I got myself a couple 901s to play with, and just got the first one apart. I had read somewhere that the ratios could be changed because gear sets could be flipped around to make different ratios. (like 2nd could be flipped and used as 5th for a different 5th gear ratio) I haven't started pulling things off of shafts yet, but it looks like some gears are actually cast into the shaft. is this the case or is it just an illusion? Am I nuts to try this gear shuffle things? (I have 3 901s to pull gears from) (I'm shooting for better ratios for a V8 conversion)

--Royce

The H gear that you are in question about in a 901 is fixed to the shaft. It was an idea I had once too. Only to get shot down when Red-Beard told me the same thing. You need an H gear set from a 915 I think, I am not sure. Good luck and I will be watching this post to find out what the solution is. I am building a V8 car too.

I was under the impression that the "H" gear was the desirable one for a 5th gear ratio for a v8, but others would work. I wasn't gonna be picky as long as I could manage anything in the 1500-2500 rpm range at freeway speed.

--Royce

Ok, my bad, the H gear is the one you want, it comes from a 915 I think. I was going to swap the 2nd gear for the 5th gear and flip them to get the better ratio, the second gear is fixed to the shaft so it is not possible. I stand corrected.

901 and 915 gearsets are NOT interchangeable. the shaft centerlines are different.
i don't think (but am not going to take the time to research right now) that the letter-designated gear ratios are not the same ratios for the same letter...

914.4 uses an 'H' gear on the mainshaft, 914.6 uses a 'GA' gearset.

however - you're still right - you need an 'H' 2nd gear to flip. they're around; they were made for racer guys using the all-gears-changeable 904 mainshaft. there aren't a lot of interchangeable 2nd-gearsets for 901's for this reason; bring money.

or check out the ratio charts for other low 3rd or high 1st gearsets that might be suitable.

the guys who make custom gears aren't very interested in making very tall 5th gearsets because they don't consider the 901 suitable for V8 use.

For V8 conversions, the H / 19:32 is the gear you want in 5th to yield about 2500 RPM at 70MPH.
Contact CarQuip ... they have NOS for about $550.
They also have a GREAT Excel based gear ratio calculator they will share with you.
Good luck ... Ed

The H gear that can be found used and swapped comes from the 4 speed 902 transmission used in 912s and 911s.

Second gear in the 4 speed is located in the equivalent of the 3rd gear position of a 5 speed transmission, so it could be turned around and used in the 5th spot of a 5 speed.

The only swap that can be accomplished from stock 914 gears is 3rd to 5th and vice-versa - which does not really gain you anything for a V8.

Well, if someone has one of those gear sets, I can take them to a friend of mine with a machine shop and have him produce several sets. There seems to be enough call for it. I know I need about 2 sets and I know several others who would like them also. $550. seems a bit steep for a couple of steel gears. I am sure I can get them made for a lot less than that.

Used, the H goes for $300-450. If you can get some made for less than $300 and closer to $200, I would certainly sign up for a set.
Might be just enough incentive to build another V8 conversion.
By the way, if your investing in the 901 box, go with a billet aluminum intermediate plate !!!

I think there is a bit more metalurgy in producing those gears than just cutting up another one...

I'm not sure if they are forged or how they are treated... but they are purposely built very hard...

b

ok, what about this thought... what if I cut 2nd gear off the shaft and machined the inside to fit where 5th gear goes? Is this possible? I have acess to the usual machine tools (mill, lathe) but nothing specialized. This sure has been rain on my parade, somewhere I had read that all the gears other than first were the same and could be rearranged any way you wanted. Now the cost of my conversion is bound to go up.. anyone have a spare 930 trans laying around?

--Royce

You would have to a have a machinist who is familiar with making gears. Most gears are made from 8620 steel but it can be done with 4140. After they are cut they need to carborized and heat-treated to harden the teeth. This is a tricky process unless you are set up for it and it can be very $$$$.

Good luck

I do think that others have tried cutting 2nd gear off before....

I honestly can't answer your question, but what pops into my mind, is how are you going to effect any heat treating and hardening processes. Not just to the shaft but also to the 2nd gear...

also 3rd and 4th/5th run the dogs and sliders on the other side.. so they don't interchange...

there are a bunch of differences...

read the pelican tranny rebuild tech article and then take one of your spare boxes apart and it will make more sense....

