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Site updated
20 March 2011

Sierra Gearbox

by James Mather

MG Midget 1500 5 Speed Conversion

Ford Sierra?

Please click here to follow a link to an interesting article about Sierra type 9/N gearboxes. The article it reproduced with kind permission of Retro Cars Magazine

Sierra gearbox in all it's glory. A £40 bargain.

Ford Sierra Gearbox£40bargain
Ford Sierra Gearbox RH view

For comparison, a Ford Sierra 5 speed box conversion (top view) and MG Midget box (bottom view).MG bellhousing already fitted to Sierra box

MG and Ford boxes02
Rear coupling3'4 view
Sierra and Midget clutches

Ford (left) and MG Midget (right) clutches. Note the different diameters and centre splines.

Avenger clutch

Hillman Avenger 1500 clutch (shown fitted to Midget flywheel with alignment tool) has the correct 23 spline x 1” diameter and is only 6mm bigger than Midget clutch. (7.5” as opposed to Midget 7.25”.) No problem as you can see. It fits without modification.

The rear coupling is too big for the Midget tranny tunnel. The donut won’t take the angular movement of the prop either. Shame.

Sierra input shaft is flush with the original bellhousing. Note original clutch cable burned through by oxy-acetylene “spanner”.

Ford clutch plate inside BH
Ford bellhousing.Side view02

The output shaft slides on splines removing the need for the MG prop-shaft centre spline. Not use of oxy- acetylene spanner to disconnect propshaft!

Rear coupling sliding out

Ford bellhousing removed. Input shaft “flanged sleeve” needs cutting from flange

Input shaft shroud &box (unmodified)

Sleeve removed for cutting. Only held by 4 x M6 screws

Input shaft shroud removed
Input shaft sleeve (modified)

Sleeve cut from flange

Modified input shaft sleeve

Note: Cast cut-out goes to bottom when re-fitting.

Input shaft shroud. Note cutout.

I almost forgot to mention:
The spigot bush
in the flywheel needs reaming or boring to fit the Ford input shaft (I actually just drilled mine). I forget the size as I post this but it is I think 16mm. Check first. Some conversions use a special bush about 3mm longer. I found the original one fine. Fit with Loctite, the flywheel stops it dropping out. You may find it was loose when you took it out.

Now here is an update. I am reliably informed that 1.6 Sierra’s also had a 7.5”dia clutch which will also fit. It’s not what Borg & Beck say,(they say it has 20 splines) but one of “our correspondents” has actually done it and says that B&B’s info is wrong and that it does have 23 splines. You may care to check it out first.