Minimize Bump Steer

In Robert “Greg” Wagoner’s book “High Performance Fieros” he talks about a simple method for eliminating rear bump steer on Fieros.  Having never driven a Fiero at all before completing this project, I wasn’t sure how bad this bump steer could be but I had read about it several times.  I usually don’t like modifying stuff without testing first but on this occasion I decided to go ahead and make the change since Greg made a lot of sense when explaining the reasons behind it.

Basically, Wagoner suggests that the rear tie rod arms are too long causing the rear wheels to turn a little as they travel up and down. Apparently this is because the designers were trying to use parts from other cars to minimize production costs so the rear end of a Fiero has some common parts with a Chevy Nova for example. Anyway the idea here is to make the rear tie rods 2″ shorter which also means that the mounts on the cradle need moving 2″ further out.

RR_TieRod_Brkts

Instead of cutting off and moving the existing mount brackets, I made up my own using a couple of short lengths of thick angle iron.

RR_DS_TieRod_Brkt1  RR_PS_TieRod_Brkt1.jpg

I worked the piece of angle iron so that it fitted snugly in place with the new mounting face 2″ closer to the wheels than the original.  Then I aligned it with the original plate and marked out where the holes needed to be.  Once the holes were drilled, the new brackets were carefully welded in place.

RR_DS_TieRod_Brkt2  Rr_Left_Tran_Mnt2

One of the lower holes was a slightly off, so I simply elongated it with a round file to suit.  Once the brackets are ready, we need to take 2″ out of the tie rods.

RR_Tie_Rod_1  RR_Tie_Rod_Dims

You can see in the picture above, the shaft necks down right where the thread ends so we cannot simply tap the thread further down the shaft of the tie rod and cut the excess off the end.  Instead, I cut 2″ out of the middle of the shaft and beveled the edges of each end.

TieRodChamf

Then I found a piece of tube 2-3″ (50-75mm) long that fit snugly over the tie rod shaft to use as a sleeve.  Based on my measurements above, the sleeve ID was probably around 13.9mm with a 4mm wall thickness (I don’t have the actual measurements in my records but I made the note that the ID was ‘a fraction large’).  If you don’t have any suitable tubing handy, head over to a metal supermarket if you have one accessible or maybe see if you can check out the scrap bins of a local machine shop?  Next I needed to align the shafts with the beveled ends together, and constrain them as straight as possible while welding.  I got a great tip for this from Rick, I clamped both parts into a piece of 2″ angle iron and laid a steel rule along the top to confirm a alignment was straight.  Once I was happy that the shafts were aligned, I tacked between the bevels, then rotated the shafts in a star pattern to minimize weld distortion; I continued to monitor the alignment at each turn with the steel rule.  Once the gap between the beveled edges of the shafts was fully welded, I ground back any excess so that the sleeve slid back over the join.  Finally, I positioned the sleeve evenly over the join and welded all around each end of the sleeve to give you a 2″ shorter tie rod, repeat for the other side.

TieRodsFinished

That picture was taken before painting.  I have had no problems accessing the nuts between the new and old mount plates and after a couple of years on the road with some spirited driving, there are no signs of any issues.  Maybe I’ll get a recent picture of them fitted in place (too late now).  I certainly haven’t noticed any bump steer but I still haven’t had the opportunity to drive a stock Fiero to compare.