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BMW Z4 convertible ...

BMW Z4 convertible top motor - "through the trunk repair"  

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The motor/hydraulic pump for my Z4's top stopped working last year.  I was about to spend more than $600 for a replacement unit and remove the top to replace it when I learned that the motors can almost always be easily repaired. I also learned that they can be repaired "through the trunk"  eliminating the need to remove the roof assembly from the car, which is a big job. 

Your Z4's pump will almost certainly fail someday unless your car has almost never seen rain.  It is attached to the roof assembly which sits inside a compartment that rain seeps into.  The compartment has a drain but it's usually clogged so it fills up with water.  The water then seeps into a plastic case, which contains your motor and pump, which has a foam lining to reduce the sound of the motor. 

Once that happens your motor is doomed because the foam absorbs water and it will probably never dry out.  It may take years but the water and dampness will cause enough corrosion to make it stop working.

The water can also cause the manual roof release to stop working, a problem I also experienced, making it impossible to lower the roof if the motor quits.  That's because a valve on the pump gets corroded and stuck. 

By the way, you roof can also stop working because of broken switch in the trunk.  Here's a good discussion about that problem.

I read on a forum about someone in Europe who had successfully repaired dozens of pump motors by soaking them in diesel oil or WD-40.  So I fixed mine by cleaning it with WD-40 and DeoxIT electrical contact cleaner.  It also had a slight corroded motor bearing that I fixed by lubricating it with a light oil and then spinning the motor shaft with a cordless drill.  I'm very confident that it'll keep working and if it does fail I can now get to it easily.

I accidentally disassembled the hydraulic pump which has some small parts in it that can very easily get lost.  The motor is the top of the pump and when I removed it the parts inside the pump fell out. I was very glad that I had a large bath towel underneath it to catch them and the hydraulic fluid. 

The traditional way to get to the motor is to remove the top from the car, which is a lot of work and requires two people.  You can also badly scratch your paint if you don't protect it with masking tape.  I couldn't retract my roof which would have made this much harder, and I was worried about having trouble finding someone who could help me lift the roof off the car and put it back on.

I also wanted to try fixing the motor and if I was unsuccessful my car was going to have to sit unassembled in my driveway for at least a few days while I waited for a new pump assembly to arrive.  So after reading about someone in Germany who had fixed hundreds of Z4s in less than a hour "through the trunk" I decided to give that method a try. With this method you relocate the hydraulic pump to the trunk without removing the roof.  

It ended being a lot faster and easier than the traditional fix.  But, that method is much less risky because the process is well documented and you're much less likely to damage a hydraulic line that will then need to be replaced. Fixing it through the trunk also requires long arms, some strength, and some discomfort from working in a very awkward position at times.

Here is a brief description of what I did.  Follow my instructions at your own risk. I've included some links at the end of this post that will lead you to more help.

You'll need to remove some electrical connectors in the side panel behind the driver's seat.  You then remove the shelf that the retracted roof sits on so you can reach the plastic housing that the motor and pump are in.  Then remove the  tape and zip ties that hold the hydraulic lines to the top of the plastic pump housing and pull the top of the housing off.  You can then pull the pump out and set it next to housing. 

You'll only be able to move it enough to get it out of the way because the hydraulic lines will still be attached to the lower plastic housing, which is still attached to the roof assembly.  At this point you'll need to wiggle and pull on it until a mounting tab on the bottom breaks.  You'll then have enough slack in the hydraulic lines to move the pump into the trunk.  At that point it'll be easy to work on the motor and pump. 

You'll need to cut a notch for the hydraulic lines in one of the mounting brackets for the shelf when you put it back in. 

It took me at least four hours to get the pump out and and most of that time was spent trying to get the lower housing's mounting tab to break. I eventually succeeded by drilling into the side of it with a 3/8-inch "bell hanger's bit" which is just a drill bit that's about 16-inches long. 

I angled the bit up and against the side of the "well" so it would act as a lever.  And then, with the bit still inside the "cup", I moved the drill sharply downward which forced the housing up and broke its mounting point.

Once they're done many people tuck the pump behind the carpet at the back of the trunk where it can't be seen.  I didn't because I wanted to keep using the "cup" to protect the motor and it's wiring and it was too big to fit behind the carpet.

I didn't expect to be writing about this repair so I didn't document it.  But here are some links you may find useful if your convertible top stops working:

Z4 roof motor relocation to boot (Zroadster.org)  - excellent with pictures

How to replace soft top motor without removing roof.. DONE! (Z4-forum.com)

Convertible Stowage Compartment Base Replacement (Pelican Parts) - Removing this shelf is necessary to fix the motor.  Here are some nice instructions with pictures.

And here are a couple of YouTube videos showing how to remove the top assembly in case you want to get to the motor that way.

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Posted : 22/02/2019 10:41 am