Words & Photos by Henry Phull
At the end of 2017 I picked up a facelift BMW E38 740i Sport for myself… I was fully loving the car (which was already fitted with BC Racing coilovers), but a voice in the back of my head was constantly telling me that something this big and ‘VIP’ needed bagging. Being Air Lift dealers ourselves, I knew that there was no specific bolt-on kit available for the E38, however, after some discussion with our friends at Only Charged Dubs (OCD), they said they could offer a solution using their newly released ‘BAGS by OCD’ air bags – these are designed to directly fit specific BC Racing coilovers. The idea is simple… Replace the springs with their BAGS. This new product range means it’s super easy to bag any car that has a BC Racing coilover kit available, which is awesome news, because BC cater for a much bigger selection of vehicles than manufacturers of bolt-on air kits. With BAGS sorted, I was left to decide on a suitable digital management system to control the air suspension. In the past, I’ve used both Air Lift and AccuAir management systems, and I highly rate both of them… However, OCD have just introduced a new budget system to the market, KNTRL. It’s a pressure based system (like Air Lift’s AutoPilot V2 & 3P), but much more simplified, customizable, and affordable. Wanting to bag the E38 as cheaply as possible, I opted to give KNTRL a go.
I was keen to see how easy it was to install, so Matt and Holly from OCD traveled down to the South Coast to take us through the process of bagging my 740i. We had originally planned to do this all on my driveway, but it decided to snow on the weekend we had booked (typical Britain!), so luckily our pals at Kustom Kolors came to the rescue and lent us their workshop floor to get to work and to keep warm! We documented the whole process to show you how easy it is to DIY with a few friends on a weekend.
This is how the E38 looked on its BC Racing coilovers, prior to the air conversion.
For the BAGS by OCD conversion, we opted for single bellow BAGS up front and slim double bellows for the rear.
The KNTRL system controller is a nice and simple 3d-printed unit.
I wanted to keep all of the air management components in my spare wheel well, so we constructed everything onto a board to drop straight into the well. This contains the KNTRL manifold and ECU, dual VIAIR 444c compressors in black, and two Air Lift 2.5gallon tanks.
The first task was to install the 1/4″ air lines to each corner of the car and route them to the spare wheel well. It’s important to take your time and fix the lines as carefully as possible. If you have a ramp, it makes this task far easier.
REMOVING THE FRONT COILOVERS
With the air lines routed, it was time to start removing the suspension from the car… we decided to start with the front. Luckily we didn’t have to deal with original parts that are usually seized, as the suspension had been switched to the BC Racing coilovers not long ago.
INSTALLING THE FRONT BAGS
With both front coilovers removed from the car, we had to dismantle them to remove the springs and replace with BAGS. The process of installing BAGS is a pretty simple one, almost too simple which can make you not quite trust it.
The key here is being clean and taking your time. Especially if you’re converting a BC Racing kit that has been installed as coilovers like we were here. Start by removing the top mount (on the majority of BC kits you will have camber adjustable top mounts), a centre nut will be holding the top mount tight and keeping the pillowball bearing secured.
From here you can remove the full top mount, splitting it from the steering bearing mount, which also secures to the top of the coil spring. The steering bearing isn’t needed for the BAGS conversion, so set this aside.
Next, remove the coil spring, dust boot and bump stop – these also won’t be needed. The next un-needed part will be the spring seat, use your BC Racing C-spanners to loosen this from it’s locking ring and unwind and remove from the damper, add this to the pile of parts no longer required.
The first main point not to miss, is that BC add an inspection sticker when testing each individual damper. It’s a thin white sticker on the top of the damper cartridge above the threads. If this is left on it can cause the BAGS internal o-ring seals to leak. Remove this sticker and clean any residue left off the damper body.
You’ll know be left with a pile of removed parts and a bare damper. Get to cleaning the threads well – a soft wire brush is great if you’ve been running on your existing BC coilovers to remove any road dirt. Then get in with parts or brake cleaner to completely remove any remaining dirt. It’s important to get the dampers looking as good as new.
Prepping for the BAGS conversion, using a multi-purpose grease, apply a thin covering to the smooth section above the threads, where the sticker was, and to the top few threads. Now mount the upper o-ring, which is supplied with the BAGS Conversion Pack, again applying a covering of grease.
The lower o-ring seals are pre-mounted inside the BAGS lower mount, ensure they are sat straight and that there’s no debris on them, then lower the BAGS over the damper until they reach the threads. Next, simply wind the BAGS to the damper threads, in the same way the spring seat would. You may find as the BAGS wind on more and more it gets tighter, this will be the airbag rubber stretching out as it seats at the top of the damper rod. Don’t worry, keep winding until the BAGS come to a solid stop. This is how you know it’s fully installed. You can then wind the existing spring seat lock ring back up and lock this to the airbag, preventing it from un-doing whilst being driven.
