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914World.com _ 914World Garage _ Regearing for a longer 5th gear
Posted by: SGB Nov 28 2006, 08:14 PM
I'm getting a tranny for christmas! 
no really, DR EVIL is rebuilding the ol' 901 for me, and I've been thinking
with my brain that a longer 5th gear would be really nice.
With a speed limit of 70 (usually traveled by EVERYONE at 80), my car gets pretty buzzy after a while.
I know it can be done, and if I ever was going to do it....
A flipped 904 "I" 5th gear might work.... of course I've already been advised that cubic dollars are needed AND another mainshaft.
I'm just dreamin'... Somebody slap me with a reality stick. What else would be involved in this? Who has details? Or better, who has a 904 5th gear lying around needing a home?
Posted by: Aaron Cox Nov 28 2006, 08:15 PM
with at type 4 bad idea...
what size tires?
ZD with short tires should keep you in the 3000 rpm range at 70...
bad idea
Posted by: Aaron Cox Nov 28 2006, 08:16 PM
BTW - you flip a second gear from a 4 speed 901/902 to get a taller 5th
2nd in a 4 spd... is the same position as third in a 5 speed...
THUS the flipped 5th into 3rd for a short third (i love it)
what size tires? are you gonna make me post my chart again?
you wont cool well enough at high speeds without some rpm to turn the fan.....
Posted by: SGB Nov 28 2006, 08:17 PM
They are 50 series tires. Is ZD what is in there now?
Posted by: Aaron Cox Nov 28 2006, 08:19 PM
ya made me do it!
here is the chart i config'd for my motor/gears/tire size
grey shading is stock gears....
A F N V ZD
ill try and find the one with the flipped H,HA, and HB gears....
Attached thumbnail(s)
Posted by: SGB Nov 28 2006, 08:19 PM
I've alway had fine cooling, and could compensate with bigger main jets in the webers.I wanna see that chart? Is it big and UGLY? WIll it shut me up?
Posted by: SGB Nov 28 2006, 08:20 PM
AAAARGGHH!!!
Posted by: SGB Nov 28 2006, 08:21 PM
but
its
kinda
COOL.
Posted by: Aaron Cox Nov 28 2006, 08:22 PM
your head temps will go up with less RPM turning the COOLING fan 
Posted by: Dr Evil Nov 28 2006, 08:27 PM
ZD is what is in there now. I do not see how smaller tires will cause lower RPMs, Aaron 
If you put larger profile tires on your car you will lower your RPMs, not the other way around. Like a said before, you should be at 4000rpm at 89MPH in stock form. the 50 series tires should only bump the RPMs up a bit. Our engines are not like the water cooled type. Air flow is life, thus higher RPM under load at fast speeds = better cooling and less fatigue on your engine. This is why long hills on hot days are particularly bad for our cars (more so than many other scenarios). Lots of demand, hard to keep up RPMs AND speed. If you want to know what it will be like to drive with a taller fifth gear just go for a long drive up a steep hill 
<:edited because Aaron posted the damn chart first 
:>
Posted by: Aaron Cox Nov 28 2006, 08:29 PM
ZD is what is in there now. I do not see how smaller tires will cause lower RPMs, Aaron
If you put larger profile tires on your car you will lower your RPMs, not the other way around. Like a said before, you should be at 4000rpm at 89MPH in stock form. the 50 series tires should only bump the RPMs up a bit. Our engines are not like the water cooled type. Air flow is life, thus higher RPM under load at fast speeds = better cooling and less fatigue on your engine. This is why long hills on hot days are particularly bad for our cars (more so than many other scenarios). Lots of demand, hard to keep up RPMs AND speed. If you want to know what it will be like to drive with a taller fifth gear just go for a long drive up a steep hill Here is Aarons chart for those of you watching at home and wandering where we pull these numbers from
taller gear = less rpm.
less rpm = less cooling.
shorter tire = MORE rpm
i dont think i said that mike....
