I have a 2004 Z4 3.0 with top issues. Everything will unlatch, I can hear the pump motor, but the system acts like it’s almost out of hydraulic oil, as the top get to mid up or down and stops. I can unlatch the manual override in the boot, and it can be moved in either direction with our much effort. I have done a lot of research and am thinking about relocating the pump to the trunk, mainly for ease of access. Relocation can be accomplished using a BMW pump or one from a Ford, any thoughts about such a project.
Hello Mr. Cooley, There are mainly 2 sources for your issues and both are common. The first, The convertible top hydraulic pump could be damaged by water, there are 2 drains on either side of the vehicle just behind the doors, they tend to get clogged and the result is the hydraulic pump gets flooded and corroded. The pump sits inside of a heavy foam case, while that does protect it from dirty an mitigates the noise from the pump, when it gets wet it will keep that water in contact with the pump. In order to fill the fluid or replace the pump the entire convertible top has to be removed from the vehicle. It is a good idea to relocate the pump for ease of service. I would stay with the BMW pump. When the pump is removed look for corrosion and leaks. The pump is made of 2 parts, the actual hydraulic pump and the motor that drives it. Usually the motor is the issue, they are sold separately. If there is any signs of a leak, I would replace the entire part.
The second possibility is that there could be a hydraulic fluid leak, I would try to diagnose that with the convertible top still installed, otherwise, it will be very difficult and not advisable to actuate the convertible top outside of the vehicle without the proper fixture to hold it. There are actuators that move the top, you can have them rebuilt or replaced. Personally I would have them rebuild or replaced regardless, you cannot relocate them, therefore in order to replace them the top has to be removed and I’ll tell you from personal experience, it is not a fun job. I hope I was able to be of assistance. Good luck and thank you for your question.