Intermittent clunk in 4 High

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Black2004EB

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2004 Eddie Bauer 4x4 with advance trac. 255 500kms.

When driving in 4 High (snow covered roads, speed 35-50mph) vehicle makes an intermittent clunk... seems to be random timing, slowing up or speeding down, coasting does not seem to matter, it just occasionally happens, when this occurs feels like momentary loss of power, or a rear brake being applie only for a second. Definitely resonates from the rear of the vehicle. I have driven it with my hand on the floor above the transfer case and it can't be felt from the tcase area.

Vehicle works fine in 4lo ,AWD, 2h. Turning Advance trac off seems to lessen the occurence but I think still happens. Only seems to occur above 35mph. This is NOT on bare pavement but snow covered roads.

No grinding, weird noises, etc, otherwise and 4 hi is indeed engaging (tested in snowy parking lot).

Anyone experience something similar. I have no access to code reader and local ford dealership says they won't even look at it for another 2 weeks.

Vehicle runs great otherwise. This has been this way for over a year, and i have had 2 different sets of matching tires on it so tires are not the problem.

I am suspecting ABS wheel speed sensor as it almost seems like the advanctrac or abs system is just momentarily activating the rear brakes... No RSC on this year of expedition, just advance trac.
 

mindgame

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I think this is by design... When a loss of traction occurs, the engine retards to slow down, thus loss of power.

I notice this a lot when I have too much wheel spin while climbing and I lose traction. The ABS kicks in and it is not a smooth squeeze.. It is hard pulsating clicks...
I wish I could disable all of this, but we cant...

But you can be on to something.. A bad ABS/Speed sensor can be faulty and start the cascade... Finding which sensor is faulty is another story... I do it by trial and error :(
Replace each one until fault goes away...

K!
:head3:
 
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