I just purchased a used Q gear set for my 901 transaxle and I am planning on flipping 5th for 3rd, using the Q for 4th, and 4th for fifth for my race car. I have read threads about how to "flip" 5th, implying that it is as simple as swapping the two gears of the 5th gear set to the opposite shafts where the old 3rd was located, driving to driven and vice versa. I haven't yet opened up and pulled the gear stack from the case, so maybe things will become clear to me when I do. Right now as I look at my new Q gear set, I see that one gear has internal splines (the driving gear I assume) and the other has a smooth bore (driven gear with syncros and dog teeth). See photos below of Q gear set.Click to view attachment Click to view attachment

I assume that the fifth gear set that is in the stack is of the same configuration, and if so, I do not see how the two gears can just we swapped onto the opposite shafts, as the gear with the internal splines would no longer be located on the splined driving shaft and the internal diameters of the gears are not the same.

Also I am unsure of how the fifth gear syncro configuration is supposed to work with the flip. Since the syncro is on the driven gear, once flipped, won't it now be in the wrong position being on the driving gear?

I apologize if my questions indicate that I really don't understand how this is supposed to work, but at this point, I really don't. Any and all help/advice will be appreciated greatly. I have already purchased Dr. Evil's rebuild DVD which I think will answer some of my questions, but I'm not sure if the DVD covers a 5th gear flip.

In Dr Evil's signature he has pages of notes you can download, I think it covers a bit about this but worth printing out never the less. It was a pretty straight forward job, but then I've also hosted two Evil tranny clinics in the past.
I have a flipped HB, my gearing is A F O X and HB flipped for 5th.

I flipped 3rd and 4th then added a tall 5th which is a 911 2nd flipped (HB) to make a tall box for cross country trips in my 3.0.

Basically the little gear is always keyed to the shaft. It works, you'll be fine.

1 2* 3 are locked to the input shaft, 4 5 are locked to the output shaft.

* 2 is part of the shaft.

Basically, for the third, fourth and fifth gears there are two types: those designed for third gear position, and those designed for fourth & fifth position. You can flip a gear designed for third position to use for fourth or fifth position, and you can flip a gear designed for fourth or fifth position to use for third position. When flipping you do two things: the ratio is reversed, and the gear is driven backwards from the design perspective. Inverting a ZD fifth gear 31:22 becomes a 22:31 which is very nearly a K gear, so they call it a KA gear. likewise the HB gear 19:31 (a 4-speed second gear is exactly the same as a 5-speed third gear because first in a 5-speed is in zero position on a 4-speed) when flipped becomes 31:19 which would be about ZG range (way overdrive .63 to 1 ratio). Most people do not worry about driving the gear in reverse which puts some of the thrust in the wrong direction. You can see the angle of the gear where they mesh is handed, and if you flip them the handedness is reversed. The factory had a solution, and from gears M through R there are two versions; one for third gear position and the other for fourth or fifth position.

Here is a picture of the gear stack. You can see that when you flip 5th for 3rd it is oriented the opposite direction (hence the thrust loads go the other way). I have a flipped 5th in my car. Only goes together one way so you cant really mess it up. If you had a flipped 5th and a actual 3rd gear of the same ration sitting next to each other the angle of the gears would be opposite.

Click to view attachment

john

if i'm not mistaken reverse and first are to the right, then 2-3 and finally 4-5. when the dr. Evil and i built my transmission we removed 1st gear because it is only supported on one side by a bearing and under high load can fail. I have a 3.2 in my car so first is not really needed.

I think the answer to your question is:

Both shafts are splined in the area where the gears go. The gear without the internal splines rides on bearings that go on a bushing that sits on the splines. So no need to worry about if the gears actually fit on the opposite shafts without machining; they do.

--DD

motovated, I did the exact same thing two years ago....3-5 and Q for fourth.
Very easy to do, syncro are the same just keep track of the orientation of the washers. Take lots of pictures of everything including the position of the forks be fore disassembly. Best, Mark

Thanks everyone. I'll be giving this a go in the next couple of weeks. Appreciate the help.

^^ Not a pic of a 901/914 gearbox, where 1st and rev are on the same swing.

915 I think, where rev and 5th are on the same swing.

Motivated, just a few pictures I took before and after. I marked new and old gears with different paint markings. MarkClick to view attachment Click to view attachmentClick to view attachment

mlinder your picture shows exactly what I was trying to descride (with the wrong picture)

john

Nice pics. Good to see you figured it out.
Flipped ZD gives you 22:31, so right between a K and L gear (Ka).
Flipped N gives you 29:23, same as stock Z gear.

Looking forward to seeing how you like it.

Thanks to Dr Evil. Your CD's made it happen and with all your help on 914world. Love your new shop, keep posting pics. Best, Mark

I'm guessing you're gearing for short tracks or AX....the A/F/KA/Q/V setup sounds interesting but it's limited to like 118mph on 24 inch rear tires....23 inch will top out at 113 using a 6800rpm rev limiter....
901 gear ratio workbook makes it easy to noodle this out....
http://www.914world.com/specs/regearing_901.php

Its my pleasure, man. Keep up the excellent work!