Ok, so I now know that for a good v8 5th gear, I need to put second gear in it's place.. flipped. 2nd gear is one 18 tooth gear and one 34 tooth gear. The 18 tooth gear is part of the mainshaft and not removable.

Then someone said the 904 mainshaft has no gears machines into it and all are equally swappable. But that is very rare, right? It's also more than I really need, as I just want the gear.

But then it's been said that a 912 4 speed transmission has first gear where 2nd is on a 901, and the second gear is where third gear would be on a 901. Presumalbly this second gear is removable, and has the same splines on the inside as 901 gears. Is the ratio of this second gear something close to 18:34? Anything lower than 22:31 and it wouldn't be any taller than the stock 901 5th gear once it's flipped. I need sure answers here, I bought two 901s (no biggie, cheap) based on a statement something like: "you just flip 2nd gear and put it in place of 5th, and voila, taller 5th gear" which turned out to be nearly (see my signature) impossible. I do not want to buy a 912 4 speed to scavenge 2nd gear out of only to find it won't work or doesn't have the right 2nd gear ratio. (expensive)

Just for the distribution of useful information, here are the ratios (tooth counts) of the stock 901 out of a 914 (side shift, but I don't think that matters)

1st (didn't count, but can if requested)
2nd 18:34
3rd 23:29
4th 27:25
5th 31:22

R&P 7:31

I think you are referring to the magic "H" gear. It came in the 912 4speed tranny although I did not know that the 2nd gear was interchangable in those either. I thought it was a third gear in those boxes. Suppossedly they are going for somewhere in the 400+ range for that gear set.

Does that come in all 912 4 speed transmissions? If I buy a transmission chances are I won't be able to open it up and poke around first

Since I'm resident nerd, I'd better add a nerdy graph. Here is what I'm trying to do... Blue line is stock, pink and yellow are options. It all depends on getting a 912 trans, or managing to get 2nd off the mainshaft (I haven't given up on that yet!)

H ( 19:32 ) is the 2nd gear out of a 902/05 4-speed box. Flip, put in 5th, slide 5th into 4th and 4th into 3rd. 2nd is fixed and 1st isn't used.

Or, find a 7:27 ring and pinion which will raise everything about 15%

Or go to a 915 or 930 ... xpensive !!!

Don't forget the billet aluminum intermediate plate.

And you might consider using a 912 case which is rated at 400HP vs the 901 which is rated at 300HP.

Good luck ...

Whoo, I had no idea a 912 case was stronger. Do the internals transfer over, or do you have to use the 912 shafts and ring and pinion and bearings, etc.? If I had to use the 912 shafts and R&P (I would think so, since the 901 stuff should be longer for the extra gears), I would have to flip the R&P.. how hard is that in a 912 trans? I guess all 912 transmissions are tail (nose) shift?

(Thanks all, I'm getting some good info here!)

Supposedly, it's a straight across move, case to case.
Looking for a case now to try it.

Flipping the R&P is no small task ... we just did it for a 930 and although straightforward, it's not for the weekend wrencher.

Good luck ...

In one of my semi-insane moments, I acquired a NOS 904 GA 2nd gear. Weird stuff like this can still be found if you know what rock to look under.

For reference, Powerhaus II charged me $250 for a H-gearset with dog teeth.
H is indeed a 3rd gearset.
If you want to get a set try PHII, Carquip or Otto's. Renegade may also have it.

Could you please?

Andrew

OK, This probably was covered at one time or another. But How common are other gears like the illusive "H" in 911 cases? I mean can you get a more common gear from a 911 case that would give you a good result in the final drive?

Here's a thought; Can the fixed 2nd gear be removed from the shaft via grinding? They grind cranks and cams all the time.

Have a machine shop grind the 2nd gear off the shaft and find a cheaper gear that could do the same job as the "H".

I'm not sure where you got this information. It may be true of the 912E case that was basically a 915 transmission. The original 911 / 912 / 914 cases were very much the same; a 901 type unit. In 70 and 71 the 911 used the 911 type tranny that was very similar to the 901. From 1972 the various flavours of 915 transmissions were used and these were much stonger.

Chris, are the GA gears valuable? I have two GA 901 input shafts and gears.




Carquip, or Powerhaus (or Powerhausll) does this.... it aint cheap though..

Ok, What other gears can one use from other more plentiful transaxles?

Is it possible that the 912 901 is an aluminum case, vs magnesium? I always hear about 901 failures involving damage to the internals, not the case. Perhaps the case flexes and allows the gears to mesh at incorrect angles leading to gear failure?

Rich, if you need a GA we can talk

oh and I really need to catalog the gears I have...

Check out Albins Off Road Gear http://www.albinsgear.com.au/porsche.html they supply a lot of the stuff you get from powerhaus etc. You can get weld on ratios for 2nd and some higher 1sts.

