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MG Midget and Sprite Technical - Gearbox mount problem

I have a problem with the gearbox mounting for my T9 installation. It uses a rectangular rubber block (see photo) which sits in a cradle on the support cross member bolted up to the cars floor pan. This then screws directly into a blind threaded part of the underside of the t9 box. I don't know if the t9s are all like that.
The problem is the thread in the box is an M12 but the studs on the mounting block that I have are both M10. I haven't been able to locate a similar block with M12 studs.
I considered welding an M12 bolt to the block but pretty sure the heat would destroy the rubber. Alternatively I need some way of reducing the M12 threaded part with an adapter or insert bringing it down to accept the M10 stud, but don't know if such a thing exists!

(The old block had disintegrated, remnant is the other object in the photo)


GuyW

https://www.ebay.co.uk/itm/126161653893

HTH 😉

Edit: Doesn't help, but this one might.

https://www.ebay.co.uk/itm/256220622469

Fingers crossed 😉
Greybeard

That's not a standard mount, they normally have something like this https://www.burtonpower.com/gearbox-mount-ford-cortina-mk1-mk2-gb2e400.html as the steel insert cradles the V piece on the tail housing. Maybe search for 'vibration isolation m12', at RS gets some results but not quite like your mount https://uk.rs-online.com/web/c/?searchTerm=vibration+isolation+m12 but maybe look elsewhere.

Edit, that RS link needs to be copied and pasted, as is it just gets 'isolation'

Welding isn't going to work as it'll destroy the interface between the rubber and metal bonding.
David Billington

Thanks David, and apologies. I really should have thought to look at the Burton Power site.

For whatever reason, lost in the mists of time, or of my fading memory, I made the cross member support with a 'shoe' that takes the rectangular support block. Since it works, if I can get one of Greybeard's reducers that he links to then that is the easiest option for me just now.
GuyW

I seem to remember you used a fiesta mount Guy.

Did your original have 12mm studs?

Can't you get the same mount again?
anamnesis

Checking those sizes, Greybeard The one I need is Femail M10*1.5 / male M12*1.75
available as either 20 or 15mm lengths.

The thread in the gearbox casting is 30mm and the stud on the mounting block is 25mm
So would you go for a single 20mm insert, or could one put two 15mm ones screwed in one after the other? What would you do?
GuyW

Anam. Well remembered. I thought the original was a Fiesta one. It's there in the photo. It has a M12 stud and fits the gearbox correctly. The 'new O S' fiesta one that I bought to keep as a spare about 4 years ago has 10mm studs so something doesn't stack up. But it does fit my cross member shoe

Greybeard's inserts solve it neatly though.
GuyW

Just as well those converters fit then. Getting harder and harder to find properly made replacement bits. Esp' if you made your own modifications using even scarcer parts.

Burton still sell fiesta mounts. You could ring them to ask stud sizes. But jeez, 67 quid plus postage. Competition rubber though for that price.

https://www.burtonpower.com/comp-g-box-mount-esc-mk4-fiesta-mk1-2-3-vibfor63mx.html

anamnesis

Or QH should be accurate to original stud sizes, and cheaper.

https://www.ebay.co.uk/itm/315393817372

anamnesis

Guy, don't fit one on top of the other. It's do-able but it's a proper PITA lining the threads up.
The 20mm one is 2xD (diameter) of the stud so it should be fine and dandy.
If you can find a bottle of Loctite threadlock or similar a spot or two on the 12mm thread would do no harm, but it's not strictly necessary. It can't really go anywhere!
Anyone with a lathe could knock out a custom bush in a jiffy for you. Sadly I no longer have access to one or I'd happily do it for you.
Greybeard

No, I will just order the 20mm one. The threads are coated in blue, which may be a form of loctight. But I have thread lock anyway so would use that when inserting the bush.

I doubt there is a lot of tension on the fitting anyway, except maybe when I brake really hard when there would be a tendency for the gearbox to pivot upwards! Otherwise it's just a support, part of the whole engine & gearbox 3 point support.
GuyW

All good then. When you install the bush I suggest screwing it in just a tiddy bit under-flush. Just to prevent any binding against the mounting.
Good luck 😉
Greybeard

This thread was discussed on 07/10/2024

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