What Constitutes A Synchromesh Transmission ?

[JSRT4]

Whenever I read info on synchromesh fluids such as GM Synchromesh, Pennzoil's version, Redline MTL, Amsoil MTF, they are mention that they are made for synchromesh transmissions. Just curious as to what constitutes a syncrhomesh transmission ?. Wouldn't the majority of automobile manual transmssions on the road be classified as synchromesh transmissions ? (outside of heavy duty trucks and the like). Just curious if someeone could shed some light on this issue. thanks

 

[Jimbo]

You are correct. The other less commonly used term is "constant mesh". The non-synchromesh slang term is "crash box". Most passenger car and light truck three-speed manual transmissions from the 1940's-1960's did not have a synchronized first gear. Reverse gear is never synchronized.

The way they work is that instead of sliding gears, all the gears are constantly engaged, but the connection to the shaft is by means of a drive "dog". There are metal cone clutches that sychronize the speed of the gear and drive dog by friction just before the instant of engagement.

The lubrication issues have to do with frictional coefficients and corrosion, as some parts may be brass or bronze, and traditional EP hypoid gear oils contain corrosive compounds. Dexron/Mercon ATF contains friction modifiers that can delay engagement. Special fluids avoid these problems.

 

[JSRT4]

thanks for that great description, it answers my question perfectly. Thanks for the reply.

 

[MolaKule]

The ease or difficulty of shifting a manual transmission is a function of the friction modifier compounds and the proper viscosity of the lube.

http://auto.howstuffworks.com/transmission.htm

and

http://auto.howstuffworks.com/transmission3.htm

 

[psudaytona]

They look easier to rebuild than any auto...

 

[mechtech2]

Some cars have a synchronizer on the reverse gear [higher end models].
Without it, getting in reverse can be balky.