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Can I bolt up 3Synco Trans to 18V motor?


Senior Member
I have a 3 sync overdrive transmission, that I would like to test out. I was going to put it in a 65 MGB but sold it. Now I'm thinking about putting it in my 1600 MGA or selling it, but would like to make sure it is operating properly. I have a junk 1973 MGB with the 18V motor that Im using to test transmissions, ( cross member is cut out)
The input (first motion ) shaft appears to have the same splines and size but the older 3 sync shaft is about 1/2 inch longer overall, I'm afraid this will bottom out in the crank? The 3 sync trans is 5/8 of an inch shorter overall then the OD 4 sync
that came out of the 73 B.
There is also a difference on the bell housing starter bolts.

I 'm not trying to test the units on the road, but have the car jacked up spinning the tires. So question #2 is could this present a problem testing out the Sync's downshifting? I wouldn't think so being the driveshaft is still turning when I downshift.

Thanks for your input.....
There a few difference between a MGB 3 and 4 syncro tranny set up, basicly, the rear engine plate, flywheels and starters are different, and have to be also change when making the conversion, now putting one in MGA is another story altogether, Bob White can tell you more about that than me, but what I sted covers the difference between the MGB tranny set ups.

tony barnhill

Great Pumpkin - R.I.P
Also, Hap, isn't the bearing inside the flywheel different?


Jedi Knight
2 Types of 3 syncro MGB transmissions. Ones for a 3 main engine with the small input shaft and the ones for the 65-67 cars with the 5 main engine and larger input shaft. All you will be able to do with your test is to tell if it engages. Hap is correct about the back plate,flywheel and starter change to bolt it up for that test. You may be able to do the same test with a good drill attached to the input shaft and a battery to power it up and a speedometer and cable to see if the speed changes on engagement since you will probably not be able to tell if its going in at that speed. You still will not have alot of info on the trans. Good luck with it. Bob

tony barnhill

Great Pumpkin - R.I.P
Another thing is to get one of each bushings from Moss - they're inexpensive - for the input shaft & test to see which fits....larger one goes in 18V.


Senior Member
Thank you for your response and the help. Taking Tony's advise I got into the Moss book the MGA's used a 10 spline input shaft until the 1622 motors came out.
If I understand correctly. Since this D type OD, transmission is a 23 spline input shaft it doesn't look like a simple bolt up to the 1600 motor job.

#1 So the natural question is will the 10 spline input shaft from my present MGA transmission, adapt into the 3 sync D type OD MGB transmission ?

#2 I already have a 3.9 rear end in the A, Im now wondering would this be worth the extra trouble?
tony barnhill said:
Another thing is to get one of each bushings from Moss - they're inexpensive - for the input shaft & test to see which fits....larger one goes in 18V.

I guess this may be the last advice Tony ever gave here, and it was spot-on !

Thank you my friend for all the help you gave us all, Godspeed Tony.
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