Gearbox Rebuild

21 02 2013

Having stripped the box down completely it was a pleasant surprise to find that all the expensive bits were in good order and could be reused. All the gears are Jack Knight and unfortunately the company no longer exists, so compatible parts have to be made by other companies – if you can find one that is, and even then it is very expensive. Alternatively there are a few spares around, especially as the majority of top Miglia runners have started using the Swiftune gears. Anyway, we will be ok for a while with what we have got…


The gearset is of the JK involute ‘dog’ type. A very close check whilst all stripped down showed no problems, so after a good clean I reassembled the mainshaft. The casing had also had a good clean and the selectors and mechanism inspected for any wear or bends. Back in my mini7 days all these parts were changed as a matter of course as we could purchase them for a matter of pence from Roversport. Unfortunately those days are gone so I tend to go overboard on checking anything pre-used, or replace it with new from Minispares London.


As mentioned in the last blog the centre oil pickup was a bit ropey so I ordered a new one from Minispares. There are cheaper ones around but some of the ones I’ve seen are pretty crap quality. I’ve never had any issues with MS stuff so I was happy to pay a few quid more.  So in went the new pipe at the same time as the laygear and reverse and the endfloats checked.  I’ve also fitted a magnetic trap in the back of the gearbox casing to try and stop any metal particles getting in to the oil pump. Every little helps.


Finally I fitted the differential unit. We have to run an open diff but can upgrade it to a 4 pin unit if we want. No LSD’s are allowed. Mine is a standard unit with an upgraded pin. The regulation 3:9 final drive is used, mine being of the Jack Knight semi helical variety. A quick check found that no shims were needed between the diff bearings and the side plates so I fitted them on with new output shaft oil seals.


Throughout the build I used new locktabs, gaskets and no sealant. A liberal squirt of oil here and there allowed the box to spin up nicely.  It’s all nicely wrapped up ready for the engine to be bolted on.




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