Finding rear gearing, confused.

[CG]

So I’m trying to figure out what the gear ratio is on my 14 Bolt FF. There is no driveshaft or body, it’s just a chassis for now. Jacked up one side, spun tire one revolution and the yoke went a tad over two. Jacked up the whole rearend spun the other tire one revolution, yoke still went a tad over two. I feel like I’m misunderstanding how this works. I really don’t want to yank the cover and look at the markings, I just want to be close.

[lowrollin70gmc]

If you only spin one drum at a time while the other is stationary then you must turn that drum twice to count the revolutions of the yoke. This is because of the nature of the spider gear’s differential action.

Therefore, I would guess you’ll find you have 4.10s when spinning one drum twice.

[CG]

Ok thanks for the info. Unfortunately for me I was hoping it was something in the 3.7 ish range. Such is life lol.

[57larry]

pull the rear end cover, the ratio is stamped. good time to put fresh rear end oil in

[CG]

I was using the running gear on this chassis (non 67-72 4x4), for a trade deal, but only if it was a 3:73. He already has 4:10's on his 72K20. Ill let the next person (if that ever happens) deal with popping the cover and looking at the stamping. I'm pretty confident its a 4:10 now.

[Mike C]

The reason you have to double the number is because of the spider gears. But doubling ONLY works if you have spider gears that are a 2:1 ratio. Not all are. It looks like the full-float 14 bolt may be 17:10 tooth count on side/spiders which is a 1.7:1 ratio.

You may well have the 3.73 you think you do. Just pull the cover and know for sure. Especially if you are going to sell it. Sell what you own what just what you think you have.

[CG]

Ok Ok, you two guys convinced me ... LOL ... Ill pop the cover off tomorrow (supposed to be ugly out and its outside) and report back.

[RichardJ]

You have no wheels and no drive shaft?
Unless you have a brake dragging, whether it has posi or not, when you turn the pinion yoke, both drums will turn the same amount.
Mark the drums so you can determine when they have both made ONE complete revolution and count the number of turns it takes on the yoke.

I've always done it this way with tires and drive shaft in place. Chalk the tires and the ground next to them. Jack the axle up in the center, chalk the drive shaft and count the turns needed to bring the tires back around to the mark.
I've always thought it was easier.

[CG]

Has tires, no drive shaft. I taped the tires and taped the yoke so I could see the rotation without being confused. I rotated the tires not realizing I was supposed to rotate them both at the same time. I never even considered rotating the yoke and watching the tires. Tomorrow a new day dawns on my chassis =)

[special-K]

Save the lube and pour it back in if you don't want to invest in fresh fluid... especially if it turns out to be a dud (Not 3.73 in your case)

[CG]

OK, here are the numbers as they appear on the ring gear.

1 GM 3977334 10 41 6 73

There are also some numbers horizontal to the long list of numbers that are sort of almost between the 3977334 and the 10 ... 213

I think the 10 41 numbers mean its a 4:10 ... Oh well

[CG]

On a side note, can this rear end be converted to dual rear wheels? Might be a topic for another place on the board and a new thread. Or maybe its a simple no, haha.

[Mike C]

Yup, it's a 4.10 geared setup. Looks like it was made in June of '73 so it is a fairly early 14 bolt as far as that goes. But at least when you go to sell it, the next owner will know exactly what they are getting.

The dually setup is completely different as far as the brakes go to clear the dually style rim.