can anyone help me as my offside rear driveshaft keeps popping out and can't find out why

 

Did you change the axle for another one, or have you fitted different lateral links before the troubles started.
If not, have you fitted a new circlip??

 

i fitted new gearbox and diff

 

Maybe the axles you had on there are incompatible with your diff.
Did you swap over your own diff's gear/pinion to the new diff centre, or just swap over the new diff.

There are different types of axle, some have a circlip fitted on the axle stub and a recieving groove in the diff's hole, some have it the other way round, and that would cause the axles to not lock (as there is no circlip on either the axle or in the hole, or there are 2 clips which leaves no groove for the circlip to sit in (as that groove is occupied by the second circlip)

I hope you understand what I am trying to say, English is not my native language.If you have any more questions ask them, and I will try to explain.

 

I think as Dutch says, 20p part. Clip

Bez

 

As above, probably incompatible rear diff to inner CV joint combination.

A 1999>rear driveshaft into the offside of a pre 1999 rear R160 diff, won't have a clip on the shaft or in the rear diff, and will obviously keep popping out. You'll need the correct driveshaft (and circlip)