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Unread 08-03-2014, 08:29 PM   #1
Charley3
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1999 XJ Cherokee 
 
Join Date: Mar 2013
Location: Longview, WA
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Things that make my tcase shift easier and run quieter

I have 242 tcase. This also applies to the Grand Cherokee tcases, and probably also applies to 231 & 241 tcases and any other tcase.

First I changed the transmission fluid in my 242 to synthetic transmission fluid. I used Mobil One tranny fluid and it help it shift a bit easier and run a lot quieter in 2wd and Full Time 4wd.

I suggest if your owner's manual calls for transmission fluid in tcase, use synthetic transmission fluid.
Yes, I'm aware that some later model tcases (like 241) come stock with synthetic transmission fluid. So for that tcase you've already got synthetic lube.
I suggest if your owner's manual calls for gear oil in your tcase, use synthetic gear oil of same viscosity specified in owner's manual.

I have experienced with my 96 XJ that synthetic tranny oil made my 242 shift easier (and run quieter) than with conventional oil. I think it also reduced wear.

-----

Tire diameter makes a big difference in ease of shifting (for any tcase) and how quiet the tcase runs when in Full Time 4WD (for those tcases that have Full Time 4WD). Tire diameter also affects how much wear occurs when in 2wd or 4wd.

The goal is to have as close as possible to same tire diameter front and rear. So you need all 4 tires the same brand, model, size, load rating, and with a similar amount of tread-wear/tread-depth.

Assuming you have 4 identical tires, the next issue is tire pressure.

I have read some threads (at various forums) saying all 4 tires need same pressure. I have also read it's best to use 2 psi less in the rear tires.

I called a transmission shop and asked their opinion. They said all 4 tires need to be as close as possible to same diameter, and they said that would be with slightly less air pressure in rear tires than in front tires. They told me it'd probably be 2 or 3 psi less in rear tires for approx same tire diameter. They suggested I test it by trying different air pressures in rear tires and shifting tcase to learn when it shifts easiest into 4wd and back to 2wd.

I already had tested it in my 99 XJ with 242 tcase. (I have 30" tires) With 28 psi in all tires it shifts easily enough (I have synthetic oil in tcase). With 28 psi front, 26 psi rear, it shifts very easily and runs very quiet in 4wd Full Time. With 28 front, 25 rear, it shifts very easily and runs very quiet in 4wd Full Time.

I prefer 25 psi rear because in addition to shifting very easy, it also has better ride quality, and quite a bit more rear wheel traction. With the increased rear wheel traction 2wd can handle the very steep gravel roads with ease. That's a convenience because I don't have to shift to 4wd for gravel roads.

The most important point is this, use whatever tire pressures front to rear that gives you the same tire diameter for all tires. My Jeep (like most) is heavier in front, lighter in rear. So i need 2 to 3 psi less in the rear tires than front tires. This may differ for your Jeep depending on your weight distribution.

I suggest weighing your Jeep on a truck scale. Then you will know if you nees less psi in rear tires, and if so, use math to figure out how much less. Weigh with front tires only on scale. Then weigh with rear tires only on scale.

If you got your tire pressures right (same diameter all tires), your tcase will shift very easily, especially if you also have synthetic lube in tcase.

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Unread 08-03-2014, 08:34 PM   #2
Charley3
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P.S. - having all tires the same diameter reduces wear on tcase, even when in 2wd.
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Unread 08-04-2014, 06:00 PM   #3
MaskedMallard
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Are you checking / adjusting your tire pressure with a full tank of gas vs. half tank of gas vs. near empty fuel tank??? Gasoline is about 6 pounds per gallon. So you are going to be changing weight by about 120 pounds.

In driving, I also imagine your brakes being out of adjustment will affect tire pressure. If your front brakes are doing more braking than they should, I imagine the heat transfer into the rim will raise tire pressure in the front.

Are you running compressed atmospheric air like found at a self service tire place, or are you running 100% nitrogen filled tires that are less susceptible to tire pressure change with heat???
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Unread 08-04-2014, 09:36 PM   #4
cruiser54
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And this helps also:

Here's how the factory suggests you shift the transfer case and I've been doing this since these things were new and I worked at the dealership. Quoted from the owner's manual. The suggestions in ITALICS are mine.

"To engage, shift the transfer case lever from 2H to 4H while the vehicle is moving at any legal speed". I let off the gas, throw the lever, and then tap the gas and let off.

4L position: " To engage, slow the vehicle to 2-3 MPH , shift the transmission to Neutral, then shift the transfer lever to the right and pull firmly rearward to 4L".

To shift out of 4L, shift the transmission into neutral with the vehicle stopped, shift the transfer case lever to 2H, then to D if you have an automatic, or into first gear with a manual, and continue on.


Revised 01-31-2014
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Unread 08-05-2014, 01:31 PM   #5
Charley3
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My shifting routine is this (242 Tcase):

From 2wd to 4wd Full Time: At any speed under 50 mph drive steady speed (ideally NOT under much load - i.e. - not going up a hill), shift firmly from 2wd to 4wd Full Time, let off gas and coast a second, get back on gas and continue driving.

To go to 4wd Part time, do the above, and then repeat the above, except the second time shift to 4wd Part Time.

To get back to 2wd repeat the above process in reverse order. (I said reverse order. I didn't say driving in reverse!)

===

To get to 4 Lo, I'm aware of the owner's manual instructions that Cruiser quoted, but I've had really bad luck following those instructions with 242 tcases on XJs and 241 tcases on Rubicons. When I followed those instructions I got nasty gear grinding and/or clunking sometimes, and success other times.

So I have my own system of getting to 4Lo that's never caused me any gear grinding or clunks.

I stop, put tranny in neutral, shift tcase to 4 Lo, put tranny back into Drive or Reverse, and idle forward or backward a few feet. Shift tranny to neutral. Then shift tranny into gear and idle/drive the opposite direction a few feet. Then I know it's fully engaged and I there was no risk of grinding gears when shifting tcase to 4Lo.

To get back to 2wd, I do same as Cruiser. I stop, put transmission in neutral, then shift tcase back to 2wd.

===

If the tcase is difficult to shift, or you aren't sure if it's fully engaged where you want it, gently drive forward or backward several feet. Put in neutral and pause for a half second. Then shift into gear and drive opposite direction several feet. That usually unsticks any partial shift. If not, repeat a few more times and/or check tire pressures as described in OP. Then later check tcase fluid level and verify tcase fluid is clean and not burnt or dirty.
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Unread 08-05-2014, 01:34 PM   #6
Charley3
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Quote:
Originally Posted by MaskedMallard View Post
Are you checking / adjusting your tire pressure with a full tank of gas vs. half tank of gas vs. near empty fuel tank??? Gasoline is about 6 pounds per gallon. So you are going to be changing weight by about 120 pounds.

In driving, I also imagine your brakes being out of adjustment will affect tire pressure. If your front brakes are doing more braking than they should, I imagine the heat transfer into the rim will raise tire pressure in the front.

Are you running compressed atmospheric air like found at a self service tire place, or are you running 100% nitrogen filled tires that are less susceptible to tire pressure change with heat???
I check with gas anywhere from a half tank to a full tank.

I use ordinary air. Nothing fancy like nitrogen.

I check in morning before driving, or in evening after vehicle has sat for a few hours or more.
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