99 Ford Explorer seems to slip in bad weather

I am driving a 99 Ford Explorer with about 140K miles and I have
noticed on a couple of occasions the the front wheels seem to slip.
The first time it happened it was really snowy and icy but I didn't
put it together with the idea that it might be my 4WD. Then nothing
happen for a couple of weeks but the roads were dry. Now the roads are
bad again. If I drive about 50mph I don't notice much of a problem but
if I get going 50mph or over it seems like the 4WD engages and then
disengages, especially on icy spots and it makes a loud noise kind of
like a clunking (the rpm does not go up or down during the slip). If
the roads are clear there is no problem. Any ideas? Obviously I have
no idea what is going on....is there front speed sensor too? What
should I do next?

"jbug" > wrote in message
...
> I am driving a 99 Ford Explorer with about 140K miles and I have
> noticed on a couple of occasions the the front wheels seem to slip.
> The first time it happened it was really snowy and icy but I didn't
> put it together with the idea that it might be my 4WD. Then nothing
> happen for a couple of weeks but the roads were dry. Now the roads are
> bad again. If I drive about 50mph I don't notice much of a problem but
> if I get going 50mph or over it seems like the 4WD engages and then
> disengages, especially on icy spots and it makes a loud noise kind of
> like a clunking (the rpm does not go up or down during the slip). If
> the roads are clear there is no problem. Any ideas? Obviously I have
> no idea what is going on....is there front speed sensor too? What
> should I do next?

I have something similar occurring with my '98, but it's at very slow
speeds. Usually like when I'm pulling out of a parking spot and need to
turn the wheel all the way. Its like the front end starts to grab, as if it
were in four-wheel drive. Very odd feeling. I'm actually glad that it
doesn't happen when I'm driving over 50! Not sure what it could be. Guess
I'm not as worried about it as you are, for the obvious reason.

John B.

The control trac (auto-mode) is supposed to react to wheel slip and engage
4WD, perhaps that is what you are feeling. If you switch it to 4WD
full-time does the "slippage" go away? (don't run it this way on dry
pavement though) It may be normal but if it seems to happen at strange
times you could have a sensor issue.

Or could it be the antilock brakes (are you braking?).

--
Allan Williams



"jbug" > wrote in message
...
>I am driving a 99 Ford Explorer with about 140K miles and I have
> noticed on a couple of occasions the the front wheels seem to slip.
> The first time it happened it was really snowy and icy but I didn't
> put it together with the idea that it might be my 4WD. Then nothing
> happen for a couple of weeks but the roads were dry. Now the roads are
> bad again. If I drive about 50mph I don't notice much of a problem but
> if I get going 50mph or over it seems like the 4WD engages and then
> disengages, especially on icy spots and it makes a loud noise kind of
> like a clunking (the rpm does not go up or down during the slip). If
> the roads are clear there is no problem. Any ideas? Obviously I have
> no idea what is going on....is there front speed sensor too? What
> should I do next?

"jbug" > wrote in message
...
> I am driving a 99 Ford Explorer with about 140K miles and I have
> noticed on a couple of occasions the the front wheels seem to slip.
> The first time it happened it was really snowy and icy but I didn't
> put it together with the idea that it might be my 4WD. Then nothing
> happen for a couple of weeks but the roads were dry. Now the roads are
> bad again. If I drive about 50mph I don't notice much of a problem but
> if I get going 50mph or over it seems like the 4WD engages and then
> disengages, especially on icy spots and it makes a loud noise kind of
> like a clunking (the rpm does not go up or down during the slip). If
> the roads are clear there is no problem. Any ideas? Obviously I have
> no idea what is going on....is there front speed sensor too? What
> should I do next?

I'm having a similar problem on my (daughter's) '97 with Control Trac. She
was trying to drive up a steep, slippery, muddy hill and the front left
(driver's side) and rear right wheels were spinning and the other two were
not moving. It behaved the same way in Auto, 4WD, and 4 Low. She also said
there is a "clunk" sometimes while turning on dry pavement in Auto. I have
cleaned both transfer case sensors and made sure the case was full of fluid.
There is a slight leak at the rear seal but I don't see how that can be
causing problem as long as the fluid is full. To me the strangest part is
that this Explorer has limited slip on the rear so it does not make sense to
me that one of the wheels would be spinning unless the limited slip is not
working. I'm not sure how the front is supposed to work but on my '91 it
did that when the auto hubs were bad. I also don't understand how one of
the front wheels could be spinning and the other not if there are no locking
hubs. It seems to me it should not happen. I tried reading the '97 Ford
manual but it's rather vague on how the Control Trac system is supposed to
work.

Right now my plan is to replace the rear transfer case seal and change the
fluid and change the rear differential oil and add the friction modifier and
see if that helps. Anyone have any other suggestions? My rear wheels
always lock up nicely on my '91 and '92. I think it's the same rear
differential but a slightly different transfer case on the '97.