Front suspension and steering, how do you know you need to rebuild the steering? Options

[DRPHIL914]

I am wondering this as I have been driving my car this week with the great weather and fall temps here in SC, and I have noticed something that just doesn't feel right, and I am not sure I can put my finger on it, or even describe what I am feeling but I feel like my steering should be super tight, since a few years ago we did all the bushings bearings turbo tie rods ball joints brakes etc etc, everything but the steering rack itself and I didn't replace the front strut inserts because the feel fine.
wheels are 16'x6" 205/55 Potenza AE11's. 4 years old about 5,000 miles of use, lots of good rubber on there yet, but regardless will have to replace in another year just due to age of the rubber...

so with that, here is what I think it feels like, kind of like it wants to jump around or shift off track. no vibration , no rattle , and I can grab the tire/wheel with car parked and try to move it back and forth and don't feel any play like if you had a loose or work tie rod or ball joint etc.,

what I guess I am wondering is if it is time to pull the steering rack and replace it with a rebuilt one from 914rubber. if that hockey puck thing is getting old and worn, what would that feel like or how would that present itself? And can I remove it by just disconnecting the inner tie rod ends and not have to mess with my alignment? ive not done a steering rack on a 914 before..

as always , advice from those that have done this is appreciated.

Phil

[Superhawk996]

Is the tendency to steer or shift "off track" associated with bumps and/or changes in the road surface?

Sounds to me like you are describing bump steer.

FYI - bump steer doesn't only mean from a road bump. When cornering and the car rolls from one side to the other as weight transfer occurs, you also get bump steer even if on a perfectly smooth surface.

[DRPHIL914]

Is the tendency to steer or shift "off track" associated with bumps and/or changes in the road surface?

Sounds to me like you are describing bump steer.

FYI - bump steer doesn't only mean from a road bump. When cornering and the car rolls from one side to the other as weight transfer occurs, you also get bump steer even if on a perfectly smooth surface.

yes, I think so. - so educate me on "bump steer" is that like "cow tipping" (IMG:style_emoticons/default/rolleyes.gif)

[Garland]

Could be a bad tire, try rotation and a test drive. See if anything changes, no cost diagnostic.

[DRPHIL914]

Could be a bad tire, try rotation and a test drive. See if anything changes, no cost diagnostic.

will do, but after being pointed in this direction, just did a search and watched a couple videos etc and I think we are on to something, I do think it is bump steer. if there is irregularity or a bump it pulls the car one side or the other , this is what happens. so now the question is why am I feeling bump steer? is it worn parts or just poor alignment? and how do we correct it. I have had an alignment done one time a few years ago when Bob Woodmans shop put in the new turbo tie rods and my new A-arms and bushings etc. that was when I had different wheels, 2 years later I switched from the 14" rims to the 16" rims I am currently running. wider tires etc might also be part of this and why I feel this now and didn't used to? (IMG:style_emoticons/default/idea.gif)

sounds like I need full realignment and leveling. basically it has to do with the geometry of the alignment of the rack and the control arm and if they are lined up correctly and do they stay on a proper plane when now moving up and down with the strut as the tire hits a bump. not sure I exactly have it down but will study this more so I can comprehend it, not sure if I can fix it myself but someone can !!! I don't like feeling that bump jump at 60 or 70 mph!!!!

[Johny Blackstain]

Have you replaced the rubber "hockey puck" that connects the rack to the steering shaft?

[DRPHIL914]

Have you replaced the rubber "hockey puck" that connects the rack to the steering shaft?

no, that is really the only thing I have not done. I also have the new front sway bar drop links from Tarrett I got at Okteenerfest last year, and was going to install them but I know if this is not done correctly will result in increased bump steer as well. I should do that also, but I am just wondering if the tire/wheel combo are causing enough change because I don't remember having this with the 14",5" wide 914/6 fuchs I had on the car back when we ran Tail of the Dragon at Okteenerfest 5 years ago. I have 1/2" spacers on the front, I might take those out and see if it changes it and do the rotation like Garland suggested and see how it feels.
Phil

[rhodyguy]

Sort of a 'shudder' in the front end? Rack spacers that elevate the box to help maintain proper tierod geometry. Simple and cheap fix.

