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Site updated
20 March 2011

G/box X-member

by James Mather

“ OK the gear box will go in...BUT it will hit the floor”

 

When the original MG Midget crossmember is cut out (see Tunnnel Mods), you remove a pice of crossmember which is just over 7” (175 mm) long.

 
The inside size of the crossmember is 60 mm sq plus a smidgeon. This means that a piece of square thick walled tube, 60 mm square x 7” long, can be slid up each crossmember to act as a reinforcement and to which the new gearbox crossmember can be bolted.

Have you ever tried to get thick walled 60 mm sq tube? Well, unless you are really lucky and you happen across some, you can buy it in lengths as short as 5.3 meters!


I also don’t really like the idea of bolting up through the sides of a hollow section (even thick wall section) without some kind of reinforcing tube or suchlike inside. The sides are bound to give when tightening the bolt.

I didn’t have any 60 mm tube but I did have 20 mm tube.
3 x 20 mm =60mm. Hey presto.


I made up a honeycomb section with 9 x 7” lengths of 20 mm sq tube. It also much less crushable. 20 mm square tube (or 3/4”) is universally available. I welded the ends of the tubes to keep the whole lot together. Then, with a few taps they slid up inside the open ends of the remaining cross member sides. The pictures below show it all. Dead easy.

You do need to make sure that when you drill through to bolt the new gearbox crossmember on , that you don’t try drilling all the way down one of the “webs”. You can easily break a drill bit that way.

Honeycomb unwelded

Weld just the ends to stop the tubes moving about. (Shown unwelded)

Honeycomb in place 2

Insert honeycomb section (you can see the welds on this pic) into cut open ends of original MG Midget cross-member. I sealed the edges and filled tube ends only with expanding foam. You could weld a plate over if you wish which is probably better. The original crossmember needs some drain holes towards the rear. I filled the lot with copious Waxoyl

Gbox rear mtg frame

I eventually made up a simple 3 mm x 1” angle iron frame to take the gearbox mounting. The rear gearbox mounting flange (the rubber bonded mount that is) needs to be higher than the car floor in order to get the bellhousing to clear the chassis rails. The engine/box assembly is mounted at the very front of the block and also at the rear of the gearbox. Moving the rear mount up or down also moves the bellhousing up or down. It can be spaced off the frame if u wish) I eventually settled to have the gearbox mounting flush with the floor. The rear of the car is to the left in the pic. I used stainless steel M10 sets to secure the frame to the car with nyloc nuts and M8 to secure the mount to the frame.

You can see (just) my 30mm x 3mm reinforcing strips on the RH of the tunnel. There is another one on the LH side too. These are in effect just very long washers which bolted through the frame and floor. I pop riveted an ally plate over the original gear lever hole (mucho silicone sealer too) after cutting the upturned flange off the tunnel The gaiter is the original MG but I eventually used one off a Mondeo which is very flexible and excellent quality. If you can’t figure how to get it off the Mondeo, just pull it up over the gear knob so that it is inside out. (I haven’t got a clue how the knob comes off). You will see a small zip tie securing the neck of the gaiter from the inside. Snip this and off comes the gaiter.

Gear lever gaiter02
Gear lever gaiter03

An MGB chrome gear surround ring cost £9 and finished the job nicely.