Flat Tow Wrangler YJ (Informational - Long)
edh...@bellsouth.net
five speed manual transmission. I assume it has the standard NP-231
transfer case.
Although I have successfully flat-towed my YJ (maximum of about 400
miles one-way and then return about a week later), I've recently
learned that the NP-231 (at least of this era) does not have a "true"
neutral position. Instead, while it does uncouple the transmission
from the transfer case, it also couples the front and rear outputs
together. If the front axle is engaged this causes gear backlash with
the potential to destroy the transfer case. If the Center Axle
Disconnect (CAD) on the front axle is disconnected (disengaged?), then
the backlash is eliminated.
The problem is that the vacuum operated CAD stays in the last position
it was put in. If you are preparing your YJ for flat towing and you
start the engine, the moment you shift the transfer case from 2WD to
Neutral the vacuum CAD engages the front axle. There you are with the
outputs of the transfer case locked together and the front axle live
instead of free-wheeling. Leaving you with the potential of blowing up
the transfer case.
The standard way to disengage the CAD under normal conditions (i.e.
you've been in 4WD and are now ready to resume normal 2WD operation)
is to place the transfer case into 2WD and then put the transmission
into reverse and back up several feet. This puts the front axle back
into free-wheeling mode (assuming everything is working properly), and
you can put the transmission into normal gear and drive off.
If you know the CAD is in this state then you can prepare for towing
simply by putting the transfer case into neutral without starting the
engine (no vacuum). Go ahead and put the transmission into neutral,
hook up to your tow vehicle and go. Some people recommend that you
leave the transmission in gear while towing. Since you have
disconnected the transmission when you put the transfer case in
neutral, this should not be necessary. Further, if the transmission is
in gear and the transfer case is accidently engaged (by a severe bump
maybe?) there will be bad consequences. You don't have to worry about
the transfer case lubrication because the rear output (which is
engaged) also drives the internal oil pump. As long as the CAD is
disengaged you are ready to tow.
Apparently when I've towed my YJ I been fortunate in that a)I
typically back in to park, therefore I've left the jeep with the CAD
disengaged and b)I normally don't have any reason to start the jeep
prior to putting the transfer case into neutral before hooking it up
to be towed. Since I didn't understand what I was doing, I could very
easily have destroyed my transfer case without knowing why.
Although I am comfortable with this, knowing how things work, there
are alternatives I discovered as I researched this issue.
1)Assuming that the CAD is already disengaged, you can just disconnect
the vacuum line from the CAD box. You'd be fine to start your engine
and move the jeep to the towing vehicle, hook up, put the transfer
case and transmission in neutral and go.
2)Install and use a Posi-Lock device instead of the vacuum CAD. Since
you control the front axle lock by cable, you should know the state it
is in.
3)Install and use external locking hubs. Not pleasant to use in foul
weather, but again you always know the state of the front axle because
you set it.
4)Install a transfer case conversion that gives you a true neutral.
You'd never have to worry about the state of the front axle when you
put the transfer case into neutral then.
5)Finally, of course, you can always tow your jeep on a trailer.
Comments and questions are welcome.
Your mileage may vary.
Vehicles in mirror are closer than they appear.
Cheers, Ed Humphries
Atlanta, Georgia
nrs
This is good to know. Thanks for posting.
Could option 4 cause problems? It seems that a true neutral might
leave the internal oil pump disconnected.
Earle Horton
false. I can't believe that neutral would lock the axles together, but then
again we are dealing with a crappy second rate American manufacturer (this
bit is for Stupendous Man).
I have always put the transfer case in neutral, transmission in gear, engine
running and let out the clutch before flat towing. This lets me know that
the transfer case is really disconnected. Then I shut off the engine,
leaving the transmission in gear, and have towed several thousand miles in
this fashion. I am sure that the center axle disconnect has indeed been
disconnected every time, and that the transfer case has been in neutral,
because I never noticed any binding, jerking, suspicious noises, difficulty
steering or transfer case damage. Next time I do this, it won't hurt to
reach underneath and verify that the front drive shaft turns freely of
course.
If you leave the transmission in neutral, it can be driven by a transfer
case in neutral because of friction and oil viscosity. This can lead to a
dry bearing condition and transmission mainshaft damage. Always have the
transmission in gear or park when flat towing.
Earle
<edh...@bellsouth.net> wrote in message
news:1170785062.5...@v33g2000cwv.googlegroups.com...
Matt Macchiarolo
<edh...@bellsouth.net> wrote in message
news:1170785062.5...@v33g2000cwv.googlegroups.com...
