Triumph TR6 Rear Axle Unit Assembly
We supply from stock, a range of fully reconditioned, ready to fit axle units on a strict exchange basis. These are available (depending upon your requirements and budget) with either a 3.45:1 or 3.7:1 ratio, with optional brand new crown wheel and pinion, and finally with a limited slip differential option (supplied only with a new crown wheel and pinion).
Old exchange units returned to us should be complete and assembled, drained of oil, and be externally clean with no irrepairable damage. Note that the front mounting plate and the rear aluminium housing (complete with 4 lugs) must be returned. Failure to comply with these requirements will result in retention of part or all of the exchange surcharge.
The original ratio of the axle fitted to the Triumph TR6 PI is 3.45:1. The simple way to check is by counting the crown wheel and pinion teeth. The crown wheel will have 38 teeth and the pinion 11. The ratio is arrived at by dividing the quantity of teeth on the pinion into the quantity of teeth on the crown wheel.
Other ratios that may be discovered fitted are 3.7:1 and occasionally 4.1:1. The petrol injected Triumph TR sports cars were the only ones to have the 3.45:1 ratio axle as standard fitment. Carburettered TR250s and TR6s were fitted with the 3.7:1 ratio, whilst the 4.1 was a special competition ratio. On the road, the difference between the 3.45 and 3.7 ratio is barely noticeable (unless you are using 60 series low profile tyres on 15” rims) whilst the 4.1 feels as though you have run out of gears!
Selected other models from the Triumph range of the same period were also fitted with the 3.45:1 ratio, i.e., the Dolomite Sprint and 2.5 PI Innsbrück. As there was no ratio change during the production period of the TR6 PI axle they are assumed to be interchangeable between model years. This is true if entire units are replaced. If the internals of a certain model year are used to repair another axle of a different model year, problems may be encountered with non-compatible parts. The major significant change was the replacement of the solid, shim adjusted pinion bearing spacer for a collapsible type. The other item to change internally was the sun and planet gear sets. The early type had plain teeth, the later ones had a groove machined into their tooth edge to aid identification, and so should be fitted in sets of four when interchanged.
For the record, we list below the original part numbers and ratios, for all popular applications. For all practical purposes, we list under ‘Rear Axle Unit Assy’ one part number (RR1112) with various options appearing as a suffix. It is then up to the customer to decide which options suits best.
Original No: 312061 RATIO: 3.45 : 1 Applications: TR6 to commission no. CP52867.
Original No: 313130 RATIO: 3.45 : 1 Applications: TR6 from commission no. CP52868.
Original No: 312060 RATIO: 3.7 : 1 Applications: TR6 to commission no. CC61570.
Original No: 313129 RATIO: 3.7 : 1 Applications: TR6 from commission no. CC61571.