Gear ratio in transaxle how to calculate.

[trinity]

i'm new here, can anyone help me to teach how to get the overall gear ratio of transaxle. I know that in transmission you need to count the teeth of the driver and driven in input shaft and output shaft to get the transmission gear ratio of certain speed and multiply in differential gear ratio. How about in transaxle. Example I go in 1st gear, do i need to count the teeth of 1st gear then also the gear in intermediate shaft and also the differential gear ratio to find the overall ratio? because someone told me that you need to count only the gear in intermediate shaft then the differential gear ratio = overall gear ratio already. thanks help me.

[dragvw2180]

To really know what you have gear wise, I tear the tranny down, count both gears of each gear set and devide one into the other to get the actual gear ratio for that gear, do the same for all four. If you tell me what gears sets you have and also the R/P gears I can put it into a program I have which does all the work for me. If you want MPH in each gear also include tire height , an example is my slicks at 26 " . Hope this helps, Mike McCarthy

[Marc]

http://www.shoptalkforums.com/viewtopic.php?t=80760

http://www.shoptalkforums.com/viewtopic ... s#p1023296

[dragvw2180]

Marc , just like was stated in your post it will give you a general idea of final ratio but not an exact number. The example was the differance between a 3.80 and a 3.78 first gear set. I can guess at what gears are in a tranny by the year, but it is only a guess. Mike McCarthy

[frankysfree]

You can do it the easy way or the hard way. They make gear calculators you can find free online. When i did mine i took gear .89(fourth gear) and multiplied it by the R+P 3.88 which gives a final gear of 3.45

[frankysfree]

The math method ONLY works if you know what your gear ratios and R+P are already. Otherwise a teardown to visually check or you can do as others have stated and turn the input shaft and count the revolutions of the axle to figure it out.

[trinity]

thanks for the reply. can anyone tell me how to count the gear, which gear i will count, example if I shift the transaxle in 3rd gear the number of teeth are these from input shaft 28 teeth and the 3rd speed gear 36 so 36/28= 1.285. now if i will follow the power flow from 3rd gear it will flow to the intermediate shaft which has two more gear one gear is 34 teeth and the other is 30 teeth so 34/30= 1.133, now the power flow will go in pinion and the ring gear, that have number of teeth 67/17= 3.941.

Now my question is how i will get the overall gear ratio for this. Because in tranmission with rear axle. I counting the teeth from input shaft then the output shaft then multiply on the axle ratio, example i will get 12:1, that means 12 times revolution of engine is 1 time revolution of wheel. I don't have problem in transmission calculating the gear ratio of them I confuse how in transaxle.

If I will multiply the 3rd speed gear ratio in the axle ratio 1.28 x 3. 94= 5.04 so it will 4.4:1 overall gear ratio.
or do i need to multiply intermediate shaft gear into axle gear 1.13 x 3.94 = 4.45 or all of them 1.28 / 1.13 x 3.94 = 4.46.

I check this already when I turn the input shaft of transaxle in 3rd speed gear position. the input shaft is turn about 4 times to turn 1 time the axle or driveshaft.

the question is which formula is correct to use? multiply the speed gear ratio into axle ratio = over gear ratio, or multiply the intermediate shaft gear into axle gear ratio= overall gear ratio, or all of them speed gear divide intermediate multiply axle ratio.

thanks guys hope you can help me the correct way of calculating the transaxle.

[Marc]

Just what kind of transaxle are you dealing with here? A 17-tooth pinion, really?
There are only two tooth-counts involved in calculating the ratio of any forward gear in an ACVW transmission. The final ratio is determined by multiplying that number by the ring & pinion ratio.
Bear in mind that the action of the differential can confound your efforts to determine the final ratio using the "counting-turns" method. One side of the differential's output must be inhibited from turning. With the trans in the car, simply jacking one rear wheel off the deck and leaving the other down will do the trick. On the bench, you'll have to stop one side from turning some other way. On a swingaxle, simply adjust the brakes up on one side so the drum can't turn. IRS? A few ways to do it, one simple method is to drive an m8x1.25 bolt through one of the CV flange holes against some piece of scrap metal between it and the sidecover.
Once you've got one side blocked from turning, the differential's action will cause the other side to rotate 2 times for every revolution of the ring gear.