[DRPHIL914]

Sort of a 'shudder' in the front end? Rack spacers that elevate the box to help maintain proper tierod geometry. Simple and cheap fix.

ok I am or was a dummy regarding this so here is a good explanation of it-
"bump steer for dummies" :

-here is a nice explanation of bump steer and why it occurs - as you said the tie rod geometry and/ or the control arms and tie rod geometry is whats happening,
specifically it is the "toe should stay as close to even as possible all the way thru wheel travel up and down" . when a bump kicks the tire up that upward motion will cause the tire to go in or out if the tie rod is too short or too long so it kicks in or out, but that is exactly what I am feeling on my steering wheel .

so

- https://www.bing.com/videos/search?q=what+i...amp;FORM=VDRVRV

so maybe my tie rod and steering rack are not in line, need to do a full alignment then as well, check the standing neutral toe position, - what is the rack spacer you are referring to Kevin?

[Superhawk996]

Could be a bad tire, try rotation and a test drive. See if anything changes, no cost diagnostic.

I had different wheels, 2 years later I switched from the 14" rims to the 16" rims I am currently running. wider tires etc might also be part of this and why I feel this now and didn't used to? (IMG:style_emoticons/default/idea.gif)

Suspension geometry is complicated. 914's and McPerson struts in general don't have great bump steer characteristics (zero bump steer being the ideal case).

You may also be feeling the effect of a changed scrub radius that occurred when you changed wheels & tires. Wider wheels and/or wheel spacers typically lengthen the scrub radius unless you changed the wheel offset to compensate for it's effect. That increased scrub radius affects steering efforts and how much distrubance is put into the steering system when you encounter a bump or surface irregularity.

Lowering your vehicle below stock ride height will also have adverse affects on bump steer. This is where bump steer spacers come into play to raise the rack back up. BEWARE adding spacers will only compound the problem if your car is running ABOVE OEM ride height.

There are no simple answers. Study up on steering geometry and it's effects. I highly recommend Carrol Smith's books Engineer to Win, Tune to Win, and Prepare to Win as a good starting point for the layman.

Once you understand more about geometry, then decide what experiments to try. Only you can determine what makes you happy and what feels best to you.

[Superhawk996]

so maybe my tie rod and steering rack are not in line, need to do a full alignment then as well

As a generalization, static alignment (setting toe, camber, and caster) do not affect bump steer which is dictated by vehicle ride height, and suspension geometry changes from jounce to rebound.

Bump steer can be measured via dial indicators, a flat plate bolted to the hub, and then stroking the supension through it's full range of travel from full jounce to full rebound. Once you have that curve of toe change vs. suspension position, you will be able to see where the toe is changing and what needs to be done. This is not something that most people will choose to do but it is necessary to prep a decent race car.

Most likely you've induced the negative effects you don't like with ride height changes, and changes to wheels/tires, and spacers The turbo tie rods only make the effect worse by providing a more direct road feel feedback to you by elimination of the rubber isolation in favor of a metal ball joint. The turbo tie rods also make the vehicle affect worse because the low compliance of the turbo tie rod makes the bump steer effect more immediate, and more effective overall since you're not losing efficiency in deforming a rubber tie rod isolator.

[DRPHIL914]

so maybe my tie rod and steering rack are not in line, need to do a full alignment then as well

As a generalization, static alignment (setting toe, camber, and caster) do not affect bump steer which is dictated by vehicle ride height, and suspension geometry changes from jounce to rebound.

Bump steer can be measured via dial indicators, a flat plate bolted to the hub, and then stroking the supension through it's full range of travel from full jounce to full rebound. Once you have that curve of toe change vs. suspension position, you will be able to see where the toe is changing and what needs to be done. This is not something that most people will choose to do but it is necessary to prep a decent race car.

