axle ratio

[vdubrookie]

OK all you transaxle gurus, I have question. Im trying to determine my axle ratio without a lot of disassembly to count teeth. I have a '67 swing axle setup in my sand rail. I jacked up the left rear tire, got my crank pulley at TDC, put the trans in 2nd gear & marked the tire w/paint stick. I turned the crank pulley until the tire made 1 revolution while counting the number of turns the crank pulley turned and came up with approx. 4 3/4 turns. this makes no sense to me as it doesn't match with any chart or post I have been able to find on this subject. It is almost half the revs that I have been finding. So what is my ratio or what am I missing here? TIA

[tcoop1100]

I don't have your answer but shouldn't your tire circumference be part of the equation? Maybe that's what is throwing off your calculation.
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January '57 Sedan, April '64 40hp big bore

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You need to have both wheels in the air, and both turning in the same direction. You need to count the revolutions of the differential only. With only one wheel moving, you are also entering in the ratio of the differential side gears/spider gears. With the transaxle in 2nd gear, 8.5 crank revolutions will turn both tires in the same direction once if you have a 4.12 r&p from a 67.

[vdubrookie]

Racer Dave said to do it exactly as I did but he came up with different revolutions. Something is getting lost in the math here I think.

[vdubrookie]

Troop, regardless of the tire diameter the shaft s only making 1 revolution.

[modok]

4.75x2(differential)/2.06(second gear)=4.6 final drive ratio

Common 4.125 final drive would be 4.25 engine revs

Assuming second actually is 2.06...and it usually is, but what if it isn't?

Do all the gears then maybe it will make more sense.

[mukluk]

[modok]

[modok]

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[vdubrookie]

Re-read the third line please. It says"To determine what Ring & Pinion you have, put the trans into 2nd gear and count the number of turns you spin the input shaft (clutch disc) to get the drive axle to turn one complete turn. Use a piece of tape or marker to get a reference point.
3.875 R&P will take 8 turns
4.125 R&P will take 8 1/2 turns

Now put into 4th and count the number of turns on the input shaft to get 2 complete turns of the drive axle. Now divide the number of turns of the input shaft by your R&P gear and divide that by 2, any you should have your 4th gear ratio.

[vwracerdave]

That response was 14 years ago, and may not be accurate. I have learned things and I have forgotten thing in the last 14 years.
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2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[vdubrookie]

Dave, so how would you go about this process today then, please.

[vdubrookie]

OK, still same procedure, one wheel down, other wheel up, 4 3/4turns for one wheel revolution, 9 5/8 turn for two revolutions, any guesses as to what my rear axle ratio might be? This still isn't coming out right. What's the next higher numerical VW ratio available after 4.37?

[madmike]

5:13
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[modok]

about 9.625,,,,,so

2.21 second and 4.375, would be would be 9.67 turns
2.35 second with 4.125 would be 9.69

2.33 and 4.125 would be 9.61
2.47 and 3.875 would be 9.57

[vdubrookie]

My notes from the PO state that my gearbox was bult by Leduc Racing Components in Midland, Mi & that it has close ratio 3rd & 4th. It also has billet side cover & dual snap rings in the carrier. What are the typical 3rd & 4th gear ratios in a box like that. I know your crystal balls are broken at the moment, just wondering what is typically used in a slightly modified trans like this.

[modok]

Fourth is usually between 1.04 and 1.32
I think you have a 1.21 fourth
Check third and first too

[vdubrookie]

Thanks Modok, I'm getting about 50-51 in 4th gear at 3000 rpm according to my speedometer on my iPhone if that makes it any clearer.

[vdubrookie]

Sorry to keep dragging this out but I keep coming up with new questions. Ok, I have determined thru various calculators & math based on input revs for 1 tire revolution divided by 2 since one wheel is locked that I might have trans ratios as follows; 4th gear 2.5 turns =1.21
3rd gear3.44 turns =1.67
2nd gear 4.75 turns = 2.31
1st gear 7.75 turns= 3.76
ring& pinion ratio 4.125 = 50mph@3000RPM - 28.3 tire height
The question now is how many if any of these gear ratios are possible & available for a swing axle transmission or are my calculations completely fictitious? Thanks.