The original intention was to keep the stock diff as our base car was already an auto with the 3.9. The more we read about converted cars using the 3.9 ratio the more we were convinced that the Cobra diff was the way forward. With the torque of the LS3 it made little sense to be stuck with a heavy gearbox that needed lots of gear changes. The TR6060 6th gear is spaced a long way from 5th so it made sense to reserve this for cruising and use the box like a 5th speed on track. The Supra hits about 155mph at the Nurburgring with 400bhp and the 3.55 Cobra ratio should be good for around 170mph flat out in 5th – perfect! We’ll see……
Images of exploded Mazda differentials was also a concern. It would have been cheaper in parts to just replace on failure, but the thought of the diff exploding 1000 miles from home at the Nurburgring convinced us otherwise. It’s 180Euros to be towed off the ‘ring, they charge you heavily for oil that you spill on the track, for the marshal time and even the admin for printing an invoice! Ignoring the finances, I often borrow my pals Kawasaki for a few laps, so am pretty sensitive to oil spills on the road and track. One slip can be pretty catastrophic at the ‘ring.
Anyway we found a new/unused Cobra 3.55 diff for sale on ebay.com. The seller was amazingly helpful and bought some low mileage axles locally for us, split the inner CV’s off and sold them on at cost. This kind of stuff is difficult for us to purchase from the UK.
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Dad got a nice surprise when he pullled the rear cover off on the bench. It was filled with preserving fluid - you can guess the outcome!
Got the rear cover machined and welded locally
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Fully mounted with poly bushes.
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