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Bumpsteer- Rack Extensions - Cont'd

12K views 23 replies 14 participants last post by  Bobby Boychuk 
#1 ·
Hi all,
Spent yesterday and today making up the final rack extensions for my bumpsteer solution. Original post is here . Started out with a kit from Heidts that has 2" extensions, extended boots and clamps. I machined them down to 1.7" and also had to bore them deeper and thread them deeper. The latter took up most of the time since I had to match the existing threads and cut them by turning the lathe chuck by had so as not to bottom out the tool (no tap available since the threads are a very odd 15/16"-20). Turn, test fit, turn, test fit, etc., etc.. Talk about monotonous!!

The goal was to have no toe gain on extension (base will be 1/16" per side) and some toe-in gain on compression. The results are 0.00" toe change on extension and 0.030" toe-in gain at full compression compared to the ride height position. A little extra toe-in should help stability on heavy braking (that's the theory anyway).

Here's some pics.

The 1.7" extension:



Extension and inner tie-rod:





Extended boot:



Outer tie-rod configuration. I had to shorten the outer tie-rod threaded section as well as the adjusting tube.



Overall pic:



Time for a
.

Cheers, Rod
 
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#4 ·
I've been following along Rod!

Put me on the list. Cheque's in the mail etc... :D

You are using Fox spindles right? Do you think either SN95 version would require a different extension? I'm guessing no since the LCA pivot point is the same (unless you are using donor arms and the inner mounting hole).

Thanks for sticking with this one. I think it's a great idea.

Gordon's Konis look great BTW.

Sean
 
#7 ·
nice work rod
 
#8 ·
I had extensions made for mine as well. Huge improvement. Remember folks, the size of the extensions are not universal. It will depend on what rack you're using and what spindles you have. The FR rack takes M14 fine threads.
 
#9 ·
Rod
you have the tie rod in the wrong location, it must go on top of the steering knuckle to eliminate bumpsteer. now you are going to have to remove your extention, it is going to be to long
Ricardo
 
#10 ·
Thanks guys!!

I'm not really set up for production and it took about four hours each to modify the extensions. I'll check with William at VPM to see if he is interested. But, as Todd mentioned, it is very configuration specific. With all the different possible configs out there it would take a lot of testing to come up with a unique solution for all of them. Stock rack vs. manual rack and stock LCA's vs. FFR LCA's vs. Forte LCA's. Not sure if there are any small differences between the different LCA's and small differences can make a big difference. For example, adding an extra 0.030" spacer on the outer tie-rod to move further away from the steering arm flips the results and gives 0.03" toe-in on extension and 0.0" on compression. The power rack also allows you to run more caster which moves the steering arm up and changes things quite a bit. If I had a manual rack and was running my current set-up (Fox spindles and Forte LCA's) I would have had to drop the rack down to get the proper geometry.

Sean, I think it would take some testing with your actual set-up to determine what the ideal length is and the position of the outer relative to the arm. But I would bet it wouldn’t be the same. Gordon's Konis are great looking but did require some small changes, front and rear, to work with my set-up. All set to go at this point though.

Sanford, DOH!! I looked at a bunch of places trying to find that tap with no luck. Even called one company that makes custom taps and never heard back from them. Thanks for the info! One per end for a total extension of 3.4".

Todd, Heidts also makes the 2" extension for the manual racks with the 14mm threads. How much of an extension did you end up with and what were your bump readings (if you know)?

Ricardo, Not sure why your saying that but you are incorrect and that set-up would be dangerous as it would go to extreme toe out on acceleration. Never good to have two tires pointed at opposite ditches at the same time!

Cheers, Rod
 
#15 ·
No problem Bobby. That ad is from a Canadian site so there is the exchange (most companies up here never reduced their prices when the rate got better :rolleyes: ) and some difference for them bringing it into Canada. Actual price was $51.42 so I guess they are one of the good ones that did follow the exchange rate to some extent. Shipping was only $7 so not bad overall.

Cheers, Rod
 
#16 ·
Originally posted by dv/dt:
Thanks guys!!

Todd, Heidts also makes the 2" extension for the manual racks with the 14mm threads. How much of an extension did you end up with and what were your bump readings (if you know)?


Cheers, Rod
Rod,

I only have a total of 2" extension installed. That only makes up for inner CAs pivot offset. I'm holding off on adding more until I have the SAI kit and SN95 spindles installed. I haven't taken any data yet but will when I get all the other stuff together.
 
#17 ·
Hey Rod, I could use a couple. I was forced to mount my joint "above" the knucle extension because it wouldn't go that far otherwise. I got mine off a 2000 Mustang so no dog-leg... just stratight.
 
#18 ·
Rod
the way you have set the tie rod is no different that from the original set up (with out bump steer kit.
the reason that the bump steering kit in the FFR was developed is to correct tie rod geometry due to the steering rack been mounted higher up in FFR frame in ralation to the steering knucke vs the mustang subframe.
If you notice in the manual states to change the inner tie rods for the ones suplied in the kit. reason they are shorter not longer.
I am just trying to save you some aggrevation.
but if you still not beleave me call FFR tech suport.
Ricardo
 
#19 ·
Richardo,
If Rod has achived the numbers listed, below or above the steering arm doesn't matter. The results are what counts. The numbers published above for toe in and out with compression and rebound are about ten times better than what I measured prior to installing my Gordon Levy bumpsteer kit. The stock FFR front end geometry ( on the MKII anyway )is just too excessive. They should have fixed this problem 2 generations ago.
 
#21 ·
Rod,
would an easy way to determine the amount of extension need for a particular set up be to drop a string from the upper a arm pivot point/mount to the lower A arm pivot point/mount and measure the difference between the string plane and the pivot point of the inner tie rod?...or am i oversimplifying?
 
#22 ·
Ricardo, I think you should go back and read the original post I provided the link for above. I assure you that you're not getting anywhere close to my numbers if your using a stock set up. What bumpsteer I do have (0.030" toe-in on compression) is intentional. I can program it to absolutely 0 bump steer in either direction if I choose. Not sure how you can argue against the numbers I'm getting. As for asking FFR I'm sure they will agree that there are simply too many variables to be able to say one solution fits all. Rack length, LCA's, spindles, rack location (dropped/raised) and even how much castor you're running can drastically affect bumpsteer. And even FFR's own ad for their bumpsteer kits acknowledge that the locataion relative to the steering arm is dependant on the set up of the individual car.

FFR Info: "Our bump steer kit is for the type of person that desires maximum performance from their vehicle. This kit allows you to position the tie rod end above or below the steering arm to minimize bump steer."

Bobby, With Gordon's Koni's installed I have about 3.25" of extension and 2.75" of compression and that is where the numbers above were measured at. But if you check out this post you will see where I dial out all bump steer from 3" compression to 4" of extension with a 1.56" extension. I went slightly longer so I could tune in some toe-in on compression.

Cheers, Rod
 
#23 ·
Grego,
That will get you close and is kind of where I started but to refine it further you need to test. It is trail and error but not as bad as you think since you can use the steering rack to simulate the different rack lengths. Find the rack center location and mark it. Then just keep extending the rack on one side and shortening the tie-rod to reset the spindle back to straight ahead. At some point you may have to cut the threaded end of the inner tie rod to make it short enough. This is where you're commiting yourself. Cycle it trough to check the bumpsteer and then adjust as required. Kind of a juggling act though since rack height relative to the steering arm has a big affect as well. You can use the info on Longacre's site to guide you in the right direction.

http://www.longacreracing.com/articles/art.asp?ARTID=13#Q3

Cheers, Rod
 
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