Also call renegade or brad or someone that has been there before with a V8......

I think overall.. it is cheaper to convert or buy what you need than it is to re-engineer or explore new territory...

b

Perhaps the most rational solution is to simply use the stock gearing for 2nd thru 5th ( you don't use 1st in a V8 914 ! ) and, after having driven it for a while, see if you like it. If not, make whatever changes you see fit.

My stock 901 is just now giving out after 17 years of mostly moderate driving but my pumped 327 has left its fair share of rubber on the California highways.

Given my experience with stock, I will be installing an aluminum intermediate plate and an H gear.

But that's after 17 years of enjoying it the ( stock ) way it was.

Enjoy ... E

To me, stock isn't an option as I drove the firebird the engine came out of on the freeway in third just to see what it would be like.. no way, not with that engine.

I have a new plan. I'll hack second gear off the old shaft (it's not a waste, 4th gear on this tranny is stripped to hell already) and machine a pocket inside of it to about half it's thickness. Then I'll take my 5th gear and machine off the teeth down to the diameter of the pocket, and then the 2nd gear will fit over it. Then I will drill a bolt pattern to bolt them together with 6-8 bolts. If it works, it'll save me big moolah, if it doesn't I'll just be out of some time. It'll have to be the most precise machining I've ever done, but I'll take it slow and see what happens. Of course I'll post pics when I'm done.

Brad did a comparison with a modified 901 type tranny and the standard:
http://www.914world.com/bbs2/index.php?act...=bitchin+tranny
Felix

Bondo,

I'm totally confused...
do you mean that you drove the firebird in 3rd, and so you don't think the 914 box will work?

Did the firebird have a 901 box in it?

It will be very different in a 914.. different box, different ratio's, different differential, different wheels and tires....

all of these cumulatively have a say in what the final gearing comes out like...

I say go drive someone elses 914-v8 with a stock box before you invest thousands into changing what might already be good enough....

maybe I'm missing something, but the firebird final drive and the 914.. will be apples and oranges.

brant

The ratio of the firebird put the rpms a bit above 3000 on the freeway, in third or was it 4th, I forget. (it was a 6 speed tranny). It's not the same as a 901 5th, but close enough. Even 5th, which put the rpms at around 2500 seemed a bit high, and 6th had it at a nice smooth and quiet cruise at around 2k rpm. This was with a much heavier car than a 914 and I still didn't need to downshift to pass. If I could get 2k rpm at cruise I'd be very happy. I wouldn't care if this was just going to be a track car or an around town car. I plan to use it occasionally for long (300 mile) drives, and I want to be happy with it. I also want decent gas mileage. (now more than ever... $2.40 a gallon, gimme a break!)

--Royce

ok....

well I would suggest that you measure your tires, and then using a gear chart figure out how far off you are....

but it sounds like you may have already done this...

hope it works out well.... Its a big job, and could be pricey if you lost a box and fresh sliders/dogs in the process

oh.. bondo, you might want to pick up a pair of intermediate bearings before you start.. They are 99% likely to come apart in the races if you open the box up far enough to play with 4th and 5th...
at least look for a sale so you can get them (and a gasket kit) at a good price......

b

I haven't done that yet, I was waiting until I got a 901 opened up so I could count teeth and see where I stood. I do know I have a ways to go to get a 1k reduction in RPM, and it's probably not possible with 901 parts. I'll do my best though. At least now I know where I stand.

--Royce

Well, there goes that idea.. I took another close look, and second gear is tiny! it'd probably give something close to the ratio I want, but I can't see any way to do what I planned and have it be strong enough. Oh well.

--Royce

Hi Ed, the 912 case is a little stronger.Just make sure its not worn out. Bought the CNC this morning along with a few goodies. Will have to raise my roof in my shop 4ft to get the goodies in.

Does Paul Guard make any 901 gearsets? I know he makes them for the later boxes.

Does anyone know if the 915 gears are freely shufflable, or do they have the same "some are part of the shaft" problem? If I'm going to spend money, I want something stronger than a 901.

--Royce
(sigh)