards the front. Also the Moog washers are thinner than stock so the result is that I am not properly compressing the bushings given the thickness of the bushings, washers, and the length of the threaded section. Playing with the original washers off of the front end I pulled from a '78 at the pick and pull, I was able to reduce the side-to-side difference to about half of what it was before. Since I have distorted (butchered) the bushings with the incorrect washer orientation, I am ordering a set of Prothane bushings. I'll install them on Sunday if Amazon is correct on delivery and see how it measures. I can't find any other dimensions that are out of whack but will see if I can snag a neighbor to help me with some more checks. Then we'll go out and do the crab-walk-of-shame to see if it wants to go straight. I have used poly bushings everywhere else on the truck so one more location isn't going to destroy the ride harshness any further than I already have.

I any of you comes up with any other ideas, let me know.

[basketcase0302]

I bet you find the correct install on the new bushings to correct it.
Did you put the radius arm brackets on the frame with bolts or do you have to pull the arms out with force, (as many guys here do against good judgement taking chances of damaging the i beams and other parts using force).

[GPatrick]

When I put the current set in I took a lot of the front end loose so it was pretty easy to get the bushings in. I had to drop the beams to replace the bushings anyway. Everything is clean now and it will come apart fairly easy. I would not worry about using proper bolts for the brackets if I had to but this time I'll pull the arms forward with only a little force. Practice makes perfect...

[SoCal250]

Has anybody figured this out or had the same problem?
I sent a PM to the remember who had posted this thread but just in case he don't see it or unable to answer my driver's wheel is a half an inch to 3/4 of an inch more forward than the passenger side it shows up on the alignment as a 6.3 caster driver side and 5.1 on the passenger side I used the same bushings left and right the Moog polyurethane.

I will eliminate all the obvious my truck is never been wrecked no cross members have ever been removed the radius arm mounts at the bushings are riveted on there is no adjustment there forward or back and they are in excellent condition.

The only thing that I can gather is this those hard composite bushings once you torque down on them 80 to 100 foot pounds and use them once or twice they're no good anymore and you're going to start to have alignment problems I don't think those bushings are designed to be reused.

What I did do was remove my eye beams because I changed coil springs and everything went right back together but I reused the old radius arm bushings on the long threaded side now my driver's wheel is more forward and when I go to tighten the castle nut the nut will bottom out before it even tightens the bushing that's where I suspect that those bushings are not reusable.

[SoCal250]

As far as the camber is concerned I'm running djm lowering beams and I cut a quarter of the coil off of the stock springs so I'm not too worried about the camber .
The 69 f250 only used a 7/8 kingpin up until about 74 ish then they started using the big king pin so you can use an F100 I beam although my suspect is the bushings it could also be the heavier duty spindle of the F-250 on a setback spec F100 beam.

But being that the original member who posted this thread had stock beams and was having the exact same problem that I am I'm doubting that it's the setback on the beams