560 sec speedo over reading

cornershop

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Gents

Have noticed the speedo on my 89 560 sec is over reading considerably compared to my other cars, using the Waze iPhone app and its GPS as a baseline.

Eg
40 on Waze = 48-49 on speedo
60 on Waze = 70-72 on speedo

Is this a common problem? I have standard 215/65/15 tyres and tyre pressures are all at recommended levels. My other cars speedos are 3-5mph overreading depending on speed.

I have standard 215/65/15 tyres fitted.

Cheers
 

Delayed Steve

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All speedos over read, I thought it was by about ten percent. I think yours might need re calibration.
If you've had new tyres fitted it might be worth checking that the tyre fitter replaced them with what you asked for, the profile size is a percentage of the width if one of those is slightly different then your gearing is changed,so your road speed will be faster or slower than your speedos reading.
 
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cornershop

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Thanks - tyres are correct size/profile

Any recommendations for speedo recalibration? If looking at a replacement I'm guessing I'd need a 560 specific part as the 420/500 126 ran a different size.?
 

Delayed Steve

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I would Google it, I think it'll need plugging in to a lap top,it might not be the speedo head, it could be the sender on the gearbox. It been years since I messed with anything like this and things may have moved on a lot. If I remember right your total mileage is recorded on the ecu so any speed head will show the correct mileage.
I think I would get it checked,there are people who can do this online .
 

Pontoneer

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I seem to recall that Jaymanek also has a 560 and / or at least , has commented on the speedo over reading on it .
 

Will

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Diff ratio correct (?)
 
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cornershop

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Ooo, fair shout re diff, will ask garage to check markings once on the ramps
 

Pontoneer

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It runs in the back of my mind that the 560 was slightly lower geared than the 500etc because the emphasis was more on top end performance than relaxed cruising ?
 
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cornershop

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would a a diff or different gearing affect speedo accuracy? I'm thinking maybe Rev counter accuracy, yes, but not speedo?
 

markjay

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would a a diff or different gearing affect speedo accuracy? I'm thinking maybe Rev counter accuracy, yes, but not speedo?
If it picks up the speed from the transmission, then yes the dif would make a difference.

But if it picks it from the ABS sensors on the wheels.... then it wouldn't.
 

Pontoneer

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From memory , which is a bit vague , my 500SEL had an electronic speedo ( not cable driven ) ; I expect the 420SE would've been the same , not sure about the 280SE which was a very early pre facelift car .
 

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