I agree with CHANMADD with regard to using the rubber bushing. Keep in mind the rubber bushes were designed for a 4500lbs sedan so will be ample stiff for the cobra. DO NOT FIT POLY bushes. ( see below)
What happens here is that the rubber bushing provides ALL the flex (read movement) of the lower A-arm. The rubber bushing is NOT designed to rotate on the shaft.
The question of washers depends on the intention of the kit maker. The designed distance between the arms of the lower a-arm is 8.88" (22.57cm).
The rubber bushes are pressed into the a-arm to be central. ie. equal bush either side. If one examines a RUBBER bush you will find the rubber part exceeds the width of the internal metal sleeve. ie. the metal sleeve is 1/4" narrower than the rubber. ie.1/8" each end.
One needs to measure the fixture on the chassis thru which the pivot shaft is fitted. If it measures 8.25" then the jag washers are required. If it measures approx 8.5" then the washers are not required.
The original Jag washer is 1/8" thick and surrated on at least one side. Some on both sides. The surration goes to the rubber bush. This washer compresses the 1/8" rubber overhang of the rubber bush.
The second washer on each side is a bugger to fit and often a small jack between the arms is needed to push them apart slightly to get clearance.
Apply copper anti-seize on the pivot pin to prevent the bushes growing to the shaft.
Don't tighten the castleheaded nut until the weight of the car is fully on the suspension.
So the sequence is: castle nut, large washer, rubber bush, surrated washer, chassis fixture, surrated washer, rubber bush, large hex end of the shaft.
That's it, clear as mud, just like the jag manual.
