Tercel 4-speed manual overdrive?

snipped-for-privacy@volpe.dot.gov wrote in news: snipped-for-privacy@g49g2000cwa.googlegroups.com:

It probably means the 4th gear's ratio is higher than 1:1.

The word "overdrive" refers to the ratio of output shaft (to the differential) to input shaft (from the crankshaft).

1) If the output shaft turns the SAME number of revolutions per minute as as the crank, then it's DIRECT-drive, or 1:1. 4th gears are often this way. 2) If the output shaft turns LESS than the crank, then it's an UNDERdrive gear. Gears 1 through 3 are usually this way. 3) If the output shaft turns MORE than the crank, then it's an OVERdrive gear. 5th is always this way, unless the tranny is a 6-speed, in which case it may be overdrive or direct drive.

ANY gear can be an "overdrive", "underdrive" or "direct drive". It just depends on the ratios the manufacturer chose for that gear set.

In a 4-speed manual overdrive transmission, 4th gear is generally the overdrive gear.

In a 5-speed manual overdrive transmission, 4th gear is direct drive and 5th gear is the overdrive gear.

"Direct" means that the engine and axles are turning at the same RPM. "Overdrive" means that the engine is turning more slowly than the axles for improved fuel economy.

If it's true, then it means that 3rd is 1:1, and 4th is going to be something in the range of about .80:1. The typical ratio of a 4 spd is for the top gear to be 1:1, but there is no reason that 4th couldn't be an overdrive. Overdrive is typically reserved for 5th, and 4th is usually direct.

Technically, it means that the transmission input and output shafts are turning at the same speed, the axle speed is a function of the gear ratio of the differential and the diameter of the tires. Technically.

In an overdrive transmission, the input speed of the transmission is lower than the output speed when the overdrive gear is selected.

True - I stand corrected! I'm thinking output shaft and typing axles.

I knew you knew. But, what happens when it detonates?

When what detonates?

"J Strickland" wrote in news:- snipped-for-privacy@ez2.net:

No, you mean when it predetonates :)

I think there are pills to cure premature detonation!

I thought those pills just let you detonate when the time was right ...