L.W. (Bill) Hughes III
appreciate it is someone with New Process transfer would confirm this, by
simple putting theirs in neutral and jack up a front wheel, if they don't
free wheeling hubs and see if you can turn the front driveshaft. I don't
believe it's true, because this would quickly destroy one of the
differentials.
God Bless America, Bill 0|||||||0
mailto:LWHug...@aol.com http://www.billhughes.com/
<edh...@bellsouth.net> wrote in message
news:1170785062.5...@v33g2000cwv.googlegroups.com...
Earle Horton
I think I have towed mine a total of maybe 3,000 miles. I moved a few times
since I bought it. No differentials destroyed yet. I can't perform the
test until the weekend, but I sure will do it. In 2HI, you can reach under
the vehicle and turn the front drive shaft with all four wheels on the
ground. In N it has to be the same way. You don't have to jack up a wheel
if you still have the front axle disconnect.
Earle
"L.W. (Bill) Hughes III" <billh...@cox.net> wrote in message
news:52scpuF...@mid.individual.net...
nrs
> Bill,
>
> I think I have towed mine a total of maybe 3,000 miles. I moved a few times
> since I bought it. No differentials destroyed yet. I can't perform the
> test until the weekend, but I sure will do it. In 2HI, you can reach under
> the vehicle and turn the front drive shaft with all four wheels on the
> ground. In N it has to be the same way. You don't have to jack up a wheel
> if you still have the front axle disconnect.
>
> Earle
>
>
>
>
> > That's true with the Dana 20 and 300 with only one lever. I would
> > appreciate it is someone with New Process transfer would confirm this, by
> > simple putting theirs in neutral and jack up a front wheel, if they don't
> > free wheeling hubs and see if you can turn the front driveshaft. I don't
> > believe it's true, because this would quickly destroy one of the
> > differentials.
> > God Bless America, Bill 0|||||||0
>
> > <edh3...@bellsouth.net> wrote in message
>
> - Show quoted text -
I think you still need to lift one tire to do the check to know if the
driveshafts lock together. For instance, if the front axle is still
connected with the engine off (both front on the ground), then the
driveshft will not turn with the TC in N. This would make me think
(falsely) that the driveshafts are locked together. In order to
eliminate the posibility that the front axle is connected, one front
wheel should be off the ground.
There are really two things to check: 1) does the axle stay connected
with the engine off, and 2) do the driveshafts lock together in N.
L.W. (Bill) Hughes III
"Earle Horton" <ap...@gracioso.usa> wrote in message
news:opudncHQOaBakFTY...@comcast.com...
Earle Horton
with the transfer case in neutral, then you have problems. I always have
the engine running when I shift the transfer case into neutral, because
sometimes you have to move the vehicle a little bit to get the gears to
mesh, and because I know about the vacuum disconnect I guess. Note that the
newer models don't have a front axle disconnect, and that you can still flat
tow them if the transfer case has a neutral. I am talking about the TJs,
newer Cherokees, GJs, etc. I am only going to do the check because you
never know about things, not because I believe that there is anything to the
OP's idea.
Earle
"nrs" <neal...@yahoo.com> wrote in message
news:1170805228.0...@k78g2000cwa.googlegroups.com...
...
nrs
> It doesn't matter what the cause is. If the front driveshaft won't turn
> with the transfer case in neutral, then you have problems. I always have
> the engine running when I shift the transfer case into neutral, because
> sometimes you have to move the vehicle a little bit to get the gears to
> mesh, and because I know about the vacuum disconnect I guess. Note that the
> newer models don't have a front axle disconnect, and that you can still flat
> tow them if the transfer case has a neutral. I am talking about the TJs,
> newer Cherokees, GJs, etc. I am only going to do the check because you
> never know about things, not because I believe that there is anything to the
> OP's idea.
>
> Earle
>
>
> news:1170805228.0...@k78g2000cwa.googlegroups.com...
> ...
>
>
>
>
>
> > I think you still need to lift one tire to do the check to know if the
> > driveshafts lock together. For instance, if the front axle is still
> > connected with the engine off (both front on the ground), then the
> > driveshft will not turn with the TC in N. This would make me think
> > (falsely) that the driveshafts are locked together. In order to
> > eliminate the posibility that the front axle is connected, one front
> > wheel should be off the ground.
>
> > There are really two things to check: 1) does the axle stay connected
>
> - Show quoted text -
Makes sense, if they locked together towed TJ's would be trash by now.
Peter Stolz
in neutral and put the tranny in a gear. Do I need to disconnect the rear
drive shaft? Or, what is the downside of putting locking hubs on the rear?
