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Wasn't there an optimun number of shims or a specified distance that our steering racks were supposed to be moved out for bumpsteer. I think the later cars had the rack moved out a little but not enough. Does anybody here know what the best distance is for shims. Does any one here really understand bumpsteer? This is another example of me having some of the story but not all of it. I'm redoing my front end so now's the time to do it right. Thanks all
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...Thanks for the comment Garth! To All, Be advised, I went by that same 'BluePrint' when I Machined My first pair of 'Spacers'. After pulling the Steering Rack, to install them, I found the Center to Center distance of the Bolt Holes was Incorrect!. And don't forget to obtain Longer Metric bolts. Last; Torque them in like 'Putting a Baby to Bed', because the Threads in the chassis are VERY delicate and will strip out with-out even trying!! (I Believe the Max. Torque is 20 Ft/Lbs??). If You Strip the threads Your NightMare has Just Begun! "You can listen to me Now OR Believe Me Later!". Good-Luck with it!...
For U.S Panteras, the shim thickness is "around 5/16" but each Pantera will be a bit different if you want to truely minimize bump-steer. And when you add the shim(s), you'll find the rack and clamps move frontward and downward, so Bill Stropp's famous rack-brace doesn't fit anymore. You can re-drill the attach holes in the brace and frame and use 5/16" longer metric bolts so you don't strip out the threaded inserts up in the crossmember.
Or you can hacksaw about 5/16" off each steel rack-clamp surface (4 total) where the bolt heads touch. File the cuts smooth so the bolt heads contact your cut surface flat without any bending. Then the entire assembly goes together with the old bolts and unaltered Stropp brace.
I also like using shims that have slotted holes in their sides so they can be slid in from the side, instead of trying to balance and align the rack, two clamp-halves and the shim, while trying to get a bolt started. Oh, and don't forget to readjust the toe-in about 1/2 turn IN (not guaranteed perfect) on the steering rods; EVERYTHING you do up front changes toe-in!
I followed Garth's thread to Dan Jones posting on the Realbig forum and found the statement that '74 cars had a factory bumpsteer correction (shims).
I took a look at 7102 (wheels off and up on stands in the shop) and that appears to be the case. The rack is shimmed away from the mount by two spacers.
Any further shimming doesn't seem possible as the rack mounting bolts pass through a stiffener attached to the other side of the rack that looks to be factory welded in place.
Two questions. May I consider bumpsteer shimming a done deal? And, is the stiffener the "stropp brace" (or equivalent)?
Any further shimming doesn't seem possible as the rack mounting bolts pass through a stiffener attached to the other side of the rack that looks to be factory welded in place.
Two questions. May I consider bumpsteer shimming a done deal? And, is the stiffener the "stropp brace" (or equivalent)?

The Stropp BRace is in fact the stiffener (or rack-brace). As far as a 'done-deal', it depends entirely on how much of the bump-steer you wish to remove from your car, and in what condition the car is in. All the spring shims should be removed from the coil-overs. And its pretty simple to arrange things so the Stropp brace fits as-stock while changing rack-shim sizes on any Pantera, pre-shimmed or not. Whats done is to hacksaw off a bit from both outside clamps where the rack bolts touch the clamps. The amount cut away should more-or-less match the changethickness of shims you're planning on using, and the cut areas filed or milled flat so the bolts aren't bent when torqued down. Then, stock length rack-bolts also fit.
Incidently, stock Stropp-braces were bolted in; perhaps yours is sunk into the undercoating added by most dealers? Having that piece firmly welded to the front lower frame extensions would make it VERY difficult to change a rack bushing since the rack should come out for this commonly-done operation.
OK, I crawled under and took a better look, with a light this time.
Yes indeed the "stropp" braces are bolted in. I see it would be very difficult to remove the rack otherwise.
The shims/spacers presently installed measure right about 5/16" thick. The spring shims are gone from the coil-overs.
I guess that means I'm probably close but likely not perfect.
According to experts like Carroll Smith, author of the "XXX To Win" series of books, all of the bump-steer cannot be removed from any given steering system because of geometry conflicts. All you can do is minimize the effect by smaller and smaller repetitive changes. You first find what you've got by removing the coil-over on one wheel, setting up a plate with two dial indicators -one touching the wheel rim on the outside face at front and one at the back, and begin raising the wheel up 1/8" inch at a time and reading the variation in wheel position, graphing the full travel up/down vs that wheel's position. Then you change the shim thickness and measure it again, seeing if the bump-steer toe change, in the area of travel used most by your car, is better with this shim size. You keep doing this until you get tired or the thing is about as good as it can get in the wheel-travel area you use in your driving. Then you realign the wheels (toe-in changes with rack position height), check one more time to verify this adjustment didn't detract from your results, and call it done. NO ONE (including me) does this outside of racecar crews on cars that earn money racing. 5/16" is close enough, I believe.
[quote]books be a good start?

Ex owner of #5012

Yes. In fact, ALL of Mr Smiths five books are valuable and quite readable for the backyard engineer. Bump-steer, Ackermann angle, toe-in settings with modern tires, and other geometry-related subjects are covered in 'Tune To Win', 'Engineer to Win' and his last one before passing on to the big track in the sky- 'Drive to Win'. I've owned mine since they were first published and re-read them constantly, always finding something new. Somewhat less readable but still good is one I recently picked up from one of your countrymen- Allan Staniforth's 'Competition Car Suspension' published by Hanes in GB.
If someone is looking for me....

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The kit I sell is $40, and includes the hardware, which can be hard to find at times.

I include instructions with pics too!

We've install a number of these at PCNC Tech Sessions. If there is enough interest, I can organize another event for this task.

Chuck Melton
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