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 - Gearbox Cross member bolts

Gearbox cross member bolts : 1966 MGB GT
Unfortunately when unbolting the gearbox cross member two of the retaining bolts sheared off in the chassis leg. This was despite being drenched in release fluid and then heated. Any suggestions on removing the broken bolts? Or options?

I could cut the section out and weld new weld nuts into the repair section But this would be a last resort.
Neil
D Stewart

Drill the centre of the stud with a drill no larger than the core diameter of the bolt and then retap the weldnut. Hopefully if you can drill close enough on centre you can get away with this. If not drill to the next larger metric size and retap the hole for this bolt. Therein lies a lesson to smother these bolts with copper grease before refitting.
Iain MacKintosh

One of the problems with this weld nut, is that it is on a plate that floats between thin metal brackets. These break off and the plates float all over the place.
2 ways to get round this - drill straight through the plate and carry on through the floor. Open up the hole in the floor to take a tube and then bolt striaght through the floor with a boddy washer to spread the load. The tube stops the chassis distorting.

The other way is more radical if the plate is fully floating. Cut a hole in the floor just the width of the chassis rail and about 3 inches long. Dig out the plate and repair the threads either by helicoil, welding a nut on etc.

Then either weld or rivet a plate over the hole. I have used a good piece of floor from a scrap car with the correct profile.

Jobs a gudun!
Colin Parkinson

Were both the failed items on the same side? If it was one each side, put the good bolt back in while you are drilling and tapping.
Allan Reeling

I had considered bolting the cross member through the floor. Using tubes and bolts but welding them. I plan to use this for the new engine mounts . It will make returning the car to original specifications’ a simpler task.

Thanks for all the suggestions.

Neil
D Stewart

A fun job, you might like to have a look at Michael Beswick's solution http://www.mgb-stuff.org.uk/xmember.htm#
PaulH Solihull

To answer Allan question: It was all the bolts. But we replaced the Chassis rail on the off side hence only two broken bolts.

While looking at the sheared bolts today I noticed that there are two sets of mounting holes. Can any one shed light on the additional set of mounting holes?


neil

D Stewart

Various gearbox options, but what used the 'other' holes has never been made clear. Possibly auto.

3-synch non-OD (from Clausager) uses the rear, as does my V8, and from memory 4-synch OD.
PaulH Solihull

This thread was discussed between 09/06/2011 and 11/06/2011

MG MGB Technical index

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