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MG MGB Technical - Simple LH Overdirve Questions - Please help

A few real quick questions on the LH overdrives:

Am I correct that the early LH overdrive (68-74) would be a top filler, would have a black tag, and would have the white colored 1280 /per mile ratio speedo drive gear?

Would this be the correct unit for my 71 B? Am I correct that all I will need is a longer speedo cable for the new gearbox/od unit that I install?

Thanks in advance hope to finish a purchase tomorrow.

Jeff
J. W. Delk

Jeff, for your 71 B I believe you need the later type O/D which is the LH type. This unit has a side filler on the mid left side and a blue tag on the bottom. The earlier O/D was the D type for 62-67 and that one had the top filler and black tag. I believe that the correct speedo for the L/H O/D is the 1000 tpm, but I'm sure someone else will advise if that is correct.

Andy

74 MGB GT (O/D)
67 MGB Roadster (O/D)
60 MGA Coupe
Andy Preston

Thanks Andy - there are actually two types of the LH and I think the side fill you mention is the 74/75 - 80 version with the speedo at 1000 tpm.

There are three types

D not sure what tags these had
LH Black Tag - top fill - 1280 tpm
LH Blue Tag - Side fill - 1000 tpm

This is what the archives seem to suggest - I think.

My car is a 71 so I think I need that early LH with the Black Tag.

Thanks for posting,

Jeff
J. W. Delk

Jeff-
I've never switched one, but I believe that all the LH units are interchangeable, and the speedo gears could be swapped. That might mean removing the rear housing, but people say that checking the clutches before they blow up is a good idea, esp on boxes that have been sitting. Speedos or converter drives might be easier to find than OD boxes. Quantum in CT is said to be expert in these.

FRM
FR Millmore

Jeff, you are correct in terms of both tag colour and speedo tpms for the LH ODs, they changed when the bumpers changed from chrome to rubber i.e. 74 1/2. It's the gearbox casing that is top-fill for chrome bumpers and side-fill for rubber, other than that the blue and black label ODs may well be interchangeable as far as attaching to the gearbox is concerned.
Paul Hunt

Thanks so much for the confirmations. I am purchasing a unit that is in Texas and I only have a picture to go by - so I wanted to be sure and ask the correct questions over the phone.

I purchased the unit today and will have it shipped to me here in GA. I am anxious to clean it up and do the general checks and seal replacements and hope the clutch material in the overdrive is in good condition.

FR. I called and talked to Mr. Esposito at Quantum yesterday - he is a very nice guy and he helped answer my many questions as well.

Thanks again folks!

I'll post a follow up once I get the unit,

Jeff
J. W. Delk

Just a longer OD speedo cable is needed. Other than that you are all set to go. Good luck. RAY
rjm RAY

"Just a longer OD speedo cable is needed."

And a large bottle of Scotch for when it comes time to fit the crossmember :)
Simon Jansen

I just went throught the cross member fitting - and it is a definite booger. It helps to go ahead and install one of the rubber mounts (I installed the right side since there is a ground strap there and it was easier to not have to deal with it while trying to install the mounting bolts. The other rubber mount should be installed on the cross member before you offer it up to the OD unit.

If your "yoke" has an offset, I had to install mine (77 B) with the offset facing forward - it definitely makes the mounting bolts almost impossible to get to, but if the yoke offset is mounted pointing rearwards, the crossmember mounting holes won't match up to the captive nuts in the frame.

And then there is the whole "front hole - back hole" issue for the rubber mount stud to go into the cross member. If you need me too, I can check that for you -

It took about four solid days of trial and error to figure that out. I am keeping my day job. It also helps to get the car off the ground as far as you can when installing the rubber mounting bolts. If you have access to a lift, that would be optimum.
B Dubuc

I dunno how many times I have posted this, but here goes again -

Drop the gearbox so it is sitting on the rear fixed crossmember, bolt both mounts and saddle to the gearbox, hook one mount thread onto the crossmember and loosely fit a nut on the end threads just to stop the crossmember falling off, then use a large screwdriver or small jemmy to lever the other mounting stud into its hole - or to make life even simpler, elongate the two holes in the crossmember and then no levering is required.
Chris at Octarine Services

This thread was discussed between 05/11/2009 and 08/11/2009

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