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Author Topic:   Wheel base 4-bar
cmiller51
Member
posted December 19, 2001 08:13 AM
I am working on a DW-8 4-bar chassis. We got the car after the season was finished and have been putting it back together. We set the car on the ground last night and the wheelbase is 2 inches shorter on the drivers side. 108 and 110. The bars measure the same on both sides..?? Is this right?


irace74
Member
posted December 19, 2001 12:24 PM
How is the front end geometry set up? Depending on the front end settings and some other variables, the bars being the same length does not equate equal wheel base. I think there are a couple of tabs on the over bars above the rear end housing. Hang a plumb bob on these tabs and make sure that the rear end is centered on the tabs. This should locate your rear end properly with the motor plate. THen review your front end settings and check the drive shaft for parallel with the axis of the crank shaft. With this done, I think you can count on the car being square.


BILLY BOB
Member
posted December 19, 2001 02:22 PM
will this work?? run bobweight off each side rear frame rail so that the string just touches there rearend then put a bolt in the factory cross-member hole, measure from the bolt to each string??


jeff
Member
posted December 25, 2001 10:44 PM
Check the wheel base from the grease fittings on the lower ball joints to the front of the rear axle. You cannot trust measuring from trailing arm mounts as I have seen many modifieds (including new ones) that if you set the wheel base off frame measurements you could be 3/4 inch off or more. Look at Billy Bobs post above. This will give you an accurate wheel base.


wfoondirt
Member
posted December 27, 2001 08:59 AM
Measuring from the lower ball joints works for a general idea of wheelbase for rules compliance etc. To square the rearend you shouldn't use the front wheels to align the rearend because changes in front geometry will change rearend alignment. Granted on stock frontend cars such as modifieds there is no adjustment in the lower a-arms but there is the occasion of unnoticed crash damage etc. I prefer to run parallel strings down each side of the car and measure off the strings to square the rear. I do this similar to billy bob with the car on jackstands at ride height and use a set up bump-steer plates to measure off, but it can be done on the ground by measuring to the wheels. Once i have the rear-end square in the car, i will make a reference mark on the underslung rail on both sides of the car for making alignment changes at the track.
By stringing both sides of the car you can also easily check for a bent rearend housing.

As far as the original question, if you are measuring off the front wheels, make sure you have the caster set properly, also if you arent using the same bars on the rear-end as before, check and make sure they are supposed to be the same length, some cars use shorter bars on one side versus the other.

[This message has been edited by wfoondirt (edited December 27, 2001).]

fellers24
Member
posted December 27, 2001 08:33 PM
I AGREE WITH BILLY BOB ON SQUARING THE REAR END. WHAT I WANTED TO PASS ALONG IS MY BROTHER GIVE ME AN OLD PAIR OF FLEXI FLYER SCALES THAT HE WELDED ALL FOUR OF THEM SOLID AT THE SAME HEIGHT. DURING THE SEASON THEY WORK GREAT TO PUT THE CAR ON AND SQUARE THE REAREND, SET PINION ANGLE ECT. YOU DON'T HAVE TO TAKE ANY THING OFF BECAUSE THE CAR IS HIGH ENOUGH IN THE AIR TO DO WHATEVER YOU WANT. IT IS REALLY NICE FOR SETTING PINION ANGLE AND INDEXING THE BIRD CAGES. THE OLD FEED SCALES WORK NICE TOO, BUT YOU COULD BUILD STANDS LIKE THE FLEXI FLYER SCALES FOR A LITTLE OF NOTHING. HOPE THIS HELPS SOMEONE.



2nd2none
Member
posted December 27, 2001 10:11 PM
will this work?? run bobweight off each side rear frame rail so that the string just touches there rearend then put a bolt in the factory cross-member hole, measure from the bolt to each string?? This is how i did mine, logicaly it seems correct to me