Piston Slap: Dat Whining Azz!

Sajeev Mehta
by Sajeev Mehta
piston slap dat whining azz

TTAC commentator EducatorDan/PrincipalDan writes:

Long time listener, comment-er, hanger-on with another question.

I have a 2004 F150 Heritage 4×2 that just cracked the 100,000 mile mark and recently I’ve noticed a distinctive rear differential whine. It has the 4.6 V8 mod motor, 4 speed auto, and (as you can see from the pics) an aftermarket flatbed.

I have owned it since 2006 and it is long since paid for and is currently my daily driver. When purchased it already had 68,000 miles on it and the only “receipts” I have for it was the insurance paperwork in the glove-box to show it was owned by a member of the AARP and registered in Sun City, AZ. It was never intended to be my daily driver, when it was purchased it was for household chores, truck type jobs, and a second vehicle. What changed was that in 2008 I got divorced and suddenly the truck was THE vehicle that I was left with.

I have replaced an alternator and battery, tires, minor AC repair, installed a Dynomax dual exhaust system, and regular oil changes.

Within the next year I will be purchasing another vehicle (some large comfortable used well depreciated sedan for racking up highway miles) and the F150 will be parked for extended periods of time only to be called on when it is needed. I intend to do the full 100,000 mile service very soon. But the differential whine bothers me. It occurs from about 10 mph to around 70 mph when it goes away, in any gear. I recall a mention in several forums about Panther platform cars getting a differential whine at higher mileages and have looked on F150 owner forms about differential whine but most of those posts are about newer generation trucks still under warranty.

So here’s the question. For a guy who intends to keep this truck until gasoline is no longer a legal commodity to be sold, is this whine an issue? Is it a case of something that will sound like that for another 100,000 to 150,000 miles before the diff finally blows up? Should I start saving money now for that Detroit Locker I always wanted for when they have to replace the internals in the axle anyway?


Sajeev answers:

Hey Dan, the mixed messages given by the aftermarket flatbed and chrome fender extensions are super rad. On one hand, it’s a blingy street truck. On the other hand, it’s got a booty that works hard for the money…but I digress…

Axle whine on Ford 7.5 and 8.8 differentials has been around almost as long as I’ve been around! And the problem is rarely bad enough to actually kill the axle. Since yours is out of warranty AND you will be getting another daily driver, let it be. If the axle ever fails, get another one (with the same gear ratio) from the junkyard, odds are it will last many more years, be cheap to buy and a breeze to install.

And labor is the big problem when it comes to differential (ring and pinion) work.

More importantly, rear axle work is not for the faint of heart. Setting up a ring and pinion requires specialist experience, letting just anyone crack open your axle to fix the problem is asking for BIG trouble. Which you do not have now…and you probably never will. So let it be, enjoy it as part of the truck’s charm. Yeah, charm.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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5 of 23 comments
  • Scottcom36 Scottcom36 on Jan 06, 2014

    I have a '98 F-150 with a .355 axle. Had the fluid changed (for the first time) at 150k. The mechanic called NAPA to make sure they sent the proper fluid and any additives needed. I understand some differentials are quite picky in this regard. I started getting a whine at 170k, loudest at 45 mph with my foot on the gas. At 202,000 miles it hasn't gotten any worse.

  • Jim brewer Jim brewer on Jan 06, 2014

    I'm still trying to get my head around the idea of that truck in Sun City. As a rez mobile, definitely.

    • See 2 previous
    • Sajeev Mehta Sajeev Mehta on Jan 07, 2014

      @krhodes1 +1.