Sorting Out Steering Kickback

[Bravoaloha]

Hello Pelican!

I am looking for some ideas on what is causing some pretty serious steering kickback while cornering at speed in my '86 Carrera.

I have been sorting the car out since purchase back in the fall of '17. I have refreshed a lot of the suspension while keeping the following parts installed by the PO- Rebel Racing Triangulated Strut Brace, 22/29 elephant bars (soon to be swapped for 21/27's), Turbo tie rods, spherical/teflon front bushings (early elephant possibly? RSR? they are black and unmarked) and Tarett sway bars front and rear (not sure size). I have installed Bilstein RSR struts (19mm raised spindles) and shocks custom valved by Steve Weiner, Rebel Racing Bump/Steer kit, new OEM ball joints, new sport rubber upper shock mounts and Rebel Racing rear spring plate bushings with new spring plates.

Car is on 15" Fuchs (7's and 8's), R888 tires.

Alignment specs here-



I know the numbers are funky... My shop cannot get more than -.7° of camber on the left side, they are saying its because the RSR Struts are de-cambered(?).

I have a great baseline to know how my car is supposed to drive- my dad's much cleaner, much less bastardized similarly setup '86 Carrera. I have gone back and read every thread I can find on bump/steer, kickback and scrub radius but most of the discussions involve widebody cars and nothing I have read seems to apply to my setup.

Any ideas? My steering wheel goes nuts when I hit bumps during spirited driving and I am desperate to sort it out.

Thanks!

[Eagledriver]

I had a similar problem in an 86 Carrera. Part of the steering rack had pushed out the side of its case. It was some kind of bushing that the rack goes through. This caused the tie rod to move around causing the steering to kick around.

[aston@ultrasw.c]

My first thought,

In summary, excessive bump steer.

Check that the control arms pitch down slightly: higher on the inside.

Same with the tie rods.

Re-reading your post, it sounds like you describe two symptoms:

serious steering kickback while cornering at speed (corning, no bumps??)

steering wheel goes nuts when I hit bumps during spirited driving (straight, with bumps??)

Can you clarify for us?

[chrismorse]

What is the ride height, torsion bar center to wheel center? With the bump steer spacers, I am guessing you could have the front ride height 17mm lower than stock spec and not have any bump steer problems, (hope someone with experience can verify). With these spacers And the dropped spindles, you might be ok at -36mm.

A second possibility is wheel offset greater than stock, or front spacers, either of which could increase the scrub radius, making the steering heavier.
On a similar note, if the aftermarket shock tube/spindle/hub depth, have greater lateral offset, this could affect the scrub radius.

Is everything tight up front, rack, tie rod ends, ball joints, wheel bearings, steering shaft joints?

Curious,
chris

[Trackrash]

Any wheel spacers? As mentioned, what is your ride height.

When the spindles were raised, were the steering arms bent to compensate? If not you will need the bumpsteer kit that replaces the tierod ball joint. https://www.rsrproducts.com/product-page/basic-bump-steer-tie-rod-end-kit
No way to restore correct steering with raised spindles with rack spacers AFAIK.

Also, maybe not the main issue, but you need to figure out why you have 1,4 degrees neg camber on your right front strut. That much difference between the two fronts will cause problems.

[Bravoaloha]

Originally Posted by Eagledriver

I had a similar problem in an 86 Carrera. Part of the steering rack had pushed out the side of its case. It was some kind of bushing that the rack goes through. This caused the tie rod to move around causing the steering to kick around.

I just had the rack out to replace the steering coupler. I was pretty sure I checked for this then but I wanted to double-check so I pulled the boots this morning and I think they look ok.

Originally Posted by aston@ultrasw.c

My first thought,

In summary, excessive bump steer.

Check that the control arms pitch down slightly: higher on the inside.

Same with the tie rods.

Re-reading your post, it sounds like you describe two symptoms:

serious steering kickback while cornering at speed (corning, no bumps??)

steering wheel goes nuts when I hit bumps during spirited driving (straight, with bumps??)

Can you clarify for us?

Here is a couple pictures of the control arm and bump/steer pitch (with the wheel jacked up to simulate being on the ground). I don't think anything looks really out of whack.





The kickback occurs when hitting bumps in the road during cornering. It is fine when going straight and hitting bumps

Originally Posted by chrismorse

What is the ride height, torsion bar center to wheel center? With the bump steer spacers, I am guessing you could have the front ride height 17mm lower than stock spec and not have any bump steer problems, (hope someone with experience can verify). With these spacers And the dropped spindles, you might be ok at -36mm.

