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Author Topic:   Bump Steer and spindles
cre93
Dirt Full Roller

Total posts: 43
posted April 24, 2005 11:19 PM  
What would be considered "good" bump steer numbers for a UMP modified running on a 3/8 mile track with about 10 degree banking. The other question I had is about spindles. Can I use a metric spindle on a 68 - 72 Chevelle stub assuming the ball joint holes are reamed for the big taper ball joints??
Thanks, Dave

wfoondirt
Dirt Forum Champ
Total posts: 505
posted April 25, 2005 07:43 AM  
I consider anything over .100 out bad. You absolutely don't want it to toe in.

A&M Motorsports
Dirt Maniac

Total posts: 117
posted April 25, 2005 08:14 AM  
WFO, I assume that you're talking about .100" per inch of travel correct. I am new to mods but on my camaro clipped car I used to set it, RF .060" toe out per inch of travel and set the LF as close to zero as possible. Will this also work on a mod?

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Artie Perilloux
A & M Motorsports

Dman
Dirt Freak

Total posts: 270
posted April 25, 2005 08:14 AM  
If your car carries the LF,does it matter how the car bumps out? I don't think you can get rid of the bump steer on a chevelle clipped car running pinto spindles with the amount of wheel travel and caster camber gain we experience on dirt.The steering arms are too high on the pinto spindles and the camber gain RF and camber loss LF wacks out the toe quickly. With oem components we struggled for hours to get it close to right on our pavement mod that only has 2 ins. of wheel travel (with metric spindles)and little body roll(sway bars keep it down).And what we did to correct it was illegal on top of it.None of the stock center links put the inner rod ends in the right place. Get it as close as you can with bump spacers and drive it! The spacers are usually in the 1 1/4 to1 1/2in.length range with a stock center link on the chevelle clip cars with Pinto spindles.
The best bump steer front end I have ever seen done on a stock part front end car was done by Ellis on their pavement mods but it was illegal for IMCA and some other associations because the steering arms were modified (and the center links might have been too).Same thing with the Fast Boys mods.
Good Luck!

dirtywrench13
Dirt Freak

Total posts: 324
posted April 25, 2005 12:03 PM  
OUR NEW AURANGER CAR HAS A BIG IMPALA METRIC FRONT CLIP WITH BIG SPINDLES, AND IT HAS LESS THAN 2* TOTAL BUMPSTEER TOTAL, FROM FULL COMPRESSION TO FULL EXTENSION.THE TIE RODS ARE ONLY SPACED DOWN 1/4 OF AN INCH. THEY ARE THE NEW IMCA LEGAL HEIM END STYLE THAT I RECYCLED FROM THE OLD D-W8.

Dman
Dirt Freak

Total posts: 270
posted April 26, 2005 07:40 AM  
Dirtywrench13,
It's not IMCA legal. Something has been altered Or is an aftermarket replacement(cheater). GM didn't make anything that good that would only need a 1/4 in.spacer to bump correct or we all would know about it and be using it.We all have been racing this stuff too long to miss it. Think about it.If you could do it with stock un-altered parts there would be no aftermarket for centerlinks and spindles other than to save some weight. If you heat it,cut it or bend it, it's not stock it's altered. Don't blow smoke here!

wfoondirt
Dirt Forum Champ
Total posts: 505
posted April 26, 2005 10:08 AM  
quote:
Originally posted by A&M Motorsports:
WFO, I assume that you're talking about .100" per inch of travel correct.

Yes, I shoot for as close to zero as possible as long as it absolutely can't toe in. Some people claim gains by purposely building in bump steer but its just one more thing that you would have to worry about when doing adjustments.

As far as IMCA legality I don't keep up with their rules but with a UMP chevelle/pinto will bump pretty good with a spacer on the outer heim. I'm guessing IMCA still makes you run stock outer tie rods?

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted April 26, 2005 10:29 AM  
IMCA allows the outer heim.

