thumping noise in 4wd
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Joined: Oct 2007
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thumping noise in 4wd
good evening! i have a 02 expy eb 4x4 when on wet pavement the other day i shifted from awd to 4wd after it engaged and about 1 mile of driving i heard and felt a thump. it feels like hitting a bump in the road. it is consistaint every mile or two it will make this noise? i have checked the fluid levels,drive shafts. no leaks of anykind.truck has 59500 miles on it?
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Joined: Mar 2005
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From: Cornelius, Oregon
that sounds about right. When you're in 4wd the front and the rear end are locked together and so must always turn at the same rate. The problem is when you make any kind of turn, or even if your tires aren't worn evenly and rollout at a different circumference, you have a difference in distance traveled by the front and rear ends. This results in a condition called driveline bind, where the difference causes torque to build up in the drivelines. On mud, snow, etc. you'll never really notice it because the tires can slip enough to relieve the pressure. On wet pavement it builds up until it's enough to over come the traction of the tires and then it "pops" like that to relieve the pressure. On dry pavement with enough traction you may end up breaking u-joints or drivelines before it can pop and relieve the pressure.
Anyway, long story short... you're probably fine, but unless you REALLY need 4wd on the wet pavement, you're probably just better off leaving it in AWD
Anyway, long story short... you're probably fine, but unless you REALLY need 4wd on the wet pavement, you're probably just better off leaving it in AWD
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