BMW E61 5 Series Wagon Hydraulic Tailgate Lift Repair

Today I spent about 5 hours repairing my hydraulic tailgate actuator. There lots of discussion about this issue on the forums, I thought I would add some photos from my experience to help those considering or performing this repair.

Correct oil level should lie within the "X"
You can see the oil level is quite low - about 25mm below 
What was wrong? The hydraulic system sounded like it was straining to lift the tailgate. Did not sound normal. The tailgate wasn't lifting up all the way - was settling back down about 10cm lower than normal. And - the hydraulic actuator on the right side of the tailgate started popping off the ball joint - when that happenned, the lift would not operate normally and had to be reset by hand.

So - did some research, and then ordered the following parts:

1. Pressurized gas cylinder for the right hand side of the tailgate.
2. A pair of new 10mm ball joints
3. The hydraulic repair kit from BMW - which includes some hydraulic fluid and a bunch of small parts.

Then - I got started.

If you are going to top up the hydraulic fluid - start by opening the tailgate, closing the tailgate, then opening the tailgate again. This bleeds the system.

Start by supporting the tailgate with something solid - like a painting pole
I started by switching out the right side gas pressurized strut. I removed the old one - it just pops off the ball joints with a bit of gentle force.

E61 Gas Pressurized Struts - New on the Right, Old on the Left
I then took a bathroom scale and measured the force of each strut compressed about half way. The old strut had a force of 96 pounds half compressed. The new strut has a force of 138 pounds half compressed - a little over 40 pounds different. This may explain part of the reason why the hydraulic system sounded like it was straining. Replacement struts are not that expensive, even from the dealer. The new OEM strut even comes with a dab of grease inside the ball joint so that it is ready to install. Check yours - make sure it is greased to protect the ball joint from wear during opening and closing.

Old vs. new ball joint for right hand side gas pressurized strut.
Not bad condition overall. 10mm diameter ball.
With the gas strut changed - I then turned my attention to the left hand hydraulic side. I began by popping off the hydraulic actuator and trying to replace the ball joint.

Left hand ball joint - rusted and frozen in place
It was jammed, and I stripped the hexagon faces trying to remove it dry. So then I soaked it with penetrating fluid, and got onto it with a pair of vice grips.

Penetrating fluid helped a lot. Vice grips tore up the ball joint, but it ended up finally coming out. 
So - I decided to top up the hydraulic fluid while allowing the ball joint to soak in penetrating fluid. Every 10 minutes or so over 3 hours I added another squirt of penetrating fluid. On to the hydraulic system.

Hydraulic pump is just underneath the left rear access panel. The radio module is Sirius satellite Radio. 
Start by removing the left rear access cover - it just unclips and comes off. Next, remove the radio module if you have one - 4 screws hold the radio module to the bracket, then 4 screws hold the bracket to the car. I didn't bother removing the radio wiring harness, I just let it hand from the back of the car during the repair.

Hydraulic pump exposed - correct oil level runs through the X - you can see the level is quite low.
There are 2 nuts holding the bottom of the hydraulic pump bracket, this comes out with a 10mm socket. The upper part of the bracket is held by an 8mm hex head screw - comes out well with a 1/4" drive socket and short extension. 

Upper bolt removes with 8mm socket, short extension. 
By the way - make sure you have a nice 1/4" drive socket with a fairly light mechanism - you'll thank youself. The folding handle is really convenient in these tight spots.

Once the bracket is undone - you go underneath the bracket and remove 3 nuts holding the pump to the bracket - 6mm. 

Once the pump is freed from the bracket - reach up to the top and free the hydraulic lines from a small clip, and free the electrical harness from a zip tie clipped to the bracket. Once these are free - the pump is free to descend. You'll also need to remove the electrical connections - one plastic connector, and two individual wires that connect to the motor underneath a black plastic circular cover over the motor. 

Motor power connections under the black plastic cover. 
Then you can continue following the BMW instructions. I drained all the oil from the reservoir into a small pan.

Draining the oil from the reservoir. 
The drain plug is a small metal plug in the very bottom of the plastic reservoir. You don't need to (or should not) remove any of the hydraulic plugs from the pump. Then you can refill the reservoir. If you purchased the BMW kit - you'll have a new drain plug complete with O-Ring to reseal the reservoir.

Installation is the reverse of removal. Redoing the electrical connections is a bit tricky. Once the electrical connections are replaced - test the tailgate before bolting everything in. It might saving you having to remove the pump a second time to check the motor connections (from my experience...).  

BMW repair kit contents. The bottle of oil has a nipple the same size as the drain fitting on the reservoir - very nice. 
Then I went back to removing the left side ball joint. Three hours of penetrating fluid loosened it up - it was still very difficult to remove.

Chewed up the old ball joint removing it with vice grips. New 10mm ball joint on the right. 

Use lots of anti-seize on the new ball joint - might save the next owner of the car a lot of trouble. 

Socket at the end of the hydraulic actuator needs cleanup. 
So - I cleaned up the socket end of the actuator - toothbrush and penetrating fluid to get all the rust and crud out of the socket. Then I blew it dry with a bit of canned air, and filled it with waterproof grease. I popped the socket back on the new ball and it held.

Cleaning out the socket. 

Completed repair. I put a small section of stiff rubber fuel line next to the actuator, just to give it a bit of support to help it keep from popping off again. I'll update the post if this works. 
So - about 5 hours to do this repair from start to finish. The topped up hydraulic system works nice and smooth - like new - no sound of straining. The tailgate now closes and locks with a firm click. All good. 

The culprit - worn ball joint - chewed up by removal with vice grips. 

Update - 2 Years Following the Fluid Top Up

I use the car daily, use the glass window typically daily, and the liftgate hydraulics multiple times a week, several times an outing. So - the liftgate sees regular service. After about two years - my hydraulic strut developed a leak at the rod seal, and eventually the oil loss was enough to prevent the liftgate from going to full extension. I just recently replaced the hydraulic strut, and rebuilt the pump. I've completed a new post on the pump rebuild at this link. I'll do a new post on the cylinder replacement as soon as possible.

Sources and Links

The replacement 10mm ball and fluid kit was sourced from my local BMW dealer - Park Avenue BMW in Brossard. Total cost was in the order of $200.