Bumpsteer...

Someone school me on what to do here.

87 Mustang, PA Racing k-member with 2" drop Pinto rack, PA racing 12" lower control arms, PA racing 2" drop spindles. Steering arm is in stock location though.

How should my tie rods look compared to the control arms? Parallel to them? If so, I need a 5" long bolt and will need about 2.5-3" of spacers to lower the tie rod on the steering arm.

Also, the steering arm has a 5/8" hole in them, but the tie rod kit that came with the rack is setup with rod ends with 1/2" bore. Do you think it's Ok to bush the 5/8 hole in the spindle with a brass bushing to 1/2" and use a 1/2" bolt? Or is something wrong with that? Can't seem to find a 5/8 bore rod end with the threaded end small enough to thread into the tie rod...

Thoughts?

Parallel is a great starting point.

http://www.teamzmotorsports.net/Mustang_bump_steer_kit_p/tzm-bsk.htm

jbozzelle wrote:Someone school me on what to do here.

87 Mustang, PA Racing k-member with 2" drop Pinto rack, PA racing 12" lower control arms, PA racing 2" drop spindles.  Steering arm is in stock location though.

How should my tie rods look compared to the control arms?  Parallel to them?  If so, I need a 5" long bolt and will need about 2.5-3" of spacers to lower the tie rod on the steering arm.

Also, the steering arm has a 5/8" hole in them, but the tie rod kit that came with the rack is setup with rod ends with 1/2" bore.  Do you think it's Ok to bush the 5/8 hole in the spindle with a brass bushing to 1/2" and use a 1/2" bolt?  Or is something wrong with that?  Can't seem to find a 5/8 bore rod end with the threaded end small enough to thread into the tie rod...

Thoughts?

My thought is, "I wish it was easier to post pictures on this site" But,

I did a rework on a guy's 1990 Mustang that had an aftermarket K frame installed. Step #1, CENTER and SQUARE IT UP. Steering arms on your 87 have no drop to them as I recall. The spindles on a 1996 are dropped 1-1/4" or so. This would reduce your bump steer kit stack height ( link posted by whatbumper). This is very important for a few reasons, but the top two are; steering arm flex. The longer the bump steer stack, the more leverage there is on the arm to brake it off! Think about leverage forces' from a long torque wrench. #2 You could use a piece of 4140-1/2"id x.187 tube welded and well braced by gusset to spindle as a stack, but If you drop tie rod end 3" you need to watch tire side-wall clearance.  

You could find a set of 1996 spindles in a scrap yard but they will push the tire out 3/4" -? per side. The car I did didn't have the room due to wheel/tire combo and being dropped 2". So, I made a fixture, constructed new arms from 4140 tubing and used 3/8" of stack to adjust bump. See pictures,,,,,,,,,, err, email me and I will send pics of spindles.

After thought; Some Kframe set-ups have rack offset bushings to raise it, if you have the room.

Thanks. I really need to make what I have work.

What do you guys do to run the suspension through the full extension/compression? Just use a floor jack?

jbozzelle wrote:Thanks.  I really need to make what I have work.  

What do you guys do to run the suspension through the full extension/compression?  Just use a floor jack?

I set the car low on stands and use a bottle jack under lower control arm near ball joint. Easy to work around.

jbozzelle wrote:........What do you guys do to run the suspension through the full extension/compression?  Just use a floor jack?

A bottle jack under the lower balljoint usually works OK when mapping bumpsteer. First remove the front springs & jack the spindle up to a given imaginary ride height measurement & set the toe to zero (using zero toe at ride height as a baseline just makes measuring/comparing a little easier). Then run the front suspension from full extension to full compression and record the different toe in/out measurements along the way. Take the measurements every so often during the travel, say at 1/2" to 1" increments in travel, (more increments/points you measure = more accurate map of what's going on).

Thanks guys, I'll get this thing back on jack stands and get to working on it.

So, I want ZERO bump steer, correct? I should be able to adjust it all out, correct?

jbozzelle wrote:Thanks guys,  I'll get this thing back on jack stands and get to working on it.  

So, I want ZERO bump steer, correct?  I should be able to adjust it all out, correct?

Zero bump is the goal, yes.

Cool. Thanks!

Having 100% zero bumpsteer/zero unwanted toe change happening during the entire suspension travel is the goal, but sometimes it's not possible to remove it 100%. The tie-rod shim/spacer kits only help solve bumpsteer problems related to having an incorrect tie-rod angle caused by the rack's height vs the spindle's steering arm height.

But the tie-rod kits don't help the many other assorted bumpsteer related problems that can also cause headaches. Stuff like mixing & matching different year/make racks, or converting an older steering box car to a rack, or converting rear-steer to front-steer, or having the rack mounted too far forward or too far back, or having a rack center body width that's too wide/narrow vs the distance between the control arm's chassis pivot points, or etc, etc.

If you're not mixing/matching/swapping in a different rack, or drastically changing the fore/aft mounting position of the rack, then the tie-rod spacer kit should get the bumpsteer at/close to zero.

X2 Dave.

 Now, Is there any wonder why the K frame manufacturers don't have an explanation of what causes bump steer on their web sites? I think most people would pass on buying the kits due to fear of curing the problems that cause the bump steer. If the design of the K-frame SYSTEM as a whole is flawed, the bump steer shim kit will only reduce unwanted bump not eliminate it. As an example only, a bump of .040 per side at a travel of 3" would be a big reduction over .040 per inch of travel. And, by SYSTEM, I mean; proper ride height setting, use of specific rack, spindles and tie rods that they designed around.

Read this and perhaps some other articles about bump steer. http://www.hotrod.com/how-to/chassis-suspension/ctrp-1001-bump-steer-explained/

And this  https://lmr.com/products/Mustang-Bump-Steer-Correction

It may be said above, but remember to only worry about the actual real travel that your suspension sees.

For example, my suspension only has about 4" of travel so it doesn't take much work to check everything.

jbozzelle wrote:Someone school me on what to do here.

87 Mustang, PA Racing k-member with 2" drop Pinto rack, PA racing 12" lower control arms, PA racing 2" drop spindles.  Steering arm is in stock location though.

How should my tie rods look compared to the control arms?  Parallel to them?  If so, I need a 5" long bolt and will need about 2.5-3" of spacers to lower the tie rod on the steering arm.

Also, the steering arm has a 5/8" hole in them, but the tie rod kit that came with the rack is setup with rod ends with 1/2" bore.  Do you think it's Ok to bush the 5/8 hole in the spindle with a brass bushing to 1/2" and use a 1/2" bolt?  Or is something wrong with that?  Can't seem to find a 5/8 bore rod end with the threaded end small enough to thread into the tie rod...

Thoughts?

Racecraft, Maximum Motorsports, and a host of other companies both sell bump steer kits with 5/8" heim joints.