If the differential drain plug is tightened to factory specifications, could it vibrate loose under normal driving conditions?

Dear Car Talk

Dear Car Talk | Nov 01, 1998

Dear Tom and Ray:

My Toyota Camry's transmission just failed completely at 76,000 miles. It seems
the differential drain plug was only finger-tight when they removed the
transmission, and because of that, the fluid had leaked out. There was less than
a pint of fluid left when the transmission died. I went to my dealership, which
is the only car shop that has serviced the vehicle since I bought it (with the
exception of the transmission replacement), and asked them to pay for the cost
of the new tranny and tow. They claim that the drain plug must have vibrated
loose while I was driving, and that they are not responsible for leaving it

My question to you is: If the differential drain plug is tightened to factory
specifications, could it vibrate loose under normal driving conditions (no off-
road, only city and highway)? Thanks. -- Tom

RAY: No. It's unlikely to vibrate itself loose. At least I've never heard of it
happening, and I can't imagine it. If that were a plausible explanation, the
country would be filled with irate Camry owners.

TOM: It sounds like they may be responsible for not tightening it all the way.
But how are you ever going to prove that?

RAY: The only way to prove it is to check your previous repair orders. If you've
had all of your regular, recommended services done at the dealership, you
probably have the evidence you need. I'm sure at least one of the scheduled
services (the 30,000- or 60,000-mile service) calls for a differential oil
change. And many of them call for a differential oil-level check. If you can
show that they serviced the differential at, say, 60,000 miles, I think you can
make a good case for their negligence.

TOM: Of course, under the circumstances, they may just plead larceny! They may
say that they were supposed to change the differential as part of the 60,000-
mile service they charged you for, but they didn't do it. That's the equivalent
of saying "we're not incompetent; we're just crooks"!

RAY: Check the back of your owner's manual and see which scheduled "services"
call for any kind of differential service. Then go through repair bills and see
if you can match one up. At that point, I'd ask a lawyer to take a look at it
for you, and if the evidence is strong, sue them.

TOM: If the evidence is compelling (if they did charge you for some sort of
differential service and you can show that's the only place that serviced the
car), they'll probably call their liability insurer and offer to settle. If not,
you'll have to decide how much time, effort and money you want to spend going
after them. Good luck, Tom.

* * *

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