Differentials turning while towing

crd liberty · **Posted:** Fri Feb 22, 2008 5:03 pm

May need some of the hard hitters here(knowledge folks)
If I have say 28,000 miles on the OD but there are
another 7 to 8 K being towed behind Motorhome.
Diff. change at 13,000, due again at 26,000.
? is Does my Diff. turn as if it has 28,000 miles or actual
miles on the tires, 36,000.
My thought is, even though drivetrain is disconnected,
wheels still turn so some of the axles gears must still turn?
Thanks
Steve

UFO · **Posted:** Fri Feb 22, 2008 5:13 pm

Without any load on the gears, I would think you could just follow the normal maintenance schedule. They turn, but there is no load pressure/temperature to degrade the lubricant.

crd liberty · **Posted:** Fri Feb 22, 2008 5:18 pm

Phew
Thanks UFO
For some reason this just came to me as I was planning a Diff change
and it hit me like a rock that maybe the diff was way overdue for fluid
change.
Least, I can take my time and just get it done fore May when I have to
tow the libby again out your way.
Thanks
Steve

rpapkey · **Joined:** Sun Jan 14, 2007 4:48 pm **Posts:** 39

Normally i think the normal change interval is a little (read ALOT) overzealous. I've never seen a car with a 12000 mile diff oil change interval. (what the heck were they thinking) But i think in your case you probably should do it by the odometer in the Liberty. I think UFO is right the gears and bearings aren't getting all of the same stresses as it would if you were actually driving it so i think you'll be fine. Personally i don't think i'd worry too much about it.

crd liberty · **Posted:** Fri Feb 22, 2008 6:08 pm

Thanks rp
That reinforces the above from UFO.
The stealership gets 70.00 each diff. so I am doing this change myself.
I have not been impressed with the stealership sine the F-37 and I drove it for like
3 days and checked the Trans. fliud, none there. Comment there was
well the TC normally comes with x fuild included. So, did they install
it bone dry? Don't know.
I have had 3 ECM Modules in this vehicle. Same story. Different days.
I don't know a whole lot about this vehicle but I know when someting
is wrong and with the help from here, I can fix it.
Thanks to all ya
Steve :wink:

InCommando · **Posted:** Fri Feb 22, 2008 6:21 pm

You know, I'd almost split the difference on the mileage. Although not under power, the diff is still turning at "X" RPM, building heat. And as the rear are "semi-float" axles that are load bearing for some weight of the vehicle, I'd think there would be some lubricant degradation.

Just a thought....

crd liberty · **Posted:** Fri Feb 22, 2008 6:37 pm

Thanks
No matter how I look at it, I have to do it soon. At least the rear diff
Might not be next late week. Mustard greens and collards out of the
garden tomorrow need to be put up.
Monday work needs me, ugh. Maybe tues. double ugh.
Thinking I am going to do the RTV deal. Looked at some
of the gaskets avialable and searched and there is some leakage sometimes
on some of these gaskets? Any upbeats here?
Thanks all
Steve :roll:

Uffe · **Posted:** Fri Feb 22, 2008 6:41 pm

The diffs are only working on the power they need for the resistance of the CV joints and the diff itself at speed. The load on the diffs is so small I wouldn't worry about it. Maybe count 10 miles as 1 mile if you want to

Otherwise just disregard towing miles altogether and change the fluids when you "feel" you should. Read up on normal intervals and check if you think you should change them.

crd liberty · **Posted:** Fri Feb 22, 2008 6:54 pm

Thanks UFFE
That is where I was earlier today. Knew it was getting close to the 15,000 miles for at
least the rear end diff. Than is when I thought about all these forgotten miles towing.
I log all the towing miles so they are not really forgotten. Just hidden away in my log book.
At 61 years young, I am going to do it rather than pay the stealership 69.95
per diff.
Thanks all Steve :lol:

tjkj2002 · **Posted:** Sat Feb 23, 2008 12:24 am

Driving or being flat towed the F/R diffs are still turning(ring and pinion),creating friction and heat,the rear diff is still supporting at least 45% of the vehicles total wieght while doing this, thus spinning the outer axles bearings creating friction and heat.The only thing is no torque is being applied to the diffs but they are still "working" and every flat towed mile is about at least 75%+ of wear/tear as actually driving it.Also the same wear/tear is placed on the t-case even though it may be in "N",it's still turning most of the internals in there also.

Quick test------

After a good distance of being flat towed feel your F/R diffs,they'll be just as hot as if you actually drove the KJ instead of towing it.

InCommando · **Posted:** Sat Feb 23, 2008 12:28 am

That is what I was thinking, too. Your 75% figure is probably better than my 50%.

warp2diesel · **Posted:** Sat Feb 23, 2008 12:41 am

... in severe environments the company I work for recommends once a year, even if they are running 24/7. One of our competitors has the customers open up a drain valve and let the water run out of the case. Since our differentials are in the shade almost all the time, we do not need to put up with solar heating and cooling like industrial gear cases do when they are outside.
Since our Liberty differentials also have breathers to prevent blowing out the seals, just like the industrial gear cases, they exhale air and inhale moisture and other contaminants in the air every time we take a trip where the differential heats up and cools down. Towing makes more heat and besides making the lubrication work harder, the differentials breath deeper and inhale more outside air that has moisture and other contaminants, thus sucking in more resulting in the need for more frequent oil changes.
For those of us who own antique tractors with massive transmission/differential/ final drive cases the quantity of moisture and other contaminants is much greater. Since antique old tractor owners don't always change the oil in the big case every year, we cheat and crack the drain plug to let the water drain out. Sometimes it is a few drops and sometimes over a quart. Since the antique tractor does not run as fast as the gears in our Liberty differentials, we have no concern of mixing the oil into the water and having the water turn into steam and steam blast all of the lubrication off the gears and bearings. For those antique tractor owners who want to put the antique tractor to work and not just putts around, we change out the transmission/differential/final drive oil and follow the original recommendations.
If you want to make an adjustment on oil change intervals consider, load, distance of trips, and weather conditions. Being towed behind a motor home will heat up the differential less than normal driving and much less than pulling a trailer. Heating up the differential less means a shallower breath of moist contaminated air being sucked into the differential.