The pinto/chevelle setup can be set to bump pretty good. I forget what our actual numbers are but I was thinking aroudn .060 out per inch, but may be better or worse than that. Seems like the first inch or 2 as really good then the lst inch or 2 was worse. I think typically spacers ended up being about 1 1/2" on the right, and maybe a little shorter on the left, but different cars could be a little different.

dirtywrench13
Dirt Freak

Total posts: 324
posted April 26, 2005 10:41 AM  
D-MAN, IF I COULD TAKE A MINUTE HERE AND EXPLAIN THIS, IMCA ALLOWS US TO DRILL THE SPINDLE AND USE A 5/8 INCH BOLT,THEN YOU CAN SPACE IT DOWN TO SET THE TIE ROD LEVEL AT RIDE HEIGHT. IT JUST SO HAPPENS THAT IT WORKED OUT WITH OUR BUMPSTEER. THE HEIM END AND STEEL SWEDGE TUBE WITH A STOCK CHEVELLE OUTER TIE ROD END ARE 100% LEGAL, AND ARE SOLD AS DIRTWORKS TIE ROD SETS ON MOST TRACK PARTS TRUCKS.

dirtywrench13
Dirt Freak

Total posts: 324
posted April 26, 2005 10:43 AM  
WE ALSO USE A DIFFERENT LOWER BALL JOINT TO GET THE CORRECT SPINDLE HEIGHT, AND THE NORMAL D-W 8 UPPER BALL JOINT.

Dman
Dirt Freak

Total posts: 270
posted April 29, 2005 07:55 AM  
I know all that is legal dirtywrench.We run IMCA. I am talking about heating and bending steering arms and/or re-locating inner tie rod hole location on the center link. And yes you can get it close in 2 ins. or less but, how many dirt cars run less than 2 ins. of travel? The left side is the one that is the most difficult to get right because it hangs or travels so much more than the right. So add the two together and the numbers aren't so good.The best you can do is level the tie rods with the lower a-arm and get it close. This is dirt racing not formula one.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted April 29, 2005 08:43 AM  
While I think its worth looking into minimizing bumpsteer I also agree with Dman in the fact that this is dirt and the precision reuired in other forms of racing isnt needed. I think if you level the tie rod with the a frame as a starting point then you can fine tune from there if you need it, but dont get hung up on trying to get it perfect. If you end up changing ride height a 1/4" or so or change balljoint, or spindle etc then its possible that your bump steer will be off again from your 'perfect' number. I know guys that missed the first race because they were hung up on trying to get bumpsteer to .020/inch, when in reality they need track time more than bumpsteer.

Something to keep in mind is that unless there is a load on a wheel it gives the driver no input. So if your LF drops a bunch and unload the spring there is no need of doing bumpsteer from complete drop especailly if the spring is unloaded for an inch or so before it even hits. On the RF you will rarely ever have that wheel in rebound so from ride height i would only worry about compression bump.

Rook78
Dirt Maniac

Total posts: 106
posted April 29, 2005 10:44 AM  
I have a question regarding B-Steer, I am currently running stock tie-rod ends on a metric front end. I have considered changing these to the heim ends with swagged tubes. Is there a way to measure bump without a guage? Or should I just be looking to getting them as paralel to the lower control arms as possible?

Thanks for your help.
Rook

dirtywrench13
Dirt Freak

Total posts: 324
posted April 29, 2005 11:44 AM  
WELL I DONT KNOW WHAT TO SAY TO TELL YOU THAT I'M COMPLETELY LEGAL. THESE METRIC SPINDLES I'M RUNNING NOW WERE SUPPLIED BY THE CAR BUILDER, AND ARE IDENTICAL TO THE BONE YARD PIECES I GOT FROM THE YARD MYSELF.

boas51
Dirt Maniac

Total posts: 190
posted May 03, 2005 07:21 PM  
dont know what i did wrong. my new chassis has less than .100 bump out on the right side in 5" of bump!!!! havent done the left yet.
metric clip, 74 nova lowers, metric spindles, 6117 lower, 6136 upper, all stock metric steering.
you can check bump by drilling a 5/8" hole in a piece of 2"angle iron 20-24" long and bolting it to your spindle. level it and clamp the brake. run your spindle through bump and rebound (spring and shock removed). use a square off the floor, and make marks on the floor, front and rear at each inch of bump or rebound. you can then measure the difference between the marks.

Rook78
Dirt Maniac

Total posts: 106
posted May 04, 2005 09:32 AM  
Cool deal, thanks for the response. Seems simple enought to measure. A can of worms perhaps to remedy.

I assume you would want your first measurment at the static position of your lower arm, correct?

Thanks
Rook

[This message has been edited by Rook78 (edited May 04, 2005).]

boas51
Dirt Maniac

Total posts: 190
posted May 05, 2005 07:51 PM  
correct, i ussually measure one inch rebound, 4-5" bump on right, and 2-3" bump and rebound on the left.
but yes, zero is at ride height.

boas51
Dirt Maniac

Total posts: 190
posted May 05, 2005 07:53 PM  
9 times out of 10 it is your centerlink that will have to be moved down, not your outer tie rod ends.

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