Taller gears for '74 tranny

[LouisCypher]

Hi Folks,

does anybody know where I can get taller gears for my '74 914 tranny?

Cheers,

Louis

[BigD9146gt]

you have PM

[Dave at Pelican Parts]

The easy way is to get larger wheels and tires. The stock tires were "about" 25.4 inches in diameter. If you get a wheel/tire combo that is 10% larger than that, your effective gearing is 10% taller.

The hard way can get really really expensive.... 2nd gear is a part of the main-shaft in these transmissions, so you have to replace it with the "904 mainshaft", which is a very pricey part. If you don't want to pop for that, then you're pretty much stuck with the stock 1st and 2nd gears. Other gearsets can be swapped around, and you can even "flip" them so the drive gear is the driven gear and the ratio is inverted.

A list of the different gear ratios that have been made for the 901-based transmissions (like ours) can be found at:
http://members.rennlist.com/chuxter/901&915ratios.htm

Many of those ratios are now quite hard to find. Paul Guard at Guard Transmission ( http://www.guardtransmission.com/ ) can supply you with most of them, but the cost for many of them is pretty steep.

--DD

[J P Stein]

Originally posted by BigD9146gt
you have PM

Don't be sellin' that 901 B first gear to anyone but me, damnit.

[LouisCypher]

Thanks to you all for the infos.

I was planning to change the ratios of the 3th, 4th, and 5th gears only, to be able to drive fast without too much rpm.

Does that mean that I can use the gear sets of the 915 trannys? These seem to be the only ones to have taller gear sets than the 901 tranny?

Thx,

Louis

[norustscott]

remember, RPM = cooling. Reduce the RPM too much and you will begin to overheat...RPM also = overheat... There is a fine range that the engine will operate correcty. Do your home work before making too drastic a change...

[skline]

Carquip and Powerhaus II both sell gears and gear sets for the Porsche transmissions.

[BigD9146gt]

Originally posted by J P Stein
Don't be sellin' that 901 B first gear to anyone but me, damnit.

*****, you made me spit my OJ all over the screen. Thats funny dude.

You still want it? I'm going to go with the stock first.

[Dave at Pelican Parts]

Originally posted by LouisCypher
Does that mean that I can use the gear sets of the 915 trannys?

Nope. The shaft spacing on the 915 is different than the 901, so the gears are the wrong sizes to fit.

You can, however, "flip" the gearset and invert the ratio. For instance, an "H" 3rd gear can be run "backwards" (swap which gear goes on which shaft) so the ratio is 32:19, or 0.597 ; noticeably taller than the stock 5th gear.

--DD

[marks914]

Here is a recent thread on tall gears for the 901. Its from the "other "board. Just put the tall gears in mine and it make the car drive much better. Much better spacing for the V8.

http://www.914club.com/bbs2/index.php?act=ST&f=2&t=24118&

Mark
72 914 5.0L

[914gem]

Is a 904 an early 911/912 4 speed? What is a 901 B first gear and ratio? If someone had boxs of gears, how would they tell what gears they are?

[Bleyseng]

A 904 is from the 904 race cars that had the removeable 2nd gear mainshaft. It is made by a couple of companys today. The gear pairs have letters stamped on them but...its easier to count the teeth to determine what you have. Zip tie the gear "sets" together! Somewhere on this site I think is the gear chart so you can see the ratios. All 914 trannys are the same gearing. 914/6's are alittle different. 911/912 have different gears sets.

Geoff

[914gem]

Thanks Geoff for the info, it will come in handy next week when I start going through my engines and trans stuff.

[LouisCypher]

Thanks again for the infos.

But I think that 0.597 would be way too tall for, let's say, a big four (that would give 146 miles/hour at 5000 r.p.m. ;-)). That ratio is maybe OK for a V8...


Louis

[red-beard]

mittelmotor in Germany has gear sets.

[LouisCypher]

does anybody run 0,597 in 5th?

Louis

[Dave at Pelican Parts]

Umm, Louis... The 0.597 was simply an example, and probably about the most extreme one I could find. Check the other gears available, and see what ratios you get when you invert the numbers. You may find something you like.

--DD