After spending three weeks talking to gurus and posting on social media about this issue, I’ve come to the following conclusion: I am going to put our two-owner 1972 Mercedes-Benz 250C onto Bring a Trailer with a speedometer that reads slow.
We bought this car specifically to prepare for the SCM 1000 and similar long-distance touring events. Stock, the Mercedes had a 3.69 rear end and came with Zenith two-barrel carburetors. The carbs, with their myriad vacuum lies to the secondaries, were a mess. Worse, the car was buzzy at 70 mph and kept feeling like it wanted to be in a higher gear.
Several SCM readers wrote to me about their positive experiences switching to Webers with mechanical secondaries. Our resident hot-rod guru, Chip Starr of Race Car Resurrections, was not afraid of the challenge. (I must note that SCM Contributor and Mercedes expert Pierre Hedary was very much against this change and encouraged me to have the Zeniths rebuilt. The stock carbs will accompany the car when it is sold should the buyer want to go in this direction.)
Along with the Webers, which provided a noticeable increase in power, it was suggested that we swap the rear end to a 3.46 from a 300D, which we did.
The car was transformed. The 250C became a perfect freeway cruiser, capable of easily spending hours on end at 75 mph. With the rebuilt suspension, 560 SL shocks, a modern Bluetooth stereo and A/C blowing ice-cold, it became our car of choice for tours.
However, the speedometer now reads 5- to 8-mph slow. This wasn’t a problem for us on tours, as you are generally just cruising with the pack, so your speed is relevant only when compared to the cars around you. Also, we just put a speedometer app on our phone and plopped it into the custom cupholders in the center console. Problem solved.
We looked at myriad other solutions but none of them were, frankly, worth the money and time involved. We even thought about putting the original rear end ratio back in the car, but our enthusiast friends who had driven the improved setup were unanimous that this would be stupid, a backwards step.
It’s taken us two years and $45,000 to get this car exactly where we want it. We have all the paperwork from new, and it still carries its original ZOL delivery plate from when it was picked up at the factory. It’s a floor-shift automatic, with power windows, A/C and (important to me) no sunroof to leak and rob headroom. It’s had one glass-out repaint in its original metallic blue and no evidence of any collisions. As it lived its entire live in Los Angeles before coming to Portland, rust was never an issue.
SCMer Ron Rader first told us about the car. He had known the owners and the car for over 40 years and ridden in it regularly.
We are only selling it to continue to thin the herd. Now that Bradley has started driving the Lotus Elise, that’s one more car we are keeping at my condo, so something has to go.
The 250C is a great car, and we will be sad to see it move on. But we’ve put several thousands of miles on it during classic car tours, and those memories we will keep forever.
Would having a speedo that reads slow cause you to have second thoughts about bidding on this car?
I do not think that the slow speedometer will be a problem, given the respect/reputation that you have in the community.
I’m in the midst of selling off several Italian motorcycles. Even if the speedometers worked, you couldn’t trust them Not a problem!
I’m not normally a negative Nelly. Any number of cars I sold had an issue or two, which I always foreclosed, and described the correction. But…
Many states have speedometer laws. They can read high, but never low. Nevada, my US address, has no inspection laws in the area I live. Other states will require an inspection before licensing, and a low Speedo may be a gong.
Just trying to prepare you for that discussion.
Can the speedo gear in the transmission be changed to match the differential?
I would try to find out (Palo Alto Speedometer, who know these units quite well) if you can change the speedometer gear and recalibrate it. On a car that old, it’s a mechanical speedometer, so if you can find the right gear for it, it will read accurately. I believe that an inaccurate speedometer also affects the odometer as well, so the longer the car operates with the wrong gear ratio, the greater the mileage inconsistency will be. I’d try harder to fix it.
I don’t think of it being a big issue.
Having restore or update my older cars I have found other options.
For example I have had 2 modified 61 Buicks over the last few years. One was a LS3/6L80 and my more recent one with the factory 401/4L60E to keep my factory dashes I have been able to use a GPS tool to translate the speed to the factory gauges. (GM offered alot of great jewerly back in the day).
Also, I use me phone after a recent issue when my needle broke on my 69 Corvette speedo.
So, I think that if someone is interested they can find a solution.
-Jay
“It’s taken us two years and $45,000 to get this car exactly where we want it.”
That’s why I would find a way to keep it….such a beautiful vintage Mercedes.
No problem. Most speedos over-read, so this is just going the other way, and you can mentally calculate for it. If it’s 5-8mph at 70 (and therefore about 2-3mph at 30) it’s just about within the legal tolerance. My Mk1 Escort hasn’t had a speedo cable since it broke in 1998. But it has got a revcounter…