Harrison Bump Steer Fix

[byroncobra]

Fellas

My car's currently with a reputable engine builder north of Brissy having a bit done

He observed that my cars pretty lively up front and that early Harrisons', as mine is, had bump steering issues.

Apparently there's a fix that will help settle things down.

Can anyone advise thanks?

[AC-460]

You may have to lift or lower the rack to fix the problem....

[Merv and Sharon]

I don't seem to have problem with that Greg. Is your steering rack higher?

[RICK LAKE]

Byroncobra The dirt track guys have a setup tool for doing this to your car. About 2 years ago the Kit Car mag did a complete bumpsteer fix on a GT-40. This will also apply to a cobra or any Mustang with a rack and pinion setup. You change the outter tierod ends to longer stud and add spacers. It will take some work but when done the handling will improve alot when turning. Dean Lampe is in the article for this. Long acre sells the board kits for the measurements. Sears sells a digital angle reader for the control arms. Yopu will need a bottle jack and remove the shock and spring. You are going to measure the car flat and then up 2" and down 2" from center. You will add shims and retest. Looking to get close to "0" as possible. Goggle Bumpsteer and there should be some articles on how to do. Good luck Rick L.

[byroncobra]

Thanks Fellas

Merv, my car has double A arms unlike the later cars with a Commodore front end. Apparently the geometry was known cause twitchy steering and one of the Qld Club members whom I thought may frequent this forum has a fix.

I think the rack needs adjusting and perhaps tierods as Rick and AC mentions.

I've always thought my car was lively in the front end, but as with most of us I guess, I've only driven my car and assumed that they're all like that. Now that I'm registered I must get up to Warwicks and get him to give it a shakedown and comment on how it feels.

[Merv and Sharon]

I think I know who is working on your car - should be a good job then! I don't seem to have had any bump steer probs so far. Still sorting out the rear however. Will be off to Fulcrum Suspensions in a week or so to get the corner weights done and associated adjustments.

[sambo]

Merv your car isn't an early one and will have the Commodore lower arms, hence no bump steer. At least this is true for mine, which is an earlier build than yours.

[Merv and Sharon]

Yes Paul - number 80.

[Krait]

Greg,

Pete Dore had bumpsteer issues as well. You might want to catch up with him at the next breakfast unless he chimes in.

Cheers

[Roush #1]

A quick explanation of bump steer problems is that the toe-in changes as the suspension moves up and down....simple enough to check!
J

[AC-460]

To check your Bump steer in your own shed just do the following;
1. Jack up the front and remove front wheel and coilover
2. Get and old Rim... on the outer bottom of the rim weld a piece of 25 x 25 rhs about 2metres long
3. put the rim on the car the rhs should be sticking a metre and a half out the front of the car
4. with the rim hanging approx. 75mm down on ride height mark the ground at the end of the rhs
5. lift the rim up all the way and watch if the rhs moves in or out at the end
for zero bump steer the Rim should travel up and down and the end of the rhs shouldnt move in or out
If the RhS moves out when the rim moves toward the top of its stroke the rack needs to be lifted

This is only a primitive method for those of us that dont have access to do it on a wheel alignment machine but it tells you exactly whats happening

[byroncobra]

Thanks for you explanation AC et al.

The steel rod is a simpler form of a the following test using laser:

Cobra Bump Steer 2.wmv - YouTube

I've spoken to Scott at Venom who has had lots of experience with Harrisons having fabricated the original A arms. He's going to take a look at the setup for me.

[Merv and Sharon]

You are on the right track with Scott. I was going to suggest him. I seem to recall that Aussie Mike had a post a couple of years ago on a bump steer measuring device.