The G Body Bump Steer Project

[85 Cutlass Brougham]

I am determined to find a solution to the horrid bump steer geometry these cars have. So, I am off to do some research with my trusty tape measure to find pitman arm/ idler arm set or center drag link that has a bigger drop than stock, and I need some help. So far, my list of possible donors includes: Jeep CJ, Wrangler, Cherokee, GM F, and B bodies as well as S trucks, and GM full size pickups and vans as well as the Astro/Safari. What else could be a possible donor? Do they all have the same stud taper? The nice thing about the 4x4 models would be that dropped arms are already available for them when they are lifted, so as long as the ball stud taper is the same they could be made to work. It really only needs to be about an inch to an inch and a half of drop to make it all work together. Then, add the taller spindles for a B body, or taller upper ball joints to fix the remaining geometry issues. ( I really want to use the Global West uppers I already own.)

 

[Alcohol]

I have an adjustable center link that is for the G body car....You can see it at Port City Racing .com. I have all of the adjusting studs and spacers for $150.00 plus freight. These work real well on race cars and are a bolt in piece.

 

[85 Cutlass Brougham]

How much of a drop does it provide? It needs to be about an inch to fully fix it.

 

[phaZe]

So you are trying to fix the problem where you hit a bump or dip in the road and the car wants to drift toward it instead of going straight ahead?

 

[85 Cutlass Brougham]

Basically, yes that's the idea, but with the added complication in my case of using the tall spindles from B body. The issue would have been easy to fix when the car was originally designed as there is enough space to drop it the inch or so it needs to go down. Why GM did this in the first place, I don't know. I need to take actual measurements before I draw my final conclusion as to how far off it is, but it is significant enough that it is obvious to the naked eye if you know what you are looking at.

For those who don't have a lot of knowledge of suspension design and geometry, I will explain what is wrong here. When a wheel moves up and down on the front suspension, it scribes an arc. Now, the tie rods also scribe an arc, but if they do not stay parallel to the imaginary line drawn from the lower control arm pivot point to the lower ball joint, the wheel will steer a little left or right, depending on how the geometry is wrong. If you look at the G body tie rod mounting location with the wheels pointed straight, you will notice that it connects to the center drag link right about where the LCA pivots in the frame. However, you will notice that the tie rod is anything but parallel to the imaginary line on the LCA, and that the two lines will at some time intersect. This is why they bump steer so badly. So, the solution is to move one of the pivot points up or down so that the two parts stay parallel.

As for the tall spindle swap, it corrects the other big fault in the suspension design on these cars. The suspension's camber curve is backwards from where it should be and the top of the tire rolls out instead of in when under compression. Unfortunately, the position of the steering arm on the spindle is different than on a G body, and makes the bump steer worse while fixing the camber curve problem. So, I am trying to fix both problems at once and have good front suspension geometry and have the car handle good without the use of excessively stiff springs to limit the camber change as is the traditional way of setting these cars up. This way, more suspension movement will plant the tire instead of unloading it.

 

[Bilster]

Best of luck to you. I've got the same problem...both with my G-body and my A-body that both use Global West control arms and the tall B body spindles. When I suggested to Global West that they had a problem, the idea landed on deaf ears. AFX has the great tall aluminum spindles and redesigned steering arms that correct both problems but they are rather pricey, don't work with Global West arms and .....are going out of business.

 

[TBRtat2]

Allright if im wrong on this, im saying sorry right now.

BUT, I think i have a fix for this (not sure with the b-body spindles).

1: I dont think lowering the whole center link will work, the "skid" on the front of the crossmember will be in the way (i think, but would depend on how far you lower it)

2: I think what should be done is to move the mounting holes on the center link for the inner tie rods out (making the tie rods shorter), this will move the inner pivet for the tie rods to almost dircetly in front of the lower control arm pivot point. Also If you weld mounts on the center link, you could mount them to the bottom side of the center link (which would lower the inner tie rods as well)

Now this is where I need a "welder" for some info. Would it be posible to weld mounts on the center link (for the tie rods) without killing the strength of the center link?

 

[pontiacgp]

get yourself a bump steer gauge, a torch and make sure you don't have any plans for the next day or two..

