MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Help - gearbox crossmember position!

Help, I am trying to find out exactly where the gearbox crossmember is located on a 3 synchro car!!

Why?

Well it is a race car, and has 3 sets of holes drilled through the chassis rail and floor, none of which have captive nuts on!

So I am going to weld up the wrong holes, and fix captive nuts in the chassis rail

Thanks

Colin
Colin Parkinson

John Twist (formerly) of University Motors has a good primer on the tranny cross member on U-Tube - plus a lot of other great tipss.
B Dubuc

Colin,

Since it's a race car, I think all bets are off. I think in stock configuration, there are only two choices, and you have three.

I don't think you will know without doing a dry assembly, and I think any advice you get will just be a guess. Maybe I'm wrong. It wouldn't be the first time.

Charley
C R Huff

I may be wrong but I seem to remember that on my car ('71 B/GT)
there are no crossmember captive nuts welded on the chassis
rails.

Instead, there is a single threaded plate inside each of the rails.
The plates are not welded and are able to slide fore and aft
in order to adjust their positions as needed.

This is a much stronger arraignment than welded captive
nuts.
Daniel Wong

Colin

Ring Carl and ask him to check one of the new shells as they are all in the same place no matter what year.

The 3 holes are to do with the postion due to no overdrive and overdrive gearboxs which reqiure the crossmember been in a diff position.

Ste
Ste Brown

There should be four holes each side which allow for two positions of the cross-member. Mine certainly aren't in sliding plates but fixed. They didn't originally go up through the floor as the tapping is in the bottom of the chassis rail. It's possible the original holes were drilled up through the floor to take longer bolts if the chassis rail threads had stripped, and quite possible there is a third *set* of holes in this area and going up through the floor if a non-standard engine and gearbox have been installed.

As to which set of holes to use you attach the engine to its mounts, attach the cross-member to the gearbox, and use whichever it lines up with! This cropped up before and as I recall at least three out of the four standard manual gearboxe/OD combinations used the rear set, the front set may have been for the auto or something that was never implemented (the engine compartment was designed to take a V4 option)

When I got my V8 I found one side was in the front holes and the other in the rear! This turned out to be because the engine mounting plates were on the wrong sides which put the engine 1/2" forward of where it should be so the crossmember didn't line up with either set. Probably done by the same person who put the left bank of con-rods in the wrong way round. This (the engine mounts) can only happen with the V8 by the way, not with the 4-cylinder even when it uses the V8 mounts.
Paul Hunt

FWIW

I endorse what Paul has said, there should be four bolt holes each side. I believe the 'captive' nuts reside in a section of plate steel shaped in a series of Z's, if you can imagine what I mean. Probably flat at the top of the apexes to hold the nuts. This plate section has some movement in it, but mainly up/down, rather than intended to 'slide for and aft. I was told if the nut threads went, it was a case of opening the chassis rail to replace the steel section.

As Paul suggests, who knows why!

I was told this by an old hand from Leyland Australia days and the chap who probably riveted the ID plate to my car here in Canberra in 1969.

Regards
Roger
Roger T

Colin,see the post on MGB General."sidemember assembly/floorpan.Simon has some pics posted about the steel plates for gearbox crossmember. Rich
rich osterhout

Paul, so there 2 sets of holes as standard? In which case I can see which is the 3rd set of holes, and weld them up.
The floor has been cut out neatly above the mounting holes, so I can make a threaded plate and drop it in.

Job is a goodun!

CP
Colin Parkinson

Colin

The 3 synchro overdrive box goes in the front set of holes but you also have to be careful as there are two types of crossmember to mount the gearbox on(one hole and two hole).

Ste

Ste Brown

Ste, thanks for that. I have a choice of crossmembers!

How is the new job going?

Colin
Colin Parkinson

Aah,aah! Found the threaded plates inside the chassis rails.
So all is well now

CP
Colin Parkinson

Colin

Not good im still a temp and it looks like i will have to look for another job.

Do you know anyone who is after a 3 bearing 1800 engine as i have one for sale on ebay fr £200 which will fit the A or B and Magnette?

Ste

Ste Brown

Ste, yes I saw it on ebay. No I do not need it, thanks.
Sorry about the job.

Maybe they will have you back at Moss?

CP
Colin Parkinson

This thread was discussed between 18/08/2009 and 26/08/2009

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now