MGB overdrive conversion

[chappj]

I’m about to embark on removing engine/gearbox/diff for rebuilds on my 1970 MGB GT.

It’s currently a non-OD drivetrain and I’m considering adding an OD given everything will be off the car.

Does anybody have experience of doing this, or can offer recommendations for good engine / transmission rebuilds? (I was going to use Oselli for the engine).

Thanks

[ReformedPistonhead]

I bought a reconditioned gearbox including overdrive from Heathrow transmissions for my son’s MGB. He has done 2,000 miles in it since and it has been faultless.

Alternatively you drop an MX5 gearbox in.

However I am a believer in leaving things as nature intended!

[300bhp/ton]

Can't help with the conversion. But all I can say is having electronic over drive is a lot more fun from a drivers point of view than having a 5 speed gearbox.

Hope you get it all sorted.

[chappj]

I was looking at Heathrow transmissions website so will give them a call given the positive experience you’re son has had

[chappj]

Thread update!

My father and I are doing the mechanical overhaul which will be a great opportunity to spend some time together.

I’ll periodically post updates and pics on progress as I always enjoy following other people’s build threads so thought a few might enjoy this one.

Background on the car:
It’s your common 1970 MGB GT with 1 former owner that is largely original having had a minor overhaul 20yrs ago whilst converting to unleaded. The car is priceless to me as my grandparents purchased it new the London Motorshow and handed it to me when my grandfather passed away. This means I want to do any work sympathetically to preserve as much originality as possible.

Progress:
Engine, gearbox and prop are now out of the car. The engine has shipped to Skiptune for a full rebuild, dynamic balancing and new cam. Carbs have gone off to Burlen to be reconditioned.

Next step is to remove the diff and send to Heathrow transmissions for a rebuild, along with dropping front / rear suspension to fully rebuild/ recondition.

We’ve decided to exchange the gearbox for an overdrive unit also from Heathrow transmissions.

[Penny Whistle]

I have a BGT with o/d and can certainly recommend it. With many cars, the models with o/d would have different gear ratios to those without o/d - I don't know if that's the case with the B.

[chappj]

Engine rebuild is in progress (it is being bored out to 1900 due to the liners being on the limit for standard sized pistons).

Rear diff / axle / suspension also now removed. The diff and gearbox will be shipped off next week for rebuilding.

Car now on dolly’s ready for engine bay strip down to respray. Overall I’m really pleased with how solid the car looks underneath. No visible rust so I’ll just wire brush the underneath and re-coat with underbody seal.

[niva441]

This looked like an appropriate article to add to this thread, I there are a few interesting references to help.

https://www.hagerty.co.uk/articles/laycock-de-normanville-the-ins-and-outs-of-overdrive/

[chappj]

Quick update: the front cross member and suspension all now removed and sent off for blasting / powder coating.

A decision is needed whether to completely remove the tar based underbody seal to spray on stone chip / correct paint, or just clean up and overpaint another coat of under seal. A messy job ahead!

[ReformedPistonhead]

I you are doing all that I would replace the front suspension.

We did the frontline developments kit, has totally transformed the handling and replaces those nasty lever arm shocks with proper ones.

Hoyle also do a great kit, allegedly even better than the frontline.

[chappj]

ReformedPistonhead said:

I you are doing all that I would replace the front suspension.

We did the frontline developments kit, has totally transformed the handling and replaces those nasty lever arm shocks with proper ones.

Hoyle also do a great kit, allegedly even better than the frontline.

This is super interesting! I’be been looking at those kits and debating with myself whether to do the conversion or keep fully original. What was the biggest difference you felt from the change?

[chappj]

Bit of a long overdue update…

Engine, gearbox & diff are all back from renovation. We’ve swapped the gearbox for an OD unit (this was the original driver for the project).

Various other parts such as carbs, cross member, suspension dampers and brake/clutch master cylinders also reconditioned from various specialists. We’ve managed to retain all original parts from the car except for the gearbox swap.

Underbody seal now removed (that was a horrid job) and ready for primer/stonechip/paint. Engine bay also now treated for surface rust, primed and repainted.

Hopefully only another few weeks away from starting the rebuilding phase.

[PositronicRay]

That looks cracking. I've always liked the roadster and used to view the GT as the poor cousin but these are growing on me of late.

[dontlookdown]

It's a very long time since a mate and I were mucking about with MGBs, Midgets and Morris Minors, but as I recall the factory OD MGB's had a lower ratio back axle fitted too.

So if you stick with the standard diff and add OD you will get a very relaxed motorway cruiser. We had one in that had been converted this way, it felt like it was barely ticking over at 70 compared to a non OD car!

ETA totally agree with the comment that OD is more fun than a five speed box. Flicking in and out of OD to 'make progress' on a good A or B road is a hoot. Especially if you have the old long reach dashboard toggle switch rather than the one atop the gear knob.

Edited by dontlookdown on Monday 29th January 08:17

[chappj]

Latest update:

Underbody fully stripped back, rust treated, primed and finished with underseal. In hindsight I’m really pleased we chose to fully remove the old underseal as a lot had dried/cracked which caused minor surface rust in quite a few areas.

Dashboard has been removed for blasting/crinkle finish powder coating and gauges have also been sent off for restoration. Bumpers and a few other chrome bits are being re-plated (gosh that’s expensive!).

We now have most parts back from being reconditioned so it’s time to begin rebuilding!!!!

[chappj]

It’s been a while since I’ve provided an update.

New wiring loom in, along with refurbished dashboard and gauges. Refurbished pedal box, rear suspension, axle, brakes and fuel tank installed. We refitted the front cross member today and hope to get front suspension assembled by end of week.

Starting to feel the pressure to have it finished in time for my daughter’s wedding in August…

[Flying Phil]

Always good to see shiny new/reconditioned parts going back into a refurbished body/engine bay.

[chappj]

The engine and gearbox are back in! Feels like a huge milestone…

Lots still to do, but hopefully only another few days of work before it’s ready to start.

Edited by chappj on Sunday 7th July 21:12

Edited by chappj on Sunday 7th July 22:14

[chappj]

It starts! Big milestone today having successfully fired up the engine for the first time. We had surprisingly few snagging issues for the first start up. Idle is sitting high at 2K rpm and I think the timing is marginally out as it ran on slightly when turning off.

Engine bay needs some cable tidying now that we know it works. Next job is to rebuild the new rear brake drums as the handbrake mechanism isn’t working properly on the offside wheel. Once this is done it’s seats in, fit bonnet, front grill and then first road test!

We’ve booked it in at a local MOT garage for a once over just to have another set of eyes on our work to be safe.

I’m desperately struggling to find a centre speaker console for a 1970 model. Unfortunately our one was accidentally broken during the dismantling phase. If anybody has one or knows where to source pls let me know.

[ferret50]

Lovely, just lovely!