General Repair Information For Your Imperial's Driveshaft


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Tips from Gary:

My recently purchased '56 C-73 was missing the left bracket (welded to the axle housing) to which the 3-01-33 hanger is bolted. The hanger secures the aft end of the 3-01-25 control strut, while the front attaches to a bracket mounted to the under side of the body. This is pictured on page 341 of the '56 FSM.

An IML reader was kind enough to remove this bracket from his '56 parts car, along with the strut, hanger, and bushings for use on "Babe". Having read the accounts of others with missing and broken control struts I consider it a minor miracle to have found good useable parts.

In an earlier posting I asked for opinions as to proper the ride height for the rear of the car, reason being that I intended to remove the rear springs, clean, rebush, and replace the interleaf rubbing blocks, and I wanted to determine if they should also be re-arched. Concessus seemed to be that the car should set level with respect to the distance from the bottom of the rocker panels front and back.

Have patience...this really is going somewhere.

We removed the axle and welded on the bracket. The springs were serviced locally and new rubbing blocks installed. The new blocks (8 in each spring) were 1/4" thick. We estimated that the originals might have been 1/16" to 1/8". This had the effect of giving the springs slightly more arch. We did not re-arch the leaves.

After reassembly we found the car 1/4" higher @ the rear compared to the front. We reassembled the control struts using what we thought was enough shims to eliminate any push or pull on the struts. This was measured with the full weight of the car on the ground.

The test drive produced a slight driveline shudder between 20 and 45 mph. Back up on the lift. With bubble protractor (see Propeller Shaft and Universal Joint Service Reference Book 115) we found the front companion flange to be 2 1/2 degrees (pointing down), and the front propeller shaft angle to be 1 1/2 degrees sloping down from transmission to carrier bearing. The rear shaft measured 4 1/2 degrees down from carrier bearing to rear U joint (full weight of the car on the ground, car resting on 6 x 6's). The front flange of the rear U joint companion flange was 1 degree positive (3rd member tilted up).

From this it can be seen that the working angle of the front U joint was 1 degree, the center U joint 3 degrees, and rear U joint 3 1/2 degrees.

Rechecking the shims between the bracket and hanger we found that there were too few to position the assembly @ zero tension. We added 1/4" of shim to both brackets and measured rear shaft angle of 3 1/2 degrees (raising the nose of the 3rd member decreased the rear shaft angle) and rear U joint companion flange angle was 2 1/2 degrees.

Now the center U joint working angle was 2 degrees, and rear U joint angle was 1 degree. With a 200 lb load on the rear bumper the angle increased to about 1 1/2 degrees. The car had 3/4 tank of fuel.

The specification for working angles is from 1 to 3 degrees. All U joints were now within that range.

The car drove beautifully! No shudder.

This page last updated October 12, 2004.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club