clunk from d to r
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With 168k on it, yeah it's possible that the transfer case chain has quite a bit of slop in it, but the noise could be coming from elsewhere under the truck too.
Does it happen only in 4wd or in 2wd as well? If in both 2wd and 4wd, I'd check the u-joints on the rear driveshaft. If only in 4wd, I'd check the front driveshaft u-joints and also how much slack is in the transfer case. Typically you'll only have one clunk when switching directions, so it's possible that you've got two or more items that are worn out too.
Crawl under the truck and give all the u-joints a good "wiggle test". Also, with the front & rear wheels in the air (the truck on jackstands or a hoist) and the truck in 4wd. See how much play you've got between the front and rear driveshafts where they exit the transfer case. Anything more than 1/8 turn or so and I'd say that's getting to be excessive slack.
I'd suspect and check/replace the u-joints first though.
Does it happen only in 4wd or in 2wd as well? If in both 2wd and 4wd, I'd check the u-joints on the rear driveshaft. If only in 4wd, I'd check the front driveshaft u-joints and also how much slack is in the transfer case. Typically you'll only have one clunk when switching directions, so it's possible that you've got two or more items that are worn out too.
Crawl under the truck and give all the u-joints a good "wiggle test". Also, with the front & rear wheels in the air (the truck on jackstands or a hoist) and the truck in 4wd. See how much play you've got between the front and rear driveshafts where they exit the transfer case. Anything more than 1/8 turn or so and I'd say that's getting to be excessive slack.
I'd suspect and check/replace the u-joints first though.