How to CONFIRM both differential ratios, front and rear.

[eightynine4x4]

[ 89 4x4 auto w/ manual transfer case. ]

I’m in the middle of rebuilding my Dana 28. My front diff has, i think, “3.01” hand written on it by someone. Although it could be partially worn off.
In any case, my VIN axle code is F7, meaning my truck was spec’d as having 4.10.
Is there a way to confirm the gear ratio’s of both front and back diff’s, without opening them both up? Are there stamps or tags somewhere? I took a look and didn’t find one on either front or back.
I’ve used the 4x4 in emergencies a handful of times. Mostly in deep snow when I was unable to get out of an unpaved driveway in winter. But I also used it one time for a few miles when I was driving slowly in blizzard conditions and needed it in order to not slide off the road.
Other than the clacking of the U joints, all of which I’m currently replacing, the 4x4 felt good.

 

[superj]

you can jack the truck up, put a chalk mark on the wheels at the bottom, put a chalk mark on the drive shafts at the bottom, and the rotate the drivehsafts.. while rotating each one, count the times it takes to make each wheel do one rotation, returning the chalk mark to the original position.

 

[eightynine4x4]

you can jack the truck up, put a chalk mark on the wheels at the bottom, put a chalk mark on the drive shafts at the bottom, and the rotate the drivehsafts.. while rotating each one, count the times it takes to make each wheel do one rotation, returning the chalk mark to the original position.

Damn, my Dana 28 is torn down to the point of it only being the front diff and front driveshaft remaining, haha. No wheels or anything for a little while!

 

[superj]

mark the input and output flanges and do the same turning and counting

 

[eightynine4x4]

mark the input and output flanges and do the same turning and counting

Ok i think i get it. I could observe the slip yoke u-joint on front passenger side since that’s still sticking out of front diff.
So i turn the front driveshaft, obviously while 4x4 is not engaged in transfer case otherwise it wouldn’t move, and mark how many times the front yoke u-joint turns. That’ll give me my ratio? So if i have 4.10 in front diff, I’m expecting the slip-yoke joint to turn 4.1 times as i turn the front driveshaft just 1 time? Or is it the other way around?
I’ll leave the rear alone for now since my truck is jacked up in front.
As for the front driveshaft…… I’ve definitely turned that thing by hand a number of times recently. I was testing the u joints at the double cardon in front of the transfer case, which need to be replaced. I never put it back to where it ”was” though. I thought it was free spinning and didn’t matter. I was planning to mark it however, in relation to the transfer case connection and in relation to the front diff connection, before disconnecting it soon to replace all u-joints on it.
Have I opened a can of worms by turning the front driveshaft by hand?

 

[2011Supercab]

My first guess would be March of 01, meaning when it was replaced or last serviced.

 

[don4331]

Driveshaft 4 and a bit for once for the slip-yoke joint.

Ideally, you put the driveshaft back exactly as it was, but you are replacing parts so it isn't as critical (like your old recliner, parts get worn in and don't like it when things move).

The biggest thing to ensure is that the u-joints at both ends of the shafts line up.​

 

[eightynine4x4]

Driveshaft 4 and a bit for once for the slip-yoke joint.

Ideally, you put the driveshaft back exactly as it was, but you are replacing parts so it isn't as critical (like your old recliner, parts get worn in and don't like it when things move).

The biggest thing to ensure is that the u-joints at both ends of the shafts line up.​

Got it.
Well that’s interesting about the putting back in place. I realized the error in my thinking after i posted that. Turning the front shaft by hand is the same thing as driving with front hubs locked but 4x4 not engaged. I’ve already done that, and according to the guide in back of driver’s sun visor on my truck, it’s fine to hop in and out of 4H when driving. So it seems like it doesn’t matter where the front shaft currently sits, and it’ll catch in gear just fine when you engage it.
But yeah i understand about old parts wearing in. I’m only replacing u-joints though, not rebuilding any gears. So I’m not sure I’m improving the health of the crucial parts for this matter haha.
I’ll go ahead and run the test. I’m hoping it requires 4.1 turns to make the yoke go one turn. I’d hate to discover this front diff was replaced with something not functional. It would be great is that hand writing is March 01, but you’d think that the guy would have maybe used a complete date so as to not make someone think it was a gear ratio !

 

[eightynine4x4]

Test complete, it is 4.10 in front. Whew! And I’m sure it’s 4.10 in back.
I also inserted the drivers inner shaft to be able to test things on both sides.
As for the overall behavior… i can spin one axle and it will rotate the opposite axle in tandem. However, this doesn’t rotate the front shaft whatsoever. I wasn’t expecting that. I guess this means that while locking the hubs and not putting the case in 4H, the front shaft is still motionless. This also means that the front shaft DOES stay in the same place at all times pretty much, and by moving it i have disturbed the peace. Fingers crossed it works out, cause there’s nothing i can do about that now.
More testing…
If i rotate the front shaft, it spins both axles. If I hold one axle in place and rotate the front shaft, it spins the other axle only. Sounds about right for a regular diff. If both axles are held it place, the front shaft finally has resistance and won’t go forward until one or both axles are free to move.
I was able to only roughly test this since my way of ”holding” the slip-yoke was to just let it dangle down and push against the frame.
But overall it seems like i have a fully functional 4.10 front diff.… assuming it’s normal that the front axles can be spun by hand without moving the front drive shaft?

