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Old 12-11-2013, 01:27 PM   #1
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Serious Thump After 4HI Disengage

Puzzled. (32rh 4.0L)
This happened once yesterday and then once again today.
Same circumstances both times.
While driving 50-55 in 4WD HI on snowy Hwy... Hwy turns to bare asphalt so I slip the 4WD lever down to 2WD. I've done this thousands of times since I've owned the Jeep with no problems, smooth as pie.
But once yesterday and once today.... everything goes as planned and nothing even feels weird BUT 7-10 seconds after I put the shift lever down I get an audible "thump" and I can feel it in my feet on the floorboards. Just one thump and something I've never heard before but scared the BJesus out of me twice now. Everything seems to be working well.
What the heck could it be? I need to address this before bad things happen.
Help and advice appreciated! I can wrench.

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Old 12-11-2013, 03:14 PM   #2
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Same thing happened here with the snow last weekend. Like the OP stated, other than the thump, the Jeep seemed normal. 06 LJ here...

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Old 12-11-2013, 06:17 PM   #3
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I had the same issue this past week, did it twice on the same day, and it scare the Jesus out of me!!! I noticed that if I shift it back to 2wd before leaving the ice/snow on the road it was smooth, but if I waited to be on concrete or asphalt it would do that loud stump about ten to fifteen seconds later. My thoughts are that the rear axle is rotating at a different speed than the front one and is creating a bind that eventually will result on the loud stump. I think this because I have a newer pair of tires on the front versus the old worn out pair on the back, difference on the diameter of the wheels will cause this. Just my .02.
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Old 12-11-2013, 08:25 PM   #4
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Only happened to me once. About 6 miles after replacing my ujoints. I pulled into a Steep ditch to talk with my neighbor out in his field and actually needed 4wd to get back up, disengaged 4 as I crested the top then it popped on me at like 20mph going to highway speeds. Never done it since even though I use 4wd everyday even at highway speeds to combat washboards when there's oncoming traffic. i guessed it was just torqued into gear. Kind of like push button 4wd vehicles refusing to shift into 2wd until you put the thing in reverse to remove the load.
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Old 12-13-2013, 06:12 AM   #5
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Bump.
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Old 12-13-2013, 08:06 AM   #6
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I had this issue but coming off the trail. Riding in 4wd and had problem getting into 2wd. At low speed I could feel I was still in 4wd so I had to drive in reverse about 15' to get the gear to catch if I didn't realize it I would get that thump. PO had a 3" BL and I now have a 1.25" BL if that helps.. What do you guys have?
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Old 12-13-2013, 08:19 AM   #7
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I have a 2" SL which shouldn't have any effect, never has anyway.
Also, I don't think it could be tires. Rear tires are a little more worn (after rotation a while back) but not significantly.
All 4 of my tires are KM2 and in fairly good condition.
I have to commute 110 miles each way for the next few days and this involves two snowy mtn passes twice each day. Most of the commute is dry but the passes require 4HI. For now I'm disengaging at about 30mph and not experiencing the thump. Pretty sure it'll thump again at 50-55 (10 seconds after disengage) but I'm not going to try it until I know what's going on. Can't afford to break down that far from home.
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Old 12-13-2013, 03:01 PM   #8
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I used to have this problem and I don't have a lift. It got to where I would stop and shift it to 2w and it just went away never did figure it out.
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Old 12-13-2013, 06:56 PM   #9
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Had a light bump and delay getting out of 4WD last week so I pulled out FSM and they suggest checking the fluid level so I'm gonna change it out tomorrow to see if it happens again.
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Old 12-13-2013, 07:51 PM   #10
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I noticed this on mine, I do shift on the fly but I let off on the gas and sort of find a sweet spot like when you shift a manual without the clutch. Haven't had a thump doing it this way.
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Old 12-14-2013, 08:10 AM   #11
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Quote:
Originally Posted by JimsJeep View Post
... they suggest checking the fluid level so I'm gonna change it out tomorrow to see if it happens again.
Which fluid are you going to check and change out? Transmission, t-case, diff?
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Old 12-14-2013, 08:30 AM   #12
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Quote:
Originally Posted by Gold Miner View Post
Which fluid are you going to check and change out? Transmission, t-case, diff?
T Case, ordered Redline ATF from Summit and changing it out later this morning.
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Old 12-14-2013, 08:33 AM   #13
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Just curious when you guys shift on the fly do you slightly back off the gas when you shift into or out of 4H? It might be worth a try, I had a similar problem with a 4x4 Ford PU and that seemed to eliminate the problem.
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Old 12-14-2013, 09:43 AM   #14
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Quote:
Originally Posted by demarpaint View Post
Just curious when you guys shift on the fly do you slightly back off the gas when you shift into or out of 4H? It might be worth a try, I had a similar problem with a 4x4 Ford PU and that seemed to eliminate the problem.
I always back off a bit, could not imagine shifting while under acceleration.
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Old 12-14-2013, 12:27 PM   #15
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That's fine; you just had a bit of bind built up from a turn or wheel slip that released when the chain slid back off the front output shaft. Slop in the chain, driveshaft, u-joints, axle shafts, hubs, and control arms lets tension build up between the front and rear output shafts; when you release front output shaft it "unwinds" and makes a thump.
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Old 12-14-2013, 12:36 PM   #16
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Quote:
Originally Posted by JimsJeep View Post
I always back off a bit, could not imagine shifting while under acceleration.