Also included in the BAGS Conversion Pack, is the pillowball support. This replaces the old steering bearing from the coilover kit, converting the top of the airbag to correctly mount and support the pillowball bearing.
The pillowball bearing will now also work for the steering, they can be tight, both from new and used, so some WD40 or lubrication can help loosen them off. If there’s play in your bearings then don’t worry, brand new bearings can also be supplied by Only Charged Dubs.
Re-mounting the camber top mount and installing the original top mount nut will secure everything back together. A lock nut is also supplied with the BAGS Conversion Pack. This again ensures the top mount nut stays tight and allows the pillowball bearing to turn without trying to loosen everything.
The final step is installing the nickel plated airline fittings (supplied with the Pack), these specific fittings do not require PTFE tape or paste. They come with o-rings installed – simply wind in tight by hand and nip with a spanner. Ideally pressure test the whole assembly off the vehicle to ensure you have no leaks, a little soapy water will be a perfect test.
Next it’s time to install back onto the vehicle and connect the air lines in. Re-assemble the hub and lower suspension components and the front is done.
From here you can adjust the static height of the suspension as you would of done with the coilover kit, adjusting the damper in the hub mount you can set the suspension strut and BAGS to reach their maximum drop, and at the same, point the suspension or wheel in arch stop. This ensures you can’t air out too far and also gives the maximum lift the dampers can offer.
REMOVING THE REAR COILOVERS
With the front BAGS fitted, it was time to do the same with the rear setup. Of course, this meant removing most of the rear interior to gain access to the top of the strut towers. This did take some time as the E38 is so over-engineered like most big BMWs.
INSTALLING THE REAR BAGS
Like the fronts, start by removing the top centre nut, remove the top mount, coil spring, dust cover and bump stop. Undo the spring seat collar and locking collars, removing the spring seat collar. Clean all the damper threads and remember to peel that sticker off! Apply grease to the upper threads and smooth part of the damper body, install the upper o-ring and grease.
The slim double bellow BAGS are quite short, and some BC rear dampers have a large amount of travel. If you’re struggling to get the BAGS down to thread on, with some assistance compress the damper rod with the BAGS slid over, so they can be wound on easily. Be careful you don’t force them and risk cross threading. Once wound on, you can install the top mounts again. As the rears won’t be turning you won’t need any pillowball supports, so the BC rubber mounts straight on to the top of the BAGS isn’t an issue.
If your kit does have pillowball rear mounts, then just spec this when you order your BAGS. Fully re-assemble and tighten everything to BC specs.
Re-install to your vehicle and connect all suspension components back together. Again, check your static heights of the damper to the hub mount to ensure you get the best drop and lift results.
INSTALLING THE KNTRL MANAGEMENT SYSTEM
With the suspension all re-installed, we could move on to fit the KNTRL management package. As we had already mounted everything on to a board, it was a case of simply dropping this into the spare well well and wiring everything up accordingly.
KNTRL is a really simple management pack to install, only requiring an ignition live and earth for the ECU. Ideally, one not affected by the engine cranking. Testing the ignition source with a voltmeter, as we cranked the engine we found a wire not dropping below 8-9v. This prevents any delays when using the ‘rise on start’ function of KNTRL.
Joining the earth and ECU plug to manifold and pressure sensors completes the KNTRL install. We wired with dual Viair 444c pack in with an 8AWG main feed from the battery and strong earth point. Fusing the 8AWG wiring close to the battery with a 70A fuse. This feeds a power distribution block feeding 2 relays, 1 per compressor, with individual fuses and joining to each compressor. This prevents one faulty compressor blowing the full circuit.
A tank pressure switch is wired from ignition as well, before sending a signal to the relays to turn on once air tank pressure has dropped below the desired pressure. We then joined the controller USB cable to the ECU, routing to the cabin and joined the controller to the other end. Taping all wiring and securing to OE wiring along the way to ensure as neat as possible install. Powering up the ignition brought the controller and compressors to life. Allowing the compressors to complete a full cycle before operating the individual corners, testing the full lift and drop of the suspension.
We set the calibration of the pressure sensors, altered screen colours, adjusted corner speed and precision before setting preset ride heights up.
THE END RESULT
What can I say? After just two days of work, I couldn’t be happier with the result. The E38 finally looks as it should, and with presets set up on the KNTRL controller, I can now easily drive on a variation of heights and stay out of trouble. Once calibrated, the system is super simple to use and you can even adjust the speed it rises or drops, as well as the precision in doing so.
If you’re considering bagging your BMW E38 or another car which BC Racing coilovers are available for, get in touch with Only Charged Dubs, Bag Riders, or FS Projects for a quote and availability. Both complete BC Racing conversion kits are available (coilovers & BAGS) or just the BAGS themselves.
SO, HOW MUCH DOES IT COST?
BMW E38 BAGS Conversion pack, ready to DIY install, with fittings and hardware required – £660 (this is what we opted for)