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Clunking Noise when Climbing Steep Hills in 4wd

Lost_Wrench

NAXJA Forum User
Location
CO
My '96 XJ has started making a fairly loud clunking noise while in 4wd low going up steep climbs. If I go really slow, like less than 5 mph it doesn't really do it, or it does more quietly once in awhile, but if I have to give it some gas to get up the hill it happens a lot and louder. The cadence seems mostly intermittent in nature, as in not perfectly timed, but does happen much much more the faster I try to get up the hill. The Jeep runs and sounds fine in all other driving conditions. It sounds like if someone was underneath the Jeep whacking something on the front end with a rubber mallet. Anyone had a similar issue?
 
That rubber mount for the exhaust would be one good suspect. Motor and trans mounts would be another.

One way of looking at this is that it has to do with when you have the most torque in play. Something is moving when there is a lot of torque involved.

Driver's side motor mount is the one most likely to go first. You may need to get a jack invovled in order to test the condition of the trans mount.
 
Thanks for the replies everyone. Of all the suggestions so far it seems like the driver's side motor mount may be in the lead as the culprit, the bushing is toast upon inspection. I'm not ruling out the others but that mount definitely needs replaced.
 
I only suggest the case chain because I used to have a 75 chevy with a 205 case and a loose chain; it would be fine except when I was climbing a hill in 4wd and it would clunk horribly.
 
Thanks for the replies everyone. Of all the suggestions so far it seems like the driver's side motor mount may be in the lead as the culprit, the bushing is toast upon inspection. I'm not ruling out the others but that mount definitely needs replaced.

Depending on your budget and your expectations for your XJ you may want to look into aftermarket options for motor mounts. Brown Dog and Stinkyfab (SFR) are both good options. Last I looked SFR was the only option for an aftermarket transmission mount. And if you are doing motor mounts you probably need to replace your transmission mount too.
 
I only suggest the case chain because I used to have a 75 chevy with a 205 case and a loose chain; it would be fine except when I was climbing a hill in 4wd and it would clunk horribly.


NP203 maybe?

An NP205 is all gears. No chain.
 
Depending on your budget and your expectations for your XJ you may want to look into aftermarket options for motor mounts. Brown Dog and Stinkyfab (SFR) are both good options. Last I looked SFR was the only option for an aftermarket transmission mount. And if you are doing motor mounts you probably need to replace your transmission mount too.

And Iron Rock Offroad. I like it because its full circle rubber, so it should be much more durable than stock while having less NVH than Brown Dog and SFR.
 
And Iron Rock Offroad. I like it because its full circle rubber, so it should be much more durable than stock while having less NVH than Brown Dog and SFR.


Thumbs up to this. If you're offroading a brown dog makes sense, but I replaced my motor mounts with a good aftermarket clone of the originals, with tons of hard rubber around the bushing and the NVH is really good. To be clear, mine are closer to https://www.quadratec.com/products/56003_0036.htm, where there is a huge pyramid of rubber to absorb the vibrations. Don't know how well they hold up vs stock, my originals were wearing out at around 175k, and I've had the new ones for 50k more so time will tell.
 
If low NVH is a super important consideration, another option is to purchase stock mounts, and then fill most of the most of the void in the stock mount with curing polyurethane filler. Fill the void so that there is only a small gap to the capture horseshoe.
 
UPDATE: It was indeed the driver's side motor mount that was the cause of the clunking while climbing in 4lo. The bolt going through the rubber housing was completely torn free of any of the rubber. I tested afterwards on a steep climb near home and all is well. Thanks anak and everyone else for the helpful suggestions.
 
Glad to hear you got it fixed.

Thank you for updating us with the resolution.
 
Energy suspension makes poly inserts for the stock mounts that work well without any major increase in NVH. Just makes the XJ feel more like a v8 pickup at idle


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