Restoration Project – Andrew Atwood
Suspension Restoration: Part Six of an Ongoing Series
While my Heckflosse (or Finback, if you will) was at the paint and body shop as discussed in parts four and five of this series, I used that time to decide how I was going to restore the suspension. I was able to do this by salvaging the front subframe assembly and the rear differential from my donor W110 – already having relinquished one of its doors and front-left fender to the cause – and installed them under my W112 restoration project. This got the body and chassis back up off the ground, making it easier to roll around during body and paintwork and allowed me to completely restore the original suspension from the W112.
Suspension restoration
Disassembling and overhauling the front suspension on an older Mercedes can be accomplished by anyone with general mechanical knowledge, but working on the rear suspension is different because of the swing-axle differential. Removing and tearing down the suspension requires special tools and specific disassembly and reassembly procedures. If these directions are not followed, you can and will destroy the differential, so make sure that you have a service manual and some mechanical confidence before attempting the task – or find someone who does. Manuals are available online and some of them can be obtained on DVDs. Having worked on these vehicles for more than 28 years, I have accumulated a lot of knowledge and literature – even some manuals on microfiche – but that’s a topic for a different day. Carefully following the workshop procedures, I disassembled all components down to the bare parts and sent them out for powder coating.
I chose to have the suspension parts powder coated rather than painting them by hand for many good reasons. In particular, the powder coating company would sandblast all individual parts, which meant I didn’t have to clean them. More importantly, the powder-coating process creates a very hard and durable finish that is resistant to almost all liquids, flying rocks and debris. This process is relatively inexpensive and also hides most of the imperfections that would be visible had I painted them with a rattle can. Finally, taking into account my time and the cost of materials, it was simply more cost-effective.
I told the shop to use semi-gloss black, which would be as close to the factory finish as possible – and a preference of concours judges. I have seen some restorations with glossy or flat-black colored suspensions, which also look good, but you can choose what you like. There are several precautions to take when having automotive parts powder coated. In particular, make sure all machined surfaces and threaded holes are covered and taped to prevent them from being painted. Also, ensure that stamped and cast-identification information on the parts isn’t obliterated when applying a coating that’s too thick. If that happens, you’ll spend hours scraping and grinding to remove the paint – at which point you’ll discover just how durable the powder coating is.
Because I have rebuilt many front suspensions and differentials, I did not take pictures during the disassembly process, but I highly recommend that you do if this is your first time. It is very easy to forget which way a certain adjuster bolt goes or on which side a washer or seal is supposed to be. This can lead to a big headache when you’re reassembling the system.
Replacement parts
As you tear the suspension systems down to their individual components, you will usually find that the kingpin bushings and upper and lower outer control-arm bushings have play in them, which will require replacement. Replacement bushings are readily available in the aftermarket or your local Mercedes-Benz parts department, and they are reasonably priced; don’t hesitate to replace them. You will appreciate the like-new tight feeling in a suspension that does not rattle or run away with every rut and crack in the road.
As you disassemble the front suspension, a good rule of thumb is to measure and note the configuration of any adjustable component so that it can be reassembled in the same configuration as the original, if possible. If not, center the adjuster when installing so that if you drive the car to an alignment shop, it won’t wander all over the road. Moreover, the alignment shop will have a good base from which to start the adjustments.
For differential and rear suspension, I followed the same process for disassembly and powder coating as for the front, except for the differential assembly. This required meticulous attention because it’s a very rare-optioned 3.91 limited-slip differential. Following the workshop manual, I disassembled the third member, as it’s called, and measured the limited-slip clutch packs. Fortunately they were still well within spec, which was good as these are very expensive to replace.
When it came to the differential bearings, I decided to replace them to prevent any kind of differential whine after reassembly, but finding replacements was a bit tough. Mercedes-Benz does offer new ones, but the cost was creeping into the $2,500 range just for bearings alone. I researched the original FAG bearing numbers and found that at least bearings for the axle and side differential bearing were available with the same specifications through a bearing supply house. Sourcing parts from outside generic suppliers is sometimes a viable option, but care must be taken when using non-factory parts. For example, the original bearings must be measured down to the last .01mm to ensure not only correct fit, but correct operation. This may sound a bit extreme, but it can make the difference between your rebuild lasting 50 years or failing in 50 days. I will always be the first to use a factory part over an aftermarket part unless the aftermarket supplier also offers factory parts as well, and recommend you take the same care in your restoration.
