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MG MGA - Chassis to ground dimension - help please

Hi Guys,
I'm about to set to work on the final chassis alignment on my push rod car, but i would appreciate some help in identifying a final dimension before i get the heat torch out.
My Twin Cam has a distance of of 16" (410mm) from the underside of the rearmost chassis point (where the rear tub mounts) to ground (on a finished car). Would you guys be good enough to measure the same point on your cars and post the results; i'll then take a view on the "norm" and adjust. (Both of these points on my rolling chassis pushrod car need adjustment as one side is 1" higher than the other and both are significantly higher than the 16" on my Twin Cam.) Loading with the body tub and spare tyre etc will drop it slightly but not enough to get close to my "norm" of 16" finished.
Any dimensions greatly appreciated.
Thanks
Colin
C Manley

Is not that measurement in the Workshop Manual sufficient?

Image attached. Enlarged image with next message.

Mick

M F Anderson

Larger image attached.


Mick

M F Anderson

Thanks Mick, i have the 8&3/16"dimension to the chasis underside from a large drawing in my possesion, but as it is a rolling chassis it is the ground clearance at the rear end i'm looking for. I thought all was ok until i lowered the rear body tub onto the chassis and found the rear valance line to be out of parallel with the axle tube. When i measured the clearance that's when i found the anomoly and then measured my Twin Cam to see what that car had (16" - see photo to follow). i was looking for an average figure and i'll adjust the chassis to that figure.
C Manley

Photo showing 16" height.

regards
Colin

C Manley

The measurement sitting on springs is not real valuable, too many variables, in judging if frame is straight. Setting the car on 4 identical stands under the datum line shown in Mick's drawing. Car must be on a flat floor also. Measure to the bottom of the Datum line then add that Number to those in the drawing.
R J Brown

Is the body higher, or is the frame itself higher on one side?

If body - the rear mounting points might need to be shimmed up on one side - on my car they are not in identical locations. Or, you could be missing the cork packing on one side at the very rear?

If frame, the rearmost spring mount could be binding, or the leaf springs are not the same anymore.

If the frame were twisted that would be bad. Has there been an accident in the car's past?

Try putting the rear of the car up on two jackstands at the same height - under the frame at the very rear of the car (and in the same spots) and then measure from frame to ground at a spot in the middle of the car - that'd tell you if things were awry somewhere.
AJ Mail

AJ and all,
It's the frame that is higher. The chassis was bent and was realigned some years ago and all is ok diagonally etc. When i took possesion i did some horizontal straightening at the chassis extension point but never noticed the rear until i put the rear tub on last week. It is just the rear end that is still a bit high and that is what i will pull down.
Thanks for the input.
regards
Colin
C Manley

This thread was discussed between 03/07/2010 and 05/07/2010

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