I recently replaced one of the air springs on my F11. I'd already had one replaced a few months ago by an indy garage while the car was with them for some other work but after it started to drop occasionally at the opposite corner I decided to try changing it myself. Armed with the help and advice of @Munzy123 and @HandyAndy_UK among others the job was really quite easy and as long as you have a good jack and some stands available the only other equipment you'd need would be a largeish screwdriver and a 10mm open ended spanner.
Oh, and a laptop with ISTA+ installed would be helpful as well. It's possible to manage without but you'll need to remove the rear underbody panels to allow access to the air suspension valve block and manually bleed the system from there. If you have access to ISTA+ there'll be less dismantling to do. Apologies for all the nerdy computer shots. I thought they might be helpful as I'd not been able to find much online showing how to use ISTA to empty/refill the sysyem.
I had to buy a decent trolley jack and axle stands for the job but considering the indy garage were saying they'd need 2 hours to properly diagnose the car before making any repairs the jack and stands have almost paid for themselves already. I took a slight gamble just changing the spring without any diagnosis other than how the car was behaving.but as one spring had already been done and the car was showing 75000 miles it seemed like a reasonable bet. In the end it paid off and I'm glad to have invested in some quality equipment.
To start with I connected a battery charger at the terminals under the bonnet. It wasn't the same power supply you'd find in a properly equipped workshop and only puts a slow charge into a AGM battery but knowing I was going to leave the ignition on for a while it seemed better than nothing. I also switched off everything else I could to minimise as much battery drain as possible. Next I slackened off the wheel nuts just enough to make it easier to undo them once the car was off the ground. I was only changing the spring on one side so only needed to remove one wheel but as I was fully deflating the air suspension I needed to support the rear of the car on both sides. Being an F11 I was able to use the stiffening plate behind the rear subframe as a lifting point. It looks flimsy but the supporting struts give it enough strength to hold the weight of the car. Just be sure to chock the front wheels securely as the car will have a tendency to roll forward.
Once lifted high enough the car was supported on axle stands combined with rubber jack pads which fit into the jacking points.
Next I used ISTA+ to fully deflate the air suspension system.
After connecting the cable and establishing a connection to the car I selected the 'service functions' tab and navigated through to the option of filling and draining the air suspension.
I selected the option to bleed the air bellows
Then confirmed all the necessary preconditions had been met... You need to remove the 40 amp air compressor fuse which is found in the boot inside the trim behind the right hand wheel arch and numbered 182.
Then clicked to confirm the bleeding procedure
and then continue
While the air was bleeding out I removed the wheel nuts and wheel after noting the position of the wheel on the hub. I'm not sure whether it's considered best to replace the wheel in the same position but it seemed there'd a better chance of getting it to sit flush with the hub and avoid any vibration issues later so I took a second to photograph the wheel before removing it.
By this time ISTA had finished the first run through the bleeding process and was asking my if I wanted to repeat. I selected yes and clicked through the same screens as before.
With the wheel now removed after the second run through I was able to feel how much pressure was left in the suspension system by pressing on the rubber bellows.
It felt very soft and was easy to push into with my fingers so I guessed 2 bleeding procedures would be enough and declined ISTAs offer to repeat.
The spring is secured at the bottom by three plastic tabs which engage with the the hole in the middle of the mounting. I used a suitably sized flat bladed screwdriver to push them toward the centre and so disengage them from the edge of the hole. At first I tried to unclip all three before lifting the bottom of the spring clear but I soon realised it was much easier to unclip one and twist the lower body of the spring slightly so as to prevent the first tab from re engaging while you're trying to free off the second. While holding the body of the spring in its twisted position I could then disengage a second tab.
With two tabs now clear it was then easy to twist the bottom of the spring a little more in the right direction to clear the final tab leaving the spring hanging free at the bottom and clear of the mounting.
To disengage the top mounting I had to turn the spring by about 45 degrees in a clockwise direction, that is clockwise if you were looking down at the top of the spring. If you look at the shape of the top of your new spring it should be clear which way you need to turn the old one. It wasn't difficult to turn, I just gripped the bellows and dust cover in both hands and the whole assembly turned quite easily. Once turned it felt quite loose and it seemed to be disengaged but was still tricky to pull down and get clear of the mounting. After trying for a few minutes and getting frustrated I stopped, looked at the spring, swore at it and tried again. This time I must've moved it in just the right way and it dropped out easily, as if mocking my previous attempts. Don't panic if it seems reluctant to come out at first. You'll soon move it just where it needs to be to pull free and you'll be left with...