Just to clarify a couple of things.

Early 911/912 gearboxes (65-68) were cast aluminum, so the housings should be stronger, but the differentials were weaker. You'd have to get around differential/ drive flange difference issues, venting differences, and nosecone/intermediate plate compatability problems to adapt the housings for a 914. Probably not worth the effort.

You can't do a 2nd/ 5th flip because 2nd is permanently attached to the mainshaft. On a 4 speed box, the gear is still permanently affixed, but now that gear is 1st gear instead of 2nd. I don't think anyone here wants to build a 901 box with two 1st gears...

GA mainshafts are pretty much standard fare in 911 gearboxes.

Just got off the phone with PowerHaus II in Colorado who quoted me $ 575 for an H ( 19:32 ) gearset.

They also advise that the stock 914 magnesium case is stronger than the early (65-68) 911/912 aluminum cases which is counter to what I had heard but this is their specialy biz and they should know. I bow to their expertise and apologize to anyone who I might have set astray.

Further, they said that if you do use the early aluminum case, you have to flip the ring and pinion !

Sure makes hooking up a V8 complicated but still a lot cheaper than the 915 / 930 alternatives.

A few more details please.

As I understand, The 914 has a fixed 2nd gear on the shaft.

If you get the "H" gear set from PowerHaus II in Colorado do you need to do anything with the 914 shaft or was this only discussed because our transaxles are not a source of "H" type gears because the gear is fixed?

Is that question clear as mud?

In other words;

Anyone have a list of parts that are required to do the conversion?

How about other parts commonly replaced during rebuild? (what bearing, syncros, seals, etc.)

How about a source for getting these parts at a discount or best pricing?

You know, wouldn't want to pay too much.......

P.S. What special tools are required to do the rebuild?

And is there a source for a manual to do the work?

And Who in the club specializes in rebuidling transaxles?

and, and, and, and,

Put the flipped H gear into 5th position.
Move old 5th into 4th
Move old 4th into 3rd
Done
2nd is fixed onto shaft - no changes
1st ... never used in V8 applications

Ok, if a 912 case isn't stronger.. what CAN be done to make a 901 stronger? Cryo treatment? My understanding was cryo treatment reduces wear but doesn't necessarily make thing stronger.. is that true? I'm not sure if I buy in to the whole billet intermediate plate thing.. anyone have any real data on the benefit of that?

Andrew: I haven't had a chance to count first gear teeth yet, but in another topic it's listed as 11:35.

Oops, nevermind.. that was for a 915.

Here are some interesting charts that might help you guys out...

Another

last

Bit more...

912.....................................................................
................................912
1965-69* 902/1 11:34 18:34 22:29 25:26 28:24 7:31
(5-Speed) 902/02 A F M S X
902/05
1965-69 902/0 11:34 19:32 24:27 28:24 - 7:31
(4-Speed) 902/01 A H Q X
902/04

912....................................................................................................912
*Late 69 902/06 11:34 18:32 23:28 26:25 29:23 6:29
(5-Speed) A GA O U Z

912E................................................................................................ 912E
1976 (5-Spd) 11:35 11:33 23:29 26:25 29:21 7:31

911.....................................................................................................911
Up to 901/0 12:34 18:32 23:28 26:25 28:23 7:31
7/26/65 AA GA O U Y
(5-Speed)
1966-69 902/1 11:34 18:34 22:29 25:26 28:24 7:31
(5-Speed) 901/02 A F M S X
901/07 or 29:23
Z
1966-68 902/0 11:34 19:32 24:27 28:24 - 7:31
(4-Speed) A H Q X
1969-71 901/06 11:34 19:31 25:26 29:23 - 7:31
(4-Speed) 911/00 A HB S Z
or 29:22
ZA
1970-71 911/01 11:34 18:32 23:28 27:25 29:22 7:31
(5-Speed) A GA O V ZA
1968-69 905/00 15:36 19:31 23:28 26:25 - 7:31
(Sporto- 905/01 C HB O U
matic) or 27:25
V
1970-73 905/20 15:36 20:31 24:27 28:24 - 7:31
(Sporto- 925/00 C I Q X
matic) 925/01

1972-73 915 11:35 18:33 23:29 26:25 29:22 7:31
(5-Speed)
Trans
73 915 11:35 18:32 24:27 28:23 - 7:31
(4-Speed)
1974 915/06 11:35 18:33 23:29 27:25 29:21 7:31
(5-Speed)
1974 915/16 11:35 20:32 25:26 29:21 7:31
(4-Speed)
1974 925/02 15:36 20:31 24:27 28:23 - 7:27

Whoo, that's more data than you can shake a stick at! Thanks! Looks to me like you could also use an HB gear as 5th with slightly less desireable results. Maybe easier to find? Time to have some more fun with excel

Data is my friend...I'm an engineer!