Oil Won’t Aid Ground-Down Gears

Question: I have a 1983 Nissan with a 5-speed manual transmission. My problem is getting into reverse.

It seems to get harder all the time. Would a special oil help? I just had the clutch replaced after 57,000 miles. -D.R.

Answer: The most likely reason you are having trouble getting into reverse is that you have slowly ground down the teeth on the reverse gears. Only a complete tear-down of the transmission will fully solve the problem.

There is a very simple rule to follow to avoid this outcome:

DON’T GRIND THE GEARS.

When you shift into reverse, the car’s wheels must be at a dead stop and the transmission gears must be at rest.

Sometimes, if you depress the clutch and shift very quickly into reverse, you can hear that awful grinding noise. That is the reverse gear trying to mesh with its counterpart gear on the transmission shaft.

The grinding noise means that the tips of the gears are slowly being ground off. So instead of nice points on the gears, there are blunt ends.

Eventually, the two gears will not want to mesh, because the blunt ends jam against each other. Then you have to force the transmission.

This isn’t a problem in forward gears. The forward gears have something called synchronizers that act to equalize gear speeds, and they are always meshed in any case.

If you find that your transmission seems to be grinding when you try to shift into reverse, it means that the clutch is not fully disengaging the transmission from the engine.

That can happen if the clutch disk becomes warped or if the splines on the clutch plate become rusty and the plate does not back away from the flywheel.

One way to avoid grinding the gears if you have a bad clutch is to first shift into any forward gear, which will stop the transmission.

Then shift into reverse. Or in severe cases, shift into reverse before you start the car and start the car with the clutch depressed. Then simply let out the clutch to back out of a parking space.

You say that you recently changed the clutch on the Nissan. Perhaps you did not change it soon enough and you ground down your reverse gears before the clutch was replaced.

All is not lost, because there are still a few tricks you can use. Rather than forcing the transmission when it becomes stuck, try shifting into neutral and then reverse. You might get lucky enough for the flat spots to move off center.

As a final resort, try parking in spots where you don’t have to go into reverse. It sure beats having to push the car backward.

Q: I understand that the SG rating on motor oil is considered the best by the American Petroleum Institute. But what about oil rated CC or CD? --C.A.W.

A: The C designates an oil rated for diesel service. Originally, it was selected for commercial service, because diesel engines were not used in passenger cars. (The S from the SG rating stands for service stations.)

CE is currently the top rating for diesel engines, far exceeding the older CC and CD, which was introduced in 1955. The American Petroleum Institute is in the process of rating an even better oil, CF.