Full-Time 4WD Question

mass-hole · **Posted:** Thu Nov 28, 2013 9:09 pm

I occasionally use full-time 4wd to cut across my lawn to get around the Fiances car. I know it gets into 4wd fine since its not spinning the rear in my grass, but I have noticed that when the 4 tires are back on the driveway(paved) and I make a sharp turn it bangs and clunks like the driveline is binding. My question is . . . does Full-time 4wd fully unlock the front and rear axles, or is there a limit to how much they can spin independently? Should a sharp low speed turn cause a clunk like its locked 4wd?

Happy Thanksgiving

ATXKJ · **Posted:** Thu Nov 28, 2013 11:30 pm

Full-time puts a limited slip at the transfer case - it does not affect the axles

it shouldn't clunk.

dirtmover · **Posted:** Fri Nov 29, 2013 9:17 am

Yeah, I get this as well. I often drive with FT4 in the winter. It tends to be more likely to do this bang/clunk thing in reverse. If I forget to disengage it before entering the parking lot at work I'll often get this almighty thud while reversing out of my parking spot.

naturist · **Posted:** Fri Nov 29, 2013 9:54 am

I use Full-time 4WD a fair amount, as it is my preferred mode when towing the travel trailer -- it feels more stable directionally in that mode, less sway and all. I've never had it do that on me, but I have had it do that after shifting out of part time 4WD. I think that what happens is that it doesn't completely disengage PT all that quickly. Of course, you do really have to be rolling when you make those shifts.

Brianawd · **Joined:** Wed Apr 03, 2013 12:59 pm **Posts:** 130

I get the pop when it comes out of part time 4wd. I now stop take it out of part time and put the jeep in revers for about 10 feet Then back to drive and go on my way. That keep it from the pop I get every now and then.

Who ever designed the tcase is a retard. Why they would put Part time engagement first makes no since to me. I would have like to see
2wd/full time 4wd/part time 4wd/N/part time 4wd low.

mass-hole · **Posted:** Fri Nov 29, 2013 5:15 pm

naturist wrote:

I use Full-time 4WD a fair amount, as it is my preferred mode when towing the travel trailer -- it feels more stable directionally in that mode, less sway and all. I've never had it do that on me, but I have had it do that after shifting out of part time 4WD. I think that what happens is that it doesn't completely disengage PT all that quickly. Of course, you do really have to be rolling when you make those shifts.

I took it for a ride and shifted to full-time at 30mph. This is exactly what the problem was, It was getting stuck in Part-time despite me jumping back and forth between R and D a bunch of times.

mass-hole · **Posted:** Fri Nov 29, 2013 5:23 pm

ATXKJ wrote:

Full-time puts a limited slip at the transfer case - it does not affect the axles

it shouldn't clunk.

Is it really limited slip? With some tru-tracs in the from and rear, this thing would be a monster in the snow.

fool4wheelin · **Posted:** Sat Nov 30, 2013 12:22 am

mass-hole wrote:

Is it really limited slip? With some tru-tracs in the from and rear, this thing would be a monster in the snow.

The NV242 does NOT have a limited slip, just an "open" differential (or in this case, a planetary).

ATXKJ · **Posted:** Mon Dec 02, 2013 6:40 pm

fool4wheelin wrote:

The NV242 does NOT have a limited slip, just an "open" differential (or in this case, a planetary).

That's correct - I was thinking about something else.

FYI- I do have front and rear TruTrac's and I do not have any problems in snow.

fool4wheelin · **Posted:** Tue Dec 03, 2013 10:48 pm

ATXKJ wrote:

FYI- I do have front and rear TruTrac's and I do not have any problems in snow.

I am envious!

Did your's have factory limited slip in the rear originally? How much did the True-Tracs cost to put in?

ATXKJ · **Posted:** Tue Dec 03, 2013 11:43 pm

fool4wheelin wrote:

Did your's have factory limited slip in the rear originally? How much did the True-Tracs cost to put in?

I bought one got the other as a Christmas present (my son's a Jeeper - he has a Rubicon)

and I installed them.

so it cost a couple of weekends.

(I did have a quote from a shop about $500 or so if I brought in the axles - that was the backup if I messed up)

geordi · **Posted:** Wed Dec 04, 2013 12:10 pm

This transfer case is yet another thing designed by a moron at Chrysler. You CANNOT properly shift it into any of the other modes without ALL FOUR TIRES ROLLING.

The tires all have to be rotating at precisely the same speeds (so drive straight) and at a speed below 10mph. The shifting in the transfer case is moved by a cable (not a direct lever connection) and the cable pushes on a small metal "fork" that can easily bend if not shifted properly.