Posted by: SGB Nov 28 2006, 08:32 PM
I'm trying to grasp this with my little tuna-like brain and I gotta ask- the colored bands- yellow is 50 series? At 5K? OK, the flipped 904 2nd gives a 0.61 in place of 0.71 for the ZD. That doesn't seem too drastic...
(I'm a stubborn ol' fishhead)
Posted by: Dr Evil Nov 28 2006, 08:33 PM
Now now Aaron, dont get testy I reread your post and relized what you were saying with the 3K at 70mph and 50 series tires.
Posted by: Aaron Cox Nov 28 2006, 08:34 PM
click the picture... it gets bigger...
if you look at the top.. you can see it is setup for a 23.59" tire.... (225/50/15)
and a 205 50 is slightly smaller 23.0" so the rpms will be SLIGHTLY more than what is pictured....
Posted by: SGB Nov 28 2006, 08:45 PM
Of course I realize you know what you are talking about (both of ya). It is just a pipe dream
The 50 tires cretainly seemed to make a profund impact on the admitidly already innacurate speedo readings-
Posted by: Aaron Cox Nov 28 2006, 09:10 PM
Of course I realize you know what you are talking about (both of ya). It is just a pipe dream
The 50 tires cretainly seemed to make a profund impact on the admitidly already innacurate speedo readings-
9% shorter than stock....
the MPH's on the chart are ACTUAL speed... not indicated
your speeds will be 1-2% lower than the chart.. (same as saying your RPM's will be a few% higher at the same speed)
Posted by: jwalters Nov 28 2006, 09:15 PM
Can first gear be flipped for a new fifth??
Posted by: Aaron Cox Nov 28 2006, 09:18 PM
no bozo
you have a few choices for first gears
A
AA
B
C
D
A is stock on most 911's and all 914's
AA harder to find... a few hundred bucks...
B/C/D hens teeth. good luck with that.
Posted by: Dr Evil Nov 28 2006, 09:18 PM
Nope. I was wondering the same thing once, but you would have to machine it and I do not think that there would be enough meat.
Posted by: jwalters Nov 28 2006, 09:18 PM
I clicked the picture - it got smaller.
Couldn't read it anymore.
Even with my coke bottle glasses and nose plastered on the screen.
I really gotta learn 'puters.
So, how again do you get a taller fifth? You guys lost me -
Posted by: Dr Evil Nov 28 2006, 09:20 PM
Change the gears.
Posted by: Aaron Cox Nov 28 2006, 09:21 PM
taller 5th....
the ratio of a gear is X:Y. you want something 'overdive' under 1:1 ratio... (less tan 1.00)
so if yo take a an H gear...
19:32...
and you flip the ratio (32:19) what is your outcome? way lower than a 1:1 ratio
Posted by: jwalters Nov 28 2006, 09:22 PM
What would you think the overall spacing would be (assuming a stock geared tranny) by using a 26" dia. tire.
Kinda like the 2005 caddie down the street from me with 23's on it and 30 series....
That thing has more ground clearance than a hummer........ 
Posted by: jwalters Nov 28 2006, 09:23 PM
taller 5th....
the ratio of a gear is X:Y. you want something 'overdive' under 1:1 ratio... (less tan 1.00)
so if yo take a an H gear...
19:32...
and you flip the ratio (32:19) what is your outcome? way lower than a 1:1 ratio
Stock tranny has an "H" gear?? - or is that the one everybody covets??
Posted by: Dr Evil Nov 28 2006, 09:23 PM
H gear from a 912 tranny
Posted by: Aaron Cox Nov 28 2006, 09:26 PM
read the posts...
GREY outline is stock 914 gears....
mike... stop selling our sources out! LOL
Posted by: jwalters Nov 28 2006, 09:27 PM
What would you think the overall spacing would be (assuming a stock geared tranny) by using a 26" dia. tire.
Kinda like the 2005 caddie down the street from me with 23's on it and 30 series....
