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MG MGB GT V8 Factory Originals Technical - B Gearbox

Is is possible to use a standard MGB gearbox on a V8 conversion? It will only be a stock SD1 3.5, but will the gearbox cope with the extra power and torque.

Joe
Joseph Phillips

To the end of the road and back maybe, from what I've picked up in conversations (and I'm no expert) there's a great deal of sucking of air through the teeth at the thought of a standard B gearbox on the end of a V8.

Rick
Rick Haynes

I put 225 Hp through a std C box, which is essentially the same as a B unit. It works fine, but does wear the laygear bearings quicker that you may expect. I have been told thet Vic Young, in the UK has a 4 bearing mod for the laygear/shaft, which I am yet to investigate.....
Chris Cooper

The factory V8 uses the same design as the 4-cylinder albeit with different ratios and casing. The laygear is slightly different although it is so close that standard ones are machined to fit the V8 box when the latter break.
Paul Hunt

That's a lot to ask of the standard box. Much better to use a stronger one and be done with it rather than have to replace it soon.

Jim
Jim Blackwood

The factory V8 box was a modded MGC box which is considerably stronger than the B box.

Remember that the factory V8 produces 137 bhp - the SD1 produces 150, so things are marginal even for the V8 box.

Chris at Octarine Services

Cheers guys,

The problem being that I haven't seen many SD1 gearboxes for sale and a new R380 from RPI is £1000, which will make my initial outlay far more than I have.

I am still at uni and I would only need the gearbox to last 8-10months before I upgrade to another box.I am also quite keen on my trackdays so I guess my conversion will have tp be put on hold until I can get another box from somewhere that won't cost me £1000.

Any ideas as to where to start looking?

Joe
joseph phillips

Look at Sherpas for the replacement. Consider using a heavier grade oil for the B G'box - same as diff.

Roger Walker

The Sherpa box has entirely the wrong ratios for a B - go hunt the scrapyards for an SD1 or look out on EBay - boxes go for around £200 + £100 for the bellhousing.

Autogear do fully reconned LT77 boxes for around £600.

I do have one complete with bellhousing I might be persuaded to part with for £300. I also have flywheel and clutch for the engine if you need it.

Chris at Octarine Services

"Consider using a heavier grade oil for the B G'box - same as diff"

Good point and more than consider, the factory V8 *does* use diff oil in the gearbox unlike the 4-cylinder.
Paul Hunt

So is the B gearbox strong enough? Some people say it is some say it isn't. I am confused now, mainly because I want it to be strong enough as it will safe me a lot of money initially.

Joe
joseph phillips

Joe.
If you intend to use the car for track days the B box will fail in no time. I got through 2 Factory V8 boxes with only 150hp, reasonably careful driving and no track days. Stripped teeth off the layshaft.

Mark
Mark

righty then! better be nice to my mum and dad for christmas, LOL!
josph phillips

Joseph

If you want to use the original B gearbox it will work - that's what Ken Costello did many years ago when he started this game. How long it works for depends on how you use (and abuse) your car.

However, a bigger problem is the availabilty, or non-availability, of the adapter plate between the Rover engine and the MG gearbox. Dave Vale (at the V8 conversion Company) used to have them made but his source has now dried up. Perhaps Clive Wheatley has a source. Wherever you get one from it is likely to be expensive.

Perhaps you should stick to being nice to mum and dad! As for me, I'm going to have to be careful with my MGB gearbox.

Good luck

Peter
P L Hills

Don't use overdrive on third gear.
Roger Walker

My experience with a factory V8 owned since new is that the original gearbox is too fragile.

Even if not abused, and avoiding using the overdrive except on top gear, I found that the standard gerabox + overdrive, will fail in less than 30k miles, sometimes much less.

I installed two replacements in the first 100k miles, then installed an R380, which is behind a John Eales 230 bhp engine, and which has been 100% to date (50k miles) mostly rallying.

It might be sensible to ask John Eales about his prices for R380's he is often competitive.

Failing whic there are a number of people offering rebuilt R380's; try the Land Rover magazines and a Google search.

Good luck
Nigel Steward

You might look at using an alloy toyota supra box, these are cheap enough and supposed to be good to 600BHP. The bell housings can be got from Dellow automotive for around $400 to 500 Australian,but then you need to sort out clutch etc
Peter

Must be how you drive it, Nigel, and you must have one of the first few if it has OD or 3rd. But if competing then I can understand it. The PO did break the layshaft in mine but he was a leadfoot. I've had it for about 9 years and 65k now on the same gearbox, and I do 'enjoy' it, but road use only.
Paul Hunt

In the MG club magazines, there are always boxes offered for reasonable prices although i would pick one up with someone like Chris who knows what he is talking about.
Regards
Peter
Peter

This thread was discussed between 01/12/2003 and 07/12/2003

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