loud bang/pop - JeepForum.com
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post #1 of 6 Old 03-11-2004, 06:30 AM Thread Starter
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loud bang/pop

i have a 98 grand cherokee with select a track. i have read all about full time, part time and such.

according to the jeep website, full 4x4 can be used any time wet or dry. people on this forum have confirmed this. so here is the prob...

i race jetski's, and have to trailer them around. well, i went to pick up my trailer (2 place jetski trailer) to service it before the season starts. it was stored in my grandmothers backyard behind the pool shed - and i drove back there in low 4x4 (no wheel slippage on the wet lawn) and hooked it up (no probs)

i drove on the grass back out to the road (low 4x4) and needed to back the trailer up the driveway to load a ski on it, and also grab something from the house. i then switched the jeep to full 4x4 right before i left the grass and got on to the pavement.

as i tried to back the unloaded trailer into the drive from the road - it was basically a straight shot (no extreme turning). i did need to straighten out slightly. as i started to back up the jeep made a loud pop/bang that sounded like i hit another car.

i know this had to be the sound of a u-joint breaking or some gears in the t-case breaking/slipping. i took the jeep out of 4x4 full time, and put it back to 2wd. i backed up the driveway with no probs.

why did i get this noise? i thought select-a-track has no viscous coupler to go bad? my jeep has intermittantly had the wheel hop issue/binding issue while in full 4x4 that is so commonly described with the vc failure on quadratrac models.

when select-a-track in in 4x4 what is in the t-case to allow diff rates of wheel spin? on quadratrac it is the viscous coupler, so what does select-a-track use?

coule the selector lever be out of adjustment? sometimes after using 4x4 full or low 4x4 i have a issue getting the jeep into 2wd directly from full 4x4 or low 4x4 - (after switching to 2wd, i have to switch to part 4x4 and then switch back to 2wd.) if this is a prob, how could it effect the driving of full 4x4?? especially since i was in low 4x4 before i switched to 4x4 full time.

any ideas??


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post #2 of 6 Old 03-11-2004, 06:38 AM
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I would try running through the 4wd gears a couple of times. Taking it in and out of 2wd to 4hi and 4lo. If you haven't done that in awhile, the jeep might have needed a little exercise. So, don't leave them at the mall, actually put them on the dirt and let them play.

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post #3 of 6 Old 03-11-2004, 07:16 AM
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You are right, the bang was caused by the drivetrain binding, then suddenly releasing. And it isn't unusual to have to back up a bit to unload the drivetrain so it can change back to 2WD.
With that out of the way, for driving around on grass and such, while slippage (which is necessary) is present, there just isn't enough to be using 4LO (or part time). You'll find that full time 4WD is more than sufficient to tow a jet ski across the yard, even the boat ramp would have to be too slimey to walk on before I would use Part Time.
Researching this TC I have found that the chain driven NP242 is a full time transfer case with a 48/52 torque split front and rear. It is possible to lock it into four low so it behaves like a part-time transfer case. When it is locked in, power will be split regardless of traction. Low range is 2.72 and high is 1.00. Older units (probably much older than yours), used a limited slip kind of set up, where vacuum was applied to the front differential to disengage it and allow the drivetrain to slip between the front and rear. Since your chain driven TC appears to be constantly locked (it does get confusing reading about this particular TC) I imagine the drivetrain slip is still introduced through the differentials in some way. Hopefully, a Selec-Trac owner will step in and clarify this.
I doubt your selector is out of adjustment, since it uses a cable, the detents you feel are in the TC, and I presume your indicator lights are functioning properly. If the dash says 4LO and you felt it click into 4LO, but the bezel says Neutral, then your selector is out of adjustment.


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post #4 of 6 Old 03-11-2004, 07:50 AM Thread Starter
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thanks for the reply. i basically used 4 low for the slow speed ability to pull the trailer. normally, i would use 4wd full.

i know slippage is necessary, but i meant no slipping of my tires on the wet grass, producing a lack of grass.. my grandmother would kill me if i left a skid mark. (i had to hook up the trailer on a small hill - landscaping berm for water drainage - almost like the car was highsided & stuck on a hill on the frame with all wheels in the air - but the hill was not that drastic and the wheels were on the ground, but the suspension was flexing.)

the lights and selector lever all work fine. maybe someone can clear up the binding issue.


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post #5 of 6 Old 03-13-2004, 12:45 PM
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were you moving at 1-3 mph when you were shifting from 2wd to 4wd low
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post #6 of 6 Old 03-15-2004, 08:08 AM Thread Starter
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actually i usually find it best to stop the jeep, put it neutral, and then put it into 4x4 low. i know what the manual says, but this method produces the smoothest gear change for me.

either way, i only shifted from 4x4full to 4x4 low.

i think that maybe the fluid in the trans case has to be changed.

after doing my first (since i owned it) oil & trans fluid change, and changing the diff fluid on the front and rear to mobil 1 synthetic - i noticed the transfer case is sweating a little from the sides of the cases.

good thing it has a warrenty. time for it to go to jeep and have them tear it down and replace whatever seals are necessary


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