We have lost count of the number of BMW Z4’s that have appeared at the workshop over the years with non functioning convertible roofs. As soon as the sun comes out, we get an influx of the little darlings.
Nine times out of ten it turns out to be the roof motor pump combined unit at fault.
The design of car means that the motor pump unit sit in a bucket-like casing in the vicinity of the drainage channels. When the channels become blocked, the water ends up in the bucket-like housing.
Generally electric motors and hydraulic pumps are not too keen to have a bath. In fact it has a distinct effect on reliability.
Below is one we removed recently when the roof stopped working.
With this particular car, even the bases of the hydraulic rams are heavily corroded (see below) so its more likely that this one has a leaky seal.
We’ll be checking these seals and rams after we install the shiny new motor pump (see below).
With proper drainage channel maintenance and a small drainage modification to the bucket-like housing this may not happen to your BMW Z. Use a specialist who understands your car (like us!!) for servicing and preventative maintenance may saves you pounds in repairs.