Considering air suspension
With the suspension components powder coated and assembled, I turned my attention to the spring portion of the suspension – I absolutely love the way the W112 and W109 chassis cars ride and handle – but the air suspension’s reliability leaves a lot to be desired. After pricing all parts needed to get the factory suspension working, I was looking at $1,200 just in airbags, not to mention $2,500 in rebuilt valves – and I would still be limited to the operating quirks of that era’s system.
As noted at the outset of this project, I wanted to make the car more reliable so it could be driven more frequently with less maintenance. Researching aftermarket air systems, I found one called AccuAir that intrigued me. Not only would it eliminate all mechanical ride-control valves, but it would give me a modern four-corner controlled air-suspension system as opposed to the original, whereby the front was corner-to-corner control but both rear corners were controlled as one. A four-corner suspension system helps keep the car perfectly level, which improves ride and handling. This system uses electronic ride-control sensors on each corner of the car, similar to the yaw and height sensors used on the 2014 Mercedes models. These sensors read each corner’s height and relay that information to the electronic ride-control valve, which will then add or remove air from each air bag individually. This translates to better handling, maintaining the car’s level while cornering. It also allows me to preprogram in three different ride heights that are accessed by the touch of a button – just like the new cars. All this with almost no maintenance – for me it was a no-brainer. Now again, there are purists out there who will call what I’m doing sacrilegious, so let me stress that this is my solution for my car – don’t send me hate mail!
To install the AccuAir kit into my car, I had to fabricate new airbag cans so that none of the original Mercedes parts were harmed in this procedure; this means I can return my car’s suspension back to stock at any time – if I want. After fabricating the airbag cans, I replaced the air lines utilizing the same material as those installed in semi-trailer trucks. This guaranteed good airflow and, more importantly, longevity and durability. As for mounting the ride-height sensors, this was the only part of the air-suspension system that required me to modify the body; I had to drill two one-eighth-inch holes for each sensor to mount them to the body and subframe. I then ran the wiring for these along the factory body-wiring harness under the inner door sills.
The next item to consider was where to place the air tank, control valve and compressors. I could have used the original tank, but that would mean drilling into and modifying it, which I didn’t want to do. Instead, I installed the new components as a package assembly under the parcel shelf in the trunk, which didn’t take up any trunk-floor space and kept it out of the way of luggage. The system also stays clean and is easily serviceable, should the need arise. All these installations took approximately 18 to 20 hours of work – not bad for a complete suspension modification. The cost to install one of these kits is about par with completely restoring the stock system, but without any of the drawbacks. There are cheaper systems on the market, but none are as good as the one I installed; nor would they have given me the four-corner control of the AccuAir system.
And, nearly 12 months after installation, the system works exactly as I had hoped and has not dropped once. So, how’s that for reliable?
Andrew Atwood owns Atwood European in Phoenix, Arizona
RIGHT: My finished front suspension assembled on the bench, including airbags and cans. I chose to have suspension components powder-coated for durability
CLOCKWISE FROM TOP LEFT: After researching and pricing the parts needed to get the factory suspension working, I decided instead to install a modern four-corner suspension system, which uses electronic ride-control sensors at each corner of the car similar to the yaw and height sensors used on 2014 Mercedes models. This modern system helps keep the car perfectly level, improving ride and handling over the original system. As a first step, I had to fabricate new air bag cans so that none of the original Mercedes parts were altered. A completed airbag/airbag can assembly. Detail of the completed front suspension with airbag system installed.
CLOCKWISE FROM TOP LEFT: My rebuilt W112 swing-axle differential. Removing and tearing down one of these requires great care, with special tools and specific disassembly and reassembly procedures. A rear airbag/air can assembly installed. View of a rear suspension stabilizer. The completed rear suspension. The vertical yellow elements are the rear anti-sway bar links. I am very pleased with my aftermarket air suspension system. The only modification I had to make to the Heckflosse was to drill two one-eighth-inch mounting holes in the body and subframe for each sensor. I have all original parts and can return the suspension to factory specification at any time.
