Gearbox info needed

[grahamwithimps]

Hi

I'm at the early stages of building a project that will (hopefully) be a front engined going to a rear diff and driveshafts. It's going to be Hillman Imp based, but of course backwards compared to how an Imp should be. So, I'm going to need a traditional gearbox that has a prop shaft. It's fairly common knowledge that Imp & Minor clutches are fairly similar.

What I would like to know is, which clutch has the most in common with the Imp? The Imp clutch is described as a 6.25" diaphragm and the input shaft has ten spines and is about 22mm across the splines (sorry, can't find an inch ruler atm).

Obviously there are many varieties of Minor out there, and other gearboxes that have been used. I'm going to need to engage an engineer to adapt the gearbox to mount onto the Imp engine. But what would be the best gearbox to start with? If the clutch is compatible, that would be one headache out of the way!

Thanks!

Graham

[DAVIDMCCULLOUGH]

Hi Graham, without actually going out and measuring anything the nearest would be the 948cc gearbox and clutch.

Heres whats available from East Sussex Minors who have a great website.

http://morrisminorspares.co.uk/shop/pro ... dbfdf4ee1f

[grahamwithimps]

That's an amazingly fast and helpful response! Thank you!

One more question, what's the casing made of? Especially the bell-housing bit as that's what I'll have to change.

thanks

Graham

[IslipMinor]

Graham,

The 1275 Midget engine has a 6 1/4" diphragm clutch, the same as the Imp, so you can use the driven plate for a Midget.

All the in-line A-Series gearboxes have a cast aluminium casing. I would go for one of the later 'rib-case' version rather than the earlier 'smooth case' - they hade a very weak synchromesh design. The later type are 'baulk ring' and work very well, but unfortunately still have the non-synchro crash first though!

[bmcecosse]

This sounds a very strange project.... the big strength of the Imp is the rear mounted engine/box assy ! You seem to be going backwards from that............

[mike.perry]

The 1275 Midget clutch is 6.5in diaphram, not 6.25in
The 918/803/948 clutch is 6.25 spring

[grahamwithimps]

Yes, it is very strange. I got the back end of an Imp with the intention of making a trike out of it. In the traditional way, weld a bike frame to the front. But the more I looked at it, the more unbalanced it seemed, with a big empty frame up front and so much weight over the rear. Given that the Imp engine is only 875cc it fits in the frame loop nicely. But then I needed to get the drive back to the rear wheels. Inverted Imp box wouldn't line up without losing ground clearance or stressing the drive shafts too much. So I started looking for a traditional layout of 'box-shaft-diff.

The clutches are different sizes but would a later 'box accept an earlier clutch, or would I be best sticking to a 'box from a 948cc pre-62 car?

Cheers

Graham

[bmcecosse]

The gearbox input shafts are essentially the same as far as clutch disc is concerned....