I have an 86' Bird (2.8) with an automatic. Is it really 4 gears or what exactly is overdrive? No one's ever explained it to me.

 

Wow Jim that's a very entry level question but here goes. Overdrive is the fourth forward gear in the automatic's shift pattern. It is called overdrive because in fourth gear the engine is spinning slower than the driveshaft. Where as when in first through third the engine is rotating faster than driveshaft. Hope this helps.

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84 Camaro ZZ4 with HOT cam. 1.88 60' (12.98 @ 105MPH E.T.)
Other Mods: You name it and I have probably changed it.

91 Firebird 5.0L TBI

ASE Certified Auto Tech
LIVE AND DIE BY THE ALMIGHTY BOWTIE!

 

The gear is set up for highway driving. It is great because it allows you to maintain a low RPM at high speed, meaning better MPG than with the other gears. But that gearing also gives you poor acceleration, which means it will eat gas worse when acellerating than the other gears.

 

You're right, VERY entry-level. There are LARGE gaps in my auto-education. Thanks a lot though, clears things up!