Sunday, 1 April 2012

DHC’s gearbox rebuild part 1

At last, and quite some months overdue I started on rebuilding the gearbox meant to replace the broken one. First job to attend to were the lubricating holes for the gears in the mainshaft. I am using  a new shaft, but when I inspected it, I found out that the lubrication holes were much larger than in the old shaft. On closer inspection I found out that the original shaft had the same diameter holes, but with restrictor pins fitted to ... euhhh ... restrict the oil flow to the gears and supplying more oil to the bearing between main and input shaft. Luckily this was sorted quite easily with a few spring dowels ...



Next on the to-do-list was measuring the clearance of the 1st/ 2nd gear set. This turned out to be spot on , so time to start in earnest. First job was to fit the bearings to the mainshaft, layshaft and input shaft. Fitting the bearings to the mainshaft didn’t go quite as easy as we expected, as they needed quite some extra persuasion to get seated properly. Needless to say the other bearings were heated a little bit longer, as a result of which they just dropped in the correct position ...



With the bearings sorted I could start with the next stage of the rebuild, mounting the mainshaft and the layshaft to the ‘boxes centre plate ..


And that nearly ended in disaster. While fitting the 5th gear to the layshaft one of the shifting plates from the 3rd/4th gear synchro hub, decided to slip out. Luckily I was able to put it back in with the help of a very fine screw driver. Otherwise it would have been a case of removing (and probably ruining) the bearing in order to re-fit it.
And I managed to forget to install reverse gear  before fitting the 5th gear to the layshaft, but that was easily rectified ...



Now waiting for the rear extension to return from the machine shop (for a little adaptation for the selector shaft seal) and some shims for the front bearings to arrive.
And some progress on the paintwork, the car is ready for painting and will be moved to the spray booth this week.

2 comments:

Kim Gibson said...

how are the spring wires for the synchronisers placed to hold the slippers that are between the inner and outer hubs of the selectors? On the edges of the open box sides of the slippers? I can't find a description or a picture. thanks.

Beans said...

Hi Kim,
When you assemble the synchro hub assembly (so the inner hub and sliding hub plus the slipper pads but without the brass synchro rings), the small "hook" at the end of the spring sits inside the slipper pads. But they should not engage in the same slipper pad. And that hook should face in the direction of the shaft's rotation. So one spring per side of the hub.
After that you can fit the synchro rings. Hope that helps, if not find an online (pdf) workshop manual