Anti-bump Steer kit installed

[fastpat]

Well, I got the anti-bump steer kit installed, no thanks to the guy who sold me the kit. It was missing the longer bolts that are suppposed to be included. It was an unused Weltmeister kit, but the M10 x 35mm bolts that came with it were shorter than the OEM bolts. Fortunately, I have a rather large collection of gold zinc plated BMW bolts, and some grade 8.8 M10 x 50mm filled the bill. The right side of the steering rack was a bit difficult to lift high enough to get the spacer in, but a little urging with a small jack enabled me to squeeze it in. Follow the description in Wayne Dempsey's 101 Projects, torque values are in the Bentley manual.

This kit works as advertised, though. The rather vicious bump steer, even over Botts Dots on local street intersections, is completely gone. All you folks that have lowered your car without this kit should consider it, available from our host (with all the bolts I'd guess).

Sadly, the threat of rain, including a few drops already coming down, made me quit early, so the rear lowering didn't get done. We'll see about later this week. The front is 25 1/4 at the fender.

[911pcars]

Correcting bump steer is not merely correcting the bump when steering.

Go to this thread.

Sherwood
http://members.rennlist.org/911pcars

[Wil Ferch]

Seeing you used a small jack to force things into place.....did you loosen and retighten the steering column universals ( that otherwise bind if you simply alter the height of the rack)..??

Wil

[fastpat]

Well, yes, that's what it is, exactly. At the steering wheel, it's the result of too much angularity between the tie rods and the steering arms. Bump steer is a symptom of this increased angle.

For going to euro-spec or a bit lower, the spacers are fine. for more lowering, and/or racing applications I'd think about a more sophisticated solution to the angularity issue, not to mention that thicker spacers aren't likely to fit under the rack mounting bosses.

[fastpat]

An illustration of severe tie rod angularity, from a lifted suspension. Look closely, you can see the tie rod at about a 45º angle down from the drivers side towards the passenger side. the likely result of this is a bent tie rod, but until that happens bump steer would be harsh.

[911pcars]

"..Well, yes, that's what it is, exactly."

Errr. no, not exactly. Please read the thread or one of these links for an industry-wide definition of the term:

http://www.racerpartswholesale.com/longtech3.htm
or
http://www.bakerprecision.com/longacr17a.htm
or
http://autorepair.about.com/library/glossary/bldef-043a.htm
or
http://www.irvansmith.com/tech9.htm
or
http://www.heldmotorsports.com/bump.htm
or
http://www.i-car.com/html_pages/about_icar/current_events_news/advantage/advantage_online_archives/2003/090203.html

It's okay. Common misuse of the term.

Sherwood

[fastpat]

I've looked at your resources, and they support my statements completely.

When you change the tie rod angularity, the resistance to bump steer; which your first reference defined as Bump Steer is when your wheels steer themselves without input from the steering wheel. The undesirable steering is caused by bumps in the track interacting with improper length or angle of your suspension and steering linkages., is lessened.

Returning the angularity of the tie rods to a stock or near stock relationship to the steering arms, reduces bump steer to the level the stock system had, if any.

[911pcars]

"The rather vicious bump steer, even over Botts Dots on local street intersections, is completely gone."

Perhaps you were looking for your descriptive words when you reviewed those websites instead of reading the definition of "bump steer". No disrespect, but you must have extraordinary seat-of-the-pants sensitivity to toe changes while rolling over Botts dots.

Bump steer = Abnormal toe change during suspension movement, as in cornering or other vehicle maneuvers that transfer weight over the front wheels.

Another symptom may be steering kickback or increased sensitivity, but the main objective of bump steer kits is to reduce excess toe change during jounce and rebound motions of the suspension.

But I'm glad your ride is better.

Take care,
Sherwood

[Ron.G]

I installed one Saturday night. The drivers side of the rack was a bear to move but a crow bar did the job nicely.

It even states in the instructions that on SC models, The rack is a bit tough to move.

[fastpat]

Originally posted by Wil Ferch
Seeing you used a small jack to force things into place.....did you loosen and retighten the steering column universals ( that otherwise bind if you simply alter the height of the rack)..??

Wil

Yep, and the lower steering column did indeed slide up, looks like about 1/4 inch or so. Before I tightened everything up, I cycled the steering from lock to lock 4-5 times just to let it all seek a position, then I retorqued the steering column clamp, and then the rack bolts.

I did miss an oportunity to lube the front stabilizer bar bushings, while I was in there, but I haven't secured the tool I need to do that without taking the bushings off the bar. The tool will be a 3cc syringe and an 18ga. blunt needle, with which I'll shoot in some white lithium grease, or maybe some of that special bushing grease from Energy Suspensions.

[fastpat]

Originally posted by 911pcars
"The rather vicious bump steer, even over Botts Dots on local street intersections, is completely gone." by Fastpat

Another symptom may be steering kickback or increased sensitivity,

Un huh.

But I'm glad your ride is better.

Actually, the ride didn't change at all since the T-bars and shocks weren't changed, only bump steer was reduced or eliminated (I haven't decided which).

[jyl]

The cheap spacer kits for "bump steer" (or whatever we're going to call the phenomenon of the front wheels steering when the car hits a bump) don't get much respect, but I think they work reasonably well for not much money. As long as the car isn't lowered too much, I say try the spacers before shelling out for a more expensive solution.

[randywebb]

Did you check that 8.8 bolts are adequately strong?

I dunno what he factory uses. I don't recall any markings on mine but just used new factory parts so was not an issue for me.

[fastpat]

Grade 8.8 was what the factory used (mine were marked), so that's why I used that grade, just longer to account for the spacer thickness.

I am curious though, since the euro-spec cars are already lowered, is the OEM steering rack thicker at the mounting bosses, or is some other technique used to provide the correct angle for the tie rods?

[Wil Ferch]

Since Euro spec cars are at ...ahem...Euro spec in terms of ride height...no special rackspacers were used.

From this, I would presume that lowering "to" Euro spec won't need spacers. The spacers....limited to about 13mm height or about 1/2 inch....would therefore allow a further 1/2" reduction in ride height ( beyond Euro) before they can no longer keep up with the angularity changes in going yet lower.

Wil

[fastpat]

Originally posted by Wil Ferch
Since Euro spec cars are at ...ahem...Euro spec in terms of ride height...no special rackspacers were used.

From this, I would presume that lowering "to" Euro spec won't need spacers. The spacers....limited to about 13mm height or about 1/2 inch....would therefore allow a further 1/2" reduction in ride height ( beyond Euro) before they can no longer keep up with the angularity changes in going yet lower.

Wil

So, what do you think conributes to the problems associated with lowering a 911 without the spacers, certainly it's not the increased toe-in.