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Site updated
20 March 2011

Tunnel Mods

by James Mather

But the gearbox wont go in now. It’s too big....

OK make it fit. Cut some bits of the body/chassis away...ahem..

Tunnel floor(Marked)

My word, just look at all that black underseal and Waxoyl! The underneath was absolutely brilliant for a 1976 UK car. All spring hangers etc (not shown, obviously) were perfect

Underneath view of floor looking back. Black fuel pipe can be seen on left of pic. Square hole is used to gain access to Hardy Spicer on MG propshaft/box. The cross member used to mount MG box is 55 mm too far forward and too high for Ford gearbox. It has to go. Everyone else gets rid of it so it was zapped.

I eventually decided where to cut it out. The reinforcing tubes must be removed to insert some 60 mm square tubes up each side crossmember. So it is cut along the white lines. The angle of the lines is exaggerated by perspective in the picture.

Bridget’s tranny tunnel looking back from engine bay. I am going to re-route the black fuel pipe on the left of the pic (R of car sitting in it) to the right of the pic. It makes sense as the fuel pump is on that side too.
The two sets of lines show my first thoughts (inner lines) and second (outer & final) thoughts on x-member removal.

Tunnel crossmember looking back(Marked)
Floor cutout

Chop, Chop. Bridget’s tranny tunnel floor and x-member removed as far back as the square hole. The X-member cut ends can just be seen on the left and right of the tunnel sides. There is about 175 mm (7”) between the cut ends.

Top view of removed gearbox x-member, looking back. Note LH cut immediately to left of horizontal reinforcing tube and RH cut to right of vertical tube. Plenty of water ran out when it was cut!!!

Crossmeber pice top view
Crossmember reinforcement

Bottom view of removed gear box x-member, looking back. Cut alongside reinforcing tubes

Crossmember piece

Side view of removed gearbox x-member. Note reinforcing tubes

The centre of the new hole for the gear lever is 2” back from the rear edge of the original gear hole. Why do they make the original hole so big? It beats me.
The new hole needs to be larger than you first think. The gear lever steel securing flange has a lip making it somewhat bigger than the tapped flange on top of the Sierra gearbox.
Note that the transmission tunnel rear and front are not in line, hence the gear lever hole appears to be offset to the left. It is in fact in line with the rear section of the tunnel

Gear hole top view
Gear lever gaiter

The alloy plate was pop rivetted in place to cover the old gear lever hole. It would be better from steel and welded into place

This may look familiar.........

Gear hole inside car
Gear surround

.....but this wont. The finished job with MGB chrome surround

Don’t forget that as this was going on, things were happening underneath with the gearbox cross member....