Drive it forever

Q I have a somewhat stupid question, but one that none of my friends could answer: After changing the left drive axle on my 1989 five-speed Ford Probe, I pulled the old axle off, and a lot of transmission oil dripped onto the floor. My buddy ran to the store and brought back 2 liters of Dexron III type A automatic transmission fluid because, at the time, I thought the manual-transmission just needed the proper gearbox oil, not ATF. But the fluid that came out was red and not that heavy just like ATF. So . . . I put in the ATF.

My Probe is running OK and shifts smoothly. But should I change the fluid and put in something more specific for the gearbox?

A Ford requires automatic transmission fluid for the manual gearbox in the Probe, and that's not uncommon. The lower-viscosity ATF is better for fuel economy, and is just as good, at least as long as the transmission is designed for it from the start.

However, this being a Ford product, they've specified a Mercon-type fluid, not Dexron, which is GM-specific. The transmission capacity is 3.6 quarts, so you've got about half of the correct fluid on board. The major difference between Dexron and Mercon is the friction characteristics, not the viscosity. One of them -- I forget which one -- is grabbier. But there aren't any organic-lined clutch packs in your manual gearbox like there are in an automatic box. I probably wouldn't go through the trouble of changing it.

Q I can hear a noisy bearing whenever I push in the clutch on the five-speed manual transmission of my 1999 Isuzu Rodeo SUV. The dealer says that if they disassemble the clutch, there's no doubt that they'll replace most of the worn parts -- an expensive repair job, I'd imagine.

If I just leave things as they are and don't replace this bearing, will this result in catastrophic failure?

A The noise you are hearing is the throw-out bearing, which only contacts the clutch pressure plate when the pedal is depressed. Eventually, it will seize, and then every time you try to shift, the stationary bearing will ride metal-to-metal with the plate. That won't last long, until the pressure plate fails from the heat and friction. You will then be able to depress the clutch pedal without the clutch disengaging the engine from the transmission. This will make driving difficult, if not impossible. Plus, you'll need to replace more parts than now.

I wouldn't try to drive this truck to anyplace further away than twice as far as you're willing to walk.

Q Fifteen months ago, a clicking sound started coming from the engine compartment of my 2001 Toyota Corolla from what would be the bell housing in a nontransaxle-type engine. At the dealership, the answer I got was that, for some reason, the torque converter bolts had come out and cracked the flex plate. Their mechanics replaced the flex plate and rebolted the torque converter. Now the click has returned, and Toyota tells me even before they open it up that it is a bad torque converter, and they need to replace the same two parts.

Are the flex plate and torque converter the only parts that could cause the problem? The dealership says that my car was in an accident sometime in the past; I think they're just priming me for when the thing falls off again.

A Could be a couple of things:

The engine and transmission aren't concentric or square. The flex-plate is bolted to the crank, and the torque converter rides on splines on the transmission input shaft. If they're out of line, the flex-plate will flex too much, and eventually crack.

Could also be a crank that's not square on the end, making the flex-plate wobble. Or it's potentially a bent input shaft or converter.

A good mechanic can check everything for run-out before it all goes together, but it'll take a couple of hours once the transmission is out.

Q I drive a 2000 GMC with 44,000 miles on it. When I pull over at a rest stop on an interstate highway and, after a short time, then get back into my truck, I'm having trouble with a hard accelerator pedal. It won't push down, and if I step down hard, the pedal will release and send the truck violently forward. So what I do for now is put the transmission in neutral and free the pedal up and then put it in drive. Do I have a throttle body problem or linkage problem or what?

A Try cleaning the throttle body.

Mike Allen is a senior editor for Popular Mechanics magazine. Questions should be sent via e-mail to driveit@nytimes.com.