That thing has more ground clearance than a hummer........
Oh, the reason I ask this is beacuse the suspension could be lowered enough in the rear to not have ass high look -
Also, back in my days street rods and sports car addicts had the need to put on larger diameter rears and keep small diameter fronts ( like the 70's - 80's LOLA'S) This actually looks really, really good onclassic sports cars!!
Think about it: matching rims with 15's on front and 21 -22's on the back and a level chassis - looks really cool and would help some with overall ratio I know - just by how much I do not---
Posted by: jwalters Nov 28 2006, 09:28 PM
H gear from a 912 tranny
Does it matter which year tranny???
Posted by: jwalters Nov 28 2006, 09:30 PM
GREY outline is stock 914 gears....
OHHHHHHHHH!
Posted by: jwalters Nov 28 2006, 10:02 PM
Posted by: 914fan Nov 28 2006, 11:21 PM
Has someone mentioned or can it be done?
Flip "K or J" gear for a .7 or .677 in fifth. only slightly less rpm.
Less rpm = less cooling. However the cars were designed for a 55mph speed limit. In 4th thats a little over 3k and 5th is 2.5k. 80 is almost 5K in 4th and 4K in 5th. I would like 2-3 hundred rpm less at 80 if it were resonably possible. If you were running a larger, stronger, more efficient motor, that should not be a problem. If you built something with "nikies" and modern FI it could probably be just fine with even lower rpms.
Just my 2 cents
Posted by: Aaron Cox Nov 28 2006, 11:26 PM
you can only flip 3rds to 5th's.... and 5ths to thirds....
or if you have a 904 mainshafts.. 2nd's to 4ths' and 4ths to seconds...
now you have to find the gears....
Posted by: Dr Evil Nov 28 2006, 11:31 PM
Has someone mentioned or can it be done?
Flip "K or J" gear for a .7 or .677 in fifth. only slightly less rpm.
Less rpm = less cooling. However the cars were designed for a 55mph speed limit. In 4th thats a little over 3k and 5th is 2.5k. 80 is almost 5K in 4th and 4K in 5th. I would like 2-3 hundred rpm less at 80 if it were resonably possible. If you were running a larger, stronger, more efficient motor, that should not be a problem. If you built something with "nikies" and modern FI it could probably be just fine with even lower rpms.
Just my 2 cents
K and J are second gears and would only be possible if you could find them and a 904 shaft to use them with ($$$$).
Your car works harder at higher speeds (thats why it takes more gas usually) so you will make more heat. If you want to put nikies on and do enhancements then you change the whole conversation.
Posted by: bernbomb914 Nov 29 2006, 01:11 AM
could you build a trans with this ratio
C
I
R
Y
HD
I have all but the I ratio's in my booty and would like to build this to go with my 78x104 engine.
Bernie
Posted by: SGB Nov 29 2006, 10:36 AM
![popcorn[1].gif](style_emoticons/default/popcorn[1].gif)
Posted by: Aaron Cox Nov 29 2006, 10:52 AM
could you build a trans with this ratio
C
I
R
Y
HD
I have all but the I ratio's in my booty and would like to build this to go with my 78x104 engine.
Bernie
you would need a 904 splined mainshaft to put an I on there.... (or you would have to cut old gear off and weld on a new one...ask brant)
Posted by: bernbomb914 Nov 29 2006, 01:23 PM
what is close to I that would fit or what would you recomend in place of I
Bernie
Posted by: bondo Nov 29 2006, 02:12 PM
what is close to I that would fit or what would you recomend in place of I
Bernie
The F is part of your mainshaft. You can't change it using any traditional means. Either learn to love the F or find an I mainshaft. (good luck)
Posted by: bondo Nov 29 2006, 02:16 PM
K and J are second gears and would only be possible if you could find them and a 904 shaft to use them with ($$$$).
H is a second gear too. You would only need a K or J made for a 902. I have no idea if such a thing exists though.
