8-3/4" axle ratio?

[PurpleBeeper]

Hey Guys, I'm working with another member, Xp29h, to figure out the gear ratio in a 489 pumpkin 8-3/4" rear end. He sent me a video....maybe I told him wrong about how to check it???

Anyway, the rear end is on the ground & he has a very clearly marked piece of yellow tape on the yoke + one wheel stud. He turned the wheel stud/axle (pass. side) & he's getting almost exactly 2 revolutions of the yoke.....roughly 2.00 gear ratio????? 2 full revolutions of yoke = 1 full revolution of wheel. What the heck?

Is the issue that he needs to turn the yoke, not the axle? I'm confused.

 

[RT K_line]

I do something similar, but I mark the tire at the inside bottom and the housing to yolk then spin the tire one revolution from under the car so I can count the shaft turns. If you do it your way you need someone to watch the shaft while you turn the tire so as not to miss a revolution.

 

[PurpleBeeper]

I do something similar, but I mark the tire at the inside bottom and the housing to yolk then spin the tire one revolution from under the car so I can count the shaft turns. If you do it your way you need someone to watch the shaft while you turn the tire so as not to miss a revolution.

Agreed....but this rear end is laying on its back on the ground. Nothing is touching & it's VERY easy to see in the video both the yoke tape & the wheel stud marks. I thought he'd missed a revolution of the yoke too (thinking maybe 2.94's) UNTIL I saw his video...plain as day. 2 yoke revolutions = 1 tire revolution. I'm baffled.

 

[moparnation74]

Have you determined posi or non posi?

If it is a non posi...You rotate the tire 2 full turns and count yoke rotation but one tire should be on the ground for accuracy.

 

[RT K_line]

So the unit isn't in the car OK Your right, it doesn't make sense. I've heard of 270s but only seen 290s, nothing like your describing. That's a good one.

 

[Yatzee]

Hey Guys, I'm working with another member, Xp29h, to figure out the gear ratio in a 489 pumpkin 8-3/4" rear end. He sent me a video....maybe I told him wrong about how to check it???

Anyway, the rear end is on the ground & he has a very clearly marked piece of yellow tape on the yoke + one wheel stud. He turned the wheel stud/axle (pass. side) & he's getting almost exactly 2 revolutions of the yoke.....roughly 2.00 gear ratio????? 2 full revolutions of yoke = 1 full revolution of wheel. What the heck?

Is the issue that he needs to turn the yoke, not the axle? I'm confused.

Rotate the yoke not the axle. Start in verticle position and go CW. Mark the axle flange on it's edge at the very top and rotate the yoke until one full rotation occurs at the axle flange, counting the number of turns on the yoke.

 

[PP1RT]

Yes turn the yoke.....not the wheel. Think driver and driven. The driveshaft turns "x" number of times to turn the wheel once. "X" equals gear ratio(roughly).

 

[moparnation74]

Feeling is mutual...

 

[AR67GTX]

Have you determined posi or non posi?

If it is a non posi...You rotate the tire 2 full turns and count yoke rotation but one tire should be on the ground for accuracy.

Yes - if not posi one tire has to be fixed so it can't turn. Otherwise the "differential part" of the differential will give you a false figure.

 

[PP1RT]

Didnt mean to hurt any feelings but turning the wheel twice isnt right. Yoke revolutions: wheel revolutions. Yoke turns 2 3/4 times:wheel turns once= 2.76:1 gears. Yoke turns a little more than four times and the wheel turns once= 4.10:1.
Sorry if i hurt your feelings but turning the yoke until the wheel has turned exactly one time is the correct way. Your are correct about having one wheel on the ground if non posi and both in the air on a posi.

Back to the OP...if the rear is a non posi you will need to keep one axle from turning while you count the other end. I suspect there may have been some unnoticed movement.

 

[moparnation74]

Didnt mean to hurt any feelings but turning the wheel twice isnt right. Yoke revolutions: wheel revolutions. Yoke turns 2 3/4 times:wheel turns once= 2.76:1 gears. Yoke turns a little more than four times and the wheel turns once= 4.10:1.
Sorry if i hurt your feelings but turning the yoke until the wheel has turned exactly one time is the correct way. Your are correct about having one wheel on the ground if non posi and both in the air on a posi.

Back to the OP...if the rear is a non posi you will need to keep one axle from turning while you count the other end. I suspect there may have been some unnoticed movement.

Lol...no hurt feelings here but you compel yourself to be click happy and then try to explain later, lol...

You can turn the wheel 500 times for all I care and count yoke revolutions and guess what number one will come up with in the end......

I do it my way and you do it your way but to disagree means that my number would be different from yours and that Sir is incorrect....

 

[PP1RT]

Have you determined posi or non posi?

If it is a non posi...You rotate the tire 2 full turns and count yoke rotation but one tire should be on the ground for accuracy.

Sorry but i disagree with this explanation. Thats all.

 

[Xp29h]

Just to confuse things more.. one side is not turning at all. I'm thinking something is messed inside.

There is nothing on the axle for tags. I have no idea what it was in before I got it. So, very big ?

No matter which I turn axle or yoke clockwise, counter clockwise it always come out to 2 revolutions! I've done this before with post and without. Tire on ground so can't spin etc but this doesn't make sense. I tried to post the video so you could see but too large to get here. If anyone is interested in it, shoot me a pm with your email. For some reason that works.

 

[khryslerkid]

He more than likely has an open rear. Just one side might turn at a time. That's the way it is designed, for going around a turn. Outside wheel turns faster than the inside one so the spider gears start spinning, transferring the torque to the axel with the least resistance. Confused yet?

Now if you're trying to count turns on a open rear, you need to keep one side from turning. Whatever it takes to do this, you have to hold one axel before turning the yoke. If you allow both axels to spin, the spider gears could be transferring back and forth between the two, messing up the counting of the revolutions.

Hope this helps.



Also...

 

[oldbee]

Well with an open diff the one side may not turn OR turn a little just from friction internally; but if ur numbers are halfways close you're gonna rip it out anyways in the near future.

 

[PP1RT]

If it is out of the car already yank it apart and look for the numbers on the ring gear. Divide the bigger number by the smaller number. Example 47.17 You would divide 47÷17=2.76 gear ratio.

 

[Xp29h]

I'm thinking rip it apart to be sure. On my list for tomorrow

Thanks all!!

 

[PP1RT]

If you hold the yoke stationary and turn one wheel will the other wheel turn the opposite way? (both off the ground) Any noises?

 

[Cranky]

Rear end out of the car you say? Do you have a couple of wheels/tires to stick on it? You can get rid of all the cornfusion by sticking on the tires and then just roll the thing evenly for one tire revolution and count how many times the yoke turns. One person can do this by themselves if you are on a level hard surface......just keep your hands etc out of the way of the yoke. Mark the tires so you end up with both in the same position and make one point on the yoke so you can keep an easy eye on it.

 

[MoparLeo]

Yes it will if it is a non sure-grip differential. The gear ratio is just that. The ratio between the pinion and ring gear rotation. 2.73 revolutions of the pinion gear, one revolution of the ring gear. Does that help explain it ?