- - speedo accuracy crosscheck ?

[lurtch]

Hello All - - I have reason to suspect that the speedometer I got through a guy on ebay is not reading correctly,  as much as 6 to 8 MPH low.  Our trusty CHP speed check units seems to indicate this. Can some of you post the roadspeed you are maintaining when the tach reads 3000 RPM?

My car is a 66 230SL auto with a new greased-up speedo cable.  The odometer reads  19,XXX.  At 3000 RPM  it tells me I am going 52 MPH. Does this correlate correctly?

I would suspect these units read low when they are worn,  - - do they?

Also - -  anybody got a ballpark price on what an overhaul costs?

Thanks Much,   Larry in CA

[Cees Klumper]

The difference will most likely be due to a rear differential ratio that is not matched to the speedometer. Mine reads about 8-10% too low since I changed my differential to a 3.69 from a 4.08; before though, it was reading about 5% too high. You should be able to get the speedometer 'matched' to the rear differential through one of the repair specialists listed on the homepage database.

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[DavidAPease]

Larry,

I also have a '66 automatic. As you can see from this photo, at about 3200-3300 RPM my speedo reads exactly 110.  Of course, this about 68 MPH.  52 MPH at 3000 RPM sounds awfully low.



A good hand-help GPS unit is an amazingly accurate speedometer, and is what I use to do speed checks.  If you have access to one, it might give you some more information.


-David Pease
'66 French 230SL

[psmith]

Don't forget tire size.  Unless you have 185 R 14's the diameter will be different and throw off the speedo.

Pete S.

[tuultyme]

At highway speeds my tach and speedo are about parallel; US model, 205R70 tires.

Bruce; 268Blaugrun(green) 1970 280SL; IL