Which gearbox...

[Arthurdaily]

Right BMC - there are loads of gears underneath H! I'm presuming it is the one on the end of the lay shaft - hardly a gear at all, more like splines? I can't get a clear pic.

However:

Gearbox 1, rebuilt I have been reliably told, has all clean teeth with no wear on any of the gears behind H. BUT all gears seem to have a little tiny bit of play in them?

Gearbox 2, I can see wear - some little chips at the front edge of the splines on the lay gear, and on what I think is reverse gear. But, no obvious play.

I'm going to try and take another pic...

[Arthurdaily]

Right, can't take a clear picture - but the rebuilt box, though a little 'looser' seems to have new gears in it. Plus it has new seals, a new clutch bearing etc. So will just do a straight swap and see what happens!!!

However, it does lead to another question... it always does doesn't it!

I have studied the gearbox internals and have worked out which each 'thing' is and how it works. Simply, the 'forks' grab hold of the little teeth (dog)at the edge of which ever gear you choose and thus the movement from the lay shaft gear is transmitted to the held gear on the 3rd motion shaft, meanwhile all other gears on the 3rd shaft simply 'spin'. Yes? So, this would seem to mean that what are marked as 'synchronisers' in the BMC manual are actually fixed to the shaft? Is that right? My question is HOW are these synchronisers held - I can't see how on the diagram...

Also, number 2, there appears to be no fourth gear marked - I'm presuming that is the one on the internal end of the first motion shaft and basically provides DIRECT drive from the engine?

[MarkyB]

Probably shrunk on.
The sycro rings do their best to get both gears spinning at the same speed before they mesh.
You can hear them working if you change from 3rd to 2nd a bit sooner than normal.

[Arthurdaily]

They are fixed to the shaft then Marky?

[Arthurdaily]

Also, just interest here - not worry! It's interesting that the first gear cog is ALSO the coupling sleeve for second - clever dual use. BUT why no synchro on first? I see now how the synchro works on the inside of the first gear, allowing it to synchronise the slide onto second - but it just 'roughly' engages onto the lay shaft splines to give first?? So ... 'crude'! No wonder it is so difficult to double de clutch into first - you would need to get the revs just right!

[MarkyB]

Any sychro at all was an utter luxury, try driving something with a crash box!

[bmcecosse]

The syncro cones are loose inside the selector hub. Otherwise you have it correct - well done. First gear is straight cut (hence the whine when driving) and slides directly into engagement with the teeth (not splines) on the laygear. Reverse is likewise selected directly - hence also crunches. Yes - 4th gear is straight through - the laygear doing nothing. Hence if there are laygear/layshaft problems - the box can often still provide drive in 4th gear - whatever use that is!! The later Mini boxes are 4 syncro but this mod didn't make it into the Minor box. And it doesn't make 1st gear selection any easier there anyway. Use the box with the 'NEW' gears.

[David W.]

I beg to differ.
This is a smooth case. There are no loose syncro cones.
They didn't bother to synchronize first because you would normally only be using it from a dead stop.

[bmcecosse]

Are they smooth case boxes?? I've no guide on that..... But yes - if smooth the syncro rings are fixed.

[Arthurdaily]

These are ribbed cases, I can't 'see' the cones as such in the actual gearbox.

So (using BL/BMC book terms) - the 'synchroniser' is attached to the shaft and is actually a tube with splines / teeth on both the inside (to grab the shaft) and outside in the case of the first gear (to grab the layshaft first gear) - the 3rd motion first gear assembly and 3rd/4th coupler 'slide' on these synchronisers to select 1/2 or 3/4 gears - the synchronising is actually done by the 'cones' which 'grip' the thrust washers which are floating on the shaft and kept in check by grooves in each gear and thus slow or speed up the gear / layshaft, as you push the gear completely in the 'pointed' end of the gears have no choice but to move left or right and thus engage...

So in fact, by comparing with modern engines on youtube, these gearboxes don't actually have 'synchro rings' in the same way.

My God I'm nearly an expert,

[Arthurdaily]

God, I hope these are ribbed boxes... better go and take a photo!

[IslipMinor]

From the earlier pictures you can see the floating 'baulk' ring ears in the second gear synchroniser hub, so it is a 'ribcase' box. These baulk ring boxes, fitted to the 1098 engines, are an early version of current designs.

[Arthurdaily]

Yes, yes, more poking and there are syncro rings - so, cone equalises speed and then this floating ring helps the gear mesh yes?

[bmcecosse]

Yes!

[Arthurdaily]

I want to retire from teaching and be an engineer! Fewer holidays though eh BMC

[bmcecosse]

No holidays at all..... 18 hour day answering questions on the internet...........

[IslipMinor]

this floating ring helps the gear mesh

Yes, exactly that. The baulk ring resists the change being completed until the two parts are rotating at the same speed, when the baulk ring stops 'baulking' and the change can be completed. All happens very quickly, and of course can be overridden with a bit too much enthusiasm!

[Arthurdaily]

It doesn't help that my workshop manual - though a latter edition - only contains a piccy of an earlier gearbox. Does the Haynes manual have an internal diagram of the latter gearbox?

I will need one as am going to rebuild the old gearbox so that the speedo worm drive works... I hope you will still answer my questions when that fateful day comes BMC... I can foresee sleepless nights for me lol.

[Arthurdaily]

And for you

[bmcecosse]

I'm sure we will see you through.....a few glasses of red wine may help........