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bang and jerk in center or rear of drivetrain


 
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Turbo
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Joined: 19 Feb 2006

PostPosted: Fri Jul 11, 2008 2:56 pm    Post subject: bang and jerk in center or rear of drivetrain Reply with quote

When I shift to reverse and/or to drive, I get a "bang and jerk." Iv'e found that when I park at work where my parking spot is "nose down", the Jeep rolls forward until Park hooks up and it stops. Now when I put it in reverse from that point, there is no "bang and jerk" because the slack is already taken up when it rolled forward in park. Now if I pull out and put it directly into drive, I get the "B and J" unless I put it into neutral first and then into drive. If shifted into neutral before shifting fully into the oposite gear it allows the drive train to tansfer direction loosely (unwind) instead of slamming directly into gear. Now my question is this. "Where" exactly is this happening? In the transfer case or the rear differential? About a year ago while still having this issue I had Four Wheelers Supply here in Phoenix put in Alloy axels and a Detroit locker in my D35. [don't even go there you D35 haters LOL ] I thought that they would have mentioned something if all was not right. I know that they did put in new bearings and seals but the B and J is still there. Then I had another garage look at it and they pulled the diff cover off and everything looked fine and thought it might be the transfer case. Then I had Aamco look at it last week and they thought it was the differential. I was going to take it to one more shop and let them tell me what they thought before I decide what to do. I've heard people say "that's just the way Jeeps are." REALLY? If I leave this alone, is the B and J going to tear up anything? That's my concern, other than the noise and big jerking movement it makes when I shift before pulling out of a parking space. It's getting so bad right now that I kinda wait to make sure no one is around before I change gears. Surely someone has has this before and fixed the issue... Anyone? Beuhler... Beuhler... Neutral
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swamp boy
Cherokee Muderator
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Joined: 01 Jan 2004
Location: New Orleans LA.

PostPosted: Fri Jul 11, 2008 3:57 pm    Post subject: Reply with quote

I would check the U joint. Grab the shaft and shake it.. (not that one you pervert) the shaft on your Jeep..

Twist it and jerk it... (god you have a dirty mind..) and see if there is any movement in the joint..

While you are at it .. Watch your pinion see if it is loose or wobbly...


If you Ujoint is good and your pinion bearing is not worn or yolk itself not loose.. Let us know.. There are other things to check..
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Orangeamc13
Got Rev Limiter?
Got Rev Limiter?


Joined: 20 Feb 2006
Location: East Springfield, Massachusetts - U.S.A.

PostPosted: Fri Jul 11, 2008 5:25 pm    Post subject: Reply with quote

I would suggest jerking your joints as well.
Then, I would check the tranny mount if the u-joints are good.

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Turbo
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Joined: 19 Feb 2006

PostPosted: Fri Jul 11, 2008 7:14 pm    Post subject: Reply with quote

OK guys, I just got in from checking everything mentioned. Everything seems real solid as far as U joints and pinion. While under there I tried twisting the rear diff while the tranny was in neutral and engine off (of course). With Tcase in 2 wheel the rear diff turns almost a 1/4 turn. With T case in 4 Wheel PT (front and rear diffs connected solid)rear diff barely turns a 1/16 turn, exactly like the front and that's what I would expect. With the T case in 4 Wheel FT I get 1/4 turn in rear diff, just like in 2 wheel. So, there seems to be excessive play in the rear diff, at least compared to the front. Is a 1/4 turn excessive? While in 4 Wheel PT the front and rear diffs didn't seem to have any play between the two. When I tried to turn the front the rear would turn right with it. That seems to tell me that there's not a lot of play in the chain in the T case. What about the connection with the shaft comming from the transmission to the T case where the top pully is and the chain wraps around. Sorry, don't know what it's called. Could there be some play in that along with the play in the rear diff? Not sure how to check for play there. That's all I have for now.
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swamp boy
Cherokee Muderator
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Joined: 01 Jan 2004
Location: New Orleans LA.

PostPosted: Sat Jul 12, 2008 12:22 pm    Post subject: Reply with quote

The problem is prolly not in your diff if you cant shake the pinion or yolk..

I would go wtih Orange's suggestion and check your tranny mounts ..
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Brad The Best
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Joined: 14 Jan 2007
Location: Kamloops B.C Canada

PostPosted: Sat Jul 19, 2008 3:23 am    Post subject: Reply with quote

you could lie down beside the jeep and have some one put in in gear and park with the brake on and see whats moving /hear were it is coming from .

engine mounts as well they shred like wax paper .

you don't have a 1/4 turn of backlash in your diff . it doesn't happen .

aamco is like the canadian tire of transmission shops .
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zjtherightway
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Joined: 21 Jul 2008
Location: Mesa, Arizona

PostPosted: Tue Jul 22, 2008 6:54 pm    Post subject: Check motor mounts Reply with quote

I would also check the motor mounts. With your foot on the brake put it in drive and give it a little gas then let off, watch the motor to see how much it moves or if you here anything. Try it in reverse too. If you have a second pair of eyes, they can look directly at the mounts or ?
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