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First of all apologies to the MB community for leaving many of you high and dry who had an interest in the coilover conversion for the SL(and CL) 600. About the time the conversion was complete I entered into a marital crap-storm only loosely related to the work on my SL600. The worst is over (I think) and now that I have some stability, I can sit down and write at least a short paragraph on the conversion. I meant to do an entire photo-expose’ on this conversion, but you are going to have to live with just a few pics and some verbiage until the entire crap-strom subsides.
My first impression of the conversion is DO NOT DO IT!!!
There are several kinks that need to be ironed out and I am not entirely sure if there are solutions to what we need for an SL600 which are not custom made.
Let’s start with the Rebuild MasterTech (RMT) kit.
Jeff Limpert at RMT designed the kit. I delivered my car to their shop in southern FL in May. Jeff felt he needed the car onsite for a prolonged period of time to get the fitment correct. The car was not a daily driver, so I obliged. I left the car there for about 3 months. Jeff eventually worked out how he was going to integrate the sway-bar into the design and connect it to the control arms. This is the tricky part of the kit and requires a custom control arm link that right now only comes from RMT.
He turned implementation of the design over to his son, who was going through his own crap-storm, the long and short of which is when I wanted to come and pick it up in late August, as I was in FL for business anyway, there appeared to me a mad scramble to get the car done, even while I was waiting in the lobby. The upshot of this is they didn’t have time to really dial the suspension in or learn what I did the hard way and gave me a car that probably wasn’t road worthy. On the 1000+ mile drive back I uncovered several flaws in the set-up.
Basis for the kit.
RMT uses the Bilstien dampers (shocks) off a Euro-spec SL350. This car was sold in Europe without an ABC system and is a direct mount (more or less) with the ABC mounting points. The problem with the SL350 is that it is over 600 lbs lighter than the SL600. To compensate for this, Jeff used the OEM springs off an E500, however, this still isn’t enough to compensate for the weight.
The net result of this is that the car sits very low. The coilovers are adjustable, and I have had them in twice to increase the ride height, but have only increased the lift by a ½ inch or so. The springs are just too weak to support the weight. The downside of this is that the new sway-bar, which must pass under the Cats, scrapes on just about everything. I can hardly go over a speed bump without bottoming out and hearing that God-awful sound of steel scraping against concrete. I have low profile 20’s on the car now which gives me about 27 inches from the ground to the top edge of the fender well. I calculated that if I went back to the stock 18’s, I could pick up another ¾” to 1” in additional clearance. I ordered a set of 18’s just to test, but unfortunately my significant other is holding them hostage in the garage. Below is pic of the sway going under the Cats
It gets a little worse…….then a lot worse
I like the look of the 20’s but the worst part about them is that I also have clearance issues between the inside tire and control arm link I mentioned when making low speed tight turns (like when you are parking). Jeff thought if I just added 10-15 mm spacers, I could overcome the rubbing. I have the spacers, but they are also being held hostage, so I haven’t given that a go yet. Going to the 18’s which have a different offset, may also solve this problem. I don’t see this as an issue with the RMT kit per se, as this car was not intended to run such a large wheel. Once I get access to my stuff, I settle this one once and for all.
However, the most unacceptable thing about this kit is high speed handling. The car corners great……up to 60-70 mph, it feels like it is on rails. When I first got the car, my cousin, who is a much better driver than me, wanted to know the quarter mile time. Out on the country road he lives on, he has a ¼ mile marked off. Just for fun we dropped the top and he dropped the hammer. My 600 has a tune so I guess I am pushing 600-ish HP at the crank. We finished the ¼ mile probably just above 100 mph and at the end of his “course” there is a slight rise in the road. So slight that at 50 or 60 mph you may just barely feel it. At 100+ mph, we both thought the car was going airborne. His eyes got as big as saucers and he stated “that was scary, I don’t think I want to do that again”. The dampers, just don’t have enough force with this soft springs to keep this car from lifting. I have done a few high speed passes myself when egged on by an M-Series et al, and confirm that above 90 mph, the car gives me zero confidence as a driver.
Next Steps
A buddy of mine has a membership at the local road racing rack (MSR Houston). This guy is the consummate gearhead. Engineer by training that spends every minute away from work, tinkering, thinking, practicing going faster. He got me connected with the tracks in-house suspension expert. We spent several hours going over the conversion and what can solve the problems. His advice was to have a custom shock built around the Bilstiens I already have but with the correct valving to handle the SL 600 weight. He also thought he could find a spring fabricator that would create a spring to spec. I also reached out to KW (Germany) and brought them up to speed on the project. They make a coilover for the Black Series, which I was hoping would work, but the mounting points are completely different. They are willing to fabricate a race suspension with the spring rates of the Black Series with adjustable damping and height for $4-5K. I am leaning toward this option primarily because I think it will advance the knowledge base provide off the self tech for those intrepid enough to follow in my footsteps and improve this design.