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thermorex · **Posted:** Wed Dec 04, 2013 6:49 pm

I had no issues shifting in any tc "gear" while stopped if I Shift the tranny în neutral and then Shift transfer case where I want. Never tried to shift the tc over 15 mph, even though I guess (if memory serves me right), you can do it till 30 mph.

jkbkwarner · **Posted:** Wed Dec 04, 2013 9:27 pm

Oops, didn't know about when to move to 4wd. I've never used the part-time mode I'm not one to rely on the engineering to always build the logic to engage 4wd as needed. So I was either using 4wd or not, hence forward, I'll be in motion (at or under 30) when changing to 4wd.

geordi · **Posted:** Wed Dec 04, 2013 10:08 pm

Part-time is not letting the computer decide anything. Part-time mode is designed to only be selected "part of the time" because it is a fully-mechanical link, LOCKING THE AXLES TOGETHER. If you use this on pavement or anything that isn't a very slippery surface, turning the steering wheel can cause very bad things to happen.

Full-time 4wd is the high-gear range that can be left on. It uses a liquid coupling to engage the front axle, so turning the wheel doesn't cause mechanical binding. This is similar to an AWD system in most other vehicles. Better than nothing... But probably not much.

The transfer case on the old 97 Jeep Grand Cherokee (Don't remember the number) is also a fully-mechanical unit, and there is no way to disconnect the front wheels from it or put it in a fluid coupling mode. It is always mechanically locked together. When turning the wheel on that, an audible clicking noise can be heard as the transfer case somehow adjusts for the difference in axle speeds.

As far as shifting the CRD transfer case while stopped... Putting the transmission in neutral doesn't change anything. The problem is in linking up the big gears that are connected to the front and rear prop shafts. If they aren't rotating, the shifting gear (being moved by the small shift fork) will just push up against the gear and "wait" to engage once it does start moving. It may have a spring, it may only be cable tension holding it in place, but that shifting gear is NOT engaged where it should be, despite what the handle tells you up in the cab.

If the rear then rotates (which spins the shifting-gear at the same time) and it finds a way to fit in to the not-rotating front (like you are stuck in the snow or mud) the shifting-gear could slam partly into position on the front gear and snap teeth off.

I suspect this is what happened to my transfer case when it mysteriously went back into gear while being towed. The handle never moved from neutral. The transfer case specialist said that one of the gears had HALF its teeth stripped bare, while the shift forks were bent rather badly and the front gearset was missing chunks and several teeth. His professional opinion was that quite a lot of mayhem happened in there, and quite possibly the transfer case wasn't ever working properly while I owned the vehicle. I hardly ever used it in anything other than 2wd, so that is very possible.

The point is that the floating shifting-gear is not very strongly built and it must match up perfectly to properly engage. For that to happen, all 4 wheels need to be turning. I'm not saying it cannot shift properly when stopped - I did it that way too a couple times... Usually AFTER getting stuck somewhere stupid... But that may cause severe damage. For reference, I don't know that the 4wd part time or full time EVER properly engaged when I was stuck, but that may be a symptom of the already-damaged transfer case. I don't know what the original owner may have done with the Jeep before I got it.

fool4wheelin · **Posted:** Wed Dec 04, 2013 11:39 pm

geordi wrote:

Full-time 4wd is the high-gear range that can be left on. It uses a liquid coupling to engage the front axle, so turning the wheel doesn't cause mechanical binding. This is similar to an AWD system in most other vehicles. Better than nothing... But probably not much.

The NP242 "Selec-Trac" has been around since '87 in the XJ's and has a decent track record. It doesn't have a "viscous" liquid coupling, just an "open" differential, so there is no torque bias between the front and rear axles. You can shift between the high ranges at speeds up to 55 mph. The cleanliness of your transfer case fluid affects the ease of shifting.

joelukex4 · **Joined:** Thu Sep 29, 2011 4:54 pm **Posts:** 386

Here is the info on the NP242:

The Jeep NP242 transfer case was introduced in the 1987 model year as a replacement for the NP228. The 242 premiered in the XJ Cherokee / Wagoneer and MJ Commache as the SelecTrac option. It was used in the 1991-1998 ZJ Grand Cherokee. The 242 persisted throughout the full run of XJ Cherokees and continued on in the 2002 KJ Liberty.
The 242 was originally tagged as the 242AMC, and as ownership of AMC was taken over by Chrysler, it was later designated as the 242J. This transfer case was later called the NVG (New Venture Gear) 242. Despite the different nomenclature, very few mechanical changes were required or made throughout their production span.
Earlier attempts at torque-biasing transfer cases were spotty in their success, beginning with the QuadraTrac in the 1970's and continuing with the NP219 and NP228. The 242 has continued in the trend of chain-driven cases and has technically and commercially been more successful than its predecessors.
Features
The 242 has a driver's side front output and centerline rear output. The NP242 features two ranges; a low range gear that is a respectable 2.72-to-1 low and a direct-drive in high range. It features three drive modes; 2wd, full-time 4wd and part-time 4wd, yielding:
two-wheel-drive, high (direct-drive)
four-wheel-drive, high (48/52 differential torque-biased-drive)
four-wheel-drive, high (locked, part-time)
neutral
four-wheel-drive, low (locked, reduction-drive)

Geordi, I understand your distaste for Chrysler but you can blame all issues on their engineering. This was designed prior to their purchase of Jeep. Most auto manufacturers use driveline component parts from third party manufacturers like Dana, Borg-Warner, Aisin, New process, Allison and others. They need to purchase off the shelf units. I have had 3 NP231 transfer cases in three Cherokees and they have been bulletproof. Would this be a kudos for Chrysler or New Venture Gear.

I also agree that the full time option should be first in the shift sequence.

tjkj2002 · **Posted:** Thu Dec 05, 2013 1:36 am

geordi wrote:

Part-time is not letting the computer decide anything. Part-time mode is designed to only be selected "part of the time" because it is a fully-mechanical link, LOCKING THE AXLES TOGETHER. If you use this on pavement or anything that isn't a very slippery surface, turning the steering wheel can cause very bad things to happen.

Full-time 4wd is the high-gear range that can be left on. It uses a liquid coupling to engage the front axle, so turning the wheel doesn't cause mechanical binding. This is similar to an AWD system in most other vehicles. Better than nothing... But probably not much.

The transfer case on the old 97 Jeep Grand Cherokee (Don't remember the number) is also a fully-mechanical unit, and there is no way to disconnect the front wheels from it or put it in a fluid coupling mode. It is always mechanically locked together. When turning the wheel on that, an audible clicking noise can be heard as the transfer case somehow adjusts for the difference in axle speeds.

1st Chrysler did not make nor design the 242,take away the 2wd selection and add a wider chain and 32 spline outputs(AMG242) it is a stout t-case but the 242J(and C and D versions) is rather weak and the 2wd selection makes it even weaker.

As far as a liquid coupling that is what your ZJ uses in the 249 full time 4wd t-cases(WJ's got the 249 if full time 4wd),the 242 does not use any type of coupling.Also in a KJ engaged in part time 4wd,any KJ regardless of engine,trans,or t-case,just simply driving in a straight line will cause driveline binding since the front and rear diffs are slightly geared differently.2.4 gasser KJ's and export 2.5's with stock 4.10's are actually 4.09 front gear ratio and 4.10 rear.If you hear clicking while turning in a full time 4wd ZJ you got bad front axle u-joints.

thermorex · **Posted:** Thu Dec 05, 2013 2:06 am

Tj, I believe zjs don't have u joints, they have axles similar to liberty (don't know how exactly they are called). Of course, if somebody replaced them with Cherokee u joints, that's another story. Regardless, I think Geordi may have some issues with knocking due to a bad axle(s) or Ball joints/track bar. Also, could be the stabilizer bar links or Bushing on the chassis. Pain in the rear to know till you don't get under the car. I replaced all my right side ball joints at Cherokee only to find out that the knocking/clunking I had and was driving me nuts was caused by bad stabilizer bar bushings (not links).

Good info with liberty's front and rear diff gearing, didn't know that...

tjkj2002 · **Posted:** Thu Dec 05, 2013 2:28 am

thermorex wrote:

Tj, I believe zjs don't have u joints, they have axles similar to liberty (planetary "gear" - don't know how exactly they are called). Of course, if somebody replaced them with Cherokee u joints, that's another story. Regardless, I think Geordi may have some issues with knocking due to a bad axle(s) or Ball joints/track bar. Also, could be the stabilizer bar links or Bushing on the chassis. Pain in the rear to know till you don't get under the car. I replaced all my right side ball joints at Cherokee only to find out that the knocking/clunking I had and was driving me nuts was caused by bad stabilizer bar bushings (not links).

Good info with liberty's front and rear diff gearing, didn't know that...

My bad,yeah forgot ZJ's came with CV style axle shafts because of that stupid 249 t-case.

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