Most likely you've induced the negative effects you don't like with ride height changes, and changes to wheels/tires, and spacers The turbo tie rods only make the effect worse by providing a more direct road feel feedback to you by elimination of the rubber isolation in favor of a metal ball joint. The turbo tie rods also make the vehicle affect worse because the low compliance of the turbo tie rod makes the bump steer effect more immediate, and more effective overall since you're not losing efficiency in deforming a rubber tie rod isolator.

makes sense.- dynamic not static measurements and testing,. trial by error could drive you crazy. Going back to standard tires and 4 lug is not happening so I have to figure out how to at least improve it as much as I can with what we have. I am not autocrossing the car just 1-2x per year trip to the mountains. if alignment and then some spacers to improve the geometry and reduce the bump steer some then that would be great. First I think getting in there to make sure we have the right starting point with the steering rack and tie rods lined up correctly so ride height adjustment if necessary and go from there. I didn't adjust the ride height but we reomoved everything when we did new A-arms and bushings and tie rods. so the mechanic at the time at Woodmans was George, a 50 year Porsche mechanic. I have to ask him what he thinks about it. they did the aligment but now both are retired!! ( I know he works a bit out of another shop here locally, but mostly rebuilding 911 motors- lots more $$ in that lol!)

[Garland]

Sort of a 'shudder' in the front end? Rack spacers that elevate the box to help maintain proper tierod geometry. Simple and cheap fix.

Here is a great link about rack spacers and bump steer 914World:

Link to rack spacers post

[Superhawk996]

You can also do some reverse engineering and math w.r.t wheel offsets that may have increased your scrub radius.

If you know the offset of your old 4 lug 14" wheels and the offset of the new 16" + spacer, find the difference.

You then have an idea of how much change you're fighting. I suspect it may be more than just the 1/2" spacer you added.

Bottom line, you could look for a new 16" wheel with more offset that would put the center of the tire contact patch back where it was at with the 14" wheel/tire combo.

Keep in mind scrub radius and bump steer are different things but too much of either will make things squirrelly.

[mepstein]

You can also do some reverse engineering and math w.r.t wheel offsets that may have increased your scrub radius.

If you know the offset of your old 4 lug 14" wheels and the offset of the new 16" + spacer, find the difference.

You then have an idea of how much change you're fighting. I suspect it may be more than just the 1/2" spacer you added.

Bottom line, you could look for a new 16" wheel with less offset that would put the center of the tire contact patch back where it was at with the 14" wheel/tire combo.

Keep in mind scrub radius and bump steer are different things but too much of either will make things squirrelly.

I can't imagine 6x16 Fuchs would give you a problem but anytime you have a front suspension issue, it's worth throwing on a different set of wheels. If it makes a difference, you've usually narrowed down your problem quickly.

[DRPHIL914]

Here is a picture from side and one of under looking at a-arm and tie rod. Looks pretty normal for height and level- how much angle of the arm from parallel should there be?

[PanelBilly]

Try snugging up the bolts on the u joints in the steering column. I found that mine were a little loose and that tighten up the steering.

[rhodyguy]

Alignment AFTER you attain the ride height you want. Put the rack kit in and see how much that alone changes things. Are the tie rods somewhat parallel to the horizon/level now?

[DRPHIL914]

Alignment AFTER you attain the ride height you want. Put the rack kit in and see how much that alone changes things. Are the tie rods somewhat parallel to the horizon/level now?

Yes agreed , and yes I think very close to level here is a better picture,
Also when you say “rack kit” ?

[Superhawk996]

@DRPHIL914

Rhodyguy is asking about the steering tie rods to the knuckle. You would like to see them close to parallel to the A-arm that you're showing. From what I can see of the tie rod in the background things look plausible.

I'll just tell you from experience that while a visual inspection isn't a bad thing . . . this will take some trial and error effort part changes. You're probably fighting a couple of differnt contributing factors here including those meaty, performance oriented tires. Wide tires with big solid block tread patterns without many sipes are only going to add to the tendency to "hunt" and/or follow road contours without steering input on your part.

Are you driving on a lot of rain grooved concrete highways by chance? Is that part of where your directional stability concerns are coming in at highway speeds?