Thought I would write up an entry for the archives on how to replace the pressure accumulators since I just did it today. Overall, I rank this as a 5 out of 10 on the PITA scale. Fundamentally it's not that hard and doesn't require special tools or brute strength. However it is very tedious and time consuming so with much patience it is a job you can do in a day or weekend. It took me about four hours which I will explain more about below.
10 mm socket on 1/4-inch drive
2x long extensions
1x short extension
Wobbly joint for above socket set
2x 10mm open/boxed wrenches
11mm open ended wrench
14mm open ended wrench
(14mm ratcheting wrench might be best but I didn't have one)
Large flathead screwdriver
Catch tray for fluid
Newspapers for back up when the catch tray isn't in the right place
Shop towels and rags (I like old T-shirts because they're more pliable)
Floor jack and 2 jack stands
Of course, more Pentosin 7.1 to refill the reservoir when done
Optional: Fuel Filter replacement. It's easily accomplished at the same time.
The driver's side accumulator is much more difficult than the passenger side because of the exhaust system running just under it. Remember that the system is under at least 30bar of pressure so proceed safely being mindful of spray patterns and loose rocks and dirt under the car. Eye protection is a must. I have a set of safety glasses I picked up at a semiconductor fab years ago but I would imagine there are even better products available in the automotive market. I am only a self trained weekend hobbyist (I would not call myself a mechanic) but have been doing this for a number of years on many BMWs. That said, let's get started...
1-Jack up the rear and support it with the jack stands. The higher the better.
2-The driver's side accumulator is located just above the half shaft. Using your hands, experiment with all the access points to get to the flare nuts, and the mounting bolts/nuts. You will find that only certain positions work and it will vary depending on your arm thickness...yes, it's that tight in there.
3-Using any combination of the 10mm wrenches and sockets, loosen the two opposing mounting bolts and nuts on the flare-nute side of the accumulator. Tool usage was trial and error for me. Sometimes the two wrenches were the ticket, other times one wrench and the ratchet. Just depends how your fingers fit and where. You can remove the nuts and washers but leave the bolts in place to provide leverage when you break the flare nuts free. I liked having these nuts off because once you have fluid running all over the place, it's faster to remove the accumulator then trying to remove the nuts with fluid running down your arm, into your shirt sleeve, etc. Leave the accumulator secured by the bolt in the other end.
4-Position your newspapers on the ground and your catch try under the flare nuts. Wrap a rag around the flare nuts in such a way that you can still get a wrench in but will protect your eyes and body if it sprays. I started with the larger fitting first using the 14mm. Note the torque you apply to break it free. It's not as much as you might think. Remember this for tightening later. On mine, the fluid did not spray but just came down as a steady stream. The more I loosened, the bigger the stream. I had a very narrow amount of space to crank the wrench so I spent a lot of time taking a turn, flipping the wrench, taking another turn, flipping the wrench, and so on. A ratcheting wrench might be more efficient here. If you loosen it all the way and pull the line out, remember there is fluid in the line and if you point it downward it too will stream out.
5-Use the 11mm wrench to loosen and remove the bottom flare nut and line. No drama here but again pay attention to the amount of torque you apply...it's not much.
6-Fluid will now be running everywhere, all over the exhaust, the half shafts and if you're like me, down your arm and into your shirt. Good times.
7-Use the 10mm socket with long extensions and the wobbly joint to get the final mounting bolt loose. The wobbly helps because there is not a straight angle access to the bolt. The control arm is in the way. The bracket that the bolt screws into has a fixed nut mounted at the top, which is a relief when you see how little room there is up there if BMW had required you to put a wrench on it. Hold the accumulator with one hand while releasing the last mounting bolt.
8-Once it's free, remove the loose bolts from the other end and note the loose bracket that holds the hydraulic line in place. Remove the bracket and the bolts. Carefully work the accumulator out through the area nearest the differential. I had to twist mine around to clear all the lines under there but it eventually came free.
9-Now take your old accumulator to the bench and if necessary remove the rubber bushing from the mounting hole and replace it on the new one, unless you had foresight to buy a new bushing. Kinda surprised it didn't ship with a new one in the first place. There is a metal insert in the center of the bushing that will push out with very little effort. Be aware of this in case it comes out with the bolt in step 7, otherwise push it out. I used a large flathead screwdriver to get the rubber bushing through the hole, being careful not to tear it up. It takes a little muscle to work this out and back in.
10-On the driver's side only there is a plastic cover around the accumulator which I assume has something to do with shielding it from the exhaust. Once you have the bushing removed you can remove this and put it on the new part. You'll see why you can't remove it with the bushing in place. Pop in the bushing and replace the metal insert. Remove the protective caps from the flare nut ends and you're ready to reassemble.
11-This is the hard part! Remember how little room there was to get the mounting nuts and bolts out. It's much harder to get them back in. One of the three is easier because you can just get two fingers on the nut-side to hold it. The other side stumped for for a while. I couldn't get a finger in to hold it and of course putting the nut in the wrench wasn't precise enough. My solution was to wrap the open end of the 10mm wrench with electrical tape on one side and then put the nut in so it sticks in place. I could then push the wrench up into position and use my other hand to turn the bolt and tighten it. I thought it was clever but I'm sure any mechanic reading this would consider that an old trick. Remember to replace the loose bracket that holds the hydraulic line first before doing any of this.
12- For some reason, I had a hard time getting the final bolt on the other side to mate up to the bracket with the fixed nut. There is so little room to negotiate the bolt, and trying to deal with the wobbly. After some time I did get the bolt threaded by hand first using fingertips only, then followed with the wobbly to tighten.
13-Be very careful when reattaching the flare nuts. It's extremely easy to cross-thread them. I used one hand to push up on the big hydraulic line to better align it on the threads. By moving it around while studying the angles you can see when it is aligned or not. Try threading the nut by hand only. Use opposite pressure on the line to position it so that the nut twists in with ease. If you can't turn it by hand and have to resort to a wrench, you probably aren't aligning it correctly. When you get it right, it's takes no effort to twist the nut on. There is some looseness of the nut as you screw it in so again, just be careful throughout the process until it's completely secure. Replace the bottom line as well. Use the 14mm and 11mm to tighten, but don't over tighten. It doesn't take much torque. A quarter turn might be just right but use your best judgment. Okay, one done!
14-The passenger side accumulator will take you a quarter of the time or less because it has easy access. I spent almost three hours on the driver's side and less than an hour on the passenger side. In my case, there was no pressure when I cracked the flare nut on the passenger side accumulator. I assume I released all the pressure was released on the other side. Your results may differ so take precautions.
15-I was advised to start the car and refill the reservoir as the SLS gained pressure. I did this with wheels off the ground and again with wheels on the ground but my reservoir did not go down. I had to drive the car around the block first, then refill. Your results may differ or perhaps I have another problem.
I've only driven the car a bit but so far it seems as if the new accumulators have smoothed out the ride. I wasn't aware there was anything wrong with my old ones, but since I had "more than 10 years" and "more than 75k miles" on them I treated it as a preventative maintenance item. I was able to buy the new accumulators for $94/ea from Eurasian auto parts (www.eap4parts.com
). They are after market units manufactured by Bilstein. They are every bit identical to the factory part but a whole lot cheaper.