By on January 6, 2014

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.


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23 Comments on “Piston Slap: Dat Whining Azz!...”

  • avatar

    Oh, my lord, it’s a flatbed Ford…

    Don’t let the sound of that rear end make you crazy

  • avatar

    Change the fluid in the diff (which IIRC requires pulling the diff cover, at which time you can inspect for any pieces/abnormal amounts of metal) and drive it till it blows.

    Major piston slap bonus points for submitting pictures of the actual vehicle in questions, its a fine looking truck!

  • avatar

    Change the diff fluid with synthetic oil. It will help quiet the whining. Synthetic trans fluid for the power steering will quiet it down too, if it’s making noise.

    • 0 avatar

      If I remember correctly the factory fill was full synthetic. Those rear ends are a PIA to set up, require measured to fit shims, a crushable spacer for the pinion preload, and even when set up to spec still stood a good chance of whining when done. Drive it till it breaks and put a boneyard assy in it. Recommend a used panther for those highway miles.

    • 0 avatar

      Yeah, I would dump it and put some thicker stuff in it, 90W140.

  • avatar

    If the diff gets really hot, there could be a problem. Otherwise it’s just a Ford feature.

  • avatar

    That truck is like an inverted mullet-party up front, business in the back.

  • avatar

    That is a heavy duty steel flat bed I bet it approaches your load carrying limit empty without a load. The 1997-2004 Aero F-150’s and light duty F250’s had rather anemic GVWR limits. Maybe while towing a trailer or with a heavy load you heated up and ruined the little 8.8 axle. Thats my bet.

    Put that bed on an F250/F350 SRW Super Duty and it will make an outstanding work truck.

    • 0 avatar

      Actually I’ve hauled a pallet of wood stove pellets (trying saying that 5 times fast) and the truck DID not bottom out. Approximate weight 2,000 lbs. Props to the guys at Home Depot for being able to get it centered over the rear axle.

      FWIW I did tow with it. This summer I towed a 1967 Ford Mustang from Ohio to New Mexico but I never went more than 500 miles a day while doing so and never topped 65 mph. Using a U-haul trailer (aluminum) and the lightweight Falcon based Mustang the load likely didn’t top 5,000 lbs.

  • avatar

    With mileage, the pinion bearings in these axles tend to get some play and can cause a variation in pinion depth causing incorrect tooth pattern, causing a whine. The bad news is that to correct this, you’re generally looking at a complete axle rebuild, including a new ring and pinion. The good news is, the parts are cheap. Again more bad news, the labor to pay someone with the tools to do it is expensive. Total job cost $1000-$1300 is a ballpark.

    So if it gets intolerably worse, a junkyard axle is your cheapert option. But in that case, you don’t really know if that axle will be any better. You could end up ripping out your ‘new’ axle right away. If you plan to keep the truck for the long haul, find someone who knows what they’re doing and have it rebuilt.

    While getting the gears ‘just right’ can be tedious, an experienced rebuilder knows how to measure for correct pinion depth settings, knows what the right pinion pre-load should be and what it ‘feels like’ and knows the right gear pattern to look for to get it right the first time.

  • avatar

    I wouldn’t sweat it as it’s probably just minor scoring/wear on the side bearing races. As others have mentioned, it’s common to Ford differentals. I have an old Impala with a 12 bolt axle that has had a whine to it for the last 10 years. It never gets worse and never impacts the operation of the car.

    Sajeev is right about diff. work, not for those that know just enough to be dangerous. The whole job can go up in smoke very quickly if you don’t get clearances, pinion depth, backlash etc. set exactly right.

  • avatar

    Agreed ~

    If it whines or sings , ignore it , turn up the radio but if it begins to change over say a 1,000 mile span , begin looking for a rebuilder or used axle complete .


  • avatar

    I’ve heard new RCMP Crown Vic trainers making that whine.

  • avatar

    I used to own a 95 F150 that exhibited what I thought was this problem–turned out the U-joints were causing it. Much cheaper/easier to fix than a differential, might be worth a look.

  • avatar

    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.

  • avatar
    jim brewer

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

    • 0 avatar

      It had a regular long bed on it until 2009 when an elderly neighbor (I was living on a quiet suburban street in Gallup at the time) forgot to set the parking brake on their Subaru Baja and it rolled down their driveway into the side of my truck. Managed to nail it right between rear wheel-well and the back bumper. They wanted to keep their insurance company out of it and I always wanted a flatbed truck. Cash exchanged hands.

      As a “rez truck” its a truck par excellence. I’ll never have any trouble selling it given the envious looks I get. One of the male 4th graders at my school wrote a letter about how awesome he thought I was “oh and his truck is really cool too.” ;)

      But hey no accounting for taste with 10 year old boys.

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