We’ve seen the news that Mercedes-Benz plans to go all-electric by 2030. That won’t affect owners of classic automobiles much, as most plan to continue driving their older vehicles. But what about those who want the best of both worlds? David Rosenstraus, the man behind Dave’s Auto Wizard in Braddock, Pennsylvania, may have an attractive answer.
“I’ve been looking at electric car swaps and technology for about four years,” David says, “and at the time I started there weren’t many options. People weren’t repurposing Tesla motors yet. Everything was expensive, and there weren’t any good battery solutions.”
Chasing technology
Electric vehicle technology is moving at (pardon the pun) lightning speed, and America’s junkyards are claiming their fair share of wrecked EVs. That means an affordable source of parts is becoming available for experimental and conversion vehicles. We have never had a shortage of clever people ready to get to work, so the mad scientists and visionaries are producing some impressive results.
“The cars that were being done had amazing performance,” David reports. “There was a Datsun that someone made using Apache helicopter batteries, and it had a zero-to-sixty time of 1.6 seconds or something ridiculous like that. It seemed intriguing, but it didn’t seem viable from my point of view. Then in the last couple of years I saw some Tesla builds being done. People had hacked the Tesla controllers to make open source controller units that would work, and people were using Tesla batteries.”
Choosing the right stuff
David set to work designing his dream electric vehicle, based on a lovely 1980 300CD coupe.
“I’ve had the car for about seven years, and it was cool,” he says. “The W123 is a great car with the inline five-cylinder naturally aspirated diesel engine, which made about 84 horsepower. It was fun to take out for a drive. The body was in really good condition, too. I thought it was a cool candidate for the transformation because it’s such a unique classic coupe.”
David sourced a Tesla drive unit, but made a different choice for batteries.
“The batteries that I used were actually two sets of Chevrolet Volt packs,” he reveals. “I priced it out and it was a more affordable swap. The drive unit itself was actually pretty easy. I purchased it from a company that refurbishes drive units and then pairs them with an open source controller. They come with an accelerator pedal. You have to wire everything in, but the controls are already calibrated to the pedal. The more complicated part was the batteries and the battery management system and the charging system, and getting all those parts to talk to each other. They’re all from different aftermarket companies.”
Get out the welder
With the parts collected, David turned to the car. The engine and the entire driveline came out, along with the fuel tank. Then he got out his welding torch to make support structures for the new driveline.
“There are conversions that use the stock transmission, but those use a manual transmission and my car had an automatic,” David reports. “So to go the Tesla route, the drive unit is a direct connection between the motor and the rear axles. The way it works in this application is that the drive unit sits in the space where the rear differential was in the original design of the car.”
David kept the Mercedes-Benz wheel hubs, and adapted them for the electric motor.
“Two axle half-shafts can come out of the drive unit because the Tesla, like the Mercedes, uses an independent rear suspension design,” he explains. “That was my template. I used the existing hubs to line up the drive unit so that the half-shafts would connect with the drive unit. I sent in a pair of Tesla axles and a pair of Mercedes axles and they used the splines from each side and then fitted them with Porsche 930 axle shafts between the two.”
The entire motor and drive structure sits at the rear of the car now, liberating the front for batteries.
“There’s no transmission and no driveshaft anymore,” David reveals. “I put all my cabling and coolant lines through the transmission tunnel in the space where the driveshaft used to be. Both the motor and the batteries are liquid cooled, so the car has two radiators in the front. one’s for the batteries and one for the drive unit.”
Adapting the high-voltage EV batteries to the older car required some thought and ingenuity.
“There’s a 12-Volt house battery to run all the regular things on the car like the headlights, the radio, and all the control units,” David explains. “That battery supplies 12-Volt power, and the high voltage battery pack has a DC-to-DC converter to step the voltage down to recharge the 12-Volt battery. Plus, when I plug in the car to recharge the main battery pack, it also recharges the 12-Volt battery.”
Much more than an engine swap
Services like power steering and vacuum for the brake booster had to be re-invented, or at least borrowed.
“The power steering and the vacuum for the brakes are both run by electric pumps sourced from a Volvo,” David says. “There were a few models of Volvo that used electric power steering and vacuum pumps, and there happened to be one in the junkyard next to my shop!”
The final stage was to adjust the car’s suspension to deal with the new driveline.
“All four corners have height-adjustable coil-over suspension,” David reveals. “The reason is that the diesel engine and transmission were about 900 pounds, and I replaced them with 400 pounds of batteries and then some other components. I estimate that I lost 300 to 400 pounds up front. But the weight just went to the back because I have two batteries where the fuel tank was, and then I have the 300-pound drive unit. Without adjustable coil-overs, the ride quality and the ride height would not be right.”
Smooth results
Now that the car is completed, David is pleased with its performance.
“I couldn’t be happier with the conversion,” David declares. “It’s got about a 60 to 100-mile range, depending on how I drive and the outside temperature,” David reports. “If I had used a Tesla battery pack, it would be about 200 miles. But the Tesla battery packs are expensive.”
The performance figures are truly impressive.
“The motor makes 400 horsepower and 332 foot-pounds of torque at 0 RPM,” David says. “It will do zero-to-sixty in about four seconds. If you are driving 40 MPH and you step on it, you will chirp the tires. Also, there’s no gear shifting. You’re in the same gear from zero to 120 MPH. This is definitely the fastest car I’ve ever driven, and it’s plenty. Driving the car is just a joy.”
Even better next time
The experience of building the W123-EV taught David many lessons, and he’s got plans for how to do it better next time.
“A lot of the challenge was making all these things work together,” he says. “There were a couple areas where I would rather pay more for something that was more streamlined, or a device that would do everything rather than making a bunch of workarounds for them to interact with each other. It was a learning experience.”
If you’re interested in learning more, David made a series of videos on YouTube about the build. Just search for Mercedes Tesla Swap and they’ll come up. If you’re interested in having a similar modification to your car, David can take on the project.
“A good ballpark would be $60,000 to $70,000 for parts and labor to do the conversion,” he says.
Now that it’s finished, David likes showing the car with the hood up at local shows, and cruising around in all-electric style.
“I feel like this is how Mercedes-Benz would have wanted the car to perform and sound back in 1980,” he says. “Smooth, quiet and fast.”