gearbox conversion

[popeye]

Hello everybody,
I have been told early herald (948) were fitted with an "all alloy casing" (bellhousing and case).
Here is my question:
Is it possible to use one of this all alloy casing to build a gearbox for a MKIV?

Some of you might have knowledge concerning these gearboxes or have ever done this conversion.
the internal dimensions of the casings are the same?
The housings for the bearings, slave cylinder, shafts are the same?
Concerning holes for the bolts of the rear housing: are they the same (amount, position??)?
What type of modification should be done to built an alloy gearbox with a four synchros gear set? does it need some machining?
By the way, a small alloy case: is it strong enough for a 1300 or 1500 engine ?

Thanks a lot  me know your knowledge and your point of view. :-/ :-/

[herald948]

I'm guessing this wouldn't work. For one, I recall reading in various Triumph books that the all-synchro gearbox was something like 5/8" longer. Exactly where I don't know, but probably in the gear casing itself. Also, when some of the earlier 1147cc Spitfires had an alloy bellhousing, it was thicker-flanged and otherwise stronger than the thin-flanged version on either the all-alloy early gearbox or the subsequent alloy bellhousing/iron case version.

[Richard B]

Would'nt have been that all alloy box on fleabay would it?

I think Bill had one or two and knows a lot more 'n me, the Mk IV Spitfire box is longer due to the extra synchro; I also was told that the 948 box was weaker than the Spit MkI - III box, but I believe certain racing people did use them after modifications.

Waiting for GTEVO to tell me I wrong and that they are the D0g's B8ll8cks/Cr&p.

I was sorta hoping Dave Pearson would go for making them (a la GT6) in his target to lighten the Triumph.

[Nick Jones]

It may be possible but I don't think it is easy.  In fact the weight difference between a cast iron gearbox with aluminium bellhousing will not be so very much more than an all alloy item so probably not worth the hassle.  The alloy bell housing definitely is worthwhile though - the cast iron ones are amazingly heavy!

Nick

[heraldcoupe]

I can lift an all-alloy gearbox with two fingers.
The iron box with alloy bellhousing needs all of one hand.
The iron box with iron bellhousing needs both hands.

The extra external length of the 4 sychro box I understood to be down to the deeper output flange. The gearset is longer, but I think this is dealt with by different machining on the inside of the casing. Someone correct me if this is wrong, it's based on conversations with others rather than firsthand experience.

The alloy box is a very lightweight casting, potentially fragile, but I can see the appeal of trying one with a better gearset. I am tempted to build an overdrive gearbox into one of my spare alloy casings.
Cheers,
Bill.

[popeye]

Many thanks to all of you.
This type of gearbox seems to be very special.
The modifications needed for the fitting of a synchro gearset are really important.
Many thanks Thomas to let us know about your experiment of a such conversion.

I think I will keep my single rail gearbox and try to find an alloy bellhousing: I will need to built a special part for the selector shaft. It seems the easier solution.

What is the benefit of the single rail ? is it better (or not) than the three rail ?

[James]

Three rail is a far nicer box to use - the action is really slick.

Single rail is slightly stronger though I think - but not enough to make up for the 3-rail being so slinky smooth.