A+ diff pinions definitely have both sides machined flat, and A series ones do not.

[edit] I'm not sure if an A+ diff pinion has the groove Ian speaks of (Yes I know the rest of the gearset does).

"How do I know if I have an a or a+?.."

If you're talking about the gears.. A+ have a small notch machined into the tip of each tooth. 

"If grinding for clearance is necessary, it is supposed to be obvious..."

It certainly is... grinding (I would suggest "filing" is a more approriate term) is necessary if the pinion bearing retaining ring stops the pinion gear from turning.  You may or may not have to file the inside a bit bigger to allow the pinion to rotate.  Its kinda obvious when you get there....

Cheers, Ian

Not sure how to tell the difference. The 3.1 set I installed into my transmission fit without any issue or grinding necessary. As stated above: replace as a set (crown & pinion together). Supposedly, there "may" be some grinding of the case required where it sort of surrounds the pinion gear - not all cases will need this. It was indicated to me that the only way to tell if grinding is necessary it to attempt fitting the new pinion. If grinding for clearance is necessary, it is supposed to be obvious. Mine fit with the same clearance as the old 3.44 set we removed.

How do I know if I have an a or a+?

Not at all, provided you fit both the A+ pinion and the A+ crownwheel, as said above. A+ gears have a slightly different helix angle, but their center spacing is the same.

Does that mean it's impossible to have an A+ FD in an A ?

 

Excellent thank you

Chris

you can put ANY final drive in ANY transmission (except the huge 72-tooth early automatic crown wheel). Just keep the Matching Crown Wheel with it's correct pinion.

But, as Chuck said, you will need to grind, file or lathe out the main bearing retainer to fit the larger pinions of the 3.1, 3.2, 2.95, and 2.76 final drives. It's not a big deal and doesn't have to look pretty. Just did one last weekend. Opened up the bearing retainer of a remote box to take a 3.1 final drive. Took 15 minutes.

 

 

What about rod-change transmissions? I received a 3.1 final drive set with the Mini I got last summer. The car has a replacement engine 1275 head, block unknown, rod change transmission. I suspect the car was originally an early 850 Deluxe for US import and still has the original speedometer. I strongly suspect it currently has something like a 3.76 final drive in it currently (thus the research in the "Speed Hut GPS Speedometer thread).

If the 3.1 final drive set I have will work, I'll hang on to it for when the engine needs to come out for fixing oil leaks eventually.

As long as you use A+ pinion and crown wheel gears together, you can swap them into an A gearbox. The only issue is that you are likely to have to do some clearance grinding to get a 3.2 or higher A+ pinion into an A box.

A+ gears are different. You can go 3.44 in A-series.

Hey all, pulling apart my 22g1128 sandwich remote transmission, It currently has a 3.765:1 final drive and when it goes back together I would rather have the 3.1 or taller which is a+ ratios. Will this fit into the earlier transmission?

 

Chris