gear boxes

 in class we pulled apart and inspected a toyota 4 speed gearbox. the gear box was for a rear wheel drive (north south) engin. the gear case  was in ok condition and had small wear and chips. bolts and threads were in ok condition.
inside the gear box there was a input and out put shaft ,revers idler and driver shaft.
on the driver shaft there were 5 gears that were all part of the shaft  and alwasy spin at the same speed as each other.there were 4 helical cut gears that were  1,2,3 and forth gear. the fith gear was a straigh cut gear and was revers gear . these gears were all in good conditon and so wear the roller bearings inside on the shaft.

out put shaft
the output shaft held the all the gears except forth wich is on the input shaft. the out put shaft also holds two sychro units wich are used to select the gears when changing gears.  these gears were all in good condition ,well lubricated, bearings were good and not lumpy or worn. when i put the gears back together i checked the play and clearinces to see if a spacer or washer  is needed to close the clearinceto reduces play wich can cause extensive wear.

HELLICAL
a hellical cut gear  is a long cut gear wich is alot stronger than a straight cut gear. the hellical cut gear is used manly in forward drive gears (not revers). altough some older gear boxes had first  and sometimes sceond gear with a straight cut gear. this has changed as manifactures have wated to improve durablitiy and overall strength of of the gear boxes.


STRAIGHT CUT
a straight cut gear is a straight tothed gear wich is mostly used in the revers system (driver ,driven and idler) . the problem with straight cut gears is that the weight of the drive is pressed on a small straight surface wich isnt as strong as a long offset cut like a hellical cut. the most common issue with staright cut gears is knocking  a tooth off or shreading teath wich creats excessive noise slippage and further damage.


SYNCRO UNITS
a syncro unit is a system that helps with the selction of gears. inside a sysncro unit is a straight cut gear wich slots into a houseing. two circlips are inserted with 3 small metal spacers locking the spacers in. having these small metal bars alowws the gear housing to slide backwards and forwards selcting the gear needed.the gear inside the houseing slots into teath on the output shaft  wich makes it fixed to the out put shaft.having a faulty syncro unit or a a syncro unti assembeled wrong can make cahnging gears extremly hard if not impossible.

SELECTOR SHAFTS AND SYSTEM
changing gear involves a few diffrent mechanisims. the gear leaver ataches to a selector shaft wich hooks on to sevral other selector shafts wich are attached to the syncros and revers system. on the toyota gear box i did there were 3 selector shafts. there were also 3 tic tacs wich slotted between the selector shafts to prevent selecting to gears at once.

 BEARINGS
the bearings inside the toyota gear box were mostly roller bearings some caged and some like the input shaft into the output shaft were free roller berings (without cage). also there were oil groves were the gears sloted onto on the out put shaft wich act like beaarings as the pump oil in and around the gear to lubricate it. on the gear box i did some bearings needed to be replaced as some rollers were missing and some were lumpy  and worn. the out put shaft ran on a caged roller bearing wich was ok and not lumpy. when re assemberling i lubricated all the bearings to ensure  as little wear as possible.