Transmission swap

I'm looking for a link, thread or any information regarding the difficulty or advisability of installing a 4 syncro gearbox in my '64 B. I have a '71 gearbox in good condition...and my '64 is beginning to sound a little rough in first gear.
I'm sure this has been discussed on this forum previously, but I'm kinda new here and haven't been able to find much info.
Thanks.

The problem with fitting a later trans to a 3 main MGB is the input shaft.

Upon the introduction of the 5 main bearing motor in 1965, they moved to a thicker input shaft on the transmissions. It's a little easier to fit the 4-synchro box to a 65, 66, or 67 because the input shafts match up, but on the "62", 63, and 64 cars, it's a little more difficult.

If you do in fact want to do this you will have to remove the input shaft from the transmission (which may require a dis-assembly of a good portion or all of the box on the later trans - I do not know - I have only been inside the early one) and have it turned down at a machine shop in order to accept the early pilot bushing and fit inside the crankshaft.

You may also have to change the rear plate and starter (I am sure someone will clarify this part more).

Just a beware, I was talking to a fella in Georgia about two months back when I was searching for an early OD trans and he specifically stated not to do this because he has heard of "issues." If you want, I'm sure I could find out what issues exactly, I could find his number and call him. But, also beware that this is not first hand experience.

I am sure you have been offered the advice to rebuild your transmission/have someone rebuilt it to keep the car original as there are very few original pull handle MGB's left, so I won't go off on that.

I rebuilt the transmission in my 1963 and purchased the parts to add an overdrive and I can say I'm very, very happy with it!!! Although, the bulletproofness of the later trans definitely is desirable. That thing is just so durable.

Good luck!

I have listed in the trader a modified turret that will eliminate the need to cut back the shifter hole and corresponding carpet mods inside the car. It is attached to a free transmission.

Royal is correct about the input shaft, unless the engine has already been swapped out during the cars life.

A friend of mine has a '64 that had a 4 synchro/OD transmission installed in it. To compensate for the different input shaft diameters, his local British repair shop drilled out the crankshaft to accept the larger input shaft of the later transmission. It's been working great for 15 years. If you retain your stock stater, you'll have to drill a hole in the transmission bellhousing for the starter motor's Bendix drive. When I did this conversion, to my '67, I had access to a '68GT parts car. I used the rear engine mounting plate, flywheel and starter from the later car. It makes the conversion a hell of a lot easier and it is pretty much a bolt in installation. RAY

There's your answer! Sounds good! 15 years, is awesome!

I'm planing on doing this very thing in the spring. I have a 64 also that I'm going to mate up to a late model tranny. To see the different diameters involved I bought both styles of pilot bearings. The difference is huge. Turning down the input shaft on the tranny scares me because the very center of the shaft is hollow and turning the shaft down wouldn't leave much metal left. I decided to enlarge the crank hole instead. The nice thing is with the crank out I'll be able to replace the bottom end bearings. I just don't trust a original 3 synchro tranny for the long haul.

Hollowing out the crankshaft sounds like it is the proper decision.

I now know what the gentleman I was speaking with in Georgia, was talking about. Turning down the input shaft is probably not the best way because of that hollow center!!

Thanks for the info. It gives me some idea of what's involved. I like the idea of having a 4 synchro gear box.
But...I also like the idea of keeping the old girl as close to her virginity as possible.
Got some thinkin' to do!!

Do a search of my posts. I've bugged the heck out of most of the folks here about this subject.