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  #1  
Old February 20th, 2018, 10:25
soyjer soyjer is offline
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Clunk/lurch into Drive, but not Reverse

I just bought a stock 1999 XJ, never been off road or abused, never towed anything, 97K mileage...all u-joints, engine/transmission mounts, leaf springs, etc. seem good, idles about 775 rpm...and yet it clunks and lurches when put into any FORWARD gear, but NOT AT ALL WHEN PUT INTO REVERSE.

Has anyone else ever experienced this ASYMMETRICAL clunk/lurching on their XJ?

The only thing in the drivetrain that I can think of that would be affected differently going in the forward direction as opposed to the reverse direction would be the transmission itself...but the noise seems to be coming more from the rear end.

Is there something about the way a differential is built that would cause it to clunk in the forward direction but not in the reverse direction?
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  #2  
Old February 20th, 2018, 10:45
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Re: Clunk/lurch into Drive, but not Reverse

When the transmission is in neutral, how much play is there in the rear differential?
Might also be a bad transmission or engine mount.
Have someone shift the trans from drive to reverse, while you look under the Jeep, to see what's moving.
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  #3  
Old February 20th, 2018, 14:13
soyjer soyjer is offline
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Re: Clunk/lurch into Drive, but not Reverse

Quote:
Originally Posted by lazyxj View Post
When the transmission is in neutral, how much play is there in the rear differential?
Might also be a bad transmission or engine mount.
Have someone shift the trans from drive to reverse, while you look under the Jeep, to see what's moving.
With transmission and transfer case both in neutral, I'm measuring 4.5 degrees of play on the rear drive shaft (2.5 mm or .1").

(2.5mm play / 200mm circumstance) x 360 degrees = 4.5 degrees of play.

I've had a friend switch between reverse and drive while I was under the rear end, and the only thing for certain is that it never clunks going into reverse and always clunks going into drive.
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Old February 20th, 2018, 14:17
soyjer soyjer is offline
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Re: Clunk/lurch into Drive, but not Reverse

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Originally Posted by soyjer View Post
With transmission and transfer case both in neutral, I'm measuring 4.5 degrees of play on the rear drive shaft (2.5 mm or .1").

(2.5mm play / 200mm circumstance) x 360 degrees = 4.5 degrees of play.

I've had a friend switch between reverse and drive while I was under the rear end, and the only thing for certain is that it never clunks going into reverse and always clunks going into drive.
I should mention that the 2.5 mm of play was measured using my own two arms to jerk the drive shaft back and forth as hard as I could.
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  #5  
Old February 20th, 2018, 19:29
GreaseMonkey17 GreaseMonkey17 is offline
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Re: Clunk/lurch into Drive, but not Reverse

Check passenger side motor mount .
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  #6  
Old February 21st, 2018, 04:51
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Re: Clunk/lurch into Drive, but not Reverse

I wouldn't worry about it. With most of the 8 Cherokees I have owned the AW-4 transmission kinda clunked or lurched when switching between Reverse or Drive. The AW-4 is a firm shifting transmission, the unibody transmits noises very well, and any wear in the drive-line or differential that creates noises, is amplified. My 1998 has 280,000+ miles and the only transmission or differential service work has been regular fluid changes.
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Quote:
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Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....

Last edited by Tim_MN; June 10th, 2018 at 16:28.
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  #7  
Old February 21st, 2018, 09:19
soyjer soyjer is offline
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Re: Clunk/lurch into Drive, but not Reverse

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Originally Posted by Tim_MN View Post
I wouldn't worry about it. With most of the 8 Cherokees I have owned the AW-4 transmission kinda clunked or lurched when switching between Reverse or Drive. The AW-4 is a firm shifting transmission, the unibody transmits noises very well, and any wear in the drive-line or differential that makes noises, is amplified. My 1998 has 280,000+ miles and the only transmission or differential service work has been regular fluid changes.
Thanks for the info...did any of the 8 have a low idle speed less than 750 RPM, and if so did they also clunk/lurch when put into drive (but not reverse)?

I haven't been able to locate any documentation that specifies what the idle speed is supposed to be except for the factory service manual that mentions 13psi oil pressure at idle speed 600 RPM... But 600 RPM doesn't seem to be the idle speed that most people in this forum are seeing with their XJ's, and so I'm not sure that 600 RPM is correct.

