bump steer kit

The term "eliminator" shouldn't be used on the Pantera or probably any car. You can reduce the bump steer, not eliminate it. With a radial tire you can reduce it to the point that it is not noticeable since the amount that is left is absorbed by the natural side movement of the tire itself.

If you run a bias tire with a stiff wall then you might notice a little still...maybe? Frankly. Stock without the kit, the car isn't bad with bump steer at all.

The movement to the rear is part of the correction.

It's a good fix because it is a very simple correction. The bang for the buck is a bargan.

By comparison. If you do the Shelby upper A-arm relocation on the 65 to 70 Mustangs the bump steer is so severe the car changes lanes on you on a strait flat road.

Doug
thanks for the info.do you know the thickness of the shimm kit? also by moving the rack to the rear, does this give the wheels more toe in when turning or toe out. some may call this "steering axis inclination" I have also heard that a wide body car has less tire scrub. any thoughts?

The best way to calculate the shims that are needed to correct bump steer is to follow Jack DeRyke's article at Pantera Place.

http://www.panteraplace.com/page135.htm

John

quote:

Originally posted by tyler5:
Doug
thanks for the info.do you know the thickness of the shimm kit? also by moving the rack to the rear, does this give the wheels more toe in when turning or toe out. some may call this "steering axis inclination" I have also heard that a wide body car has less tire scrub. any thoughts?

I used 10mm thick like Marlin did. I believe that it increases the toe in very slightly. It would be a good idea to check it though.

I have no experience with wide bodies and this change. I would presume that the wider the track is the greater the toe in change would be?

As far as tire scrubbing on turns with a wide body, this is a very slight change to the car.
Anything that widens the front track will increase the scrub action on the tires.

For that reason, ideally the way to put 10 inch wheels on the front would be in a way as not to widen the track. I think that is impossible on the Pantera.

The way those things dart around, if you have been driving them for awhile then you should be used to that. In that case, don't worry about it.

Also. If you have a lowered battery box, like I do, you will need to change the rear bolts to allen head socket bolts.

Those bolts will be right against the box and there is no way that you can get a hex socket or even an open end wrench on them.

Why don't you ask Marlin to make you a kit? Maybe if you ask, pretty please, he might agree?

Thanks guys
just so i am clear, 1/4" to 5/16" or 10mm i understand. but the toe in or out i am refering to was when turning. as i see it, if the rack is moved forward it will toe out more on turns, the opposite if moved rearward. does anyone know what the stock car was doing during the scrub? too much toe in or out that is.

Bump steer is the term that we call the toe out change, that we don't want including in turning, of the wheel as the wheel travels up or down.

If we are going to eliminate bump steer, we eliminate that toe change.

It seems no really understands my question. mabe i need to state it differently part 1 bump steer. i am up to speed. Part 2 toe out on turns, or S.A.I.(steering axis inclination). the way i understand it, this is the difference between the inside wheel circle and the outside wheel circle as it travels through the turn. the inside wheel cicle or arc is smaller therefore the wheel must turn sharper or "toe out when turning" which will vastly decrease wheel scrub.(see i avoided the eliminate word ha ha)
This is built into the geomerty, but in making the change for bump steer it also changes the rack position to the rear. which will affect S.A.I. Since panteras have a tire scrub issue I thought I would address this at the same time. Thanks for all your input hope i made my a little more clear this time. sorry for the confusion. Larry

A lot of very precise steering talk here, thus I assume you have corrected the atrocious 2 degree caster angle the Pantera has stock to a more relevant 5 degrees. Until you do that all the rest is just semantics IMO.

Julian

yes i have, thanks for the reminder.

quote:

Originally posted by tyler5:
It seems no really understands my question. mabe i need to state it differently part 1 bump steer. i am up to speed. Part 2 toe out on turns, or S.A.I.(steering axis inclination). the way i understand it, this is the difference between the inside wheel circle and the outside wheel circle as it travels through the turn. the inside wheel cicle or arc is smaller therefore the wheel must turn sharper or "toe out when turning" which will vastly decrease wheel scrub.(see i avoided the eliminate word ha ha)
This is built into the geomerty, but in making the change for bump steer it also changes the rack position to the rear. which will affect S.A.I. Since panteras have a tire scrub issue I thought I would address this at the same time. Thanks for all your input hope i made my a little more clear this time. sorry for the confusion. Larry

The bump steer kit is a patch not a fix. All it does is move the bump steer arc so it's not as noticeable. Bump steer could be nearly eliminated if the steering raq was actually altered (fixed from geometry issues). They used a raq form something else and the outer rods pivot at the wrong width. I am putting in a power steering raq but I am re-welding the raq to the proper width.

