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MG MGA - gearbox rebuild

Hello all,

I am taking apart the gearbox on my 62 MkII and was wondering if the end of the input shaft looks normal. The gearbox had been taken apart prior to my receiving it so I don't know what it's supposed to look like. I believe that there should have been some needle bearings in the hole? Does the end of the mainshaft sit in this hole?

Andres


Andres Losin

Is this gear too damaged? There are 5 teeth that are pitted.

Andres


Andres Losin

first picture is missing, The teeth are too damaged, it will make a very noisy gearbox, and you will also find that the teeth on the mating gear are also shot.

If the first photo is of the input shaft, then yes there need to roller bearings in there. Use a big dollop of grease or vaseline to glue them in place for assembly.
dominic clancy

That is odd that Dominic can't see the picture of the back side of the input shaft. He is correct about the needle bearings and grease that goes there. As he states both the second gear shown and the slider that mates with it will be worn.
Read the service manual and this website http://mgaguru.com/mgtech/gearbox/gt1.htm completly. After that ask away with any questions. I learned how to rebuild a transmission with just a book and an MGA in 1976. Lots of trial and error. Parts are a little harder to come by now but there is much more help and information available today.
Good luck with the project,
Randy
R J Brown

Thank you for the feedback. I have an extra gearbox from a 1600 that appears to look allright from a quick inspection but I have not broken it down yet. If it is good is it possible to take all the "guts" and just swap them into the case for the Mk II gearbox?

Andres
Andres Losin

What is the engine number of your 1600 MKII?
The gearbox of the 1600 MKII has 10 clutch splines on engines up to #3929 and 23 clutch splines from engine #3929.
The 1500 and 1600 MKI have 10 clutch splines on the gearbox input shaft.
This is not a problem as you just use a clutch plate with either 10 or 23 splines as required.

Mick
Mick Anderson

If the starter position is the same, then you just use the correct friction disc and install the 1600 box as is. It would be wiser to dismantle and check, particularly to replace second gear synchro, which is almost always shot.

The internals are the same except (as I learned today) for the speedo drive gears.

dominic clancy

Mick, I don't know the engine number right now but it definately has 23 splines on the input shaft.

Is there any benefit to using the 23 spline shaft over the 10 spline?

Doesn't the extra bracing that was cast on the MkII gearbox make it better?

I will be taking the 1600 gearbox apart to see what needs to be taken care of. I don't have a history for it so I don't know if anything was wrong with it.

With the shifter mounted, I should be able to move into different gears? Right now I cannot move the shifter to change gears but it does move left and right a bit.

Andres

PS The nut on the end of the flange sure was tight. I needed my cheater bar on the end of my wrench!
Andres Losin

An involute 23 spline would be stronger than a plain 10 spline, but I have never heard of trouble with the earlier 10 spline.
The 1600 MKII gearbox casing would be stronger with the extra bracing, but again the earlier casing has always been satisfactory.

Mick
Mick Anderson

Dominic, I'm curious, what did you learn about variations of speedo drive gears? Steve
Steve K

From Barney:

Early MGB gearbox uses different speedometer drive gear ratio (inside the gearbox) to turn the speedometer considerably slower, something like 1280 vs 1450 turns per mile, so no go.

And yes, in the parts lists, there are different part numbers for the gear and speedo drive pinion
dominic clancy

I misunderstood, I thought you meant that the late 1600 MkII gearbox with 23 spline first motion shaft had a different speedo gear than the MGA gearboxes with 10 spline.
Steve K

This thread was discussed between 13/09/2007 and 23/09/2007

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