Steve

gmctd · **Posted:** Sat Feb 23, 2008 1:43 am

The ring and pinion seldom spins when vehicle is in motion - the spider and side gears do spin - the disconnected axle spins it's side gear, which spins the spiders, which spins the side gear of the disconnected axle shaft in the opposite direction - the ring and pinion and transfer case offers much more resistance than the side gears, which will spin with not near as much friction - also why this axle-disconnect type setup seldom works with a front anti-spin differential

So, yes, the front diff will get warm

rpapkey · **Joined:** Sun Jan 14, 2007 4:48 pm **Posts:** 39

Think about it though. most cars won't have you change the diff oil till 50,000 and 7-10 people probably never do that. Lets be real here. If he leaves it till the libs odo says 12000 he's probably traveled closer to say 25000. Well under the average automobile interval. I'd say at the very worst change it every two years, if you want to be anal about it every spring.

crd liberty · **Posted:** Sat Feb 23, 2008 5:17 am

Looking back thru my logs. I have around 14,000
driven miles since fluids were changed and around
22,000 actual miles (8K flat towed).
Putting it on my list of things to do very soon.
Thanks all.
Steve

tjkj2002 · **Posted:** Sat Feb 23, 2008 10:46 am

Quote:

The ring and pinion seldom spins when vehicle is in motion

While in motion the ring and pinion is always spinning,towed or driving.The only way it wouldn't is if the axles where removed or broken or the wheels are not touching the ground.

Quote:

the spider and side gears do spin - the disconnected axle spins it's side gear, which spins the spiders, which spins the side gear of the disconnected axle shaft in the opposite direction

Only while turning,your spider gear will not turn while going straight unless your doing a burnout.There is no way to prevent the rear ring and pinion from spinning unless you use dolly's,otherwise the rear tires would not spin.The spider gears can not both spin in the same direction,they can only spin in the oposite directions,and this will only happen in a turn or a burnout,not possible with the vehicle while driving/towed straight as both rear wheels are turning the same speed,the spider gears are then staionary and not moving.

Quote:

also why this axle-disconnect type setup seldom works with a front anti-spin differential

So, yes, the front diff will get warm

The front diff is the exact same as the rear from the factory(unless you got the rear trac-lok),the front diff is a open diff and has no traction aids from the factory(LSD/locker).So if the front gets warm the rear will to.

gmctd · **Posted:** Sat Feb 23, 2008 2:21 pm

My bad - you are correct - these KJ's are too small to have the electric\vacuum de-clutching axle disconnect - the entire front geartrain - axles to transfer case - always spins at any vehicle movement - well, that's whatcha get for buyin' cheap stuff....................

tjkj2002 · **Posted:** Sat Feb 23, 2008 2:26 pm

gmctd wrote:

My bad - you are correct - these KJ's are too small to have the electric\vacuum de-clutching axle disconnect - the entire front geartrain - axles to transfer case - always spins at any vehicle movement - well, that's whatcha get for buyin' cheap stuff....................

I believe your 3500 Dodge is the same way unless you put lockouts on it.The same goes for the raer diff also even if the t-case is in "N".

gmctd · **Posted:** Sat Feb 23, 2008 2:41 pm

The Dodge has SFA - most all modern 4wd IFS vehicles with auto-shift and particularly those with shift-on-fly have the FAD system to prevent the entire drivetrain from spinning, which helps when engaging the system - I just haven't been around our KJ enuff to be up close and personal familiar with the drivetrain - some question will flit across my mind, and I'll be halfway out the door B4 it dawns on me that the little mule is stabled 20mi away - bummer!

tjkj2002 · **Posted:** Sat Feb 23, 2008 11:58 pm

gmctd wrote:

The Dodge has SFA - most all modern 4wd IFS vehicles with auto-shift and particularly those with shift-on-fly have the FAD system to prevent the entire drivetrain from spinning, which helps when engaging the system - I just haven't been around our KJ enuff to be up close and personal familiar with the drivetrain - some question will flit across my mind, and I'll be halfway out the door B4 it dawns on me that the little mule is stabled 20mi away - bummer!

Almost all newer pickups,IFS or SFA,are just like our KJ's,the front axle is always locked in.You would need auto/manual locking hubs to "disconect" the front diff from turning.I believe the '06 SuperDuty was the last truck to have any OEM front hub lockouts(automatic or manual),I believe Dodge did away with the lockable hubs for the '96+ trucks(at least 1/2tons),and Chevy stopped using them when they went to IFS in there trucks,Jeeps haven't used any type of lockouts since sometime in the '90's and there last thing was those very terrible vacumn disconnects that are a nightmare.The rear diff can never be "unlocked" unless you remove the axles and/or ring and pinion gear set,towed or driving,and unless you have a semi-float or full-floating rear diff you can't remove the rear axles and still have the vehicle roll.Our drivetrain is is almost identical to all other newer 4wd trucks(1989+),sans the SFA and the bigger trucks will use HD parts compared to the stuff used in a KJ.

Differentials turning while towing

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