TQ lock unlock clunk

quickster

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I have an opportunity to buy back my old 91 F350 dually from my son's friend. He's had it a year and a half, and is looking for a Cummins or PS. I haven't seen it yet but what he's telling me is there is a clunking in the trans. At highway speed going from coast to throttle it clunks. So I guess if he's braking at say 60, then back on the throttle it bangs. Any idea what it could be? I put a new TQ in it about 5 years ago, and the kid that bought it only put 3k on it since he's had it. ???
 

chillman88

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Could be drive line too. Maybe u-joint or carrier bearing.

This would be my first thought. I've been fighting issues with the pinion loosening on my 91. The splines in the yoke are wore out and it clunks just the same.
 

quickster

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Is this a tough fix? something I've never tried. I don't think it's a deal breaker, but I don't know what I'm getting myself into.
 

Fixnstuff

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Is this a tough fix? something I've never tried. I don't think it's a deal breaker, but I don't know what I'm getting myself into.
I think it's a pretty basic fix with basic mechanic skills (properly using tools and having the right tools always makes things easier) and fortunately there are a lot of good references like on Youtube and I'll link a few below to get you started.
Most u-joint jobs I've done were back in the 1960s and a few in the 1980s/90s. Except for once or twice I've always done them one at a time from under the vehicle with twe vehicle raised enough to give me room to crawl under and without completely removing the entire drive shaft and doing the job on a work bench.
HOWEVER, in this case I'll recommend removing the entire drive shaft because it's easier to see what you are working on and you'll better be able to properly identify the exact size of the u-joints you will need for replacement (as there are several sizes) AND if you encounter a problem you can if needed you can take the 2 individual sections of the drive shaft with the u-joints and hanger bearing (which also has a u-joint) to a parts store and usually SOMEONE there will be competent to properly advise you. Where I live NAPA stores seem to have older personnel with more experience. Secondly they can confirm from the parts what size u-joints and hanger bearing you will need, so you won't end up ordering wrong sizes. You can also take the driveshaft and u-joints anywhere to get advice from an experienced mechanic, such as a transmission/drive-train shop or a shop that works on some pick-up trucks including diesels, instead of just tiny little cars and minivans.

Videos: Chris Fix has excellent instructional videos so I'll start with one of his:
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IF YOU WANT TO LEARN A LOT (or not, I still recommend this multi-part series)
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Fixnstuff

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In addition to checking universal joints and carrier bearing I suggest examining very closely the engine and transmission mounts. Look for damaged/deteriorated, separated or missing rubber parts of the mounts or damaged rubber bushings anywhere that could be causing a clunking sound.

If you chock up the wheels you can have someone inside the truck with the engine running and FOOT ON THE BRAKE while you are under the truck observing) shift the transmission from neutral to a forward gear and then to reverse a few times and if there is a clunking sound you can probably detect and see where it is coming from. This works especially well for finding broken motor/transmission mounts (and also bad u-joints). You can do that yourself from inside the cab to find out if you can detect the clunking sound from any of the components we have discussed so far (including u-joints and hanger bearing)
 

quickster

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Thanks for the info. I replaced the converter years ago and I'll bet the u bolts are loose. When I did the clutch on my 97 I checked the u bolts after a few months and one was super loose.
What I never tried was replacining the pinion and ring gears. I'm going to have the guy check it out before anything else. Problem is he's 9 hours away now.
 

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