About a year or so ago I did the later model 11.75" front disc conversion on my '71 Dart...changing out spindles and replacing all the front-end parts in the meantime.

Today I heard someone say if you do that, you need to use a later '73-76 A-body center link or else you'll have bump steer. Is this true? I've never heard of this before.

I doubt you have a bona fide bump steer problem.

What causes bump steer is the tie rod and the lower control arm swinging through different arcs. Only if the new lower ball joint put the outer tie rod in a different location than the old lower ball joint would you have a change in bump steer. And only if the later center link moved the inner tie rod would it change or correct the bump steer. Now I've heard roundy-round racers sometimes say A bodies don't have good bump steer in the first place, but I'm skeptical.

It's not that hard to check for severe bump steer. You just have to support he car on jack stands and move the suspension up and down to see if the tire toes in and out as it goes up and down. My '96 Dakota had bad bump steer and you could see the tires toe out as the suspension drooped. Since the tires toed in when the suspension compressed the truck had pretty serious roll over-steer.

To accurately check for bump steer you need a plate to bolt to the rotor in place of the wheel and a couple dial indicators.

_________________
Joshua

OK that makes sense, i'll check for bump steer by compressing the front suspension.

I also don't really understand that rule either, because what if you are using the '71 disc brake ball joints, like these:
http://justsuspension.com/vaf/product/l ... &year=9273
then shouldn't you be using the matching '71 year range center link, idler, and pitman arm? Wouldn't it cause problems if you used the earlier disc-brake compatible lower ball joints, with the '73+ pitman, idler, and center link?

What rule do you not understand? You changed the lower ball joint and the attached steering arm. Only if the outer tie rod location changed in relation to the lower ball joint pivot will the bump steer have changed.

You appear to assume that the center link change made in '73 changed the inner tie rod location. I do not believe that to be true.

_________________
Joshua

The rule I did not understand was the one I heard, if you use the '73+ bigger spindles, you need to use all '73+ parts or you'll get bump steer --- I did not understand that and I agree with you.

ESPECIALLY so as you can buy '72 and down disc brake lower ball joints that have the correct length so the tie rod doesn't move, thus making it perfectly compatible for the '72 and down parts.

Oh, you mean someone else's rule. This is why understanding the fundamentals is key. If you don't understand how the system works it's easy to believe false information.

Early and late disc brake ball joints do not interchange. The bolt pattern on the spindle is different.

_________________
Joshua

There is nothing to suggest bump steer increases with the 73 up brake swap. Its very plug and play.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Yes that's why I asked, and thanks for explaining it to me in detail. I understand now and will test for the tire to toe in and out this weekend.

The Mopar Performance Chassis manual, has a complete chapter on adjusting/modifing the steering system to achive zero toe change throughout the full range of suspension travel.
I have never done it, but a friend used my book to do his Chevy Nova.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I believe E-Booger is the one that says the later model spindles will cause bump steer, but that will be the spindle you get in most aftermarket brake kits. No proof has ever been provided that it hurts anything.

What it changes is the height of the upper ball joint.

_________________
Official Cookie and Mater Tormentor.

My alignment guy has a function for checking bumpsteer on his Hunter rack. He has done it once on my '64 Dart and bumpsteer was quite low over the range of travel we checked. I'd have to look up numbers...

Lou

_________________
Home of Slant6-powered fun machines since 1988