If the geometry were perfect you would still get some bump steer from the SAI not being in the middle of the tire patch. Worse with larger tires.

It is true you cannot alter one thing with out changing another. Ackerman is the change in toe during a turn but it will change very little with the shims you speak of. With Ackerman the more the inside wheel turns in a turn the easier it is to turn in a parking lot. I have a 1976 Cutlass with a lot of Ackerman. It makes it easy for grandma to turn the wheel (and it is very easy) but if you jerk the wheel at speed it is actually dangerous.

When I read Pantera articles on Ackerman I knew it was misunderstood when it was improperly addressed with toe in. It was suggested the Ackerman be adjusted for the turn. Since a large track with a large radius needs less movement of the inside wheel some Ackerman was taken out or so it seemed. It was mentioned latter however the toe out in the straight aways made running a straight line squirrelly. With to much toe out in the straight away there was less toe in in the turns. This was not a properly adjusted Ackerman but a misunderstanding of how the whole thing works after reading an article in Hot Rod.

The Pantera does not have much Ackerman compared to most cars which is more suited for track to some degree. Generally going forward or rearward with the raq will alter Ackerman but I don't think the shims will change it much.

Larry, your description of bump steer is correct. Bump-steer cannot be totally eliminated from any car but it can be minimized, by two methods. The first is two shim strips between the rack mounts and the underside of the front trunk floor where the rack is held by split-clamps. Each car will ideally need a slightly different thickness, but when the factory addressed this in mid-'73, they used about 5/16" thick shims. This seems to work to eliminate most bump-steer on most Panteras. But it causes three mini-problems. First, it also modifies the Ackermann-toe since the trunk floor is slanted. So shimming the rack not only lower the rack (for bump-steer correction), it also moves the rack forward (which changes Ackermann. On a street car, you'll never notice an Ackermann change). The second problem is, shims require 4 ea. 5/16" LONGER rack-mount bolts for the same thread depth as stock, for safety. The third problem with using rack-shims is, it misaligns the holes drilled thru the front subframe to hold Bill Stropp's rack-brace on U.S. cars. To rectify this, either re-drill 4 more holes, or cut the same amount of material off the outer rack-clamp surfaces where the bolt-heads touch. This allows the original rack-brace holes to be used, and also the original bolt lengths.

A different way of correcting bump-steer involves removing both metric tie-rod ends and replacing them with 1/2-20 SAE heim joints. These particular metric and SAE threads are so close in dimensions, SAE rod-ends and jam nuts will screw onto the metric steering rack threads without interference and has worked fine on our car for 3 years now. Use a Speedway Motors tierod-conversion stud to go into the tapered holes in the steering arms, and make your own shim-stack to fit between the heim joints and the steering arms. Such a set-up is sold by D. Quella for bump-steer adjustments, but his kit uses an allen bolt thru the steering arms, which means drilling the tapered hole out of the arms- an irreversible change. By using the Speedway conversion stud (p/n 535-AK35; $4.99 ea) no irreversible drilling need be done and you can go back to the stock setup at any time. With heim-joints, I recommend also using Speedway's heim-joint seals (2 per joint) for weather protection. Again, each Pantera will ideally need its own shim-height but about 5/16" thickness seems to be a one-size-fits-all, at least for street cars. This mod does not change the Pantera's Ackermann, if that concerns someone. Be sure to readjust toe-in after any front end changes; about 1/2 turn on ONE steering rod will get you close enough to drive to an alignment shop.

who is Speedway? How can I get in touch with them. Are they on the WWW?

http://www.speedwaymotors.com/

quote:

535-AK35

Their search engine didn't find this part #.

You can indeed get rid of Bump Steer; just not with the patch that is available (shims). The bump steer patch doesn't change the bump steer; just the apex of the arc where it is not as noticeable.

I built a jig from the existing suspension. Each tube bolts to the A-arm locations. the purpose of the jig was to get accurate measurements of the A-arm pivots. I then put this info into the suspension software. In the software I played with all the data points till I got a zero bump steer. This has been some time ago.



I assembled everything and I am close; close enough now I need to finish the car and work the remaining adjustment at assembly.

One thing that will have to be done is to modify the length off the raq itself. You don't make one change with out it effecting other aspects of the suspension. You pretty much need the data points in a suspension prog to get it this close.

The mount is removable and can be changed or shimmed. Plates on the rails for reinforcement and the box become a bit of a stiffener as well. I am way beyond these photos but the suspension is on hold till final assembly.






The steering box powdercoated and ready to go in:

quote:

535-AK35

quote:

Their search engine didn't find this part #.

http://www.speedwaymotors.com/...VERSION-KIT,555.html