Posted by: Dr Evil Nov 29 2006, 02:40 PM
Ya, but he was just asking about swapping in a K or a J and those require the same thing as an H (as stated, 904 shaft). It looks as if I need to get a picture laden thread about what a swap is and why it can be a bitch started some time in the near future. 
Its not like I dont have a bunch of parts
Scott, your stack is on my front stoop. I'll gat a look at it as soon as possibel so we can start spending your money on replacement parts
Posted by: bondo Nov 29 2006, 02:47 PM
Ya, but he was just asking about swapping in a K or a J and those require the same thing as an H (as stated, 904 shaft).
He's talking about flipping it and using it as 5th. You don't need a 904 shaft for that.
Posted by: Dr Evil Nov 29 2006, 03:17 PM
Ah ya, maybe I need pics. I get it now, Royce. Its hard to halfass tranny talk of this nature. Next I'll be telling you that you need to perform a sphincterotomy and an endoscopic retrograde cholangiopancreatography if you want to get a taller 5th gear and remove the gall stone obstruction
I kind of like spelling poorly, it makes people nervous regarding my medical abilities 
Posted by: bernbomb914 Nov 29 2006, 03:27 PM
Is the main shaft in a 4 speed sportomatic the same as a 904? or could it be used in a 901? someone out there knows
Bernie
Posted by: bondo Nov 29 2006, 03:32 PM
I kind of like spelling poorly, it makes people nervous regarding my medical abilities
Have you mastered the "doctor's scribble" yet?
Posted by: Dr Evil Nov 29 2006, 03:51 PM
Is the main shaft in a 4 speed sportomatic the same as a 904? or could it be used in a 901? someone out there knows
Bernie
Bernie,
Some day soon I may have an answer for you
, but not at the moment.Royce, I always wrote that way
Posted by: bd1308 Nov 29 2006, 04:12 PM
lol doctor scribble. My dad is a MD (oral surgeon) and I cant read ANYTHING he writes, even shopping lists.
I feel sorry for the pharmacist 
Posted by: SGB Nov 29 2006, 06:17 PM
Scott, your stack is on my front stoop. I'll gat a look at it as soon as possibel so we can start spending your money on replacement parts
LOL
Posted by: Aaron Cox Nov 29 2006, 06:24 PM
Is the main shaft in a 4 speed sportomatic the same as a 904? or could it be used in a 901? someone out there knows
Bernie
Bernie,
Some day soon I may have an answer for you
, but not at the moment.Royce, I always wrote that way
To catch the line drive that went through my other fielders royce and mike...
a sporto 4 speed had a removable second gear... because that is the position of a third in a 5 speed....
a 904 mainshaft hs NO GEAR on it... where your stock F or GA (/6) mainshafts have a big gear on em...
a 904 is SPLINED to accept a removable second gear.
Posted by: bondo Nov 29 2006, 06:32 PM
a 904 is SPLINED to accept a removable second gear.
And from what I understand, those splines are different than the rest of the splines, requiring special gearsets made for that position.
Posted by: Aaron Cox Nov 29 2006, 06:47 PM
didnt know that....
time to call otto
Posted by: Dr Evil Nov 29 2006, 07:53 PM
I dont know any of this. So far my swapping has been a little more on the mild side with stock 2nd. I do have a 5 speed 912 tranny to tear down and photograph before figureing out what I want to do with it. It ought to prove educational for many. Then there is the sporto that I need ot pick up, and the 923, 915 and 930. Gonna be busy with the camera this holiday season
Posted by: lybones Nov 29 2006, 11:55 PM
Okay, where can I get one of these "taller" 5th gears for my v8 teener. My wife tells me to drive my Toyota Tundra instead of the 914 to "save" on gas.
Posted by: bd1308 Nov 30 2006, 12:23 AM
I really need to figure out how to get a sporto bug tranny into my 914.
