Are MB speedometers calibrated to specific drivelines? - PeachParts Mercedes-Benz Forum

lietuviai · #1 11-30-2004, 03:32 PM

I was wondering if MB used different speedometers for different gear ratios or did they use the same type of speedometer and just used different speedometer drives in the various models. I was looking to get a speedometer with a higher limit and was hoping that it would be a simple swap.

cornblatt · #2 11-30-2004, 03:55 PM

I looked into this a while ago (I wanted to get a metric speedometer/odometer because I'm in Canada), and here's what I found out...

http://www.peachparts.com/shopforum/showthread.php?t=93088

adamb · #3 11-30-2004, 08:26 PM

I dealt with this as well.
I converted a 240 to a 300, rear end and all.
I finally discovered after trial and error that the way to get the speedo you want is to find one that has the shift ticks on the same spot for the ratio you have installed. For example, The shift ticks on the speedo face were different on the 240, than on the 300, compared to the gasser model 123 series (which I bought by mistake thinking it would work and that the 140 mph would have looked cool).
As the other gentleman mentioned, the rear end ration determines what speedo head it has, but a quick way for you to determine which it is you need is to determine where the ticks are on the speedo face next to the exact mph for where the shift is supposed to occur.
I hope this wasn't too confusing,
Adam

lietuviai · #4 12-01-2004, 04:45 PM

I was afraid that it might be that way. It makes the issue quite a complicated one if you don't know what rear axle the donor vehicle has.

dieseldiehard · #5 12-01-2004, 05:40 PM

There is a calibration factor on the back of the speedometer plate (its a three digit number as I recall) - another speedometer can be recalibrated on the test bench at a speedo shop where they know what they are doing, using that factor to set up another replacement speedo that you then install yourself.
Or they can recalibrate your new speedo on the car using a Dyno (more accurate) - costs more this way of course but it should be more accurate. If you don't have a speedo shop locally, there are several that you can send the units to for calibration service, there was one in Austin TX, maybe R Leo knows them. On the west coast we have Palo Alto Speedometer as the chief place for VDO service. If I knew what little thing to tweak I would try it myself, hit or miss kind of thing, but since I never have much patience when working on instruments I leave that to the experts.

lietuviai · #6 12-02-2004, 11:01 AM

With my luck I would botch the attempt. I almost ruined my speedometer once by trying to repair a slipping odometer.

rwthomas1 · #7 12-02-2004, 08:32 PM

Here you go. http://www.speedometer.com/ They can recalibrate your speedometer to whatever you need. RT

lietuviai · #8 12-05-2004, 08:07 PM

When I pulled the cluster out I found a sticker on the back of the speedometer that said K=1440 which I guess is the calibration of the speedometer. Is this what I should be looking for when matching speedometers?

phantoms · #9 12-09-2004, 10:35 PM

I don't know if that's a calibration code or not.

As for making a 150 mph speedo work in other cars (or any non-stock speedo for that matter), it seems someone could design a two gear adapter to splice in either at the speedo end or trans end of the cable. The gears could be made to reduce or increase cable speed to compensate for the difference. A 10 or 20 mile drive using mile markers for reference against the odometer of the speedo you want to use would let you know the amount of reduction/overdrive you would need.

The problem with trying to do it with the speedometer is that the speed and odometer/trip gauges are controlled separately. The odometer looks like it would be easy to remove the gearing from your old odometer and change, but the speedo part looks much more involved. There is a good article on VDO speedometers at http://members.ispwest.com/jkcaplan/Speedofaq/speedo.htm.

rwthomas1 · #10 12-09-2004, 10:50 PM

Borrow a GPS unit and record actual (GPS) an indicated (speedometer) speeds at several intervals, like 25 mph, 50, 75 and then send the info and speedo to www.speedometer.com and they will figure out the difference and calibrate it for you. RT

lietuviai · #11 12-10-2004, 05:56 PM

Quote:

Originally Posted by phantoms

I don't know if that's a calibration code or not.

As for making a 150 mph speedo work in other cars (or any non-stock speedo for that matter), it seems someone could design a two gear adapter to splice in either at the speedo end or trans end of the cable. The gears could be made to reduce or increase cable speed to compensate for the difference. A 10 or 20 mile drive using mile markers for reference against the odometer of the speedo you want to use would let you know the amount of reduction/overdrive you would need.

The problem with trying to do it with the speedometer is that the speed and odometer/trip gauges are controlled separately. The odometer looks like it would be easy to remove the gearing from your old odometer and change, but the speedo part looks much more involved. There is a good article on VDO speedometers at http://members.ispwest.com/jkcaplan/Speedofaq/speedo.htm.

I was told by someone that there are similar devices used by speedo shops to calibrate a speedometer for that very purpose. I think the guy told me that it can be expensive too.

phantoms · #12 12-10-2004, 09:09 PM

I was under the same impression, that rebuilds can be worth-while, but recalibrating to a different speed can be very expensive. Hence the post above. I know that a few people on the forums have access to (either personally or through a friend) machining equipment and figured maybe one might give it a go.