My toyota duet rear gear failed. I bought another gearbox, 2 months down the front gears D4,3 and 2 have failed, the reverse gear is working What is the problem

Sorry to tell you that you have a failed transmission and it will need to be rebuild or replaced.

possible problem with gearbox

I'd start by looking at the clutch hydraulic circuit. "...could not put gear into 1st or reverse" suggests that the change cables on the transmission may be failing. And just in case, make sure there's nothing in the cabin that's jamming the gear change lever.

clutch not fully disengaging
air in the system /problem master cylinder or clutch cable failing

hi mate , sounds like the SPIGOT bearing its a little bearing that allows the gearbox to be at a different seed than the engine flywheel and if this is in bad condition it will take the gearbox front shaft to a higher speed than comfortable for gearshift , in the meantime when you go for 1st or reverse gear just engage a gear like 4th without taking your foot off the clutch and then go for 1st or reverse, this will stop the gearbox spining long enough for a smooth shif, oNLY USE THIS METHOD WHILE STaTIONARY and see a professional when you get time.

This information is from my genuine service manual. I hope it is of help.
Non-turbo
Turbo
Sedan Wagon
Type 5-forward speeds with synchromesh and 1-reverse
Transmission gear ratio
1st 3.454 3.454
2nd 2.062 1.947
3rd 1.448 1.366
4th 1.088 0.972
5th 0.780 0.738
Reverse 3.333
Front reduction gear Final
Type of gear Hypoid
Gear ratio 4.111 3.900
Rear reduction gear
Transfer
Type of gear Helical
Gear ratio 1.000 1.100
Final
Type of gear Hypoid
Gear ratio 4.111 3.900 3.545
Front differential Type and number of gear Straight bevel gear (Bevel pinion: 2, Bevel gear: 2)
Center differential Type and number of gear
Straight bevel gear
(Bevel pinion: 2, Bevel gear: 2 and viscous coupling)
Transmission gear oil GL-5
Transmission gear oil capacity 3.5 2 (3.7 US qt, 3.1 Imp qt)

you need to have the gear linkage adjusted, using a dealer tool.you should be able to engage all gears when engine is off.

it is a gearbox problem and should be taken to a gearbox specilaist you do anything more than taking it to the specialist

2.2td estima enima,the auto gearbox stopt change gear from 3 to 4,can somebody help me please?

gears slipping out of mesh indicates
1 ---not properly engaged on selection
2--- failing output shaft bearings
3-- worm slip joint bush in the extension housing not maintaining alignment of the output shaft
The gear engagement is by dog teeth in the synchro ring for 5th gear and if that connection alignment is not maintained exactly by bearings and bushes the dog teeth move out of engagement at each revolution
AS reverse gear operates through a moveable spur cut gear to engage the counter shaft and the out put shaft and you are having trouble with reverse as well , indicates the out put shaft rear bearing is suspect or is moving in the box housing