The most common 3rd gear ratio in ACVW transmissions is "1.26:1"....achieved with a "coarse" tooth count of 29:23, for a true ratio of ~1.26087:1. Multiply that by the common 33:8 ring & pinion of an "AH" trans and you get a final ratio of ~5.2011:1 in 3rd. "Lock" one side of the differential and the other side will rotate once for each 2.6 turns of the input shaft.

[trinity]

I open already the manual transaxle unit. What I want to know is how to calculate the teeth gear there to find the overall gear ratio of the gear in different speed position. from the speed gear I choose going to the axle gear.

[trinity]

I open one transaxle, I saw a number of gear, from input shaft that meshed in the mainshaft and on the mainshaft 4th counter gear there is intermediate shaft with gear, at the end of that shaft also got one gear which is the pinion gear meshed in the ring gear. now which of those gear meshed i need to calculate to get the overall gear ratio for the speed gear i choose example is 3rd gear speed. the number of teeth of them.

3rd gear = 36/28= 1.285
Intermediate shaft with gear= 34/30= 1.133
Pinion and Ring gear= 67/17= 3.941

which of these i need to calculate to get the overall gear ratio for 3rd speed gear.

[trinity]

MARC

There are only two tooth-counts involved in calculating the ratio of any forward gear in an ACVW transmission. The final ratio is determined by multiplying that number by the ring & pinion ratio. ???

what is the two tooth-counts? which final ratio i need to determined and multiply to the axle ratio, the axle ratio i get is Pinion and Ring gear= 67/17= 3.941. now which gear ratio i need to multiply there for is it also the speed gear ratio such 1st 2nd etc or the gear in the intermediate shaft.

because in RWD the transmission is count the driven and driver gear between the input and output shaft and to multiply in axle ratio = overall gear ratio. how about FWD transaxle?

[trinity]

hope somebody reply and help me to find out about gear ratio.

[dragvw2180]

I believe it is the same on any geared shaft system. You have to know the tranny gear ratio and R/Pinion ratio, does not matter what system . Mike McCarthy

[trinity]

i just want to know which gear i will count because i will report it in class. i dont want make mistake. otherwise if i count wrong teeth or gear the overall ratio is wrong.

[Marc]

In a transmission with a layshaft there are in fact two pairs of gears involved, except when in "direct" (high gear on a non-overdrive trans).
VW transmissions do not use a layshaft, and there is no direct power flow in any gear...all (forward) ratios use one pair of gears.
Obviously this is NOT an ACVW transmission under discussion, so asking for help at a forum devoted to ACVWs was probably not the quickest way to find it.

http://thecartech.com/subjects/auto_eng/Auto_eng_3.htm (refer to the "Compound Gear Train" section)

To calculate the "final" drive ratio (the relationship between engine RPM and axle shaft RPM), multiply the transmission ratio by the ring & pinion ratio. Rarely, there could be an additional reduction performed by spur gears (as on a swingaxle VW bus) or planetary gears in the hub (heavy earth moving equipment, for example).

In almost ever case, since the objective is to multiply the engine's torque, every gearset involved will have a ratio that's higher than 1:1 (fewer teeth on the "driving" gear than on the "driven" gear). Overdrive gearsets will have a ratio that's lower than 1:1 so the opposite will be true.

If we assume that on the transmission you have the power flow goes first into a 28T gear on the input shaft, meshed to a 36T on the layshaft, then from the 30T on the layshaft meshed to a 34T on the output shaft, then to a 17T pinion gear meshed to a 67T ring gear, the overall ratio is ~5.473:1

(34x36x67)÷(28x30x17) = 82008÷14280 = 5.74285714...