4 speed auto gearbox question - W124

[HECKLER]

I have a 300 CE W124 (12V), with auto 4 speed box. It runs perfectly, but i must say i am surprised that the revs at speed are soooooo high, over 5,000rpm at 80 ish mph. The car is new to me, has been regularly serviced from new and seems to be fine. In sports mode you can hear the 3 changes, although in E mode, only 2 changes can be heard, but it starts in second (yes??).

Someone mentioned a change up relay, but i am just not sure it isn;t just runnig fast.... it idles at 750 rpm.

It does change up deep in the red zone when floored in sports mode - c7,000 rpm.

Any ideas?? Have i got a problem, or is this normal??

Thanks in anticipation.

 

[NormanB]

Hi Heckler

No expertise with your model - hell I am no expert at anything!

But your rpm/mph does seem to be a tadge high - in my beloved wagon I recall 80mph achieved sub 4000.

I will check next time I am out and about.

 

[kid-jensen]

Heckler,

5000 rpm should be more than 100mph, and the change points should be way below 7000rpm.....

Sounds like your Rev-counter is over-reading.

You would run out of revs before it reaches top speed (140-ish) if the rev-counter was correct.

 

[NormanB]

Hi Heckler

I said I would get back.

Popped over to Germany so that I could drive at 80mph :wink: - Revs =3800ish

 

[DavidBlake]

Hi,
Your revs should be 3500 at 80, and if you want to check without looking for jam sandwiches at the same time, about 3100 at 70, allowing for torque converter slip.

 

[BadTasteUK]

As I'll be driving through Germany in the summer, what's a safe cruising speed from a revs point of view?

Is 5,000 (or 100mph) ok to do for a long journey, or is it too high for the engine to cope? :?

(Sorry if this is a stoopid question, can't find the answer elsewhere on the board :roll: ).

 

[talbir]

Hi,

I can virtually guarantee that you have the wrong rev counter in your car. Although, check the integrity of the tack loom connection on the firewall, next to the ECU. It's a green wire and may have corrosion, causing a faulty signal.

It appears you have the 4-Cylinder engine tachometer - you should have the 6-Cylinder tacho. The symptoms you describe are exactly those you would have with a 4-Cyl tacho connected to a 6-Cyl engine.

I guess that what has happened is that at some point in the past, someone has had to change the tacho gauge (probably due to a faulty clock) and they inadvertently put in a 4-cyl tacho from a 200/230E instead of a tacho from a 260/300E. Probably some breaker who didn't mark up the tacho properly.

I reccommend you go to a MB breaker and have them fit a 6-Cyl tacho. That should solve your problem.

By the way, the tacho gauge doesn't have to be from a 300E - a 260E tacho meter is exactly the same....so long as it's from a 6-Cyl W124 model. Should cost about 45 pounds minus some money back for your 4-Cyl tacho meter.

Always bugs me when people change the entire tacho/clock meter when the clock gives up. To fix the clock, all one needs to do is change the two capacitors on the circuit board of the clock. But MB don't tell you this and neither do they sell you the capacitors. They just sell you a whole new tacho/clock meter for 250 pounds plus.

 

[HECKLER]

thank you all, i agree, i reckon it is a tacho prob, i shall get the tacho changed as recommended by Talbir. Thanks heaps.