Odometer doesn't match speedometer

[miked_md]

I am recommissioning a 230SL that sat for several years.  I recently acquired the car and I don't have much history.  Now that it is running and driving I have noticed that the odometer registers 2.12 miles for every mile driven.  The speedometer is pretty accurate, 50 mph is indicated for 48 mph using GPS.  Doing the math it doesn't seem to be a metric odometer reading KM as that would be around 1.61 for every mile driven.

I sent the speedometer off to be serviced and they fixed the broken trip odometer but didn't correct the incorrect readings.  I have posted a photo of the back of the speedometer to see if anyone recognizes anything that might explain what is going on.  Any insight into the hand written note on the back would also be appreciated.  The car is an automatic and has a 4.08 rear end from new.

Thanks,

Mike

[rwmastel]

Is this originally a US spec car or no?  Many 230SL around the world (like mine) came with 3.75 rear end.  Maybe it's metric and had a differential ratio change.  Is it still drum brakes on the rear axle?

[miked_md]

Thanks for the reply.  Here is a photo of the numbers on the rear axle.  The number matches the data card!  The car is a December 1966 build so one of the last couple hundred 230SL's.  US spec car.  Still rear drum brakes.

[rwmastel]

Ok, that makes it more difficult to explain the odometer behavior.  Could it be one from a different model car?  That writing you point out is probably a note documenting the last time it was refurbished, and maybe it was messed up then?  The speedo connects to the transmission, right?  Is the transmission correct per the data card?

[Pawel66]

If we are to believe the speedo housing, it is miles speedometer for differential ratio 1:4.08. You have it here: https://www.sl113.org/wiki/Electrical/Speedo

The number "W" (or K) divided by 1.6 will give you W in km and you can use the conversion table there to see the differential ratio (mile W is above 1, km below 1).

The same ratio is stamped on your differential.

Perhaps someone changed the differential ratio  - maybe you will see bigger difference in speed shown at higher speed. The error will be increasing as speed increases.

I cannot make out the first two lines of the hand written note. The last two lines: "Speed-o-Tach" then "37,893". Something was done at 37k miles?

[miked_md]

Thanks.  The transmission is numbers matching.  I rebuilt it as it was totally locked up due to a failed front pump and resulting clutch disc lining separation.  The fact that the speedometer is accurate while the odometer is off by a factor of 2.12 seems like something within the speedometer as they are both driven off the same cable.

[rwmastel]

Miked_md,

This forum is seldom stumped!  I think we should give it another week or so before officially declaring Stumped, but it might go that way.

You may have to validate your 1:4.08 diff ratio by lifting the car, spinning the rear wheel, and counting the axle rotations and drive shaft rotations.

Perhaps an odometer from a different model car, with different odometer gearing, was installed when unit was serviced years ago.

[Pawel66]

I would perform the suggested gear ratio verification.

I would also test it at higher speed.

Can you post a picture of the face of the speedo?

It can be as rwmastel suggested, it can also be that the speedo part of the unit lost its magnetic power and shows too low reading that just happens to be correct.

You can also roll the car on a distance of 10 meters and count the speedo shaft revolutions to get the W delivered to speedo. Need to do it fairly accurately.

But seems to me that if there is discrepancy between speedo and odo, there some internal problem in the unit itself. Could be indeed that someone fixed the odo using wrong gears.

[miked_md]

Thanks for the replies.  Here is a photo of the front of the speedometer.  I'll do a few more checks, but the speedometer seems accurate so I suspect someone along the way installed the wrong gear inside the odometer.  I had it fixed by Specialty Gauge in Manassas VA.  I am going to reach out to them to see what they think.  I would have expected them to test it but who knows.

The other thing that is curious is the 4.08 rear in the 230SL, maybe they switched late in the model run?  I have the data card so I know the rear is original.  I had read that 230SL came with a 3.75 rear, maybe not entirely correct.  Anyone else have a 230SL equipped from new with the 4.08 rear?

[Jack the Knife]

My car was equipped with a 4.08 from the factory and according to the data card it was produced in March of '65, though curiously my car is titled as a '64. It was a tourist delivery and I believe it was ordered in '64, not sure if that impacts things. Then it was shipped back to the USA.

[Pawel66]

Thanks for the replies.  Here is a photo of the front of the speedometer.  I'll do a few more checks, but the speedometer seems accurate so I suspect someone along the way installed the wrong gear inside the odometer.  I had it fixed by Specialty Gauge in Manassas VA.  I am going to reach out to them to see what they think.  I would have expected them to test it but who knows.

The other thing that is curious is the 4.08 rear in the 230SL, maybe they switched late in the model run?  I have the data card so I know the rear is original.  I had read that 230SL came with a 3.75 rear, maybe not entirely correct.  Anyone else have a 230SL equipped from new with the 4.08 rear?

You can look it up in our Technical Manual. I also looked at the Mercedes parts system. Standard was 1:3.75, 1:4.08 was on special request. It then should be reflected on data card  that should show option 232. But again: your speedo is for 1:4.08 and so is differential (at least markings). Both can be verified.

If you do not ask specifically to check the speedo gear ratios and W numbers - i do not suppose the re-manufacturing shop would do that. I suppose if you ask them specifically about the issuse, they will be able to verisy and correct.

[neelyrc]

- - - curiously my car is titled as a '64. It was a tourist delivery and I believe it was ordered in '64, not sure if that impacts things. Then it was shipped back to the USA.

That is curious! My tourist delivery was four years later (1969), I also ordered in the year prior to delivery. At delivery an International Registration was supplied with a date one day earlier than the factory delivery date. A Statement of Origin was also provided with the actual date of delivery shown.  I used these documents as a basis for first registration in USA in 1970 when I imported the car. The International Registration does not show a model year however the Certificate of Origin states the model year.  Perhaps the original owner used his confirmation of order from 1964 as a basis for declaring the model year.

[66andBlue]

...
The other thing that is curious is the 4.08 rear in the 230SL, maybe they switched late in the model run?  I have the data card so I know the rear is original.  I had read that 230SL came with a 3.75 rear, maybe not entirely correct.  Anyone else have a 230SL equipped from new with the 4.08 rear?

My 1966 230SL also came with 4.08 rear end which was standard at the time for cars delivered in the USA. The 3.75 rear end remained the standard for European deliveries. See attached copy from the Technical Data Book 1969.
I am guessing that your speedometer was swapped out at 37K with a different one but the soft white backcover with the W=1.54 stamp was retained to match the engraved numbers on the differential.
For an experienced repair shop it is not difficult to adjust the mph speed reading but an odometer change requires a different gear set that is NLA.

What is the part number of your speedo on the top of the dial somewhat hidden under the chrome ring?
Also what tire size do you have?