What I would have done differently
I retrospect I should have just repaired the ABC system. This seemed straightforward initially but has been far from it. I also wander if I would have replaced the steering knuckle with the Black Series could I have bolted the BS sway bar and coilovers more easily. When I look at the EPC for the BS, it only appears that the knuckle and control arm links are different Vs the SL600. Perhaps I am reading it wrong, but if this is the case, this would be the way to go. I’ve got about $6K all-in to this conversion. Roughly equivalent to a major ABC repair. I’m probably another $6K, to get it fully functional, which makes this payout Vs ABC replacement dubious. My only redeeming hope is that handling to far improved Vs stock when all is complete, otherwise this has been a bit of a fools errand.
You tried one of the kits for sale for a coilover conversion and it did not work as expected for you?
Or it's not meant for a 600 series model?
I know the feeling when you do that much work and doesn't come out the way it supposed, so feel sorry for you I guess owning a 600 model it's quite different than a 500 or 550. Good to know.
If you will have time, i am curious about what's different on a 600 from a 500 model under the car or chassis that makes the kit not applicable? As a FWI info for others.
Any way it's lots of hard work you got there! Hope you'll figure the way out of that problem. My ABC is solid so far, but considering the costs of a major repair i'd consider a kit as well
The 600/65 with the V-12 has a completely different undercarriage geometry. The "kits" from Rebuild Mastertech should work fine. For the V8 model there is clearance for a sway bar to go in front of the of oil pan. The V12 unfortunately does not allow for this routing. The only way we could get it to work was to go under the cats, as shown in the pic.
Just to be clear......there is no commercially (aftermarket) available coilover kit for the SL600. This to my knowledge is the first of its kind, although I have heard (and talked to) SLRSpeed is also developing one, but I think they are encountering some of the same issues of sway bar routing on the V12. If SLRSpeed can crack the spring/damper nut I'm set, as the sway bar set-up from RMT is solid for lateral movement....it is the up/down vector I have issues with
Need stronger springs and better shocks. I can deal with a scrape here and there on the swaybar. It would be so nice to get rid of ABC and to have a car I could drive cross.country with little to no worries.
I've connected this new company in FL VVK/SLRSpeed and they claim to have a package for the SL in development. FlyinFlynn has been pushing their solution on some of the other forums. I offered my car as a test mule, since it should be a direct drop in, but they haven't taken me up on my offer.
I have also been in contact with Bilstien and KW. Both are offering me a race package that should address both the dampening and spring rate issues. I should have one of this solutions on my car by Feb and will let you guys know how it works out.
I swapped out the 20" rims for stock 18"s and the rubbing as all but ceased. Maybe a little at full steering wheel lock, but I can live with that. Also, the ride is significantly more comfortable now that I have some side wall to absorb road imperfections.
I have been in discussion with RMT, KW and Bilstien. I've been really impressed with the response from Bilstien. They are putting the finishing touches on a design from their motorsports division that will be a direct drop in. This will be a 3-way (bump, rebound and height) adjustable and will be rebuild-able with replaceable internal valving. Haven't got an exact price yet, but we are looking at around $900 per corner. I'm to the point were Bilstien wants me to get the corner weights so they can get the spring constants just right. Delivery time is 6 weeks from time of order. I'm excited that for less than $4000 I can get this suspension right once and for all.
I also spoke with the VVX/SLR folks listed in other posts. They have an interesting product and I offered my SL600 as a test mule since they should be able to drop their coilovers in for final fitment and spring rate determination. I even offered to pay for shop and track time at MSR but have heard nothing but crickets from them. I'll leave the reader to draw their own conclusions.
That VVX product looks great. Shame they wouldn't use your car to show the results. They seem to have a different sway bar option which works for the V12's. Not sure if it has the same issues with it sitting too low.
Question about ABC: I recently drilled around the MB website looking at the 2016 models. I played with the build-a-car feature and tricked out a new SL. ABC is offered as an option.
What is the "standard issue" suspension system on SLs if ABC is an option?
That VVX product looks great. Shame they wouldn't use your car to show the results. They seem to have a different sway bar option which works for the V12's. Not sure if it has the same issues with it sitting too low.
Has anyone on this board actually fitted the VVK on their V12? I have a bit of discomfort ordering this kit until it is proven it exists and or works on the V12 models.
Hey Everyone!
Below is copied from what Sean at VVK (vvk-usa.com) wrote me to post here:
"VVK has the kit out now that fits and addresses all the issues that RMT overlooked. Glenn, we have been in contact with a price for the kit without the swaybars, since you said you were happy with your swaybars currently - we’re ready to fix your issues ASAP and get you back on the road!
