Gearbox Gap?

[sjb2oak]

Hello Everyone,
First time posting, so here it goes.

I am currently rebuilding a gearbox for my Dolomite 1850HL and I have come across a problem.
Whilst checking tolerances and making sure everything fits where it should before I actually put
it back together. I've notice a gap! it doesn't look like it should be there and it's quite sizeable.
(see image)
In the Haynes manual there is mention of a spacer which might fill this gap. But that's a
three-rail box and I'm pretty sure I didn't have a spacer there when I took it apart.
(forgot to mention its a single-rail OD box)
The Autobooks manual doesn't mention any spacers being there, and that's a single rail.

Should there be a gap? or am I missing something else??

[sjb2oak]

Forgot to mention it's between the first/second synchro hub and the second gear washer.

[tony g]

Does the hub push up to fill this gap? If so I would say the issue maybe the other side. Maybe the gear needs moving in?

Tony

[Jon Tilson]

The gap is filled with split collets IIRC....They often fall out in the box as the mainshaft is tilted upwards for removal and the first gear
slides backwards letting the collets drop out. Blob of grease sticks them back for reassembly

The inner part of the synchro hub stays still on the shaft. Only the outer bit moves...

Jonners

[DOLOMITE 135]

The inner part of the synchro hub stays still on the shaft. Only the outer bit moves...

The inner part of the synchro hub needs to move along the shaft, when changing gear the inner part of the synchro hub pushes up against the synchro ring which in turn spins the gear up to the same speed as the synchro hub. The synchro hub outer is the part of the hub that engages the gear (initially it does not engage because of the spring loaded ball bearing in the hub allowing the various speeds of the components to synchronise), if the parts are not spinning at the same speed when the outer part of the synchro hub engages the gear will crunch.

One point to note is the synchro hub inners and outers need to be round the correct way, otherwise they will wedge on the shaft and the gearbox will effectively be in gear. No other gears can be selected as the gear train cannot run at two speeds, I always check the input shaft rotates in neutral with no movement of the output flange and the correct engagement of all the gears before re-fitting to the car, as its not always obvious the inner part of the hub is back to front.

[tony g]

Dolomite 135, when you post you make me want some of them badges again

Tony

[sjb2oak]

I can move the synchro hub so it's up against the second gear washer. But the first gear can't move any further up because of a split collar that sits in a groove on the mainshaft. So I end up with the same gap put on the other side. So if I were to assemble the mainshaft like this the first / second gear synchro hub would be able to slide up and down the mainshaft by about 3mm, which doesn't seem right to me.

I've put together another amazing paint diagram to demonstrate this.

[sjb2oak]

dolomite 135,
but the third / fourth synchro hub doesn't seem to have that level of play?

[DOLOMITE 135]

but the third / fourth synchro hub doesn't seem to have that level of play?

The third / fourth synchro hub does not incorporate the reverse, I expect the first / second sychro hub has to include clearance to ensure forward and reverse gears are not selected at the same time. Additionally have you tried the first gear in position as the synchro cone incorporated into the gear and the synchro ring will also reduce the available movement range.

edit.
I have a unused reconditioned single rail overdrive 1850 gearbox in my spares, checking the free movement of the synchro hubs I measure approx 1.5 mm for the third / fourth synchro hub, and 2.5mm first / second sychro hub.

[sjb2oak]

Thanks dolomite 135, this makes more sense now, I didn't think about reverse!
I best get back to building it, I'll probably came up with a new problem soon.