Posted by: Aaron Cox Nov 30 2006, 12:27 AM
I really need to figure out how to get a sporto bug tranny into my 914.
that was an autostick...
why not use a sportomatic from a 911?
but why????
4 gears vs 5... most likely less overdrive....
Posted by: bd1308 Nov 30 2006, 01:48 AM
sporto 911 = 901-ish tranny?
Posted by: Racer Chris Nov 30 2006, 08:15 AM
Installing an I gear on the mainshaft isn't really that difficult (for an experienced fabricator, lol). I did it for my race box last year.
1) grind the F gear down, don't let the shaft get hot.
2) turn the shaft to the correct dia for the new gear
3) I built up 4 splines onto the mainshaft so the gear welds would not take all the load.
4) carefully weld the gear in the correct position - don't let it get too hot!
Now I need a C or D first gear.
Posted by: Dr Evil Nov 30 2006, 10:30 AM
Installing an I gear on the mainshaft isn't really that difficult (for an experienced fabricator, lol). I did it for my race box last year.
1) grind the F gear down, don't let the shaft get hot.
2) turn the shaft to the correct dia for the new gear
3) I built up 4 splines onto the mainshaft so the gear welds would not take all the load.
4) carefully weld the gear in the correct position - don't let it get too hot!
Now I need a C or D first gear.
Ya, simple for Chris the welding magician
Some day I may have the set up to mess with such things, but not now.For H gears I have heard that Otto's in Venice,CA can source them for you. Also you may try GPR (call them), or Raby may have one.
Posted by: bondo Nov 30 2006, 10:52 AM
Installing an I gear on the mainshaft isn't really that difficult (for an experienced fabricator, lol). I did it for my race box last year.
1) grind the F gear down, don't let the shaft get hot.
2) turn the shaft to the correct dia for the new gear
3) I built up 4 splines onto the mainshaft so the gear welds would not take all the load.
4) carefully weld the gear in the correct position - don't let it get too hot!
Now I need a C or D first gear.
What the heck did you use to turn it down? I tried machining one of these shafts with a carbide tool and it ate it. I assume this would be easier to do with an A mainshaft, since there's a lot less gear to take off. How hot is too hot?
Posted by: Racer Chris Nov 30 2006, 01:07 PM
What the heck did you use to turn it down? I tried machining one of these shafts with a carbide tool and it ate it. I assume this would be easier to do with an A mainshaft, since there's a lot less gear to take off. How hot is too hot?
The only part of the shaft that is real hard is the outer skin. That's typical of parts that need good wear properties combined with strength and toughness. After grinding off the gear teeth with a belt grinder the interior cuts pretty easy.
Too hot is when the metal starts to turn color. Anything beyond a light straw color is the end of whatever heat treat properties were done at the factory.
Posted by: jwalters Nov 30 2006, 04:27 PM
Two questions please:
1: Would someone please give me the formula for figuring out final drive ratio vs. tire diameter.
2: Could someone post an exploded view of the 901 - one from a manual is fine, but actual pics would go even further.
Jonathan
Posted by: Dr Evil Nov 30 2006, 04:37 PM
If you search the links in my sig you can find some good pics of the tranny. Also try the links in the thread, and onthe pelican site.
Posted by: JPB Nov 30 2006, 05:07 PM
Doing the trany thing is cool but what about putting a real engine that redlines at 10K?
Posted by: Racer Chris Nov 30 2006, 05:19 PM
Doing the trany thing is cool but what about putting a real engine that redlines at 10K?
High rpm engines are great for peak horsepower but generally suck at making torque.
Posted by: smontanaro Nov 30 2006, 09:31 PM
2: Could someone post an exploded view of the 901 - one from a manual is fine, but actual pics would go even further.
http://www.partpricer.com/ has lots of diagrams.
Skip
Posted by: 356&914&912E Dec 1 2006, 10:38 AM
FYI
http://www.carquip.com/parts/911/trans/gears/901gears/index.asp
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