Checking Bump Steer on my Aftermarket Schwartz Chassis for my 1964 Chevelle...Lots of Pics
I decided to check the bump steer on this chassis. Ultimately, this is very, very important and means a lot when cornering. All of the aftermarket people try to eliminate bump steer to get your car to handle.
Dale Schwartz pointed out that I have an early chassis and improvements have been made in later models. That being said, I currently don't have any initial set-up information for this chassis, but there are a couple of initial problems.
-The lower control arm and tie rod angles don't seem to be the same. The tie rod is on much more of an angle and the rack position isn't adjustable.
-The upper control arm was severely bound up. This required removing about 1/8" from one of the spacer/reducers which go into the upper control arm heim ends. The previous owner had to pound the heck out of the control arm to install it, and then it wouldn't move like it should.
-That being said, even with the heims screwed into the control arm as far as they would go, there is about 3 degrees of positive camber, when you want about 3 to 5 degrees of negative camber. The upper control arm needs to be shortened, but it isn't as easy as chopping about 1/2" from it. There is a cross bar in the way, so that also needs to move, but may interfere with the shock.
So, before any bump has been checked, modifications are required to the spacers and upper control arms.
Doing the bump...
I initially centered the rack, set the lower control arm parallel to the cross member and leveled the lower control arm. I also set the toe to zero with the bump steer plate.
http://i1302.photobucket.com/albums/...psautxn8iw.jpg
http://i1302.photobucket.com/albums/...ps1klcizuk.jpg
Bump at 1" thru 3"
1"
http://i1302.photobucket.com/albums/...ps1vfdplbz.jpg
2"
http://i1302.photobucket.com/albums/...ps8vhegfsj.jpg
3"
http://i1302.photobucket.com/albums/...psucijz5zt.jpg
Bump at 1" Droop
http://i1302.photobucket.com/albums/...psiorjjfac.jpg
And back at Zero - Only .002 different from start, so repeatability was good.
http://i1302.photobucket.com/albums/...pspin9mqg2.jpg
All was toe in
1" was.057
2" was .109
3" was .170
Droop at 1" was .040.
Normally, when it is a consistent toe in, you lengthen the tie rod. So, I literally moved the lower control arm and tie rod end out 5/8", which was at the end of the threads on the rack. This made everything worse, much worse.
So, I moved the tie rod down with spacers, just to see what will happen. This brought the tie rod and control arm angles a little closer together and helped the bump quite a bit, but I need a bit more.
I moved it down about 7/16" which was as far as I could and still get a nut on it. Since this has a conventional OEM tapered rod end, then only thing I can do to fix it is make a new steering arm, or drill the arm and use a female heim on it with spacers. The arm actually looks as if it was built upside down. There is about 1/2" of material machined from the bottom of the steering arm with spacers as shown in this last picture. If the arm was the other way, then I think the bump would be a lot closer. It can't really be fixed because of the ball joint and tie rod tapers
http://i1302.photobucket.com/albums/...psmixcjsnu.jpg
This is not very good for a competition car. It was nearly 3/16" at 3" of travel. Normally a car with stock type spindles, this should be no more than .020 and aftermarket racing spindles, this would be less than .010.
Once again, the camber wasn't set which affects everything, but not a whole lot. It seems I have quite a bit of work to do as this was just the drivers side and I am sure the passenger side is about the same.
grr
Corrected The Bump Steer....
After figuring out which rack is installed on this chassis and finding out you can buy offset bushings and a bump steer kit, I fixed my bump steer on this chassis.
The bump steering was terrible and totally unsuitable even for a regular street car and something needed to be done.
I bought a set of offset bushings for the rack mounting bolts. The holes were too small for the steel bushings so I tried drilling them out. Have you ever tried drilling semi-soft rubber with a 7/8 drill bit? Well, it doesn't work very well. I have a nice drill press and vice but once the drill got about 1/4" into the rubber, it would catch and pull the bushing out of the vise and send it for a ride. I tried everything to get it to work, but whenever I tried clamping the bushing tighter, it would collapse more, oblong the holes and still not work...I finally just got out my die grinder, chucked up a round wood rasp and enlarged the holes that way. It was much faster than drilling and worked pretty well.
So, after installing the bushings and raising the rack about an inch, installing my bump steer kit putting a bunch of spacers under the tie rod end, I got the bump seer to go from 3/16 in to 1/4" out. I knew then I was heading in the right direction...I moved the rack back down about 1/2", took out most of the spacers and the bump went back to toe-in.
After fiddling with spacers I got the bump to within .005 toe -out which is pretty much ideal. Now all I'll have to do is cut about 1/2" from the rack threaded end and this will be all taken care of...
grr
Start and End at Zero - Everything level
http://i1302.photobucket.com/albums/...psis7btoez.jpg
1" of travel - About .005" Travel
http://i1302.photobucket.com/albums/...ps98ylrzv3.jpg
2" of Travel - Less than .005"
http://i1302.photobucket.com/albums/...psnnhlksil.jpg
2-1/2" of travel - Back to Zero
http://i1302.photobucket.com/albums/...ps16t9jvcv.jpg
Bump Steer Kit
http://i1302.photobucket.com/albums/...ps8rx1wfdx.jpg