Take care not to twist the air line too much or it'll get kinked and need replaced or repaired using a hot coat hanger which was one method I recall reading someone had used.
Next I had to undo the fitting attaching the air line to the spring using a 10mm ring spanner. .
It wasn't screwed in particularly tightly and was easy to unscrew
With the air line removed from the spring I pulled the threaded part of the fitting from the end after prising off the olive which grips the pipe and had a look to assess the condition of the pipe. NewTIS says the pipe needs to be in pristine condition to to ensure a good seal. Mine was not in pristine condition having score marks round the circumference presumably from the unscrewing of the fitting. I could have cut the pipe back to a clean section but would have needed to cut off almost an inch. I didn't want to leave the pipe too short or risk not making a straight cut which might not seal properly so decided to take a chance and just refit the pipe as it was. I put some tape over the open end in an effort to keep any foreign particles from entering the system. The bare air line was then able to be pulled through the hole in the dust cover and moved to one side out of the way. All that was left was to manoeuvre the spring clear of the car. This turned out to be the most difficult part of the whole job but after some perseverance I realised I had to separate the dust cover from the spring. Once I'd done that it was easy to bend the dust cover enough to pull clear and then I was able to pull the spring out from the car and give it a good inspection. It was interesting to get a good look at it. It hadn't looked too bad while on the car but now it was off and fully deflated I could see the true condition of the rubber and some of the strange symptoms resulting from failing air springs made a lot more sense. The car might drop one day but not the next. It all depends where the rubber folds.
Original BMW unit with dust cover removed and Arnott replacement side by side. The Arnott one looks quite a bit smaller and came with the the new pipe fitting already in place. There was a plastic plug sealing the fitting which you need to leave in place until just before fitting the air line.
I'm not sure whether you're supposed to get a new dust cover with a new spring. Mine didn't come with one but the old one looked ok and seemed to be a good fit with the Arnott spring, notwithstanding the following, so I just swapped it over. The only difficulty I had here came from the shape of the recess at the top of the Arnott spring through which the air line passes. It's a little different to the BMW unit, I guess in an effort to make it harder to trap the air line between the top of the spring and the car but makes it difficult to get a good alignment with the hole in the BMW dust cover. The hole needs to be a little lower down.
Perhaps there are some specific Arnott dust covers to use with their springs. I'll look into that sometime but for now I had to get the car back together without any further delay so just had to go with what I had. I positioned the dust cover so the airline could pass through and line up as closely as possible with the connection, removed the tape I'd previously used and the plastic plug in the air inlet and pushed the air line in until it stopped. I then pulled it out gently to seal the olive as per Arnotts instructions.
Re assembly is, in classic Haynes style, the reversal of the removal procedure. Offer up the top mount of the spring into its mounting hole and rotate to engage. Take car not to trap the air line at the top of the spring or you'll end up with fault codes and need to take the lot to bits again. Mine felt quite loose just hanging there but when turned seemed to be engaging positively so I was confident it was in the right place and went on to attach the bottom mount. It was difficult to pull the bottom of the spring down with enough force to engage the tabs in the hole so after a bit of trial and error I decided I'd just get it in position, try re inflating the system and see whether air pressure would do the hard work for me.
I replaced the air compressor fuse and after clicking to continue I heard the compressor start working and soon after that the bellows was hard and the bottom mount was pushed fully home with tabs engaged.
Referring to the photo taken earlier I replaced the wheel after giving the mating surfaces a good brush off with a wire brush and let the car back down onto the ground. It sat there, not dropping. So far so good. Torqued the wheel nuts to 140Nm, removed laptop and battery charger, put tools away and went for a drive. The Arnott spring felt much nicer that the BMW one. I'm not sure whether the ride quality degrades over time/miles or whether Arnott units are just better from the start but it's a great improvement. The car rides a lot better and the symptoms the car was displaying are no longer evident so I'm pretty happy at having done the job myself.
If anyone's thinking of doing this and being put off by thought of it being too difficult... Don't think that way. As long as you don't mid getting some dirt on your hands and have the tools needed it's really very easy and will save you plenty of money for an hour or so of your time.