Piston Slap: Of Ford's Locking Seatbelts, Differentials

Sajeev Mehta
by Sajeev Mehta
piston slap of fords locking seatbelts differentials

This week, let’s answer two short questions with equally short answers! – SM

William writes:

I have a Ranger-based question for you: my 2010 XLT four-cylinder regular cab’s passenger side seatbelt will not “pull out” at random times when the wife is getting in the car. Is there a relay or something that controls that?

Sajeev answers:

I do love it when a question’s answered by my shop manual library. Per 2011 Ranger manual, you have a Belt Tension Sensor (BTS), which is a pretensioner assembly within the seat-mounted buckle. This interfaces with the seat-belt assembly, presumably getting a signal from the seatbelt to activate in an accident.

Long story short: I can’t tell which triggers which, so either the BTS is flaking out or the tensioner assembly in the B-pillar is giving out bad advice. Good luck with the diagnosis and repair.

John writes:

I saw a vid of the clutch controlled rear “diff” used on the all-wheel-drive Focus RS in which there is no spider gear set, just the slippage of the inner drive clutch to allow turning. I do understand how the use of this setup along with good computer control of the clutches can provide some real gains in handling and safety. My question is one of life span and the reliability of this setup: will it last 100K miles, when does it start to lose accuracy, and at what cost can it be rebuilt? And of course, when will the tuners be able to program this “monster”?

Sajeev answers:

This video perhaps?

This unit’s durability won’t be a concern for most, especially for its first owner. The computer turns down the power when the differential feels the heat, suggesting there’s no problem on public roads with legal driving, or many weekends of drag strip action, monthly autocross dashes, and even the occasional (non-endurance racing) track day.

Just don’t modify it! Or buy a used one with no service history, signs of being recently returned back to stock, indications it’s been driven hard and slid into a hedge, etc.

This is still a mass-market vehicle dressed up to play with the high-power, high-dollar sports and GT platforms. If this hypothetical is a big concern for would-be Focus RS owners, keep the car bone stock with the exception of a differential cooler. Or use the money for something loony like a boosted Coyote Mustang/ LSX Camaro/ 370Z with appropriate suspension upgrades to keep the power planted(ish), any number of track-ready pre-owned German machines on a purpose-built sporting chassis…or a C6 Z06 and spank ’em all.

[Image: Shutterstock user jeffy11390]

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.

Join the conversation
5 of 25 comments
  • Redapple Redapple on Jun 02, 2017

    Lockers are complicated and expensive. Stay with the tried and true and simple. Posi. With side gears and spring clutch packs. 1/4 the cost of a locker. longer life. Locker added performance not worth the added $.

    • Gtem Gtem on Jun 04, 2017

      "longer life." I'd strongly disagree there. I also don't see how they're much more complex than an LSD. LSDs are the ones that wear their clutch packs out, can't say I've ever heard the same of a manually actuated locking rear diff, short of a very un-used one getting a frozen actuator.

  • AVT AVT on Jun 02, 2017

    Isn't a posi basically a locker, just without manual control since it "always on." Thus the reason they suck in snow since the back end goes out in turns since the wheels are still spinning at the same rate.

    • See 1 previous
    • Gtem Gtem on Jun 04, 2017

      AVT you're probably thinking of GM's "G80" auto/spin locker. It does in fact fully lock up the rear axle when a speed differential of 120rpm is detected between the rear wheels. Most "true" LSDs are never fully locked up, there is a limit to the amount of torque that can be transferred.

  • Kat Laneaux What's the benefits of this as opposed to the Ford or Nissan. Will the mileage be better than the 19 city, 24 hwy? Will it cost less than the average of $60,000? Will it be a hybrid?
  • Johnster Minor quibble. The down-sized full-sized 1980-only Continental (which was available with Town Car and Town Coupe trims) gave up its name in 1981 and became the Town Car. The name "Town Coupe" was never used after the 1980 model year. The 1981 Lincoln Town Car was available with a 2-door body style, but the 2-door Lincoln Town Car was discontinued and not offered for the 1982 model year and never returned to the Lincoln lineup.
  • Zipper69 Some discreet dwebadging and this will pass for a $95k Lucid Air...
  • Zipper69 Does it REALLY have to be a four door?Surely a truly compact vehicle could stick with the half-door access with jump seats for short term passengers.
  • ToolGuy See kids, you can keep your old car in good condition.