Hi all, If i select reverse gear when the car is warmed up after a journey it will go into reverse and as soon as it engages and the car moves back, it loses reverse with a very slight knock sound from the rear of the car. When it is cold it selects reverse and drives bacwards normally. There are no faults showing at all. Occasionally if you select reverse you appear to get nothing at all. The gearbox was replaced at a franchised dealer in Ascot with a brand new unit about 3 yrs ago probably 40 k miles after it randomly spat all the fluid out on a motorway about 25 miles after the car was serviced at the same dealer (they denied any responsibility as they said they had not touched the transmission during the service) the car drives faultlessly and smoothly in forward at all times and when reverse works it is smooth and normal. This is a 54 plate last of the bmw cars, had it from new 120k ish on the clock. Any help advice guidance would be massively appreciated. Many thanks

What does diagnostics say ?

Assuming your L322 is a V8 and not a TD6 (?), next time it refuses to select reverse try selecting 1st gear in Manual mode and see if you get overrun (engine) braking - or if it just freewheels. This will determine if the F-clutch/brake is the cause.

maybe get a service on gearbox. firstly check cooler as these block/clog up

Ok, its a 4.4 bmw engine v8 diagnostics say nothing, iid tool says nothing, no faults or warnings anywhere. There is engine braking, all forward movement is perfect, changes are perfect, sport, manual, kickdown etc, all perfect. I have had one additional symptom to add. I put the car in reverse and it engaged and stayed in reverse but with virtually no strength to the reverse motion almost like a slipping clutch only in reverse. What does the presence of engine braking indicate? would a cooler problem not effect the transmission in all modes? I am not sure what you mean by getting a transmission service? There doesent seem to be much in the way of a service schedule for it? I have been told that the transmission is sealed for life and has no service requirements! I am not sure which of the two types of transmission is in the car? There seems to be two variants of transmission possibly used. A ZF box and an alternative. Any guidance on identifying the box type? Many thanks again.

Your transmission is a ZF 5HP24 unit.

Two clutches are engaged in reverse gear - C & F. The F clutch is also used in 1st gear in Manual mode to bypass 1st gear sprag clutch which only drives in one direction i.e. the car freewheels when on overrun. If your car has engine braking in Manual 1st gear it indicates that the F-clutch is engaging correctly and therefore points to a possible problem with the C clutch.

Bemble said:

Your transmission is a ZF 5HP24 unit.

Two clutches are engaged in reverse gear - C & F. The F clutch is also used in 1st gear in Manual mode to bypass 1st gear sprag clutch which only drives in one direction i.e. the car freewheels when on overrun. If your car has engine braking in Manual 1st gear it indicates that the F-clutch is engaging correctly and therefore points to a possible problem with the C clutch.

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Spot on post !