A second possibility is wheel offset greater than stock, or front spacers, either of which could increase the scrub radius, making the steering heavier.
On a similar note, if the aftermarket shock tube/spindle/hub depth, have greater lateral offset, this could affect the scrub radius.

Is everything tight up front, rack, tie rod ends, ball joints, wheel bearings, steering shaft joints?

Curious,
chris

I am not sure about ride height. It was pretty low before but I raised it up today.



I didn't have a chance to really drive the car after raising her up but on my ride home from my shop I did not notice any improvement or difference.

I'm not sure about offsets but these wheels are off my dad's '86 and there was no issue with them on his car. I do know my hubs are pushed out a bit compared to my dad's and other's '86 Carerra's. I found this out when I bought a set of Minilites from a guy with an '86. They fit his car and my dad's car fine but were pushed out about 3/8's of an inch on my car for some reason. No spacers. Everything is tight up front.

Originally Posted by Trackrash

Any wheel spacers? As mentioned, what is your ride height.

When the spindles were raised, were the steering arms bent to compensate? If not you will need the bumpsteer kit that replaces the tierod ball joint. https://www.rsrproducts.com/product-page/basic-bump-steer-tie-rod-end-kit
No way to restore correct steering with raised spindles with rack spacers AFAIK.

Also, maybe not the main issue, but you need to figure out why you have 1,4 degrees neg camber on your right front strut. That much difference between the two fronts will cause problems.

RSR Bump/Steer Kit installed! No wheel spacers.

Thanks everybody for your responses and thoughts

[Tyson Schmidt]

How much were the spindles raised?

Hard to tell from the angle of the pic, but it looks to me like you don’t have a big enough bump steer kit. They sell a racing one that is adjustable, and can be dropped further to get the toe curve better. They sell double sheer braces that I’d recommend using with the longer drop links.

[Bravoaloha]

Originally Posted by Tyson Schmidt

How much were the spindles raised?

Hard to tell from the angle of the pic, but it looks to me like you don’t have a big enough bump steer kit. They sell a racing one that is adjustable, and can be dropped further to get the toe curve better. They sell double sheer braces that I’d recommend using with the longer drop links.

Spindles raised 19mm. That is the adjustable racing kit. It has some room to go and I could buy more spacers to drop it even more but it is close to parallel with the control arm now. It's hard to get the camera in there to show how its really sitting.

[porsche930dude]

My car has this problem as well. its lowered and small rack spacers. So is it ideal to have the tie rod exactly paralell with the control arm or rack slightly above or below?

[Bravoaloha]

Originally Posted by porsche930dude

My car has this problem as well. its lowered and small rack spacers. So is it ideal to have the tie rod exactly paralell with the control arm or rack slightly above or below?

My understanding is that the tie rod is supposed to be almost parallel with the ground, but angled slightly down towards the outside of the car. With that being said I'm here for advice and I could be wrong!

[eastbay]

Your alignment guys should have set your cambers even, if you can only get -.7 on the left you should set the right to the same. I don't like the mismatch of cambers on the rear either, or toe in at the front.

[Trackrash]

Originally Posted by Bravoaloha

My understanding is that the tie rod is supposed to be almost parallel with the ground, but angled slightly down towards the outside of the car. With that being said I'm here for advice and I could be wrong!

Perhaps. I used to think that as well. That is until I installed raised spindles. Getting the bump steer correct is more involved than eyeballing the tie rod angle.

[Bravoaloha]

Originally Posted by Trackrash

Perhaps. I used to think that as well. That is until I installed raised spindles. Getting the bump steer correct is more involved than eyeballing the tie rod angle.

Is there a guide you used to sort it out correctly? Thanks

[Trackrash]

There are guides, but here is basically what you have to do.

Measure and record your front toe at normal ride height.

Lower the front of the car one inch, us weights don't adjust the suspension, measure the toe.

Raise the front of the car 1 inch above the normal ride height, measure the toe.

Adjust the washers or spacers on the bump steer kit so the toe changes minimally from normal. You will be OK if it changes the same direction going up from normal to down from normal.

A royal PIA, but worth the effort. I used strings.

In your case, it doesn't sound to me like a bump steer problem you are having. If your bump steer is off you will have a darty and unstable feeling when gently turning at speed, like on the freeway.

[Bravoaloha]

Thanks Gordon! I would agree- the car feels pretty much fine on the highway. She can be a bit darty in a straight line, but I blame that on the tires.

