K5 clunking

jmoody8500

Member
Joined
Oct 20, 2015
Location
US
Here's the story. GF driving the truck yesterday and the rear u joint breaks. (The one on the slip yoke) I replace it, start reversing and hear a clunking sound. Have her repeat process while I watch the driveline and I notice the front drive shaft intermittently engaging causing the clunk. Any ideas? Thanks.
1987 K5 Blazer
5.7/700R4/NP 208
 
Specifically on 86-87 K5s there is an issue with the trans cross member that is always my first check on a "clunk"
They used an industrial "rivet" to fix the cross member to the frame rails and over time it starts to separate or people change it out when doing maintenance with ill fitting bolts. Look at the edges where the cross member meets the frame while doing above test and see if the cross member is rotating and banging into the frame.


That said, unless its hella bad and a few other factors are coming into play...should not cause the front shaft to spin.
Only time front driveshaft should spin is if the front hubs are locked or the t-case is in 4wd. If neither of those are present and the front shaft is spinning I'd be worried about my tcase health
 
Go ahead and junk those auto hubs and get some Warn Premiums, or even the standard Warn hubs. The auto hubs aren't worth the hassle. The best way to test it is to jack the front wheels off the ground and, with a friend or your girlfriend, roll the front wheels simultaneously and see if it happens without the truck running. If that doesn't do it, then you likely need to adjust a t-case shifter linkage, replace the transmission mount, or you have an internal case issue.
 
It's more than likely a problem with the auto hubs as previously stated.
 
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