bump steer

[orion4096]

I've been trying to figure out why my 93 has bump steer.  It came with a samberg subframe and samberg bump steer kit with rack spacers.  They were purchased several years ago so I don't know if there have been different revisions since then.  It isn't severe, but it's definitely noticeable and annoying at higher speeds and rougher roads.  Was thinking of getting one of those longacre measuring devices, but ended up going the cheap route this morning and zip-tied a laser pointer to a level which attached to my rotor with a magnet.  Drew a line on a level sheet of paper taped to my tool cabinet 9 feet away.  Over 6" of travel there was 1" of movement to the right (toe-in for driver's side).  I forgot to check where resting height is on the line when the car was on the ground, but I definitely passed through it somewhere in the middle of the line.  Given all that I came up with 3" of compression resulted in .12" (about 1/8") of toe-in on the driver's side tire.  3" of travel is a lot, but it's possible for one wheel to be in droop and one in compression for 1.5" of travel each resulting in 1/8" (actually, just 1/16") change in steering to either the left or right.  This assumes that the passenger's side bump steer measurement comes out the same.

The next step is to try adding a washer to the bump steer kit to see if that changes the way the line is drawn.  There's also the possibility my bushings are getting old (177k miles), something is bent, or my rack is going out.  But other than wiggling or replacing stuff I'm not sure how to figure out which of those could be the problem.  Wheel bearings and hub have less than 1000 miles.  The car was raised up 0.25" last weekend, but the problem is still there.  Seeing how straight the line is I can understand why nothing changed.  I attached a pic of my bump steer kit in case it's installed incorrectly or I'm missing a part.  The largest diameter part is about .8" tall.  The rack spacers are .75" thick.

Any ideas?

[DDv8]

Mattster03 did a video     http://www.norotors.com/index.php?topic=195.msg3361#msg3361

DD

[orion4096]

Thanks for the link.  I'm pretty much going through the same process with zipties, a laser pointer, and some geometry.  The problem is I shouldn't have bump steer with Samberg's subframe and bump steer kit/rack spacers.  Mattster03 had some custom work on his subframe and needed to fix his bump steer kit to account for that.

3/8" of additional spacer later and the line is pretty much straight up and down for 6" of travel.  I can't drive with the spacer because there's not enough thread engagement to get the pin through the castle nut.  There's almost no room to move the rack up so now I need to figure out why my bump steer kit isn't long enough.  Anyone have some measurements from their kit?

[largeorangefont]

Can you just get one of the tie rod adapter studs from speedway that is longer to add the extra spacers?

[orion4096]

Maybe, but I want to understand why the current stuff isn't working right before I try to solve it with a different kit.  Would also prefer using the castle nuts with pins.  I'm hoping I just got an old revision or something since it was bought in 3/2011 by the previous owner, but from searching it looks like the fixed height bump steer kit is the newer revision.  I'll try calling Samberg again on Thursday to see if he knows why.

[orion4096]

I tried adding 0.25" of spacing this morning and it seemed only marginally better, but even that was probably my imagination.  Think I'll try bypassing the power steering pump and see if that changes how it drives over bumps.

[orion4096]

Bypassed the pump.  Still does the same thing.  I was expecting it to be a lot harder to drive with lots of caster and 255s up front, but it actually wasn't that bad.  Not sure what else I can test at this point without throwing money into replacement parts.  It's beginning to seem like a problem with the rack itself.  Some possibilities:

bushings - They all look reasonable and don't have any noticeable play.
bent suspension parts - I figure this would have showed up when checking toe changes against suspension travel.
steering rack

[Speedfab]

Have you checked your rear toe links?

[orion4096]

I've replaced all 4 of the toe link bushings along with the 6 pillow balls and 2 big diff mount bushings.  The rear wheels don't move when I shake them on the ground or up in the air and the toe links feel solid.

[Exidous]

http://www.speedwaymotors.com/Adjustable-Tie-Rod-Adapter-Stud-to-Heim,3333.html

I dunno if this would fit. Almost certainly would have to be cut unless you were running 19" wheels but it may be worth a try. I may buy a set and see there is gets me. With my car up as high as I can get it and samberg pats I still get a lot of bump steer. It;s not overly noticeable with the 255's but the 285's it's pretty bad.

[orion4096]

I might try those since they are cheap, but with the extra spacers installed on the samberg bump steer kit there wasn't really any difference.  I'll also try dialing back the camber since I'm running -3 in front and -2.5 in back with no plans to track this car.

[orion4096]

I let a friend drive the car today and he gave me the idea that my power steering is over boosted.  Thinking back on that I've done two things that may have changed this from when I first got it:

- Went from a 25% under drive damper to a stock diameter ATI damper.
- Swapped the power steering pump and used the longer spring/hex piece in the new kit instead of the old one that might have been cut down.

I have the turn-one fitting with 1L(?) written in it which has a .093" hole according to the previous owner.  Maybe I should open it back up and check.

EDIT: Actually, I have to remind myself I got a shorter belt and tried without power steering and it didn't help.  I pulled out the wallet and ordered a refurbished FD rack from ebay.  Bushings, suspension arms, bump steer kits, power steering pump, ... everything shows some evidence it's not the problem so I'm ready to start spending $$$.

[Bowtie7]

I might try those since they are cheap, but with the extra spacers installed on the samberg bump steer kit there wasn't really any difference.  I'll also try dialing back the camber since I'm running -3 in front and -2.5 in back with no plans to track this car.

IIRC when you run a bunch of negative camber in the front it tends to cut back on the available caster which will make the steering feel nervous and not want to return to center. I did not see what you cater measurement is but I would try for as much as possible hpefully around 6.5 deg or a little more.

[orion4096]

Here's what it was aligned to 6 months ago.  My scanner died so you get a crappy low-light iphone 3gs pic.  I've lowered it a little since then and changed the toe to be 1/8" total toe-in on the front.  I want to say it's always had the problem, but can't say for certain since I don't drive it much and it was warmer back then.  There are a few patches of really bad road near me where it's easy to check if it's still there and going from a slight toe-out (probably because I lowered it and forgot to fix toe) to 1/8" total toe-in didn't get rid of the problem.

Going to try a new set of tie rod ends while waiting for the steering rack.  The driver's side makes a metallic click when I push it up and down with moderate force.  Maybe the 20k miles the previous owner put on them is enough to wear out the heim joints.  If that doesn't change anything, I'll get a shop to reduce the camber and push caster up as high as possible and then change the rack.

[orion4096]

I got the torque wrench out and made sure all the front subframe and suspension nuts and bolts were tight.  Several of the subframe nuts were loose.  This did get rid of an annoying rattle I started hearing at idle a few months ago.  Didn't fix the steering problem, though.

New tie rod ends got rid of a creaking noise from the front end and made the steering a little smoother, but didn't do anything to fix the problem.  The old heim joints were much stiffer.  My steering rack order got cancelled because they didn't have any in stock and I'm starting to think it's not the rack so next up is the control arms and bushings.  With 177k miles on the chassis this stuff probably needs to be replaced anyways.  It sucks that I can't figure out the exact cause of the problem without replacing parts.

The one thing I forgot to mention is the car came with megan coilovers which I plan to sell, but I don't see how they could cause what feels like bump steer.

Another idea is to zip-tie a camera in my wheel well and go drive around.  Haven't tried that yet.