Suspension Restoration: Part Six of an Ongoing Series
While my Heckflosse (or Finback, if you will) was at the paint and body shop as discussed in parts four and five of this series, I used that time to decide how I was going to restore the suspension. I was able to do this by salvaging the front subframe assembly and the rear differential from my donor W110 – already having relinquished one of its doors and front-left fender to the cause – and installed them under my W112 restoration project. This got the body and chassis back up off the ground, making it easier to roll around during body and paintwork and allowed me to completely restore the original suspension from the W112.
Suspension restoration
Disassembling and overhauling the front suspension on an older Mercedes can be accomplished by anyone with general mechanical knowledge, but working on the rear suspension is different because of the swing-axle differential. Removing and tearing down the suspension requires special tools and specific disassembly and reassembly procedures. If these directions are not followed, you can and will destroy the differential, so make sure that you have a service manual and some mechanical confidence before attempting the task – or find someone who does. Manuals are available online and some of them can be obtained on DVDs. Having worked on these vehicles for more than 28 years, I have accumulated a lot of knowledge and literature – even some manuals on microfiche – but that’s a topic for a different day. Carefully following the workshop procedures, I disassembled all components down to the bare parts and sent them out for powder coating.
I chose to have the suspension parts powder coated rather than painting them by hand for many good reasons. In particular, the powder coating company would sandblast all individual parts, which meant I didn’t have to clean them. More importantly, the powder-coating process creates a very hard and durable finish that is resistant to almost all liquids, flying rocks and debris. This process is relatively inexpensive and also hides most of the imperfections that would be visible had I painted them with a rattle can. Finally, taking into account my time and the cost of materials, it was simply more cost-effective.
I told the shop to use semi-gloss black, which would be as close to the factory finish as possible – and a preference of concours judges. I have seen some restorations with glossy or flat-black colored suspensions, which also look good, but you can choose what you like. There are several precautions to take when having automotive parts powder coated. In particular, make sure all machined surfaces and threaded holes are covered and taped to prevent them from being painted. Also, ensure that stamped and cast-identification information on the parts isn’t obliterated when applying a coating that’s too thick. If that happens, you’ll spend hours scraping and grinding to remove the paint – at which point you’ll discover just how durable the powder coating is.
Because I have rebuilt many front suspensions and differentials, I did not take pictures during the disassembly process, but I highly recommend that you do if this is your first time. It is very easy to forget which way a certain adjuster bolt goes or on which side a washer or seal is supposed to be. This can lead to a big headache when you’re reassembling the system.
Replacement parts
As you tear the suspension systems down to their individual components, you will usually find that the kingpin bushings and upper and lower outer control-arm bushings have play in them, which will require replacement. Replacement bushings are readily available in the aftermarket or your local Mercedes-Benz parts department, and they are reasonably priced; don’t hesitate to replace them. You will appreciate the like-new tight feeling in a suspension that does not rattle or run away with every rut and crack in the road.
As you disassemble the front suspension, a good rule of thumb is to measure and note the configuration of any adjustable component so that it can be reassembled in the same configuration as the original, if possible. If not, center the adjuster when installing so that if you drive the car to an alignment shop, it won’t wander all over the road. Moreover, the alignment shop will have a good base from which to start the adjustments.
For differential and rear suspension, I followed the same process for disassembly and powder coating as for the front, except for the differential assembly. This required meticulous attention because it’s a very rare-optioned 3.91 limited-slip differential. Following the workshop manual, I disassembled the third member, as it’s called, and measured the limited-slip clutch packs. Fortunately they were still well within spec, which was good as these are very expensive to replace.
When it came to the differential bearings, I decided to replace them to prevent any kind of differential whine after reassembly, but finding replacements was a bit tough. Mercedes-Benz does offer new ones, but the cost was creeping into the $2,500 range just for bearings alone. I researched the original FAG bearing numbers and found that at least bearings for the axle and side differential bearing were available with the same specifications through a bearing supply house. Sourcing parts from outside generic suppliers is sometimes a viable option, but care must be taken when using non-factory parts. For example, the original bearings must be measured down to the last .01mm to ensure not only correct fit, but correct operation. This may sound a bit extreme, but it can make the difference between your rebuild lasting 50 years or failing in 50 days. I will always be the first to use a factory part over an aftermarket part unless the aftermarket supplier also offers factory parts as well, and recommend you take the same care in your restoration.