To put it simply: the SL350 suspension is simply not equipped to handle the mass of the V8 and V12 cars. The SL350 in various trims can weigh from 3880-4015lbs, V8 R230 cars start at 4200 and can reach 4555lb, and all of the V12 cars are over 4600lbs (except SL65AMG BlackSeries).
It's not just that the engine weighs more, since the V12 is actually barely heavier than the V8, but the turbos, the intercoolers, and then the massive cooling capacity for the boosted V12 in a tight engine bay with a low hoodline. Then you add the massively upgraded drivetrain components to deal with turbo V12 torque.
We decided early on to go straight for a completely bespoke coilover solution and then after purchasing SL350 swaybars myself in the UK and evaluating them on our project car (FlyingFinn) we decided to just do our own bars also. This added some development time, but we are very happy with the end result and the car handles like it should: as a complete package that complements the SL and manages this massive car amazingly.
The guys at RMT are nice people, but their main business is servicing Mercedes cars, not designing specialist suspension components, so their solution was to take the SL350 swaybar, and simply turn it 180° so it now sits behind the engine. In the pictures you will notice that the bar appears to hang low, well once the suspension of the car compresses, that actually gets even LOWER as the bar pivots. They dealt with the parts they had, but we opted to make a completely custom bar which is stiffer to deal with the V8 and V12 cars, while also actually fitting in the OEM location (quite a tight fit) so the design had to be millimeter perfect.
Furthermore the reason most cars have the swaybars in FRONT of the axle rather than behind is because of the very problem Glenn has run into: when you steer, the INSIDE wheel turns more than the outside wheel, so the back edge of the wheel/tire will contact anything in the wheel arch before the front edge will. A rear-mounted swaybar must tuck under the frame rail in order to offer adequate clearance on the SL, and there is barely room there even if you were to design your own bar (plus nothing to mount it to, hence the need to weld plates on the SL frame rails). We decided this was not a solution many customers would be OK with, and especially not suitable to ship all over the world for shops to be installing on customer cars.
One more thing. If E-class springs were installed on an SL-class, then someone made a massive error of judgement. Again, I don't want to say anything bad about RMT because I think they are really great people, and I've been there several times myself. Their facility and staff are impressive. The error in judgement comes from them being a great service company, but not being engineers.
There is something known as motion ratio and wheel rates. In dealing with so many various cars over the years, but especially BMW's and Mercedes, and especially in race setups, often people didn't understand why the rear of many BMW's required a HUGE spring rate compared to the front, even though it's a front-engine car.
The simple explanation is LEVERAGE. The SL-class basically has a 2:1 leverage over it's springs. The E-class has nowhere near that high of a motion ratio, therefore the SL350 springs for the V6 are most likely stiffer than any E-class spring.
I can tell you this, when specifying the spring rates for the VVK coilover, I had numerous suppliers say “what?? are you sure???” Two companies didn't even make spring rates that high because almost no other car in the world uses a motion ratio like the SL and CL do.
One last note, the SL65AMG BlackSeries is a truly special car and I am amazed Mercedes even built the thing to be honest. I am jealous of those engineers, because they absolutely just had fun on that project. Here's the basics: NOTHING from the suspension of an SL65 Black will fit a normal SL. The suspension is almost DTM style with totally unique front and rear layout. The upper arms in front do not connect to the normal SL location and necessitated a unique frame structure which meant a special dedicated assembly line and new tooling just for this car. All of the arms are longer to accommodate the widebody, and they are all aluminum as well PLUS the custom DTM style knuckles which bolt radial calipers and ceramic brakes, plus incorporate brake ducting through the hub! The motion ratio is also different and the KW coilovers used do not use the same attachment points or even the same TYPE of attachment except for top plate.
I hope this helps clear up some of the key differences between our products and the other 'kits' out there and also why our development cycle took slightly longer than we initially expected. The extra time hasn't gone to waste for sure and the final product really performs even better than we aimed for!
All the best, Sean @ SLRspeed, (Design partner/engineer @ VVK)"
If anyone want's to call me personally, I am available at 561-460-6551. We can meet for a test drive with my VVK equipped SL55 if you're in the area!
Also would love to see a review on a V12. I think VVK really need to do a V12 and get some real on the road and track data and they will sell a lot of these kits. Probably 75% of the V12 owners on this forum.
Also would love to see a review on a V12. I think VVK really need to do a V12 and get some real on the road and track data and they will sell a lot of these kits. Probably 75% of the V12 owners on this forum.
Agreed. It seems that the V12 owners have the most problems with ABC. Could it be the extra heat generated by the V12 Bi-turbo engine or could it be the weight? I believe the extra heat causes the hoses to fail earlier than the V8 models.
12-12-2015, 07:57 PM
I guess owning a 600 model it's quite different than a 500 or 550. Good to know.
