MGB & GT Forum

Hello
I have a 69 MGB GT with a standard 4 speed transmission. Does anybody know if you can retrofit a new Overdrive unit to a car that was not fitted with one originally?
Thanks

Personally, if you have an o/d main shaft and the o/d adapter, then yes, I believe it should be technically possible to add the o/d unit.
Others will know more than me.
The way I see it though is it would likely be easier and more expedient to just find a used complete o/d tranny and have it rebuilt (if it haven’t already been).

Brian W.

Yes, just locate a complete transmission with LH model OD and swap it out, also purchase a replacement transmission sub-harness to handle the wiring.



Edited 1 time(s). Last edit at 2024-08-06 08:25 AM by ClayJ.

It is possible but impractical to do so. What is impractical, and nearly impossible, is to find an overdrive unit, adapter housing, and mainshaft/third motion shaft separately. I recall only ever seeing one such package of parts available in all my years of rebuilding these boxes.

For the record, the gearbox main case, top fill or side fill, is the same for non-overdrive and overdrive, as are all the internal gears, synchros, etc. But if you were able to find the overdrive unit, adapter housing, and mainshaft for sale, you'd still have to completely dismantle the non-overdrive gearbox in order to swap out the mainshaft.

The only practical solution is to find and buy a complete overdrive gearbox. If you choose to do so, best to find one that's known to be in good working condition. Overdrives that have sat unused for extended periods of time can develop problems even if they worked when originally removed. The fat o-rings on the operating pistons can become flattened over time, becoming unable to properly contain the 400-420 psi of operating pressure generated by the overdrive hydraulic system. And the cone clutch can become stuck to the annulus due to the strong spring pressure that will have been pushing against it constantly during storage. And separating a stuck cone clutch often results in the lining separating from the cone clutch, and the result is an expensive repair.

Shameless self-promoting plug: I usually have 4-synchro overdrive gearbox cores and can rebuild them for sale upon request.

End of shameless plug...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Dick
do you sell the complete overdrive transmission refurbished? Or know somebody that does other than the $6000 Moss unit?

I do, at a very reasonable price. I've sent you a Friendly Private Message with my contact info, and you are welcome to call to discuss...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

@Bob. Dick is generally regarded here on the MGE as the "Overdrive Guru". He's been building gearboxes for the folks here for a long time. I used one of his gearboxes in the only resto that I've done for a customer, because I knew it would be Right! Regardless of the distance between you, you should talk to him about your gearbox needs.

There Dick, that takes the "shameless" out of it for you.

Have fun

ps, here is a photo of one of Dick's gearboxes, with one of Haps engines with one of Sean's cylinder heads.

pps, I had no idea Moss asks $6K for an O/D.

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If ignorance is bliss, I must be the happiest man alive!
Signed

RUFUS
67 Roadster



Edited 1 time(s). Last edit at 2024-08-06 01:29 PM by Rufus.

@Dick #4

"Overdrives that have sat unused for extended periods of time can develop problems even if they worked when originally removed. The fat o-rings on the operating pistons can become flattened over time, becoming unable to properly contain the 400-420 psi of operating pressure generated by the overdrive hydraulic system. And the cone clutch can become stuck to the annulus due to the strong spring pressure that will have been pushing against it constantly during storage. And separating a stuck cone clutch often results in the lining separating from the cone clutch, and the result is an expensive repair."

So mine out of the GT has sat horizontally in a galvanised trunk since 2015 when I took it out. Is it too late for me or should I set about dismantling it?

PS it's accompanied by my 3sync box which was on it's own for the preceeding 4 years but it's a non OD version.

I had figured if I got tired of my 4sync non OD but c/r box I could swap it out for the 4sync OD or take the Mk1 back to OEM. All my time is taken up with my GT rocket but I work at my pace = snail.

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Superpro. Nut and bolt rebuild 2010 - 2015. Tartan Red.

GT: 12/78. VW Golf guards, flush fit front and rear valances, frenched indicators, Mk1 rear lights - LED lights. 'Worked' Rover V8, Monsoon ECU for EFI. Commodore VSV8 GM4L60E, Lokar tiptronic shifter & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.



Edited 1 time(s). Last edit at 2024-08-06 06:47 PM by MGB567.

So mine out of the GT has sat horizontally in a galvanised trunk since 2015 when I took it out. Is it too late for me or should I set about dismantling it?

As they say in the financial community, it's all about your tolerance for risk. The best approach would be to bench test it, preferably with a pressure gauge. If the overdrive engages, you'll know that the cone clutch is not stuck. Then the pressure gauge will help you determine if the box is holding enough pressure to reliably engage and stay engaged...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Ahmed (a regular here) some years ago found a kit to retrofit the OD onto the standard gearbox. Apparently it worked well. Unfortunately the kit is no longer available so the only viable option is to replace the entire unit. The good news is that OD gearboxes are available and *well* worthwhile. I'm sure Dick will find you a great unit. The OD transforms the car.

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Terry Ingoldsby
terry.ingoldsby@DCExperts.com

Call dick moritz he's done two for me they work great.

You can't beat Dick......he has a golden rep up in here...

Today I asked my helper if he understood about the "cone clutch" - he did not (but it could be he does only under a different name). Might you click here and tell me the number for it? M-E says there's 105 parts to the OD but one: you can no longer ask "show all parts" as a list and two: IDK if M-E calls it a cone clutch so if I read all the parts it may well not be and I'll be none the wiser. TIA.

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Superpro. Nut and bolt rebuild 2010 - 2015. Tartan Red.

GT: 12/78. VW Golf guards, flush fit front and rear valances, frenched indicators, Mk1 rear lights - LED lights. 'Worked' Rover V8, Monsoon ECU for EFI. Commodore VSV8 GM4L60E, Lokar tiptronic shifter & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.



Edited 1 time(s). Last edit at 2024-08-08 12:48 AM by MGB567.

Barrie,

Your link doesn't work for me, but it's also commonly called the sliding member, shown here as item number 4. https://mossmotors.com/mgb-042-late-type-lh-overdrive-1968-80

Not usually available from Moss, Rimmer, etc., but available remanufactured from www.quantumechanics.com here in the states and perhaps elsewhere worldwide...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Thanks Dick. M-E also calls it a sliding member #61 in my link. Ever since M-E changed their schematics it's not been the same as it once was.

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Superpro. Nut and bolt rebuild 2010 - 2015. Tartan Red.

GT: 12/78. VW Golf guards, flush fit front and rear valances, frenched indicators, Mk1 rear lights - LED lights. 'Worked' Rover V8, Monsoon ECU for EFI. Commodore VSV8 GM4L60E, Lokar tiptronic shifter & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.