Front Differential Question

[rc1626]

My wife has an 01 Explorer 4.0 V6 4WD. Recently I started to feel a bump-bump-bump-bump etc. while driving at low speeds (from a start to about 25mph. It is not a heavy bump and seems to disappear at about 30mph and above. (Sorry, bump - bump is the only way I can describe it.) Definately a drivetrain issue. It's not tire related as far as I can see.

I put the truck up on jack stands and put it into drive to see if I could pick up where it was coming from. To my suprise while in 2WD the driver side front tire spun along with the rear. The passenger side intermittenly kicked in for a split second with a minor jolt. As I gave it a little gas the jolt would get stronger and more frequent.

When I switched it into 4WDHigh the driver side tire still spun and the passenger side stopped altogether. (no jolting)

My questions are:
1.) How is the front differential supposed to act when in 2WD and in 4WD?
2.) Could the intermittent kick in of the passenger side front tire while in 2WD be a sign of something wrong in the front differential?

Any help would be appreciated.
Thanks.
Rob

 

[imp]

You had all 4 wheels off the ground up on stands, yes? Your options for drive type, I assume, do not include "2WD" as such, but actually "4X4 AUTO"? The others being "4X4 HIGH", and "4X4 LOW"? If so, in AUTO, the fact that brake-drag is never equal on all the wheels, and frictional variations in the differentials, the wheels side-to-side, and front-to-rear, tend to turn at different speeds. Indeed, on front or back axles, a wheel on one side may turn while the other side does not (unless a non-slip diff. is present). The computer interprets these conditions as wheel slip due to traction loss; it does not know the vehicle is not being driven on the ground!

It then attempts to to bring front & rear axles to equal speeds, by engaging the electronic clutch in the transfer case. This is a "pulsed" affair which results in jerking, bumping noises, etc. (only with veh. up in the air, though). If you engage "4X4 HIGH", this will eliminate that by essentially turning on the clutch constantly.

If you actually have the choice of "2WD" the above discussion is only half applicable. The part about unequal wheel speeds on opposing ends of the same axle remains true. imp

EDIT: I think about 1996 or so was the last year in which "2WD" was offered as a choice; later it became "4X4 AUTO".

 

[rc1626]

You are correct. It is 4X4 Auto. Thanks for the explanation. Certainly answered a number of questions. Now to find the cause of the bump - bump - bump. I'm thinking maybe a CV shaft up front? Back to work.
Thanks again.
Rob

 

[Wakeboy1337]

It could be that your tires are not worn evenly, if that is the case some tires may be spinning just a little faster than others and it's trying to engage 4x4 on the pavement. Engaging on the pavement causes major binding in the transfer case (at least in first gens, idk about second) and then you can get tire chirping or the bump bump bump you speak of.

 

[gmanpaint]

Start by swapping tires front to back. See if that helps. Tires are one of the most overlooked problems when diagnosing.

Check the front suspension by lifting the front of the rig by the cross member and support the frame with jack stands.

With tires on, wiggle the tire side to side to check the tie rods. Lift up and down to check the ball joints. There should be NO play.

Remove wheels and inspect the brake caliper bolts, pads, & rotors. Look at the hubs for unusual wear. Inspect the C/V axles. Look for a broken shock, sway bar end link.

Check both diff fluid levels. Trans & T-case fluid level. Look for excessive metal shavings.

Inspect the U-joints, third member bushing, trans mount, pinion seals. Check the rear axle seals, and bearings.

If everything mentioned checks out fine, the problem could be internal in either the trans, t-case, or difs.

Good luck.

 

[rc1626]

Thank you, thank you, thank you! I so do appreciate the feedback.

Recently had a vibration problem at high speeds and it turned out to be the rear universal joint at the differential. This was along with current problem. Had hoped changing out the universal would have cured both but did not. Front differential was low on fluid due to a slow leak in pinion seal. Changed seal and filled up. Just noticed sway bar end link is broken on the passenger side. Will change that. Any way to check CV shaft(s)? Will inspect the rest of the seals, bearings, caliper assembly, hubs, fluid levels etc.

Thanks again.
Rob