Smart move, you'd be surprised how many people shift into and out of 4WD while accelerating. I used to shoot with a guy that shifted his Cherokee into 4H while passing someone in a snow storm on I-80.

I like to back off the gas a bit to take some of the load off the drive train. Opinions vary.
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Old 12-14-2013, 01:14 PM   #17
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Quote:
Originally Posted by Gold Miner View Post
Which fluid are you going to check and change out? Transmission, t-case, diff?
I used the royal purple in my TC and could tell a much smoother shift into hi and lo.
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Old 12-14-2013, 01:32 PM   #18
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Yeah, I try to relieve pressure on the gears. This'll be something I watch out for in the future. I definitely try to unload the driveline when transitioning to and from 4wd.

06 LJ, stock height, auto, 31's
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Old 12-14-2013, 02:20 PM   #19
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Quote:
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Yeah, I try to relieve pressure on the gears. This'll be something I watch out for in the future. I definitely try to unload the driveline when transitioning to and from 4wd.

06 LJ, stock height, auto, 31's
Good idea, I think you'll notice a difference too!
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Old 12-15-2013, 07:20 AM   #20
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Quote:
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... when you guys shift on the fly do you slightly back off the gas when you shift into or out of 4H?
Of course. I've owned this Jeep since '01.
This is the first (and second) time it's ever made a noise coming out of 4HI.
I'll try changing out the TC fluid if it ever gets above zero here again. I'm also leaning toward front driveshaft u-joints as a possibility (still factory orig over 200K mi). I replaced the rears last year but didn't replace the front.
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Old 12-15-2013, 07:51 AM   #21
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200k on u-joints is a lot.
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Old 12-15-2013, 08:25 AM   #22
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200k on u-joints is a lot.
I know, and I meant to replace them before winter set in but got extremely busy and it fell off the short-list. They don't look or feel bad but they are ready based on mileage alone. Definitely might be the culprit. Stock CA bushings are pretty worn all around too and I plan to replace all CAs also. These things may have to wait until spring though unfortunately. Until then I'm going to keep disengaging at 30mph or slower. It doesn't make the thump at lower speeds.
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Old 12-15-2013, 09:01 AM   #23
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It's the 7-10 seconds that has me curious, but I don't know enough about transfer cases to be any help. Could it be as simple as a chain hang up internally that sorts itself after a bit?
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Old 12-15-2013, 09:21 AM   #24
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It's a total gray area for me too which is why I'm hoping to get some insight from this thread. Maybe a TC guru will chine in.
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Old 12-16-2013, 04:23 AM   #25
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After changing the fluid mine seemed to be much smoother and no bumping back in. Goes in and out of lo like it should.
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Old 12-16-2013, 09:51 AM   #26
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Well, here's a new twist.
Woke up to a 1ft dia puddle under my skid, couldn't ID the fluid.
Too damn cold out to wrench right now so I dropped it off with my mechanic so he can put it up on the lift and diagnose it. I'm guessing a TC leak somewhere. He should be calling me in the next couple of hours with the verdict.
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Only thing we have to fear is, fear itself....................................... and bears
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Old 12-16-2013, 11:06 AM   #27
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Update.
Just got a call from my mech. Said that it's a transmission seal and he'll have to drop the TC to get to it. Est cost $210 and that's a good deal in my opinion. I'm kinda remote so the seal won't be here til later today or tomorrow. Cabin fever, byaaaaaa! If it were summer I'd attempt the repair myself but the $210 will be worth it in this case.
I'm not sure if this is associated with the thump I described or just a coincidence. I'll know once she's done.
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Only thing we have to fear is, fear itself....................................... and bears
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Old 12-16-2013, 01:27 PM   #28
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Excuse my newbness, but I was under the impression that the vehicle must be in neutral and stationary before one switches between 2WD and 4WD. I've never had a thump sound like that, though it sometimes seems a bit stiff starting off.
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Old 12-16-2013, 02:52 PM   #29
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You can shift "on the fly" from 2hi to 4hi, you need to stop, or mostly stop, to shift to 4low.
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Old 12-16-2013, 05:12 PM   #30
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Quote:
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You can shift "on the fly" from 2hi to 4hi, you need to stop, or mostly stop, to shift to 4low.
yes and it's actually recommended to be moving 5-10 mph to go from 2hi to 4 hi.

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