I'm also not seeing posts from people who had a clunk/lurch only when put into forward gears and never when put into reverse... I'm hoping that the fact that mine is completely asymmetrical will help me to figure out which component is causing the problem, but I can't find anybody yet that has had this clunk/lurch only when put into forward gears and never when put into reverse.
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Old February 21st, 2018, 11:34
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Re: Clunk/lurch into Drive, but not Reverse

750 rpm plus or minus is what I would consider normal idle speed. I do find that pausing in NEUTRAL when changing from D to R or R to D reduces and softens the clunking. Maybe the pause lets the pressure in the AW-4 go down a bit.

As suggested, a clunk is somewhat normal. If there are no metal sparkles in the gear oil, and no chunks missing from the gear teeth, and the spider gear cross pin is tight, it will be fine.

Don't forget you are driving one of the finest examples of 1980's AMC engineering. Noise/Vibration/Harshness was not a huge design consideration.
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Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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Old February 21st, 2018, 22:18
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Clunk/lurch into Drive, but not Reverse

They all clunk into drive regardless of good or bad condition. Certain angles help but like Tim said. Best bet is to just give it a second to spin down. Also don't throw it into gears. These transmissions are not delicate or prone to breaking and Jeeps are not the only cars that clunked into gear. Yours may have been made in the 90's but motor trend had already reviewed it as part of the 1984 AMC line up in 1983. It's not a modern vehicle

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  #10  
Old February 22nd, 2018, 22:48
soyjer soyjer is offline
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Re: Clunk/lurch into Drive, but not Reverse

I jacked up the rear end today and grabbed ahold of the rear wheel and pulled it in and out, and there was very noticeable play (and another interesting clunking noise, of course)...so now I have another clunking noise and play where I don't know whether it's normal or not.
My neighbor was implying that I was applying Japanese tolerance standards to an old American vehicle, which is an exaggeration, but I'm starting to think that if you pull on the rear wheel and the drive axle doesn't actually slide out of the differential, you give a thumbs up and hit the trail. I don't mind the clunks, I'm just trying to establish when I should ignore a clunk and when I should take care of it to avoid further more expensive damage. I think I need to join a local offroad club so I can get some idea of which kind of clunks to ignore and which to take care of soon. ☺
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  #11  
Old February 24th, 2018, 19:12
Afireinside Afireinside is offline
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Re: Clunk/lurch into Drive, but not Reverse

I'm gonna say drive shaft u-joints on this one.
Good luck
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  #12  
Old February 25th, 2018, 08:15
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Re: Clunk/lurch into Drive, but not Reverse

Quote:
Originally Posted by soyjer View Post
I jacked up the rear end today and grabbed ahold of the rear wheel and pulled it in and out, and there was very noticeable play (and another interesting clunking noise, of course)...so now I have another clunking noise and play where I don't know whether it's normal or not.
Normal.





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Quote:
Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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  #13  
Old March 29th, 2018, 19:37
soyjer soyjer is offline
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Re: Clunk/lurch into Drive, but not Reverse

I spoke to an ex dealership Jeep mechanic, and he said the spec for that In-Out play is .070" max. Mine on both rear wheels measured >1/32" (.031) and less than 1/16 (.063), so in fact it does fall within the .070" max spec.
Amazing how the brake drum acting almost like a dull bell can make that little bit of movement sound so loud.

I also had the ex Jeep dealership master technician take a look at my clunking lurching problem when shifting into drive, and he said that it definitely was excessive compared to all the other XJ's he has dealt with, and he said it was almost certainly the transmission because the driveline looked tight otherwise and because it does not happen when I shift into reverse. I'll post back here again next week when the transmission shop tells me if it's the transmission or not.
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Old March 30th, 2018, 05:59
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Re: Clunk/lurch into Drive, but not Reverse

Just have a minute to chime in. Have you checked your mounts? I had a weird clunk 20 years ago on my XJ and it was actually the exhaust support at the cross member coupled with the other mounts. I don't remember that much about it but it did it only in one direction.

Good Luck.
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  #15  
Old March 30th, 2018, 18:31
Waynerd Waynerd is offline
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Re: Clunk/lurch into Drive, but not Reverse

Did you also pull the rear driveshaft out and grease the heck out of the splines on the slip yoke? Worth a shot and if it doesn't fix it I'm sure it's likely needed anyhow.
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