M5R1 output shaft in a M5R2 trans - strange

[65comet]

Hey all, I couldn't find a way to change the topic of my speedometer post so I'm starting a new one. This deal with this trans is really bugging me.
I'm just copying and pasting from the speedo post but this is all about the trans.

I'm halfway thru the swaps in this '71 to a 302 aluminum headed roller motor and M5R2 transmission. Bought an 88 F150 with the 5.0 & M5R2 trans. I took this to my local trans guy to go through it, he said it had been rebuilt and looked great, needs nothing. The trans fits in fine with moving the crossmember back several inches and moving the shifter hole in the floor hump back about 2 ". The major issue with this transmission is going to be when the throwout cyl. needs replaced. This trans only fits into the truck from the front, the engine compartment. It will not go in from the rear without taking out the crossmember the big stabilizer arms are attached to. Major bummer, that means pulling the motor to change the slave cyl. It has the tailshaft for speedometer cable so I'm set there.

Got the hyd. clutch master mounted on the firewall on drivers side of brake vacume booster and found a steel braided flex line at RockAuto. I took the clutch rod pin piece off the '88, cut it and welded up a bracket I'll weld onto my factory clutch pedal without removing it. I'll be able to use the entire factory clutch master and rod. I'll have to fashion a stop on the floor to prevent over travel. The clutch master has 1 1/4" stroke.

My factory steering box had a lot of play so I bought a new unit from Redhead with quick ratio gears of 3 turns lock to lock. Since my truck has power steering, this will be a welcome change.

I'll be changing the 9" gears this weekend from 3.0 to 3.5.

One thing really baffling me. The Transmission is definitely an M5R2 case, I.D. numbers are E8TA DD. However when I bought a new speedometer drive gear for an R2, it was way too big (old one was damaged). After measuring, seeing pictures, I find there is an M5R1 output shaft in this trans and I need the R1 speedo drive gear.
No one has an explanation of why this R2 trans has a R1 output shaft in it. I'm told the R1 gear sets won't go together in the R2 case but I don't know. I'm bummed I've got this smaller, weaker output shaft in this trans. Anyone know why there would be an R1 shaft in this R2 case ? Did Ford build a trans that way ?

[mmerlinn]

I am thoroughly confused. I don't see ANY way that you can put an R1 shaft in an R2 transmission. The R1 spline counts are (front to rear) 32-40-34-34-28 and the R2 counts are 32-40-38-38-28. No way to swap them.

As for R1 guts in an R2 case even if they fit into the case the input shaft would be TOO SHORT to reach the flywheel.

Since BOTH the R1 and the R2 speedo gears have the SAME bore (1-7/32") I strongly suspect that you got the wrong gear. My notes say your gear should be 8 teeth and green with 3 half ballways in the bore.

[65comet]

Yep, I'm confused too. Now I don't know what output shaft is in this trans. All parts places that I looked up listed the same speedo drive gear for the R2. Yet when I ordered that part, it was way too big for my trans shaft.

Here are the measurements (close) of my trans output shaft, ID of 1.22, OD of 1.93, width of .69.
The part number and measurement of the drive gear sold by the parts houses for the R2 that I received were E7TZ-17285-B and did not have the 3 ball detents in the I.D. and were a much larger I.D. I can't find the measurements of that part anymore

I did find the right drive gear with the 3 ball detents in the I.D. I can only guess that Ford made early R2's with the smaller output shaft, then changed to larger.

Still a mystery. Update: the project is done and I love the trans, what a great improvement over the T 18.