Thread: Mustang II narrowed control arms

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This being my first rod alot of things are new to me. I recently installed a mustang II front end under my 28 Hupp, and after looking at different options in replacement control arms, I noticed you can buy 'narrowed' control arms. My question would be what part of the control arms is narrrowed (the width)? Also, what do you gain with narrowed control arms? Eliminating tire interference with steering? Thanks for the info.

The "narrowed" is somewhat of a misnomer as it applies to the arms themselves. What's narrowed is the track measurement for the entire front end. Based on a comment you made in the other thread it sounds like you're thinking of only the upper arms? You need to have both upper and lower to "draw in" the spindles. Another way of looking at it is the control arms are shorter, the distance from the chassis mounting point to the ball joint. As an example, the Heidts ones I used on my '36 are 5/8ths of an inch shorter, narrowing the track a total of 1 1/4". Odds are you'll have to shorten the tie rods on the steering rack a small amount in order to get enought toe adjustment.

Bob, I'm also putting in a Mustang II front end under my 33 plymouth and was asking the vendor if i could have the tower and the lower control arm shortened up 3/4 of an inch (because i have inch and a half coil clearance) and was told that it would throw off the whole geometry of the front end. I would like to have more tire clearance is why I asked.Your thoughts on the idea?

Technically, he's right. It does change the geometry. However, I question whether it's a SERIOUS effect. "Throws off the whole geometry" sounds a little severe, but I can understand why he says that. It there's a problem, it's on him.

With the very limited travel most street rods have, I don't see a problem. This is not just conjecture. I shortend the upper A-arms on my '30 A-bone by an inch, and moved the lower ones inboard an inch. I saw NO problem with steering, no bump steer, no wandering, no effect at all. Interstate, city streets, drag strip (at 119 mph) . . . drove like a go-kart.

Jack's right, when someone says "whole" in a context as you mentioned they're guessing or totally ignorant (which may be the same thing in a way). Although on second reading of your post I see you said "tower" and I'm not sure what you mean by that. We're talking here about both upper and lower control arms, not the crossmember/hat assy.

It won't change static camber, caster, or anti-dive. It will change Ackermann a little, but that's not an absolute spec anyway and will still work well with small deviations from ideal. Caster would be changed slightly in the context of change over the range of motion, likewise camber (though hardly at all). Comparing two different rods that might be similarly equiped can be a bit dicey since no two are ever precisely identicle, but I've driven fairly closely built cars with both and like Jack, could not feel any adverse effect.

If you go to the 5th page of my gallery, the next to last pic is of my '36 in mock up. If you look closely you can see the front wheel has a fair bit of negative offset (2 1/4" back space on a 6" wide wheel if I remember correctly) and the tire is still well tucked into the fender.

Yup, What Jack and Bob said... The effect on the geometry of narrowed arms is negligible. I've used them on a number of cars with little or no effect. Typical front end movement with a coil over is only about 3" anyway, so 1 1/2" of movement from the center of travel does not cause noticeable deviations in the geometry if the set up on the front suspension is done correctly on the initial build and the alignment is spot on.

thanks guys, but i was thinking of moving the coil spring hat in 3/4 of an inch (i'm going to use stock upper control arm) and shorting up the lower control arm 3/4 of an inch if it doesn't have any effects of the steering, am i on track?

I sure don't see a problem with that. It's probably a better solution than I did on my A-bone.

Have you thought about moving the mounting hole for the lower A-arm inboard 3/4" rather than shortening the arm? That way, both arms stay at stock length, and you're just moving the whole assembly inboard.

I'm thinking that the rack and pinion mount is in the way Henry, I'll take a close look at that....thanks

Thanks for the info. Im thinking some narrowed control arms would be good to go with in that I had to widen the stock Mustang II subframe 3 3/4 ". With some narrowed control arms and some longer tie rod ends, Im thinking I can get things back to where they need to be.

Originally Posted by Henry Rifle

Have you thought about moving the mounting hole for the lower A-arm inboard 3/4" rather than shortening the arm? That way, both arms stay at stock length, and you're just moving the whole assembly inboard.

When you start messing with the control arm pivot points, the inner tie rod ends on the steering rack won't be compatible with your front end geometry. As the suspension moves up and down, the arc that the outer tie rod ends move will be different than the arc at the steering arms, so you'll be forcing the toe-in to change . . . and you'll have the dreaded "bump-steer".

Originally Posted by Hot Rod Roy

When you start messing with the control arm pivot points, the inner tie rod ends on the steering rack won't be compatible with your front end geometry. As the suspension moves up and down, the arc that the outer tie rod ends move will be different than the arc at the steering arms, so you'll be forcing the toe-in to change . . . and you'll have the dreaded "bump-steer".

I do know that on my 48 F1 pu the width is a litte wider then stock mustang II and the rack has rack extenders to make up the differance NOT longer tie rods. I believe that is to resove the bump steer problem, which I do not have. Works great.

Originally Posted by Hot Rod Roy

When you start messing with the control arm pivot points, the inner tie rod ends on the steering rack won't be compatible with your front end geometry. As the suspension moves up and down, the arc that the outer tie rod ends move will be different than the arc at the steering arms, so you'll be forcing the toe-in to change . . . and you'll have the dreaded "bump-steer".

In theory, you're correct. However, I'll repeat what I said above:

With the very limited travel most street rods have, I don't see a problem. This is not just conjecture. I shortend the upper A-arms on my '30 A-bone by an inch, and moved the lower ones inboard an inch. I saw NO problem with steering, no bump steer, no wandering, no effect at all. Interstate, city streets, drag strip (at 119 mph) . . . drove like a go-kart.