Suspension setups for racing/rally, early Mercedes

[pedrocamp]

I am planning and collecting parts for a 68 W110 230 that will be built in hopes of running the Carrera Panamericana in a few years. I did the 2023 event in a 53 Porsche 356 Pre A I built and enjoyed it so much I want to go back. The owner of the car and I drove it from Charlotte, did the event and drove it back, no trailer or support crew, a failed coil and dodgy street corn our only real challenges. Anyway the old Fintail (so much roomier than a 356) will get a M116 3.5 V8 and manual 4 speed from a 72 Euro 350SL. I harvested the suspension, rear axle, brakes and engine mount bits from a 72 280SE 4.5. I am soon pulling a rear axle, brakes and steering bits from a 300SE 6.3. I acquired a hydropneumatic compensator (needs rebuild) and a W109 rear anti roll bar setup. Out of this I need to determine what to fit to the car to make it a good Carrera car. I'm especially trying to figure out the rear axle dynamics. The race is 99% paved road but there are many, many topes (speed bumps)... fortunately only on the transit and not speed stages. Anyone here have any experience setting up the old swing axles MBs for road/rally racing? I want to build the car as if it was built by AMG in 1972, a mini Red Pig, a White Piglet in effect. The only modern parts would be safety equipment, roll cage design, Micro-Megasquirt D-Jet control or similar and possibly ignition control. Suggestions, leads, links greatly appreciated.

[Todd Miller]

Sounds fantastic! I'm looking forward to seeing the progress. I have zero suggestions. I put the 4.5 V-8 car's rear axle with compensator, in my Coupe a few weeks after buying it in early '92, in order to make it a better freeway machine by dropping the rpm's by about 900 at those speeds. Zero regrets with the manual 4spd 4-on-the-floor that the car was built with.

[pedrocamp]

Todd this project actually started when I located the 4.5 axle for the reasons you mentioned, I bought the complete car. Initial plan was a 2.8 mech injected six to accompany axle. From there it has snowballed… hmm, I need a V8!

[Todd Miller]

Nice! Back when I purchased my Coupe, the 4.5 cars were sort of all over the place for cheap, and no one wanted them. I paid $500 for the entire car, swapped rear axles, and had it towed to the wrecking yard. It was an amazing upgrade, and transformed my Coupe into a real/normal car to drive. I was also really happy to have gotten a hydropneumatic compensator out of that exchange, and amazingly, it is still operational.

[Frank Reiner]

pc:

As one who is admittedly not a fan of swing axles in competition, especially on pavement, I would suggest consideration of the next generation of MB rear suspension - 107/114/115/116/123/126 semi-trailing arm configurations. Yes, they also exhibit substantial camber change, however without the alarming jacking of swing axles.

[cth350]

Glad to hear that you are doing something fruitful with that standard trans finally.
No turbos?

If you find yourself needing something, this is a good place to ask.

Fun race... https://www.panamrace.com/

-CTH

[Tony H]

I had driven my 250SE VERY aggressive with no problems when stationed in Gemany. Many miles at top speed and lots of windy roads.

[Todd Miller]

Yes, Tony. These are low pivot swing axles, so they're very nice to drive, even when being pushed.

[Tony H]

I think the swing axles got bad press due to cars like VW and Corvair with more primitive setups. I have never heard of any unexpected/uncontrollable handling events. These cars were raced in countless rallies, road events etc. all with the same basic setup.

[Todd Miller]

Originally Posted by Tony H

I think the swing axles got bad press due to cars like VW and Corvair with more primitive setups. I have never heard of any unexpected/uncontrollable handling events. These cars were raced in countless rallies, road events etc. all with the same basic setup.

I believe the concern for the Mercedes cars with swing axle, dates to the very first race cars, and then to the gullwings, all of which had what is referred to as, "High Pivot" versions of the axle. This caused huge camber changes and body roll at the rear, if a corner was entered "hot" and then the throttle was snapped closed. The tail would lift, and swing around 180 degrees. As far as I know, the high pivot was done away with on the 300SL roadsters, and that designed is what remained through the cars in the 60's, like my Coupe for example, and the w110 that the OP wants to road-rally prep.

I think the tail swapping with the Corvair, the VW's, and the 911's, was related to having an engine over the tail, and a light front-end. So a hot corner with quick let-off on the throttle, brought the tail around quickly.

[rwd4evr]

The low pivot swingaxle still has some nasty habits all the way at the limit. It will snap oversteer. You definitely want to do power steering and a quick ratio box. I think I was going to put a r107 560sl in mine but I haven't touched it in years. There's a guy that bought the molds from cox racing for polyurethane bushings for all the 111/108 rubber.

The 107 chassis is so much better. My fintail will be getting a 107 subframe or a custom tubular with 107 geometry. Big gen2 w126 Brakes , anti dive geometry is just miles ahead. Plus I've already built custom arms and adjustable roll center parts for it. The rear is still across up between a live axle and an IRS swap. The "diagonal swing arm" 70-80's rear is very capable in its usable range and extremely tough, but a multilink is better. Sorry went off on a tangent there.

The 3.5 is great but there's no reason to not use a 4.5. it still revs high and torque is considerably better.

Sent from my SM-G991U using Tapatalk

[pedrocamp]

I agree Frank that the later rear suspension design is an improvement over the low pivot swing but I wanted to put a year limit on what I could do otherwise the skies the limit, more likely my pocketbook and credit limits. I suppose I also welcome the challenge of making it work and learning what the engineers and mechanics did. 1972 seemed like a reasonable limit since it encompasses the early Mercedes approach to chassis design.

I am sharing a bit of a DM about a relevant discussion.

Found a description of why the spring suspension cars have the center spring that seems plausible:

By 1957, Daimler-Benz had begun to switch to the Eingelenkpendelachse (“single-pivot”) layout, which hinged the axles at a common point under the differential, rather than on either side, and added twin trailing arms for better wheel control. A “camber compensator” spring was also added to support part of the weight of the rear end, allowing the regular rear springs to be softer.

From 1994 to 2008 I worked as a mechanic for the Newman Haas Indycar (Champcar) team and the cars had a third spring and shock that was used to control the high downforces of the aero. It was attached to the anti-roll bar system and only stiffened the car in flat vertical bump, it did not affect roll stiffness or if one wheel hit a bump. The main springs and anti roll bar blade settings controlled the roll stiffness. This setup allowed the car to run lower, support the aero load and still have some compliance over bumps. Of course the Lola did not have swing axles, it had the common for racing double wishbones.

I am trying to apply some of these ideas into the old Benz, of course I am not dealing with 100x the aero load.

I appreciate the discussion.

[Todd Miller]

I'm looking forward to progress photos and hearing your thoughts on all the things you put into the build.

There are a couple areas on these 60's era cars that are really mind candy to me, and the rear axle is one of them. Especially with a compensator fitted, and seeing the car self-level as it drives.

[pedrocamp]

@rwd4ever, interesting project, have you or will you post more info as you progress? The 3.5 has a shorter deck height than the 4.5 (shorter stroke) and is easier to fit in the car, less width to clear other things in the engine bay. I am not looking for big power, that's another endless quest, reliable and tractable my goal. That said I do like the sound of revs.

Todd, I do intend to try the compensator but am thinking a 109 rear anti roll bar with a transverse shock (no leveling) as an option to try as well. That said when I did the Carrera in the 356 we carried all our spares and clothing (including toothbrushes and underpants) in the car with us on the stages (since the race goes from city to city) so maybe load leveling isn't a bad idea?

[t walgamuth]

There is also a compensator with steel spring. Simpler and works fine.