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1980 720 4x4 clunks with hubs locked in 4wd

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#1 Paulz



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Posted 08 January 2018 - 02:52 PM

I use my truck to get up to my cabin, steep dirt road.  Particularly when I go downhill or make a tight turn with the hub locked there is a loud and noticeable clunk ever so often, like something in the front hubs is skipping.  Anyone run across this?  It seems to be OK going uphill, which is really when I need the 4wd. I can take it out when descending or turning on flat ground if necessary but it's nice to use the engine when descending. 

#2 ]2eDeYe



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Posted 08 January 2018 - 04:44 PM

Possibly a CV axle going out, maybe a bad hub. 

Put the truck on jackstands and put it into 4wd. Block one front wheel and turn the other backwards and forwards and see if you can duplicate the noise or pinpoint the slack in the system 

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#3 captain720


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Posted 08 January 2018 - 05:04 PM

You can visually inspect the hubs, only takes a couple minutes. The CVs are usually shot in our trucks so I would consider that like ]2eDeYe said. The CVs will usually not have a boot on them at all if they are going out.

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#4 Paulz



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Posted 09 January 2018 - 07:34 AM

Thanks guys.  I'll let you know what I find. 

#5 Paulz



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Posted 12 January 2018 - 08:01 AM

Got out to my ranch yesterday and crawled under the truck.  Sure enough, one inner boot missing, two others cracked (I just got this truck).  Could a bad joint actually skip?

#6 datzenmike



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Posted 12 January 2018 - 04:15 PM

It can't work part of the time. Either it transmits power or it doesn't. In either case it may or may not make clunks.

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#7 bottomwatcher


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Posted 12 January 2018 - 07:32 PM

Yes the boots rot. You didn't mention the year but the 80 to 82 are nla. Check the snapring on the end of the halfshaft. For some reason I have had a couple where the ring wears off the end of the shaft and the axle slips in the hub causing a clunk. I ended up welding the shaft to the steel piece that engages to the hub and no more issues. Now my boots are ripping so time to tackle this again. There is a poly kit for 240sx that with modification should fit but have not tried it myself.

#8 Paulz



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Posted 13 January 2018 - 01:21 PM

Thanks guys.  It's a 1980, and when it clunks I think it does momentarily skip.  I'll check that out.  One of the old boots looks like it's a split boot that you put on without removing the axle.  I'll check into the 240 kit.