Some 4HP20 info here - under Xantia
http://citroeny.cz/servis/servis.htm
Aren't all ZF gearbox names in the following format:
(4) - number of speeds
HP - type name for all hydraulic transmissions
(20) Box model no.
Which means that things like AL4 are actually model numbers - which may cover tings like gear ratios - but the overhaul and general construction will be covered by the 4HP20 bit.
30,000 mile ATF change interva on ZF auto boxes.............
Moderator: RichardW