Lemons car.
Track is NHIS.
There is a turn that requires a quick 2nd gear downshift, turn and go up a hill.
This would happen.....500 times in two days.

How would you build a tranny that.
Is driven by a 100 hp motor
Has 4 gears
Top speed, maybe 100, if we have a tail wind
Will last two days of downshifting into second.

Requires you to stop, think, and possibly move a metal tab to shift into reverse.
No possibility to nicking reverse.

My main concern is there will be four of us driving.
Three of us know how to baby a transmission, one of us does not.
I have spares, and I would build at least two transmissions for this....

So, given what we know about the weak point, any suggestions?
I am thinking about going to foley to get him to do his custom shaft with a smaller second gear, so no need for first.
Then a small 3rd and fourth gear...
Maybe three speed tranny.
I may limit the top end speed, but it's not a top end type of course.
I was at the last race, and while you an get down the straight pretty fast, the remaining 75 percent of the course could be done in a stock third gear, except the downshift area that requires you to downshift and go up a hill at a 75 degree angle turn....and from what I saw, it gets three cars wide at this turn, so you do need to downshift.

I have done this course alone, and while you could do this corner in third, if you like siding, it works better in second.

My main concern is longevity
We need to make it at least one whole day with second still working
The aggresive shifting person will drive last, maybe.
But that might leave him stranded....cause Ike I said, there are three of us that could do this corner in third, but it would take some balls to do it....

classifieds

http://www.914world.com/bbs2/index.php?showtopic=225284

might work for you ? Bill D.

I appreciate the thought, and I know he is selling that, but it's not what we need here.
I have quite a few transmissions and I am capable of building one, just looking for some off the wall ideas to keep it alive for two days of getting beat up.

Typical failure at one of these things is the transmission, so I am trying to plan ahead a bit.

Rich

Can you change 2nd gear? I thought it was part of shaft. Isn't there an early 911 box with a removable 2nd gear? Isn't that the limitation with the 901?

Assuming all this is based on stock 914/4 ratios...

It sounds like a low gear in-between 2nd and 3rd would work well, so consider putting a 19:32 "H" in 3rd position. It was a stock 2nd gear in 4-speeds, but would be a 3rd gear in a 5-speed. You can use your existing "V" in 5th, and find an "O" for 4th gear. You would then run in 3rd-4th-5th, and have your stock 2nd as a back-up...

A-F-H-O-V

Jon B.
Vista, CA

since 2nd is not swappable, can you use only the locations for 3rd 4th 5th for a 1st 2nd 3rd, not use 1st or 2nd at all?

I would assume so.

then the questions is what gear ratios do you want and what gears or gear flipped would most closely to achieve this?

what are the weak points? cantilevered 1st gear?

** a smaller second (18:34) means using a 1st as a second it seems? cause none of the gears sets used from 3,4,5 have a gear with less than 18 teeth, probably because of the thickness of the shafts in this area. so if F is not low enough, seems you have no choice but a custom shaft that allows for second to be swappable to something between a stock 1st and a stock 2nd.

if you lathe, you'll need to lathe all the way to where stock third is on the output shaft?



integral 2nd gear

1st gear set

Second is part of the shaft.
You can put the shaft on a lathe and spin off the gear, then weld on whatever you want.
The 904 main shaft which Carquip has and Ottos Venice made a run of a while back( not sure of where those went) have a removable 2nd gear.

I had one of those shafts, but sold it to someone who really wanted it at the time.

I have a lathe, and tig, so I can do it if needed...and I might.

It's still in a bad place so I am thinking of putting a small 345 setup ( in those positions) but use a smaller gear than second...and go from there.

Just need a gear slightly smaller than second to get moving....then wind it up to get into the next gear.

Have you thought about change rear tires size to effect the ratio?

Btdt, it's not enough to get off the line in second without potentially killing the clutch....

Rich

Low buck solution would be to run short sticky tires and a really good clutch. Once your rolling your rolling. It's not stop light racing.

Have you thought about changing out one of the drivers?

I think these pics are of a 904 shaft with removable 2nd.

and one pic of stock shaft with a gear welded.

904 main shaft.
I had one and sold it a while back.
I can weld on what I need as LNG as I can find the right gear.

Ideally I would go to a three speed with a small gear in 3rd position...
It's a better place to start and reduces the risk of kissing reverse.

I could also leave 1st in place for pit traffic.

I think Rick might have part of the solution! just get a racing clutch that will last longer and go for it.
we will have spares

This is a 2 speed using the stock F second a starting gear......no trick clutch just a stock 911 set up. Starting was a piece of cake,with a 2.7L 6. The clutch held against 4K side step and 10 inch slicks.

A flipped ZD third gear is good for AX but not necessary for a track car.

You can figure what needs to be done from the pic. First (spacer for 1st) & reverse were eliminated.....no neeed for spacers for a 4 speed. .......
Click to view attachment

I have everything you need Rich.
I can tell you expected speeds and rpms for every turn at NHMS.
I ran with a 100hp engine for years there.
You want 4 usable gears with first only to get the car rolling and for driving around the paddock.

There is also a 901 mainshaft that has an A gear on it. It was used in the 4 speed 901 in the early 912.

That would give you a 4 speed using the same 3 other gears, and nothing on the shift plane with reverse.

I know, but can we make it idiot proof to last two days?

The box will handle continuous use behind 100hp, just not too much abuse.
I don't think that will be your weak point.

The weak point will be human, so we need to design around that.

At some point soon, I will pull the car out and strip it.
We can talk when we get there....it needs some steel....
And a cage
And........

Shift Linkage
Missed shifts will destroy the engine, not the gearbox.

It can destroy the gear box, hence the epression "Grind a pound for me"......unless you think that dog teeth, sliders & what not are free for the asking. In fact, most 914s cannot be down shifted into first gear at anything above an idle because the above are toast. When I tell folks that my trans could do the trick at any rpms they think I'm BSing them.

I will admit that painless shifts of a 901 is an art form.

True, and I had not thought about your setup....
That may get use past the issue.
one of the drivers will not miss a shift, but he will (as JP says) jam that shifter in no matter what force it takes.....he gets a bit high strung.....and he is a key part of this cause it's my kid.....
The other two are both long term racers, no worries there.
Me, I never grind that car....I know the pause...I am a third gear sliding driver....