Speedo telling porkies

[oldcelt]

This may sound silly, but my recently aquired 190 (1985 manual) has the annoying habit of fluctuating readings on the speedo. I really can't believe that at 3,400 RPM I'm doing 110 mph in 5th gear. Has anybody any info on roughly what speeds relate to RPM in which gears please, it's very frustrating.

 

[pascal]

THat Sounds wrong to me.

20 to 25mph per 1000rpm in top, depending on engine & gearbox would be normal.

Your reading suggests over 30mph per 1000rpm.

Having said that, the 2L W124 could go faster in 4th than 5th, suggesting a pretty high ratio.

 

[SLinKyjoe]

you should find a measured mile, and drive along it at 60mph on the speedo and time it...if it take between 60 and 66 seconds your speedo is okay. then try it again and see what happens.

 

[42864]

190 speedo

I don't know if this helps by my 190E 2.6 Auto at 70 mph reads 3000 rpm, to add to a previous message a mesured mile (between phone boxes on the motorway = exactly 1 mile apart) 60 mph == 60 seconds exactly.

dave

 

[pascal]

42864

Thats 23.3mph per 1,000 rpm, not over 30 as with oldcelt. That sounds right for a 6cyl. is it Auto.

Either celts rev counter or speedo is off, I'd say

 

[oldcelt]

Sorry, forgot to add that it's a four cylinder 2 litre manual with approx 180k on mileage and the rev counter seems more reliable than the speedo

 

[pascal]

So you're saying, you don't think your actually going that fast.

BTW 5th in those is fairly high, I do beleive; but over 30mph per 1,000rpm I would say is too high.

It is an analouge speedo, and the flyspring on the back of the clock could be damaged. This would cause it to be very erratic, and a loose tension would give a higher reading.

Breakers yard, would be my choice (for a new speedo, not your car )

 

[oldcelt]

Ta

Thank you everybody will try and source (mm I like that word) a replacement speedo head

 

[pascal]

Source? (a bit posh?)

Well if you go to a scrap dealer, don't say: 'Dear Man, I'm trying to source a replacement head... ?'

Better to say: 'Would you have a cheap speedo dial for my old 190 ?'

 

[SUE.]

This may sound silly, but my recently aquired 190 (1985 manual) has the annoying habit of fluctuating readings on the speedo. I really can't believe that at 3,400 RPM I'm doing 110 mph in 5th gear. Has anybody any info on roughly what speeds relate to RPM in which gears please, it's very frustrating.

Try changing the speedo cable,a lot of times the cable is at fault..
To work out rpm to speed you would need to know the exact tyre sizes and gear ratios.........Try a cable or another speedo head ......

 

[oldcelt]

Worth a try

I've managed to track down a speedo head at the right price, will give it a try and see what happens, thank you all very much.

 

[190]

Has the differential ever been change on your car? I changed the diff on mine and the Speedo was reading lower than the actual speed I was doing.

 

[300CE24Coupe]

Hmmm, when I was in Malaysia recently, many taxi drivers were driving W124 series cars. There was not one that I got in where the speedo was working correctly - so i think it could possibly be a common problem.

 

[mark999]

See if qanyone you know can lend you their GPS or road Angel. this will give you an accurate MPH