Considering air suspension
With the suspension components powder coated and assembled, I turned my attention to the spring portion of the suspension – I absolutely love the way the W112 and W109 chassis cars ride and handle – but the air suspension’s reliability leaves a lot to be desired. After pricing all parts needed to get the factory suspension working, I was looking at $1,200 just in airbags, not to mention $2,500 in rebuilt valves – and I would still be limited to the operating quirks of that era’s system.
As noted at the outset of this project, I wanted to make the car more reliable so it could be driven more frequently with less maintenance. Researching aftermarket air systems, I found one called AccuAir that intrigued me. Not only would it eliminate all mechanical ride-control valves, but it would give me a modern four-corner controlled air-suspension system as opposed to the original, whereby the front was corner-to-corner control but both rear corners were controlled as one. A four-corner suspension system helps keep the car perfectly level, which improves ride and handling. This system uses electronic ride-control sensors on each corner of the car, similar to the yaw and height sensors used on the 2014 Mercedes models. These sensors read each corner’s height and relay that information to the electronic ride-control valve, which will then add or remove air from each air bag individually. This translates to better handling, maintaining the car’s level while cornering. It also allows me to preprogram in three different ride heights that are accessed by the touch of a button – just like the new cars. All this with almost no maintenance – for me it was a no-brainer. Now again, there are purists out there who will call what I’m doing sacrilegious, so let me stress that this is my solution for my car – don’t send me hate mail!
To install the AccuAir kit into my car, I had to fabricate new airbag cans so that none of the original Mercedes parts were harmed in this procedure; this means I can return my car’s suspension back to stock at any time – if I want. After fabricating the airbag cans, I replaced the air lines utilizing the same material as those installed in semi-trailer trucks. This guaranteed good airflow and, more importantly, longevity and durability. As for mounting the ride-height sensors, this was the only part of the air-suspension system that required me to modify the body; I had to drill two one-eighth-inch holes for each sensor to mount them to the body and subframe. I then ran the wiring for these along the factory body-wiring harness under the inner door sills.
The next item to consider was where to place the air tank, control valve and compressors. I could have used the original tank, but that would mean drilling into and modifying it, which I didn’t want to do. Instead, I installed the new components as a package assembly under the parcel shelf in the trunk, which didn’t take up any trunk-floor space and kept it out of the way of luggage. The system also stays clean and is easily serviceable, should the need arise. All these installations took approximately 18 to 20 hours of work – not bad for a complete suspension modification. The cost to install one of these kits is about par with completely restoring the stock system, but without any of the drawbacks. There are cheaper systems on the market, but none are as good as the one I installed; nor would they have given me the four-corner control of the AccuAir system.
And, nearly 12 months after installation, the system works exactly as I had hoped and has not dropped once. So, how’s that for reliable?
Andrew Atwood owns Atwood European in Phoenix, Arizona
RIGHT: My finished front suspension assembled on the bench, including airbags and cans. I chose to have suspension components powder-coated for durability
CLOCKWISE FROM TOP LEFT: After researching and pricing the parts needed to get the factory suspension working, I decided instead to install a modern four-corner suspension system, which uses electronic ride-control sensors at each corner of the car similar to the yaw and height sensors used on 2014 Mercedes models. This modern system helps keep the car perfectly level, improving ride and handling over the original system. As a first step, I had to fabricate new air bag cans so that none of the original Mercedes parts were altered. A completed airbag/airbag can assembly. Detail of the completed front suspension with airbag system installed.
CLOCKWISE FROM TOP LEFT: My rebuilt W112 swing-axle differential. Removing and tearing down one of these requires great care, with special tools and specific disassembly and reassembly procedures. A rear airbag/air can assembly installed. View of a rear suspension stabilizer. The completed rear suspension. The vertical yellow elements are the rear anti-sway bar links. I am very pleased with my aftermarket air suspension system. The only modification I had to make to the Heckflosse was to drill two one-eighth-inch mounting holes in the body and subframe for each sensor. I have all original parts and can return the suspension to factory specification at any time.
Subscribe
The Star® Magazine is a benefit of Membership in the Mercedes-Benz Club of America.
Become a Member to get exclusive access to the full Printed and Digital editions of The Star®