The kickback happens during tighter, bumpy back road cornering. It also happens on the track during cornering. I have to really think about those symptoms as I have not been on track with the car since the fall and it doesn't look like I will be getting back anytime soon.

[Bill Verburg]

Originally Posted by Bravoaloha

I just had the rack out to replace the steering coupler. I was pretty sure I checked for this then but I wanted to double-check so I pulled the boots this morning and I think they look ok.








Here is a couple pictures of the control arm and bump/steer pitch (with the wheel jacked up to simulate being on the ground). I don't think anything looks really out of whack.





The kickback occurs when hitting bumps in the road during cornering. It is fine when going straight and hitting bumps



I am not sure about ride height. It was pretty low before but I raised it up today.



I didn't have a chance to really drive the car after raising her up but on my ride home from my shop I did not notice any improvement or difference.

I'm not sure about offsets but these wheels are off my dad's '86 and there was no issue with them on his car. I do know my hubs are pushed out a bit compared to my dad's and other's '86 Carerra's. I found this out when I bought a set of Minilites from a guy with an '86. They fit his car and my dad's car fine but were pushed out about 3/8's of an inch on my car for some reason. No spacers. Everything is tight up front.



RSR Bump/Steer Kit installed! No wheel spacers.

Thanks everybody for your responses and thoughts

You have multi interrelated issues
* you must address the front camber disparity
* the steering tie rod ideally wants to be horizontal when the car is on the ground, the reason is that wheel travel pulls the arm when in droop and pushes the arm in bounce, you want to minimize the magnitude of the push/pull which will be when the arm starts off horizontally when at static ground position, a contributing factor is to try to keep wheel travel to a minimum
*any bump steer issue is magnifored by any increase in scrub radius w/ stock hubs and 7ET23.3 a 911 starts w/ a lot of feedback caused by the s/r of 52.4mm, push the same wheel out another 3/8" and that increases to 61.925mm, so any feedback from the wheels is amplified by ~18%
*any time an aggressive bump steer kit is added you need to measure the bump steer to see if it helps or hurts, either can happen. To measure bump steer you need a flat, rigid plate bolted to the hub, a strut w/o a spring or internals and a dial indicator, attach the plate to the hub, move the wheel through it's arc while measuring the toe and recording it correlated to travel from the neutral condition seen when the tire is on the ground and full weight is on it. You can still do it w/ the spring and shock internals in situ but it's going to be harder. The stack of steering arm o/s's that you keep should be chosen after measuring the effects of as many of them as you have the patience for. W/ an extra dial indicator you can also measure camber and draw a camber curve for you setup.

Here are the curves for a stock 3.2 Carrera at stock ride height

[Trackrash]

Originally Posted by Bill Verburg

* the steering tie rod ideally wants to be horizontal when the car is on the ground, the reason is that wheel travel pulls the arm when in droop and pushes the arm in bounce, you want to minimize the magnitude of the push/pull which will be when the arm starts off horizontally when at static ground position, a contributing factor is to try to keep wheel travel to a minimum

This is true if the a-arm pivot (torsion bar center) and the ball joint are also level when compared to the ground. Actually the tierod needs to be parallel to the horizontal plane between the torsion bar center and the ball joint center.

[Bill Verburg]

Originally Posted by Trackrash

This is true if the a-arm pivot (torsion bar center) and the ball joint are also level when compared to the ground. Actually the tierod needs to be parallel to the horizontal plane between the torsion bar center and the ball joint center.

This is what you want, in compression the steering is moved opposite to the motion in droop, they average out as much as possible.


not this, which is what I believe you just described, here the steering arm movement is always the same way, it just gets worse the more compression


Bumpb steer comes from the diffeening arcs of the oute end of the tie rod and the outer end of the A arm

here are 2 examples of relatively clean bump steer

this one is aspirational as in practice it's virtually impossible to do



This one is closer to a 911, the plane you describe is far from the case. It's also far from the 911 case in that though the steering movement is all in one direction it at least decreases w/ bump travel. The arcs are determined by the relative geometry between the ends of the 2 relevant arms


Again whatever bump forces are present are magnified when the wheel centerline is moved further outboard and a stock 911 starts w/ a large bump force component to the steering wheel

[Trackrash]

Yes, Bill. But you will notice I said in the plane of the ball joint and torsion bar. NOT the a-arm.

Like this.

[Bill Verburg]

Originally Posted by Trackrash

Yes, Bill. But you will notice I said in the plane of the ball joint and torsion bar. NOT the a-arm.

Like this.