AO trans question

[63busguy]

I purchased a rebuilt transmission from a shop that was going out of business and now that I am getting ready to install I have some questions.

First the trans was tagged "Type II". After looking at the code sticky the AO code on the case shows it as a 70 on ghia trans which should have the 3.88 r&p and the .87 4th.

Second, since RBG boxes are reverse rotation, how do I tell if it is reverse (bus)or standard (bug)? If turning the main shaft clockwise which way should the ring gear spin?

Third what is the best way to determine what the R&P and gears are actually in the case?

Fourth, since I will be using the small nut mountain gear RBG will this trans give me better highway speeds and reliability?

[aircooledtechguy]

Any factory markings on the outside of the trans are now ONLY reflective of what used to be in there and NOT what is in there now. I would tend to believe the tag from the shop where you got it since they are likely the ones who either rebuilt it or had it rebuilt. The only thing you can see without taking it apart is if it has 2 or 4 spider gears in the diff. If it has 4, that would indicate that it likely has other HD work done (folks typically won't spring for a super diff if they aren't doing a lot of other beefing inside).

As for the gearing and R&P, you will have to mathematically figure that out by getting it into usually 4th gear and counting revolutions of the input shaft vs one full turn of the axle. with a wheel/tire mounted and the rolling diameter established, you should be able to determine the R&P and all your gear ratios, but you would need to install an axle and wheel/tire cranking it by hand. Hope this helps. . . Good Luck!!

[Marc]

You can count the ring gear teeth through the drain plug hole, all you need to do is look for something which distinguishes one from the next (perhaps an etch mark on the O.D. of the ring gear) or failing that make your own by cleaning a spot with a Q-tip - add a mark with a Sharpie if needed.
`70 'Ghia ratios should be 3.80/2.06/1.261/.889 (early) or 3.80/2.06/1.260/.883 (late, fine-tooth 3rd & 4th).

[63busguy]

What should the tooth count be for each ratio (4.37, 4.12,3.87)? once i find out the ratio, what is the formula for finding out 1-4 gear sets?

[melville]

What should the tooth count be for each ratio (4.37, 4.12,3.87)? once i find out the ratio, what is the formula for finding out 1-4 gear sets?

I think it was Bruce2 who posted a brilliant gearing check based on the fact that you are almost guaranteed to find a 2.06 2nd gear in every ACVW trans you might find. Search his posts in the Transaxle forum.

4.63 (rare), 4.37, 4.12, and 3.88 R/P all have 8 tooth pinions, so, respectively they'd have 37, 35, 33, and 31 tooth ring gears. 4.86 uses a 7 tooth pinion, so ring of 34. And 3.44 uses a 9 tooth pinion, so 31 tooth ring there, but super rare and aftermarket only--if it was in there you'd have been told, if only to get more money for the trans.

Edit: Not Bruce2, but Marc. Thanks Marc!

[Marc]

If it's a swingaxle it's most likely got a 4.125 or 4.375 ring & pinion...if it's 4.125, 3rd should be 1.26 and if it's 4.375 3rd could be 1.26 or 1.32.
Most IRS Type I transmissions you'll come across in the US will be AH (4.125 R&P) or AT (3.875). 2nd gear will be 2.06 and 3rd will be 1.26 99.5% of the time, so for example if you put it in second with one wheel off the ground and it takes 4¼ turns of the crank to get one turn of the wheel, you have a 4.125 R&P. (2.06x4.125)/2=4.25
If it takes 4 turns it's a 3.875 (2.06x3.875)/2=3.99
If it takes 4½ turns it's a 4.375 (2.06x4.375)/2=4.51
This assumes that 1st and 2nd gear are still stock - considering the expense involved in replacing the mainshaft to get different 1st/2nd gears, that's a pretty safe assumption unless you're dealing with a trans built by/for a hardcore drag-racer.
If in doubt you can repeat in 3rd gear, if it takes just over 2½ turns it's a 4.125, if just under it's a 3.875. A 4.375 will take either 2-3/4 or almost 3 turns depending upon which 3rd it has. Since it's not uncommon to replace 3rd with an aftermarket shorter gear, keep an open mind when using 3rd to determine R&P. The most common is 1.48 but there are many others.

Once you've confirmed what the R&P ratio is you can check to see which 4th you have, you may need to rotate the crank enough to get 2 or more turns out of the wheel to be able to discern the difference between, say, a .89 and a .93 here. Late AH transmissions had a .88 4th, earlier were all .89 unless the trans started life in a bus in which case it could be .82.

Simply multiply the R&P ratio by the gearset ratio to get the final (overall) ratio...for example 3.875x1.26=4.8825:1
3.875 with a fine-tooth `70/`71 Type I 4th: 3.875x.883=3.422:1
3.875 with a "bus" 4th = ~3.18:1

[63busguy]

Since it is the trans only with no axles on it can I still check the ratio by turning the mainshaft and counting the rotations of the diff? I looks like a stock diff as there are only 2 spider gears.

I tried to count rotations already but am confused. I put a clutch disk on the shaft to make it easier to tell full rotations, marked one area of the diff to see one full revolution, put it in 2nd gear and started counting. WTF? it only takes 3.5 turns on the mainshaft to 1 rotation of the diff!! Is it in the wrong gear? I rotated the shift fork toward the drivers side of the trans (left) and pulled the rod towards the front. Also the diff turns counter clock wise when looking through the passenger side axle plate, is that correct for a RGB bus trans?

[Marc]

The procedure quoted above is for a car with one wheel on the ground - there, differential action doubles the number of turns that the other axle makes.
With no drag on the differential both side gears will turn in unison, so there's no need to divide by 2.
In a stock late `70 'Ghia the overall ratio in fourth is 3.422 - you're in that ballpark, so I'm presuming you aren't in Second.
In Second, 3.875x2.06=7.98 ...it should take nearly 8 turns of the input shaft for one turn of the differential.

[63busguy]

Finally went through all the gears. These are approximate as I had no degree wheel to get exact readings.

3.75:1
5.25:1
8.25:1
15.25:1
16:1

The trans is supposed to be a rebuild for an early type II. The code is early ghia, who know whats inside. Does anyone have the gear ratios for 1-4 (all possibilities) so I can plug in numbers to see what is close?

If anyone is kind enough to crunch the numbers for me, THANKS IN ADVANCE!!!!

[Marc]

1st gear - all through October 1972: 3.80000
  "     "     from November 1972: 3.77778
2nd gear - "all": 2.05882
3rd gear - through April 1970 (coarse tooth): 1.26086
  "     "      late `70-up (fine tooth): 1.26000
4th gear - through April 1970 (coarse tooth): .88889
  "     "     late `70 thru `72 (fine tooth): .88333
  "     "     `73-up (fine tooth): .93103
Reverse - 3.61344, 3.80952, or 3.77777

Ring & pinion, Beetle/SuperBeetle through 1972 ("AH"): 4.125
       "                 "          "            `73-up ("AT"): 3.875
       "             Karmann-Ghia `71-up ("AO" swingaxle or "AN" IRS ): 3.875   


With the numbers you've provided the most likely gearing I can come up with is stock early "AH" (4.125 ring & pinion - not what an "AO" case had inside originally) with gear ratios as above: 1st=3.80, 2nd=2.06, 3rd=1.26, 4th=.89). Reverse is perplexing, but 3.80 comes closest.
Need more accuracy to tell for certain (count again, using 2 or 3 times as many input shaft rotations...and take up all the slack before you start to count) - but I see nothing to indicate that it's anything special.