Front Diff Going Out? | Ford Explorer Forums - Serious Explorations

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Front Diff Going Out?


Explorer Addict
July 29, 2008
Reaction score
City, State
Long Island, NY
Year, Model & Trim Level
98 XLT SOHC, 99 EB 5.0L
Vehicle History: 98 Explorer XLT, SOHC, 4x4, 191k miles. Original engine, rebuilt trans. Original front differential, transfer case, front driveshaft/joints, CV axles. All front suspension components are fairly new, in good shape, greased, no play. LF wheel bearing assy replaced today (Moog), RF wheel bearing assy replaced at 120k (Timken).

Complaint: Low pitch pulsing rumble that varies with vehicle speed. Almost sounds like tire noise, but lower pitch, more 'solid', and more sinister. First audible around 27mph, resonates most between 30-40, is overtaken by wind noise over 55-60mph. Pulsing is 8 Hz at 40mph, which corresponds to wheel rotation rate. Turning (fast/slow, small/large radius) does not change the sound. No clicks, bangs, etc. Sound seems to be coming from just left of centerline, forward of the passenger compartment, in the vicinity of the pumpkin (if I had to guess). No gear whirring or whining, except in 4x4 HI/LO. No pulsing in the brake pedal or steering wheel. Sound is independent of acceleration or deceleration.

"Corrective" Actions: Badly worn front tires (severe camber wear) removed. Rear tires (50k) rotated forward. New tires (<800mi now) installed on rear. Front end aligned, all wheels balanced. LF wheel bearing replaced today (my gut reaction was a wheel bearing). Differential fluid topped off (has slow leak, passenger side axle output). Swapped LF and RF tires---sound did not move/change.

It may be my mind, but it seemed like the noise got slightly quieter after topping off the diff. I don't think it's the CV joints, as those usually make clicking/banging/popping noises, especially in turns, when they're going out. The fact that the pulsing coincides with wheel rpm makes me fairly confident it isn't a driveshaft u-joint or pinion bearing.

Thoughts? Thanks guys!

Put the truck up on a lift, in drive, step on the gas slightly and lfrom under the truck, listen to the diff. You'll know if a bearing is shot in there. Happened to mine, it was pretty obvious.

Drop the front drive shaft and take a short test drive to isolate the noise. Vibration and noise are pretty common issue with front drive shaft and/or the transfer case. Also, having mis-matched tires causes issues with the truck engaging 4wd. Normally should be replaced in sets, not pairs.


For ***** and giggles, I rotated the wheels front/rear. New ones on the front, old ones back in the rear. Sound is gone from the front and very very faint in the rear. I guess those old tires were worn in a way that made them extremely noisy up front. They look fine visually---even wear all the way around. Hmm.

In short, I feel like a dumbass. This should've been step #1 . Thanks for the help though!