Help figure out ratios

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Dorian

Dorian

dorian
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Hi everyone,

Can anyone help me figure out my gear ratios in my 18 spline hemi 4 speed?


chooch said:
whats the gear set up in this 4 speed?
Click to expand...
Hey chooch

Ran it thru each gear and came up with these counts on each shaft. I rotated the front spline once and counted the splines from start to finish On the back spline.

Total teeth input and output shaft: 18 teeth - 30 teeth


1st gear: 18 - 12
2nd gear: 18 -17
3rd gear: 18 - 24
4th gear: 18 - 30
 
Dorian said:
Hi everyone,

Can anyone help me figure out my gear ratios in my 18 spline hemi 4 speed?



Hey chooch

Ran it thru each gear and came up with these counts on each shaft. I rotated the front spline once and counted the splines from start to finish On the back spline.

Total teeth input and output shaft: 18 teeth - 30 teeth


1st gear: 18 - 12
2nd gear: 18 -17
3rd gear: 18 - 24
4th gear: 18 - 30
Click to expand...

You've got some'thin screwed up because 1st should have the greatest difference number of tooth count from one to the other. . Fourth gear is a straight through coupling, unless it's an OD (impossible, I think? on an 18 spline) in which case 3rd on the shifter, but really the same gear, is coupled.

So mathematically, all you do is divide one tooth count by the other, so your numbers are

1st is 1.5:1

2nd is 1.05:1

3rd is 1.33:1

4th is 1.66:1

So something is seriously wrong with "how" you counted. You have to figure the input shaft mating the cluster----how many teeth are those two?

And then figure that with the ratio of the other gears. But there IS NO tooth count for 4th, so I have no idea what it is that you are actually counting.

Here's a diagram:

Look at part labeled 31 and 51. You have to count those two mating gear teeth. That is, the largest gear on the front of the cluster

Then starting at the REAR of the cluster (part label 51) You have in order 1st, the reverse is the only "straight cut", then 2nd, then 3rd. So you have to count those teeth and the gears which mesh with them on the main shaft. Notice how the gears get larger from rear to front---the cluster will be spinning a lower (numeric) ratio, higher speed, with each gear.

So that's the part labeled

18--1st gear

9--2nd gear

42--3rd gear

19a20600.jpg
 
hi, according to mopar race manual, hemi is considered a course pitch gears.
std ratio was, 2.65, 1.93, 1.39. 1.00.other setup was , 2.44, 1.77, 1.34, 1.00.
red stripe set was, 2.65, 1.64, 1.19, 1.00.
2.44 set, d/p=22, 3rd=26, 2nd=30, 1st =33, on main shaft , counter shaft is, 26 direct, 23 3rd, 20 2nd, 16=1st gear.
2.65 setup, d/p gear 21, 3rd 26, 2nd =30, 1st =33 mainshaft, counter shaft is direct is 27, 3rd =24, 2nd =20, 1st =16, red stripe set , direct =21, 3rd=24, 2nd=28, 1st =33 main shaft , direct is 27, 3rd =26, 2nd =22, 1st =16, counter shaft.
 
Take all your observed tailshaft spline count numbers and divide them into 30...
 
Lets start over again I see where I may have been confusing.

there are 18 splines on the front shaft and 30 splines on the rear. I marked the spline at the top on both the front and rear.

So with the tranny in 1st gear I rotated the front shaft 1 revolution (18 splines) the rear shaft only turned 12 splines
30/12=2.5 to 1.0

2nd gear one revolution (18 splines) the rear shaft only turned 17 splines
30/17=1.76 to 1.0

3rd gear one revolution (18 splines) the rear shaft only turned 24 splines
30/24=1.25 to 1.0

4th gear one revolution (18 splines) the rear shaft turned 30 splines
30/30=1.0 to 1.0


a little crude without taking the whole thing apart but accurate enough.

so to break it down,

1st - 2.5 to 1.0 ratio
2nd - 1.76 to 1.0 ratio
3rd - 1.25 to 1.0 ratio
4th - 1.0 to 1.0 ratio


thanks everyone for their input.
 
Well I see what you are trying to do now, but you are doing it wrong. You should be turning the front shaft and counting splines, and turning the rear shaft ONE turn.

So working backwards from your figures for 1st gear, 1 turn at the front and 12/30 for the rear, this equates to 1: .4 and you need the "other way around."

This APPEARS to be a 2.66:1 first gear, which with your figures works out to 1.06 instead of 1. This COULD be because you made that much mistake when trying to count the splines.

What I would do for accuracy is turn the rear shaft either 5 or 10 turns and count the front. 10 turns would give you a "figure in your head, IE 10 at the rear is 26.5 at the front, so an easy 10:1 figure.
 
Let's keep this simple. If you want the exact ratios, pull the side cover and count the teeth. Let me know how many teeth on 4th gear of the cluster, then 3rd, then 2nd, and finally 1st. Then count the teeth on the input (4th gear), then 3rd, then 2nd. and finally 1st. Let me know the numbers and I'll give you the exact ratios.

Another not so exact way to do it, is to mark the output shaft and input shaft. I would recommend a yoke in the rear with a clutch disc on the input and a Sharpie to mark the yoke and the disc. Shift the trans in 1st, turn the output shaft 10 revolutions and count the number of turn on the input. If the input turns (as an example) 26.5 turns, the ratio for 1st is 2.65 to 1. You can do the same for second and third. It won't matter in 4th because the teeth physically don't even have to be there, the trans input will be locked up to the output via the hub and slider, but you have to have the numbers to find the spur ratio for the rest of the gear ratios.

If I've got you and others all spun out, PM me and I'll give you my number, it's easy once you figure it out.

Also, the "books" aren't always right. They (sometimes) don't carry the decimal point out far enough to get the ratios exactly right.

Russ.
 
The easiest method is to rotate and count the input shaft enough in each gear to turn the output shaft one time.

Don't have to take anything apart and will get you close enough to make a judgment.

This is close to is it a 3.54 or 3.55 gear... really? You won't notice the difference.
 
Thanks Cracked back



so then this is right



Dorian said:
Lets start over again I see where I may have been confusing.

there are 18 splines on the front shaft and 30 splines on the rear. I marked the spline at the top on both the front and rear.

So with the tranny in 1st gear I rotated the front shaft 1 revolution (18 splines) the rear shaft only turned 12 splines
30/12=2.5 to 1.0

2nd gear one revolution (18 splines) the rear shaft only turned 17 splines
30/17=1.76 to 1.0

3rd gear one revolution (18 splines) the rear shaft only turned 24 splines
30/24=1.25 to 1.0

4th gear one revolution (18 splines) the rear shaft turned 30 splines
30/30=1.0 to 1.0


a little crude without taking the whole thing apart but accurate enough.

so to break it down,

1st - 2.5 to 1.0 ratio
2nd - 1.76 to 1.0 ratio
3rd - 1.25 to 1.0 ratio
4th - 1.0 to 1.0 ratio


thanks everyone for their input.
Click to expand...
 
Backwards

Turn input shaft enough to turn output shaft 1 time. In first gear, you'll be turning the input at least 2 times.
 
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