4x4 question

My 66 CJ5 has a later (70s?) front axle with disk brakes. I am pretty sure the transfer case is a Dana 18. Both drive shafts come off the transfer case and it has the parking brake drum. So my question is.....I had the original front shaft made up with the bigger yoke for the front end. But if I'm not mistaken the gears have to be the same front and back. How do I figure out if they are so I don't mess something up? The front shaft has never been on since the previous owner did the swap. I know the hubs work and all that. Any help would be great and sorry if this has been covered!

 

The easiest way is to lift both the front and rear tires off the ground. Get some masking tape and put a strip on the tire and one on the driveshaft. Turn the tire one full revolution while counting how many times the driveshaft turned. Do the same for the front. Should be the same number of turns on the front driveshaft as the rear. Gives you a close idea to the gear ratio also. Other than that you can pull the covers off and count the ring and pinion.

 

If both driveshaft yokes are on the lowest portion of the transfer case it is the Dana 18.

Best/most accurate way of determing gear ratio is to pull the differential covers, and count the gears on the ring gear andf then on the pinion gear. Divide the ring gear number by the pinion gear number and the answer is your ratio.

There are often numbers stamped into the ring gear. If you find the right numbers you again divide the bigger number by the smaller number to get the ratio.

There might still be a small metal tag mounted under one or two of the differential cover bolts that will have the gear ratio on it. You can't be certain that nobody put the wrong tag on the wrong differential though. It probably won't be wrong but if it is it will cause real trouble down the road if you assume it is right.

You can also check by spinning a tire and counting the number of turns that the driveshaft yoke takes. Make sure the transmission is in neutral. Mark the yoke and the differential housing with a thin piece of tape, or chalk (or something that you can see easily) so that when the yoke turns you can easily see when the mark comes around again. If you have an open differential (not "posi", and I use the term posi as a generic name not a brand affiliated name), jack up one wheel, and mark the tire (I usually just make a mark at the 12 oclock position). Slowly turn the wheel two complete revolutions while counting how many time the yoke spins. The yoke revolutions will give you the ratio. One problem is the end position isn't giving an exact number but if you knoe wth common ratios you will probably get it (like if it goes around about 3 3/4 times it is probably a 3.73 ratio).

Note: If you have a posi type differential you have to have both tires on the axle off the ground, and you only turn the tire one revolution. You can generally check for the posi by jacking up both tire off the ground and rotating one. If you watch the other tire and it rotates in the same direction you have a posi, if it spins the other direction you have an open differential.

2nd Note: If you have locking hubs on the front axle make sure that they are locked while testing.

I see that Beach66bum is a faster typer than I am.

 

Thanks guys! Spot on advice.

 

I would not depend on turning the wheels and counting the driveshaft turns. Instead, I'd pull the covers and look at the edge of the ring gear. The tooth counts will be stamped into the edge of the ring gear, ie "41 11" is 41/11 = 3.73.

 

This. Best way to check sans actually counting the ring and pinion teeth and doing the math.

 

Am I the only one here who thinks if you jack only one wheel, the wheel will spin twice as as many times as the actual ratio (on an open diff)?

 

drive it down the driveway. youll find out right away

 

That's right. The total turns must be two, with two wheels. One wheel can turn two times (open differential) or each wheel can turn once (locking or limited slip).

 

Your post reply is much more detailed and in depth fesser ! That's a great write up.

 

Yes. I understand the tru proper way now but....if I do the tire spin prosedure on both the front and back at least I'll know they are turning the same. And won't break anything putting it in 4x4.

 

Nope. You are right.

Thanks. You told him what he needed to know to without having to dismantle anything. I just had a case of the blah blahs.

 

do this and be sure. its easy, you get to change the gear oil and check the gears themselves. you should be taking off the cover to look inside anyway in an unfamiliar axle assembly.

 

If you just want to see if the front and rear turn at the same speed, stick the JEEP up in the air on jack stands so all four clear the ground, stick the transfercase in gear, choose either high or low range 4 wheel drive, make sure the lockers are set so the front wheels are both engaged and spin a tire by hand. All the others will spin at the same speed if the gearing is the same in both differentials. Doesn't matter what the final drive number is. If the front is a different ratio from the rear, then the rears and fronts will not spin at the same speed.

 

This.

 

Do mine first. Because if the ratios of the front don't match the ratios of the rear, then you have to get a different axle, or at least a different set of gears to go in one of them.

Then open them up. You will already have the JEEP up in the air to work on them.

 

thatll only work if he has lockers or limited slip front and rear. it would work with both open diffs if only one side is jacked up. if only the front or rear has a locker then it wont work at all

 

Only if you are worried about directionality. Watch and you will see that two wheels spin clockwise and two will spin counter clockwise. We are looking for number of turns, not if they all turn the same way.

 

if youre turning one wheel and the other wheel is turning the oposite way then the driveshaft wont be spinning at all. and if it does it certainly wont be an accurate amount