Trouble downshifting? Could be the torque converter clutch.

Dear Car Talk

Dear Car Talk | May 01, 1997

Dear Tom and Ray:

I live in Spring Hill, Fla., where most of us drivers are over 70 (they
sometimes call this God's Waiting Room!). I've enjoyed reading your
responses to other people's problems for years, and now it's my turn. My
1989 Buick Century (blue, with sun-and-car-wash-damaged paint) has 160,000
miles. This week, after the car has been running for 30 miles or so, it
doesn't seem to downshift very well. When I slow down, it shudders and has
twice stalled out. I checked the transmission fluid and added some, but it
still did it the next day. What's happening here, and what should I expect
to pay to fix it? -- Bill

TOM: I think your torque converter clutch is on the fritz, Bill.

RAY: Don't confuse the guy by using technical jargon, Tommy.

TOM: What? Torque converter clutch?

RAY: No. "Fritz!"

TOM: Oh. Let me explain, Bill. Modern automatic transmissions have a device
called a lock-up torque converter, which locks the transmission into high
gear whenever you exceed 35 mph or so (which we know is rare for you guys
in Spring Hill, Fla!).

RAY: Why does it do this? To improve fuel efficiency. Automatic
transmissions use a fluid connection, and are always "slipping." The fact
that they can slip makes it possible for you to stop the car without
taking the transmission out of gear.

TOM: If you stopped a manual-transmission car without taking it out of
gear, it would do what? Stall, right?

RAY: But that slipping, because it's less efficient than a hard, mechanical
connection, does cost you some gas mileage. So the lock-up torque converter
locks the automatic transmission into high gear at speeds over 35 mph, as
if the transmission were manual. That gives you the best of both worlds.

RAY: And it sounds like your torque converter clutch isn't disengaging.
It's as if you were driving a manual-transmission car, got off the highway,
and tried to come to a stop with the car still in fourth gear. What would
happen? The car would buck and eventually stall. And that's exactly what's
happening to your car.

TOM: So, normally you would fix this by replacing the torque converter,
which requires taking apart the transmission. But since your car has
160,000 miles on it, and its future is even more in doubt than yours, Bill,
you might consider just unplugging the torque converter clutch, which does
not require opening up the transmission, and takes only a few minutes. Your
mileage may get a tiny bit worse, but you won't notice any other difference
in performance.

RAY: Some mechanics may try to convince you that damage can eventually be
done to the transmission by just unplugging the torque converter rather
than fixing it, but we haven't seen any proof that that's true. And
besides, after racking up 160,000 miles on this car, you've earned the
right to do whatever you want, Bill.

* * *
TOM: Well, you asked for it, and here it is. My brother and I sat down and
wrote down everything we know about how to make your car last forever.

RAY: And it only came out to eight lousy pages!

TOM:But now this gold mine of information can be yours....

RAY: Get your copy of "Ten Ways You May Be Ruining Your Car Without Even
Knowing It!" by sending $3 and a stamped (55 cents), self-addressed, No.10
envelope to Ruin No.1, PO Box 6420, Riverton, NJ 08077-6420.

Get the Car Talk Newsletter