"CHASSIS SET-UP

BUMP STEER-As a front wheel moves up and down through its suspension travel, unless the steering box is directly connected to the A frame, the wheel will tend to turn either left or right when the steering wheel is held firmly in the same position. This tendency of the front wheel to turn during suspension travel even though the steering wheel isn’t moving is called “bump steer”. It is caused by the fact that the steering box is attached to the chassis and doesn’t move while its steering rods are connected to the steering arms, which do move up and down. In some supermodifieds, attaching the steering box directly to the front axle eliminates bump steer. In most other cars, bump steer is a fact of life.

Most stock car chassis experts feel that the amount of bump steer in a racecar should be minimized. However, another opinion has it that if the bump steer is in the correct direction (say the car has a tendency to turn left when the brakes are applied as on entry to the turn. It’s a big help in handling. If bump steer is in the incorrect direction (say the front wheels turn right when the brakes are applied on entry to the turn) the car is very difficult to drive. Bump steer might fight everything that the driver is trying to accomplish with the steering wheel. In general, the rougher the racetrack’s surface, the more important it is to minimize bump steer. Just as the name implies, bump steer causes the car to turn itself when a wheel encounters unevenness. To measure bump steer, first set up the chassis with caster, camber, and toe-out all being correctly adjusted. Then unhook the front shocks, springs and anti-roll bar. Put the car up in the air on four jack stands. Lock the steering wheel straight ahead. Remove the tire and wheel and bolt a flat plate to the hub.

With the spindle about half an inch below its normal ride height, adjust the dial indicators on the right and left of the gauge so they are level. Then measure the orientation of the plate with respect to the bump steer gauge by setting both dial indicators to zero. This will be your baseline. Jack the spindle and hub assembly up one inch and read the changes seen on the gauges. The difference between the gauges is the measure of bump steer. I suggest that with late models and modifieds, the left front should bump .030” out and the right front should bump .015” out in one inch of upward spindle travel. I recommended that with cars using stock spindles, such as GN or NASCAR LMS cars, the left should bump .030” out and the right front should bump .015" out. If the cars bump steer is off, it can be adjusted in most cases. If you are working with fabricated spindles and a rack whose height can be moved up and down, adjusting the height of the rack with respect to the height of the spindles through the use of spacers is the solution. If the steering box’s height can’t be adjusted (if it isn’t a rack, chances are that it can’t be adjusted) and if the steering rods join the steering arms with tapered rod ends, adjusting bump is very difficult, it can only be accomplished by heating and bending the car’s steering arms. Even with that kind of effort, bump is still pretty tough to get right on the numbers with non-rack cars.

Adjusting bump is a matter of taking some time, yet it’s important. No car should go onto the track until bump steer has been set. Setting bump steer can’t be done in fifteen minutes. In the worst of times, it’s an all day project to set bump. But once the job has been finished, it doesn’t need to be done again until the car suffers damage to the front frame rails or spindle arms."

 

[85 Cutlass Brougham]

Well, I don't have access to the tools to do all that, and my welding skills are... well... not something I would trust on something important or structural. I don't think it would affect the strength too much in this application, but if your welds are not as good as you think, the results would be potentially deadly. Now if you could find a center link with a slightly wider hole spacing, that would be great. If I had access to Autocad, I would consider redesigning this part and having an upgraded item manufactured. It wouldn't be too hard, if I knew how to run a CAD program, and had finished my classes in things other than just engineering math. The question of a market for such an item in a large enough quantity to be profitable to make a small run of them is huge though. Then again, maybe the part already exists and it is up to someone with a trusty tape measure to go to the junkyard and find it.

However, I may have found the cheap solution. I didn't get a chance to measure it, but the S-10 2wd seems to have a lower pitman arm and idler arm with a bigger bend in it that is also the same length as a G body arm. I used a piece of junkyard scrap to estimate it, and it seemed similar enough that I have to remember my tape measure next time (Doh!). If so, it would be cheap enough to buy the parts used and try them on the actual car. The drop is probably around 1/2-3/4 of an inch (eyeballing it), which I do not think will cause interference. If this works out, the next project will be finding a big brake upgrade kit for the B car spindles that can be had cheaply. Either that, or designing a new caliper bracket for a better caliper off a newer car that will bolt to the B car spindle.

 

[TBRtat2]

I found something for this,

http://images.marketplaceadvisor.channe ... 6/bs-d.jpg

I found them on ebay, But there about 160.00 plus shipping. From this guy, http://stores.shop.ebay.com/Spohn-Perfo ... bZ13239573

Me myself, I am going to keep looking around to this if I can find everything to build it myself (hopefully for cheaper)