BMC C series gearbox code

I've got a 1958 Morris Isis and I've just bought an overdrive gearbox that was fitted to a Wolseley 6/90. This should be a 4-speed gearbox but unfortunately I suspect that it is a 3 speed overdrive unit from a 6/99 because on the top of the gearbox is a 'badge' which says Type 29-O-3 Can anyone here confirm/deny that I've got the wrong gearbox?

thanks in advance,

-- Robert

Reply to
webmonster
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I've a feeling those three speed boxes are in fact four speed ones with first inhibited by the selector mechanism - so could well be just fine if you use the right bits from your original. IIRC, there was a floor gearchange conversion for that series which 'released' first gear.

There can't be many Isis left on the roads - pretty rare car even when new.

Reply to
Dave Plowman (News)

I've got a 6/99 and Isis workshop manuals and although the gearboxes are very similar, the layshaft gears and the mainshaft look very slightly different. The later 6/110 has a floor change 4-speed 'box, but this looks quite different.

Given that the overdrives themselves are the same unit what I really need is the right mainshaft. If I was brave I'm sure I could get my existing mainshaft shortened and machined to suit.

True - I've only seen a photo of one other (a nice red one) on the road here in NZ. Both the red car and my Isis are the late ones with the RH floor change and the little fins at the back. I wonder why they never sold well when new. It certainly goes and handles quite adequately (running on radials and I've renewed all the steering/suspension bushes).

regards,

-- Robert

Reply to
webmonster

It would be easy to tell from that if it were a true three speed box or a modified four?

I'm not well up on this series - but I'll ask my brother who has had several 6 cylinder BMC cars. Indeed he may have a spare A95 box which is 4 speed column change. Although I know he had a clear out of such things when scrap prices were high.

The 'B' series box had openings top and side to allow the same basic box to work with either floor or column change - I assumed the 'C' series one was the same.

The Austin version was far more common here. Dunno why. The Isis looked perhaps rather ungainly against it, though. But beauty is in the eye of the beholder. ;-)

Reply to
Dave Plowman (News)

On Sat, 16 May 2009 09:39:21 +0100, Dave Plowman (News) screamed:

36 left on the road in the UK according to this month's Practical Classics. Of course, that doesn't say how many are lying in barns, fields or garages.

Mike P

Reply to
Mike P

Not for a gearbox oaf like me. "Look! whirring bits and pieces!" ;-)

I'll open up the 'box and have a look. That will settle it.

From what I can tell, all early C-series gearboxes were linkage driven - they all had a shifter and selector lever on the side. Even the Healeys had their centre floor shift lever offset to the left.

The series I Isis looks a little out of proportion to my eye, but the little fins and 2-tone paint work of the series II Isis look better to me.

True. And I like my Isis :-)

regards,

Reply to
Robert Greenfield

That figure will be both series I and II, I imagine. How does that compare to the A90 and A95 I wonder?

I wonder how many might be left on the road here in NZ.

regards,

Reply to
Robert Greenfield

The message from Robert Greenfield contains these words:

The 1955 BN1 I had back in 1969 had the gearstick offset to the left and the gate transposed as well. (IIRC top was left and back). First was supposed to be blanked off (leaving 3 gears) but wasn't and the O/D was only supposed to work with the top 2 gears but would have worked with all.

Reply to
Roger

Assuming they are genuine BMC manuals they'll include line drawings of the box? My Magnette ZA one does. So just count the gears on the layshaft. The one at the front is the drive gear off the input shaft. The next one along first gear, then second, etc. No gear for top as that is direct - the input and output shafts get locked together.

First gear (on the four speed) is spur teeth - ie at right angles to the shaft, and slides to engage the rest helical cut and are constant mesh, the engagement being by synchromesh clutches.

I thought all these boxes were four speed - the old first gear still being needed for reverse.

Right.

I learned to drive on my father's Series II Oxford - ie the same basic body.

Reply to
Dave Plowman (News)

The reverse idler on the Isis diagram has spur teeth whilst the 6/99's idler has helical cut gears.

Actually... thanks to your good description above I think I can see what is the main difference - On the Isis the smallest gear on the layshaft has spur teeth.

On the 6/99 the layshaft has the same number of gears, but the smallest gear has helical cut teeth and the gear next to it is *exactly* the same size (so the equivalent to 1st and 2nd gear on the Isis are identical - solves the reverse-speed dilemma).

I've got a series II Oxford too - my first car which I bought when I was

  1. It was a real minter - 54,000miles when I bought it - 2 previous owners. Now I'm the ripe old age of 34 (and the Oxford has done
89,000miles) and I've got it off the road for a 'quick tidy-up'. The boot and engine bay need a repaint and the engine is getting a bit tired. And the gearchange linkages need re-bushing and I want a new gearlever knob (column change - the white plastic has cracked like they all do).

regards,

Reply to
Robert Greenfield

Yes - what I'd suspect.

Right. So it looks like a specially made three speed. Perhaps the later engines produced too much torque for the basic box and this was the way round?

There's a silly bent wire link which fits into rubber bushes and makes the change very sloppy - even when perfect. My father, who was an engineer, replaced it with a rose jointed arrangement. Said it improved things no end - but I only ever drove it after the mod so can't comment on the difference.

That was the very first programme I worked on after moving from the BBC to Thames TV and was delighted to see how everyone sent it up after the deadly serious BBC children's department.

Reply to
Dave Plowman (News)

My Oxford is a late series II with many (most? all??) of the factory mods already installed for the gearchange. They must have made these changes for a reason :-)

I've always thought it is quite a nice gearchange until recently when I noticed I was stuggling more often to find 1st or 2nd. The other oddity is that the reverse gear 'lockout' on the column lever needs a surprising pull overcome the spring. My wife can't easily get the Oxford into reverse.

It was a fun show :-)

regards,

Reply to
Robert Greenfield

Just a thought - have you tried disconnecting the change mechanism from the gearbox and testing how the column change feels when unconnected? It is possible that the problems you are experiencing could be in the mechanism rather than the gearbox.

My brother had a column change Ford years ago, and when he thought he had gearbox difficulties it turned out to be a column linkage bush instead.

Also, make sure the 3rd/4th selector returns cleanly to neutral before the column can go across to the 1st/2nd position or the interlock in the gearbox can block the engagement of the lower gears. The Ford had adjustments on the linkage between the rods at the bottom of the column and the gearbox, but I don't know the BMC layout so you may or may not have similar adjustments available. But I thought I would mention it because it might be something you hadn't thought of.

Jim

Reply to
Jim Warren

I am 90% certain that the problems are in the mechanism/linkages rather than the gearbox.

Hmm! I hadn't thought of that. Thanks.

I'll need to have a look - I'm sure the ball-jointed linkages will have some adjustment, however I doubt this will make up for slogged out bushes.

regards,

Reply to
Robert Greenfield
2009. május 16., szombat 9:08:50 UTC+2 id?pontban webmonster a k övetkez?t írta:
Reply to
papeeesz

IIRC, it is still the same four speed internally. If you have both, it should be possible to make a good one from the two.

Reply to
Dave Plowman (News)

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