"L.W. (Bill) Hughes III" <billh...@cox.net> wrote in message
news:52scpuF...@mid.individual.net...
Earle Horton
rear in neutral. You need to get an owner's manual and see what it says.
An NV4500 upgrade doesn't really change anything in that respect. For your
vehicle disconnecting the rear drive shaft sounds like a good idea. Locking
hubs require you to install a free floating axle, which is a good thing, but
there is the expense.
Earle
"Peter Stolz" <peach...@yahoo.com> wrote in message
news:Lcoyh.3542$4H1....@newssvr17.news.prodigy.net...
edh...@bellsouth.net
I need to note two things:
First, I was researching YJ Wranglers specifically (although we own
and tow a TJ in the same manner).
Second, I see that my original post did not copy in (from the file on
my computer) my "Sources" information. I herewith correct that fault:
Please mentally add the following to the bottom of my orignal post:
Sources:
1. Petersen's 4Wheel & Offroad, How-To, Beefing Up the NP231 Transfer
Case
This article was my first exposure to the internals of how the NP231
works and the first place I read anything about how the vacuum
operated CAD works. Besides the obvious idea of not starting the
engine, this article discusses options 1 and 4 above.
2. Jeep Owner's Bible (Moses Ludel), especially his discussion on how
transfer cases work. Also, although I'd learned about backing up to
disengage the front hubs, this book is the first place I ever saw it
documented.
3. JeepTech, on the web, had a good discussion of the NP231.
4. Many articles I've read in magazines and on the web discuss the
towing limitations of the NP231, although most do not mention the
mechanism of the locking together of the front and rear output shafts
as the culprit. Many articles about Slip Yoke Eliminator (SYE) kits
have some brief information about the rest of the NP231 internals.
5. Novak Adapters, online technical articles.
6. RV Net (and some other RVing sites). Lot's of people flat tow jeeps
and are very willing to share their experiences.
7. Off-Road Adventures (from 4Wheel Parts); an answer to a question in
the Gearhead column actually prompted me to post this note to the
list. Some of what I've said comes from Jim Allen (who obviously
agrees with the other sources I've read). Any errors remain my own.
Further -on comments in this thread-
Frankly I find it hard to believe myself that Jeep would install a
transfer case that would engage the front and rear output shafts
together simply upon you moving the transfer case lever from 2WD to
Neutral! Of course, I don't know why they used chain drive instead of
gear drive either. But in any case, I've read the information about
the output shafts multiple times and from apparently knowledgeable
people. However, this is always in reference to early NP231 units as
installed on YJ Wranglers. I have no idea why this isn't true for TJ's
transfer cases.
Despite my own comments in my original post, I acknowledge that DC
(and earlier owners of Jeep) always say that if you are going to flat
tow to do so with the transmission either in gear (manuals) or in park
(autos). I've not had a problem, nor have others who tow with the
transmission in neutral. I'm not sure what kind of "fluid currents"
would be needed to spin the transmission enough to cause a lubrication
problem. However, I'm willing to stipulate that Jeep knows best in
this regard. Please mentally correct my original post accordingly. In
Gear, that's Clear.
It may have been made clear earlier, but to be complete: it is the
rear output shaft on the NP231 that spins the internal oil pump. The
commercial adaptors that add 2WD-Low to the transfer case (at least
those that result in adding a "true neutral") do not disturb the rear
shaft: it still pumps oil while you flat tow.
So stock YJ and TJ owners can:
Back up about 10 feet in 2WD, drive jeep to tow vehicle and attach,
turn off the engine, place the transfer case in neutral, place the
transmission in gear (or park if auto), proceed to safely tow away.
I'm afraid you CJ owners are left to your own devices. NewJ owners are
expected to follow the instructions found in their spiffy new
manual :-)
Peter Stolz
magazine's website at
http://www.jpmagazine.com/howto/154_0701_jeep_transfer_case_upgrades/more_cases.html
"Flat tow: If your case is in the stock orientation, remove your rear
driveshaft from the axle and fasten it out of the way. If you've clocked it
flatter than stock, you may get away with the same method mentioned for the
Dana 20. Basically, it needs to have at least one gear on the rear output in
the pool of oil so it slings the oil around when the Jeep is moving. In the
stock clocking setup, this doesn't happen."
They also talk about most or all other tcases in jeeps and what to do with
them.
Pete
"Earle Horton" <ap...@gracioso.usa> wrote in message
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L.W. (Bill) Hughes III
"Peter Stolz" <peach...@yahoo.com> wrote in message
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