You have been warned
Dave sources a more modern gearbox for his Silver Shadow… but all doesn’t go to plan
Ireplaced the engine in my Silver Shadow (PC, June 2018) with a newer one from a Silver Spirit that should give up to a 10mpg increase in fuel economy… but in my enthusiasm I had made a huge oversight. While I knew this engine would fit as it was used in the final versions of the Corniche, I had failed to check that my existing gearbox would simply bolt on to the back of it and I was now being quoted an eye watering £3540 for a reconditioned unit.
A visit to Wikipedia told me that the gearbox I needed was a GM4L80E usually fitted to GM pickup trucks and vans,but more importantly for me, the Jaguar XJS and XJR in the UK. Modern gearboxes have come a long way since the standard three-speed units of the past with, in this case, the final drive ratio raised from 0.75:1 for the old three-speed unit to 1.25:1 for the fourspeed box. Scouring the internet I found two such gearboxes for sale and, by studying the pictures of the housing, I was fairly sure they would fit.
One of the boxes was being sold by a classic car garage that I can’t mention for legal reasons but turned out to be not far from my auntie’s house in Bishops Cleeve, Gloucestershire. When I reached the garage the owner was out but his mechanic knew all about the sale and told me that they had bought the gearbox for a customer whose XJS gearbox had broken, although in the end the customer had insisted that his old box was repaired in order to keep the cars originality. Meaning the box they had bought for the job was now surplus and, even though they had paid £850 for it, they would let it go for £325 cash.
I parted with my hard-earned £325 and together we lifted the gearbox into the van and I trundled back towards my auntie’s house along the B4035 and A46.
With the car already on axle stands and no pit, the only way to put the gearbox in was to mount it securely on a board and slowly jack up each end a couple of inches at a time, securely chocking each end when not lifting, not ideal but considering Brunel lifted the Tamar Bridge into place using the same process, what could possibly go wrong.
Months then passed as I moved onto other jobs, but one evening while painting the engine sump I thought that, as the car was up in the air and the paint was already on the brush, it would be the perfect time to drain the gearbox and paint the gearbox sump. Plus with the sump removed I could check the condition of the gearbox filter.
Box of tricks
Once the oil had been drained I removed the sump and found that, to my horror, the valve block of the gearbox had been removed, so my ‘new’ box was effectively scrap. The garage that can’t be mentioned for legal reasons had obviously used components from this box to repair the XJS gearbox and had then refitted the sump and put the old oil back in to cover it up. But for me it was £325 down the drain and back to the drawing board to source another gearbox.
david@simmonds.org.uk