How I adjust my 3-Speed
02-17-2009, 10:35 AM
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How I adjust my 3-Speed
I see a lot of posts concerning shift adjustment on the Savage 3-speed so I thought I'd make a post on the subject. It can be a real pain to adjust the 1-2 shift as you have to take the tranny apart. With the original 3-speed, you had to take the whole truck apart to get the tranny out. With the new one, you still have to take the tranny top off. The 2-3 shift isn't exactly fun either as it's fiddly working through the tranny housing opening. So I came up with another method. I'll rehash it here, and then go farther with some actual numbers.
What I wound up doing was to take the tranny shaft with the gears and shift dogs in it, and chuck it in a drill press (largest gear towards the chuck). There's not a lot of shaft to put in the chuck, so make sure it is tight and wear safety glasses. Increase the speed of the drill press until you it makes the shifts you want. Start out slow and gently hold the bottom two gears (they won't spin when you hold them). As the drill-press speeds up, they will engage and start spinning, so be gentle holding them.
The nice thing about this, is you can immediately tell if you are skipping the 1-2 shift and making a 1-3 shift only.
You need a variable speed drillpress or lathe (that can handle over 5000 rpm) as well as a tach (airplane infra-red type, for example) or a stroboscope (maybe borrow one from the local high school physics dept.) to check the rpms.
Now, if a person was to take a perfectly shifting tranny apart, check it out this way and record the numbers, he could easily readjust his tranny should it ever need it (crash damage, etc.) But I tried to claculate the numbers out.
I calculated them three different ways and used the method I like best. Here goes:
Preliminary Data:
1st gear: spur to wheel ratio of 8 (based on rolling the truck one tire revolution and counting spur gear revolutions.
2nd gear: Spur/Wheel ration of 6.39 (based on 18/44 first gear ratio and 21/41 second gear ratio)
3rd gear: Spur/Wheel ratio of 5.18 (based on 18/44 first gear ratio and 24/38 third gear ratio)
1-2 shift engine rpm reduction (assuming no wheelspin during shift) is 20.1%
2-3 shift engine rpm reduction (assuming no wheelspin during shift) is 18.9%
CB/Spur ratio is 17/47 or 0.361
Peak Horsepower is at 28,000 rpm (for OS 30VG)
Peak RPM is 36,000 rpm (for OS 30VG)
Tire Circumference measured at 18.5 inches (does not allow for ballooning at speed)
First 3-Speed Adjustment for Max Performance
This method accepts the fact that you always want to shift around max horsepower (which I don't like, but is a bona-fide test with full-size cars).
So for shifting around 28,000 rpm, we want the 1-2 shift to occur at ½ of the 20.1% change, which is at 31128 rpm. The 2-3 shift to occur at ½ of the 18.9% change which works out to 30922 rpm.
This translates through our tranny ratios to having 2nd gear kick in at an intermediate shaft speed of 4597 rpm and later having 3rd gear engage at a shaft speed of 5717 rpm.
If you do this, your engine will hit the screaming mark for every shift. Personally I don't like that.
Second 3-Speed Adjustment for Max Performance
This method says to shift when you hit max horsepower at 28000 rpm.
Multiplying 28000 by the CB/Spur ratio and the 1st gear ratio, we should adjust the 1-2 shift for 4135 rpm. Similarly , the 2-3 shift should be adjusted for 5177 rpm, (using the 2nd gear ratio). These are earlier shifts than the above method and seem to work the best so far.
3-Speed Adjustment for Max Fun
Let's suppose we want the truck to shift at certain speeds (mph) vs max engine power. For a max engine rpm (36000) we can calculate the vehicle speed at 43.9 mph. Now let's say the truck goes about 5 mph when the clutch is engaged. We have a total speed range of 38.9 mph to work with. Now let's have the 2 shifts spaced equally apart (13 mph spacing). This works out to a 1-2 shift at 18 mph and the 2-3 shift at 31 mph.
At 18 mph, the tire rpm is 1027 and the 1-2 shift can be adjusted for a shaft speed of 3362 rpm (the engine will be at 22759 rpm).
At 31 mph, the tire rpm is 1769 and the 2-3 shift can be adjusted for a shaft speed of 5791 rpm (engine speed will be at 31313 rpm).
I found this last method to give me a 1-2 shift too early and a 2-3 shift too late, but certianly other speeds (mph) could be chosen.
In the end, I found method #2 works the best. I deducted a few 100 rpm from each shift point as I don't have my engine tweaked for max HP (running rich for longevity). With my engine and my CB/spur ratio, I use 4000 rpm for the 1-2 shift point and 5000 rpm for the 2-3 shift point. Seems to work pretty well, although may not be quite perfect.