 

[rusty ol ranger]

3.01 was never a gear offered in the ranger, or by ford period as far as i know.

 

[eightynine4x4]

This driveshaft position thing has got me a little confused.
I have a double cardon U Joint at the back of my front drive shaft going into the transfer case. This is the STX version, to the best of my interpretation of the shop manual. Many front driveshafts, maybe even most of them, have a single cardon u joint, the NON-STX version.
But for my version, the Double Cardan STX, I’ve already marked off with a paint pen the connections from the shaft to the double at back to the yoke/bracket of T-case. I’ve also already marked off the front of driveshaft relationship to front yoke/bracket going into the diff.
So, when go to reinstall this thing, it’ll all go back together with the same connection points… and the front-yoke to shaft to double carbon to back-yoke, will all be reassembled in the same balance/order.

Yet, this whole “hand spun“ position of the whole front shaft, in relation to other things, has me confused. Is that really the way it’s designed? I mean, does that mean that someone with ill will who knew what they were looking at could just reach under someone’s truck and spin the front driveshaft by hand 90 degrees and they’ll throw off the balance of the whole system? It seems weird that the engineers would design it that way.

But it seems to be the case…

”Mark the driveshaft in relation to the transfer case attachment flange, and at the rear axle companion flange to maintain driveshaft balance.“

This is from the shop manual, for “Front Driveshaft with Double Cardon U-Joint: Removal”

Is the balance of the driveshaft continuous from front diff to rear diff? I had thought that each segment had its own balance, and that so long as the front driveshaft was reassembled using the same connector points, and so long as the rear shaft was also reassembled using the same connector points, then each shaft is balanced and good to go.

And also, if the front driveshaft is idle, yet the rear driveshaft is spinning, if the whole front/rear system is required for balance then it seems this would be catastrophic to the balance to have half of it idle. What makes more sense would be that the rear has its own balance and the front has its own balance, and that free rotation of each independently of each other makes no difference for balance… and further more, that the free spun position of front shaft has no impact and is on no concern.

But is the shop manual really saying that the free spinning position of the front axle can throw off the balance of things?

In any case, when I go to reinstall all of this, i will be putting it back together exactly as it was originally, with the only exception being that I could spin the whole front shaft by hand and try to guess where it was before disassembly. But is that really an issue?

 

[eightynine4x4]

Wait, actually, the shop manual has a big error.
Those are instructions for the REAR double cardon shaft. The whole section is mistitled as “Front”.

There IS no instruction for FRONT Double-Cardon driveshaft in the shop manual.

I was interpreting this to mean that i had to mark the rear stuff, behind the T-case, while working on the front shaft.

 

[SenorNoob]

Looks like someone copy-pasted the rear info for the front double-cardan joints. They didn't even bother to correct it for the front.

 

[Curious Hound]

This is getting confusing. Maybe I can boil it down to a few simple statements for clarity.

1. There is no special relationship between front and rear druve shafts. Either can turn independently of the other. When you put the transfer case in 4-hi or 4-lo, it will engage the front shaft and everything will be fine.

2. Turning one wheel or axle shaft and seeing the other side turn the opposite direction is normal for an "open" differential. That is how they work. Turning the driveshaft and seeing this behavior is also normal.

3. When we say "open" differential, we are talking about one that does not have a limited slip assembly or differential lock assembly installed. Do not confuse this with engaging the transfer case or engaging/disengaging (locking) the hubs at the wheels. All totally separate assemblies and events.

4. Gear ratio is "inpututput". Ie; you turn the drive shaft or pinion X.X turns to get 1 revolution of the axle shaft or wheel. As you found, 4.10 turns of the driver shaft = 1 wheel revolution. Therefore, 4.10 ratio.

5. The differential gears are always engaged from input to output.

6. You manually or electrically shift the transfer case to engage or disengage the front drive shaft to attain 4-hi, 4-lo or 2-hi operation of the transfer case.

7. The hubs, engage or disengage independently from everything else. Either manually by you Turning a knob on each hub. Or automatically though mechanical design of the hub. Or by use of vacuum or electrical devices designed to do it. Or, in some layer vehicles or modified vehicles, the hubs are permanently engaged.

 

[Blmpkn]

Pop thr cover off the rear and see what it says on the ring gear. If the truck drives in 4x4 without breaking itself.. you'll know the front matches the rear.

Don't worry about losing the fluid.. probably due for fresh lube anyhow.