The transmission used in the original cars is a bit of a mystery. Jaguar had intended to use a five speed of their own design, but this did not develop well. At the time of LeMans, there was no suitable box available. It is likely that the cars as raced used ZF five speeds. In any event, the transmissions used at LeMans let the car down, at least two out of three failed before the race was over. The 11 surviving cars, some of which had four speeds of various sorts, were all converted to the ZF box by 1965. The ZF box, whether used at LeMans or later, proved to be a poor match to the engine. Several cracked engine blocks were attributed to the great weight and high drag of this transmission.
After lengthy consideration, I will be using a modern five speed. This is in keeping with Jaguar's intent for the car: there is no historically correct AND mechanically sound choice. The entire drivetrain: transmission, driveshaft, and rear axle will be supplied by Waterloo DTR of Austin, TX. The photo above is a Waterloo TX51, basically a Tremec 3550 reworked to fit up to a Jaguar tunnel. With a torque handling capacity around 400 Ft-Lbs, it should be a good match to the capability of the engine. It will drive the rear axle by an aluminum drive shaft. See my transmission page for more information.
The flywheel and clutch were supploied by GTJ . The flywheel weighs just seven pounds. It has aerodynamic slots which draw air through the wheel for cooling. The friction surface is replaceable high grade steel. The clutch is a Tilton twin disk.
The rear axle is built around a standard Salisbury posi differential: Jaguar attempted unsuccessfully to build a diff using aluminum castings, and installed ZF diffs in some Lightweights, but the standard Salisbury seems most correct. The axle ratio will be 3:31:1, which, in conjunction with the big Dunlop racing tires and overdrive transmission yield a theoretical top speed in excess of 200MPH. The rear axle track has been widened in conformance to the original Lightweight spec. This required modified lower control arms and spacers on the half shafts. The diff rear cover has been replaced with a finned aluminum cover, which also reduces weight a bit. The cage has been modified for strength and weight reduction: the bottom plate is aluminum, as are the radius arms (below). The hub carriers have been drilled for cooling and lightness in keeping with the original spec. Bronze bushings have been used throughout, and a special mechanism has been added to allow rapid adjustment of wheel camber. It will be solid mounted to the body. Bakes are vented XJ6 units, with cooling scoops. The suspension is based on HAL shocks and springs,which are fully adjustable units.
Aluminum Rear Suspension Components
Text and Photos Copyright©2000 Michael Frank, all rights reserved.
May not be reproduced without permission.
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