[RSA560]

I've done an extensive search - but am still in the dark.

My car reads 115km/h (@ 71 mph) at 3000rpm when it should read 150km/h (93 mph) at 3000 rpm.

It is consistantly 35km/h (@20mph) out accross the rev range.

Mileage: 300 000kms and the FSH sort of makes me think the speedo hasn't been 'fiddled' with
Orig 260km/h speedo
Needle does not bounce.
Transmission and rear-end orig

What gives?
Is there something minor needing adjustment or could the cable be shot?

 

[Gene Horr]

Speedometers are often 5-10% in error even when brand new. These aren't calibrated instruments. Changing tires and wheels from stock will compound the error. But 30% is further out than I've ever seen. Most likely it is just a worn out speedometer and needs to be refurbished. The cost in the USA is usually minor for the Gen 1 (US$100 when it was done to my vehicle about 4 years ago by the PO.)

Errors are usually linear, though. Are you _sure_ that the error is fixed? Have you compared with a GPS?

 

[mclare]

MB 126 Speedo's are electronic, not cable. It is the wire on the back of the cluster. The round one in the back of the speedo.

Look in the "Cruise Control" section of the Electrical Troubleshooting Manual.

 

[cleeves]

yeah i'm pretty sure my volvo reads about 5-10 under what i'm really going. gotta drive "60" in a "60" to avoid a big fine, given that cops give you 5MPH of grace.

 

[RSA560]

I've done a search in the elec trouble shooting manual but am having trouble accessing it.


... my tyres are correct 215/65/15's as well.

I have since determined that the speedo in fact consistently reads 25km/h under ie. 115km/h at 3000 rpms in stead of 140km/h at 3000rpms.
Also at 3500rpms it reads 135km/h in stead of 160 km/h.
155km/h comes up at 4000 rpms in stead of a true 180 km/h.
Is this due to low voltage?

This morning I noticed after a long high speed run that the oil pressure guage is slightly erratic and would also jump from 1,4 bar at 750rpm to 2 bar at 800rpms.
I'm sure of the rpms as I hardly apply pressure to the throttle and the rise in revs is barely audible...
Worn out oil pressure sensor?

I suppose the above 2 scenarios are nit related.

 

[Aspect]

My car reads 115km/h (@ 71 mph) at 3000rpm when it should read 150km/h (93 mph) at 3000 rpm.

I was just wondering. Where do those speed vs rpm numbers come from?

 

[RSA560]

Like I said, it is actually supposed to read 140 km/h at 3 000 rpms - according to a road test by CAR in June 1990 - and confirmed by fellow MBCSA members with similar vehicles.
BTW, my 1991 W126 500 SE with a longer final drive does a true 160km/h at 3000rpms and 180km/h at 3 500 rpms.

In the pic I took yesterday I took my foot off the accelerator as I reached 180km/h - hence the drop in revs from 3 500 to @ 3 250.

 

[420 SE]

Your oil pressure gauge fluctuation is fine, but I would be checking the speedo with a GPS rather than relying on printed tech data.

My speedo overreads - ie; when my speedo says 120kph I am doing 110kph - within tolerance however.

BTW - if you know of any good repair shops in South Africa, would you mind posting them to the Repair Shops section on the forum front page? We are trying to build up a list of them.

I will be going to Durban in June - looking forward to it.

 

[RSA560]

Thanx Ross,

I still need to do the GPS - 10km/h optimistic is normal as you say - but 25km/h under true speed and consequently 35km/h under 'indicated' is a bit much.
I have only compared the 560's speed with my 2009 Toyota Hilux 3.0 D4D Raider in tandem - when the Hilux reads 140km/h (and I know for a fact its 10km/h optimistic) then the 560 only reads 105km/h - so that's 35km/h under what it should indicate - and I'm pretty damned sure 25km/h under true speed!

Anyways, as for the repair-shop info - I'll get on it!

And as for yr trip to Durbs - its the best time of the year, weatherwise, to visit as its the start of winter but still remains warm - lows of 14 deg C and highs of 24 deg C.
If you have some spare time while yr here, drop me line - it would be nice to meet a fellow Benz enthusiast :thumbsup:

Cheers,

Le Fre

 

[Aspect]

I see. I hadn't seen anything correlating speed to RPM.

With no throttle @ 3250RPM I'd expect the economy gauge to be pegged to the left.

 

[RSA560]

Aspect,

I took the pic as I was taking my foot off the accelerator - I guess my foot was still partially on it when I took it - enough to cause the drop in revs but as the econ is so sensitive, I guess the slight pressure caused it to register.
Anyhow, had the cruise been set at 180 on a level road, the econ guage would at least have been pegged halfway up the scale and revs at exactly 3 500.

Cheers!