Anyway, the idea is it gets you close quickly and keeps the tranny dissasembly times to a minimum.
Did you read this far? Here's your reward, a very poor (dark at teh beginning) video on doing this....LOL:
http://www.youtube.com/watch?v=JtPNVlKo3DI
What I wound up doing was to take the tranny shaft with the gears and shift dogs in it, and chuck it in a drill press (largest gear towards the chuck). There's not a lot of shaft to put in the chuck, so make sure it is tight and wear safety glasses. Increase the speed of the drill press until you it makes the shifts you want. Start out slow and gently hold the bottom two gears (they won't spin when you hold them). As the drill-press speeds up, they will engage and start spinning, so be gentle holding them.
The nice thing about this, is you can immediately tell if you are skipping the 1-2 shift and making a 1-3 shift only.
You need a variable speed drillpress or lathe (that can handle over 5000 rpm) as well as a tach (airplane infra-red type, for example) or a stroboscope (maybe borrow one from the local high school physics dept.) to check the rpms.
Now, if a person was to take a perfectly shifting tranny apart, check it out this way and record the numbers, he could easily readjust his tranny should it ever need it (crash damage, etc.) But I tried to claculate the numbers out.
I calculated them three different ways and used the method I like best. Here goes:
Preliminary Data:
1st gear: spur to wheel ratio of 8 (based on rolling the truck one tire revolution and counting spur gear revolutions.
2nd gear: Spur/Wheel ration of 6.39 (based on 18/44 first gear ratio and 21/41 second gear ratio)
3rd gear: Spur/Wheel ratio of 5.18 (based on 18/44 first gear ratio and 24/38 third gear ratio)
1-2 shift engine rpm reduction (assuming no wheelspin during shift) is 20.1%
2-3 shift engine rpm reduction (assuming no wheelspin during shift) is 18.9%
CB/Spur ratio is 17/47 or 0.361
Peak Horsepower is at 28,000 rpm (for OS 30VG)
Peak RPM is 36,000 rpm (for OS 30VG)
Tire Circumference measured at 18.5 inches (does not allow for ballooning at speed)
First 3-Speed Adjustment for Max Performance
This method accepts the fact that you always want to shift around max horsepower (which I don't like, but is a bona-fide test with full-size cars).
So for shifting around 28,000 rpm, we want the 1-2 shift to occur at ½ of the 20.1% change, which is at 31128 rpm. The 2-3 shift to occur at ½ of the 18.9% change which works out to 30922 rpm.
This translates through our tranny ratios to having 2nd gear kick in at an intermediate shaft speed of 4597 rpm and later having 3rd gear engage at a shaft speed of 5717 rpm.
If you do this, your engine will hit the screaming mark for every shift. Personally I don't like that.
Second 3-Speed Adjustment for Max Performance
This method says to shift when you hit max horsepower at 28000 rpm.
Multiplying 28000 by the CB/Spur ratio and the 1st gear ratio, we should adjust the 1-2 shift for 4135 rpm. Similarly , the 2-3 shift should be adjusted for 5177 rpm, (using the 2nd gear ratio). These are earlier shifts than the above method and seem to work the best so far.
3-Speed Adjustment for Max Fun
Let's suppose we want the truck to shift at certain speeds (mph) vs max engine power. For a max engine rpm (36000) we can calculate the vehicle speed at 43.9 mph. Now let's say the truck goes about 5 mph when the clutch is engaged. We have a total speed range of 38.9 mph to work with. Now let's have the 2 shifts spaced equally apart (13 mph spacing). This works out to a 1-2 shift at 18 mph and the 2-3 shift at 31 mph.
At 18 mph, the tire rpm is 1027 and the 1-2 shift can be adjusted for a shaft speed of 3362 rpm (the engine will be at 22759 rpm).
At 31 mph, the tire rpm is 1769 and the 2-3 shift can be adjusted for a shaft speed of 5791 rpm (engine speed will be at 31313 rpm).
I found this last method to give me a 1-2 shift too early and a 2-3 shift too late, but certianly other speeds (mph) could be chosen.
In the end, I found method #2 works the best. I deducted a few 100 rpm from each shift point as I don't have my engine tweaked for max HP (running rich for longevity). With my engine and my CB/spur ratio, I use 4000 rpm for the 1-2 shift point and 5000 rpm for the 2-3 shift point. Seems to work pretty well, although may not be quite perfect.
Anyway, the idea is it gets you close quickly and keeps the tranny dissasembly times to a minimum.
Did you read this far? Here's your reward, a very poor (dark at teh beginning) video on doing this....LOL:
http://www.youtube.com/watch?v=JtPNVlKo3DI
