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18 spline input shaft diameter ? #2447330
02/06/18 12:32 PM
02/06/18 12:32 PM
Joined: Sep 2003
Posts: 19,237
north of coder
moparx Online content OP
"Butt Crack Bob"
moparx  Online Content OP
"Butt Crack Bob"

Joined: Sep 2003
Posts: 19,237
north of coder
this is a really stupid question, so please, just consider it from my "old timers" diseased mind ! what is the spline diameter of the 18 spline shaft ? here is the reason for asking. sunday, a buddy showed up with a plastic pilot tool that had 18 splines. however, it was just a tick over 5/8" in diameter, and the pilot was only about 7/16". neither one of us has a transmission, but i said it looked way small, i "thought" it [the spline] should be closer to 1" or so ? i tried the google, but didn't have any luck. so, help this dum old guy out, please ? TIA as always !
beer

Re: 18 spline input shaft diameter ? [Re: moparx] #2447427
02/06/18 03:56 PM
02/06/18 03:56 PM
Joined: Jun 2004
Posts: 1,672
Virginia
HemiStan Offline
top fuel
HemiStan  Offline
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Posts: 1,672
Virginia
I just measured across the splines of my 18 spine transmission input shaft and across the splines of a plastic 18 spline alignment tool. Both are measuring right about 1 5/32".

Stan

Re: 18 spline input shaft diameter ? [Re: moparx] #2447519
02/06/18 06:34 PM
02/06/18 06:34 PM
Joined: Jan 2003
Posts: 25,618
Rio Linda, CA
John_Kunkel Online content
Too Many Posts
John_Kunkel  Online Content
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Rio Linda, CA
The official input shaft spline dimension is 1-3/16 x 18T.


The INTERNET, the MISinformation superhighway
Re: 18 spline input shaft diameter ? [Re: moparx] #2447601
02/06/18 08:36 PM
02/06/18 08:36 PM
Joined: Dec 2004
Posts: 350
Houston
I
it's Bob Offline
enthusiast
it's Bob  Offline
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Joined: Dec 2004
Posts: 350
Houston
HemiStan "missed it by that much"....Holding fingers 1/32" apart.



Better than I could measure, probably.

Last edited by it's Bob; 02/06/18 08:38 PM.
Re: 18 spline input shaft diameter ? [Re: it's Bob] #2447647
02/06/18 09:38 PM
02/06/18 09:38 PM
Joined: Jan 2003
Posts: 16,376
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dogdays Offline
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Posts: 16,376
If the splines are the same diametral pitch then the diameter corresponds to number of splines linearly.

If, however, the diametral pitch is changed then you have things like the larger diameter shaft with fewer splines. A prime example of this is on GM and Ford input shafts. A common style is 10 splines. The Ford is 1 1/16" diameter, the GM is 1 1/8", and there are trucks with 10 splines with input shaft 1 3/8". Each example is using a different diametral pitch when they design the splines.

We're luckier when it comes to axles, because MOST of the popular axles use the same diametral pitch. So in general, we know that a 29 spline axle is stronger than a 27 spline and weaker than a 30. This is disregarding the strength of the axle material, of course. However the strength of the axle in torsion increases by the cube of the increase in diameter, so you can see that increasing from a 27 spline to a 31 spline increases strength by 51%.

Had enough?

R.

Re: 18 spline input shaft diameter ? [Re: dogdays] #2447679
02/06/18 10:09 PM
02/06/18 10:09 PM
Joined: Jul 2011
Posts: 953
Chicago
PurpleBeeper Offline
super stock
PurpleBeeper  Offline
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Posts: 953
Chicago
Originally Posted By dogdays
If the splines are the same diametral pitch then the diameter corresponds to number of splines linearly.

If, however, the diametral pitch is changed then you have things like the larger diameter shaft with fewer splines. A prime example of this is on GM and Ford input shafts. A common style is 10 splines. The Ford is 1 1/16" diameter, the GM is 1 1/8", and there are trucks with 10 splines with input shaft 1 3/8". Each example is using a different diametral pitch when they design the splines.

We're luckier when it comes to axles, because MOST of the popular axles use the same diametral pitch. So in general, we know that a 29 spline axle is stronger than a 27 spline and weaker than a 30. This is disregarding the strength of the axle material, of course. However the strength of the axle in torsion increases by the cube of the increase in diameter, so you can see that increasing from a 27 spline to a 31 spline increases strength by 51%.

Had enough?

R.


Or in other words....some of the Centerforce clutch kits & tools have 18 splines & come up in a search for "70 Road Runner" but are the wrong diameter... ask me how I know.

Another thing to consider is that my eyes aren't good enough to determine the pitch of splines...so I just count them....stupid non-bionic eyes


70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"
Re: 18 spline input shaft diameter ? [Re: moparx] #2447683
02/06/18 10:11 PM
02/06/18 10:11 PM
Joined: Feb 2012
Posts: 637
SoMd, USA
1
135sohc Offline
mopar
135sohc  Offline
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Posts: 637
SoMd, USA
The 1990 and older FWD manual transmissions in the K based cars are about 5/8" across and 18 spline input.

Re: 18 spline input shaft diameter ? [Re: 135sohc] #2447932
02/07/18 11:31 AM
02/07/18 11:31 AM
Joined: Sep 2003
Posts: 19,237
north of coder
moparx Online content OP
"Butt Crack Bob"
moparx  Online Content OP
"Butt Crack Bob"

Joined: Sep 2003
Posts: 19,237
north of coder
Originally Posted By 135sohc
The 1990 and older FWD manual transmissions in the K based cars are about 5/8" across and 18 spline input.


i said it was more than likely a front drive tool, but i didn't have a clue what brand or model. thanks john k for the answer ! up
beer

Re: 18 spline input shaft diameter ? [Re: moparx] #2447948
02/07/18 12:16 PM
02/07/18 12:16 PM
Joined: Dec 2004
Posts: 10,549
Rittman Ohio
fourgearsavoy Offline
I Live Here
fourgearsavoy  Offline
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Joined: Dec 2004
Posts: 10,549
Rittman Ohio
Yeah just type in "18 spline" on E-bay and you come up with lug nuts,boat props,and spindles then a few Mopar related items sprinkled in there laugh2

Gus beer


64 Plymouth Savoy
493 Indy EZ's by Nick at Compu-Flow
5-Speed Richmond faceplate Liberty box
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