I know that bump steer has been discussed in other threads but I am hoping to open up a new discussion.

I am considering modifying my 87 GT cradle as indicated in the picture below.

I understand that the toe change is caused by the unequal length of the control arm versus the toe link length. I have a number of questions:

1. If the link connection point was revised as shown wouldn't the majority of the bump steer be eliminated?
2. Would there be a twisting stress placed on the cradle at the new location? Are these stresses severe enough to damage the cradle?
3. Any comments or concerns?

Thanks
Sour

One important point is that the strut does not remain at the same angle throughout the complete travel of the wheel. The top of the strut is fixed yet the bottom moves in and out as the control arm goes over center. Because of this, any design that uses a tie rod with one end attached to the stock location on the knuckle and the other end fixed to the frame will have bump steer.

How much? You'd have to draw it up on paper to figure it out.

Or build it and measure later.

If you decide to build it, that location of the cradle should be plenty strong.

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Doug Chase
Chase Race
Custom roll cage and exhaust fabrication

Bump steer is an ugly beast.

What you have described is very similar to what the RCC bump steer kit does.

The real cause of bump steer is that the extension line of the toe link does not intersect the instant center of the strut and control arm.

The only way to eliminate bump steer entirely is to do something like the Held kit which ties the toe adjustment to the control arm.

If you could get your hands on a set of '88 rear hub carriers, you could build a pair of control arms to use them with your early style cradle.

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'87 Fiero GT: Low, Sleek, Fast, and Loud
'90 Pontiac 6000 SE AWD: None of the Above

Luck, Fate and Destiny are words used by those who lack the courage to define their own future

I dont find "bumpsteer" to be a major issue, but I dont race. I do hate the wobble when switching lanes on old rutted asphalt tho. I have noticed just simple things like alignment & tire air pressure have a big affect. My approach to the bumpsteer has been stiffening up the rear. less up-down movement, less bumpsteer. last peice will be the rear sway-bar. but, what sour's proposing is a good plan. I got my 85 cradle out right now, and have been looking at the geometry on the toe-links vs. the a-arms, and it looks like there no total cure, just get the change of angle minimal to the expected ride height. I was thinking of moving the toe-link mounts more inward, to minimize the swing angle. or maybe double toe-links, front & rear, so instead of a steering affect, it will have a camber affect.

I was looking at my 86 cradle the other day, thinking the same as Sourmug. I was going to get a LH threaded 1/2" rod end, and a LH die to thread a cut-off toe link rod (in order to adjust toe) and see what happens. I figured a simple hole and grade 8 bolt and locknut would be strong ehough to hold it. A 1/4" plate could be welded on to the area for extra bearing strength if needed.

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1986 SE 350 V8

So, does anyone think that this is worth pursuing? I know that it wont completely eliminate bump steer, but it should substantially reduce it's effects for the majority of the suspension travel. Going to a stiffer suspension should also help to eliminate the extreme ends of the suspension travel. I was thinking that the two in concert would go a long way to eliminating the problem. What do you think?

Sour

quote Originally posted by Sourmug: So, does anyone think that this is worth pursuing? I know that it wont completely eliminate bump steer, but it should substantially reduce it's effects for the majority of the suspension travel.

Go for it. If you've figured out that it will reduce the bump steer in the area of travel that you'll be using then I see no reason not to. It should be fairly easy to do and it should be fairly easy to undo if it doesn't work. Give it a try and let us know how it works.

Doug

Most of what I've had on this has been covered enough....

What you are proposing is similar to one of the kits. (RCC?) It has an extension that bolts into place and uses a Hiem joint for the inner end. I think it shortens the link 3-4 inches.

This changes the "sweet spot" for bump steer but doesn't eliminate it. At extreme wheel travel I understand it makes it worse.

Any sort of strut system with toe links tends to have some bump steer. There is no way to eliminate it completely short of designing out the toelinks as some of the more expensive options do.

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The only thing George Orwell got wrong was the year.

The Ogre's Fiero Cave (It's also at the top of every forum page...)

Get the kit. It will save you headaches.

Bumpsteer can be worse in lowered cars cars as the suspension is more out of line to begin with. RCC and a rear swaybar should almost eliminate its effects.

You may have a good idea but be careful. You're working on something that directly affects your safety and others. Make sure any welding and parts that you use are high quality and up to task of negotiating potholes, curbs, and bridge expansion joints.

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RickN
White 88GT 5spd - Grey Interior
White 85GT Auto - Grey Interior

I was looking into doing the same sort of mod. I was however planning to use a 4" block bolted in the stock location with a tapered hole threough it on the horizontal and using 2 tie rod ends per side one mounted in the hub and one sitting horizontal in the block to get the smothest transision( forgive spelling)

Then I cut down my rear springs by 1/2 coil and added a sway bar and now I dont notice any bump steer at all. So it isn't a problem any more.

RickN:

Yes I agree, that's a definite concern that I have. All I need is for the connection to snap off and it's all over except the crying. If I do this I will make sure it's done right. Any other comments anyone? Thanks for all your responses so far.

Sour

Here is most of the parts you mentioned.

The steel plate is to make it easier to find a suitable place to locate the inner pivot point. I used a high strength studbolt and nylon locknuts on that end.

The rod is aluminum, although swagged steel is also available.

On the knuckle end I used the adaptor you see. 4130 steel, it allows raising or lowering that mounting point....more things to fiddle with.

Here you see it mounted, with the knuckle reversed. In this install, it was easier to locate a less complicated mounting point by reversing the knuckles. Locating just the right spot on that upwards curving rear cradle tower is difficult.

David Breeze

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Pantera Rebody Kits

Dave:

Thanks for the pics! Have you had this set up on the road yet? How is it working out?

Sour

I was in need of new struts so I replaced them with KYB performance ones. Before I had bumpsteer and now I havent noticed an incident in over three months. It will still probably do it but it is greatly reduced. Like I said before it happened all the time but after it has yet to happen even once.

No, mine has not been on the road. It did align in the shop & as best as I can measure, it works pretty well thru most of the range of motion of the wheel.

This is a basic adaption of the Joe Wynman suggestions, which he did run quite successfully.

BTW, It doesn't remove BS, just sort of lessens it. But you can tune the sweet spot.

David Breeze

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Pantera Rebody Kits