rev counter

8 replies [Last post]
kashi123
kashi123's picture
Offline
Joined: 06.11.2003

Hi,

The rev counter on my 1989 300 GD seems to lead a life of its own, normally it does not work then sometimes it will shoot up to 6000 revs giving me hartfailure. Then it settles down to the correct revs for a few minutes then it goes back to sleep for a very long time.
Can someone please explain to me in very very simple terms(eg the shiny black thing connected to the silvery thing etc..) how to investigate this problem and maybe how to fix it. Please bear in mind that I am a complete idiot when it comes to mechanical things but am also too tight to spend any money on it!

thank you very much,

Richard

mortinson
mortinson's picture
Offline
Joined: 05.11.2003
Location: Old beehive, Madrid, Spain
Alternator?

Richard:

I believe that at least in the 460 series 300 GD the rev counter is powered by the alternator. Bearing in mind that you are not reporting any failure in the battery to get loaded, I would assume that your alternator is working properly and therefore suggest that you check the cable that runs from the alterantor to the rev counter. It is possible that the connection closest to the alternator, which is quite exposed is being intermitently cut by muck/moisture/etc, leading to the problems you describe.

I trust this helps.

whelanrob
whelanrob's picture
Offline
Joined: 10.11.2003
Location: ireland
alternator????

Hi Richard and Jesus,
I am not so sure about the alternator theory,at least not on all Gs.I am scrapping a swb 300gd at the moment and it has a tacho,that I am trying to transfer to my G.The signal cable of the back of the instrument goes to a black cylindrical box on the inner wing next to the glow plug relay.From here there is a grey screened cable down to some sort of a pickup/sensor on the crankshaft pulley,where the timing marks are.Having said all that ,I have as of yet failed to produce any results,with all the gear transferred to my G.
There was some talk of the "w" connection on the back of the alternator being related to tacho installations but I do'nt know,maybe the answer will appear here
bob

kashi123
kashi123's picture
Offline
Joined: 06.11.2003
rev counter

Thank you for your advice, will try and sort it tomorrow and let you know how I got on,

richard

RodWiles
RodWiles's picture
Offline
Joined: 12.07.2004
Location: Winchester, UK
rev counter

Hi there,

This may be an old topic, but I have almost the same problem with my 1988 300 GD rev counter. It almost never works and then sometimes if I blip the throttle when I shut off the engine it jumps up a little. It would be nice to get it working, as everything else on my G works well!

Any new advice (in simple terms please)?

Thanks.

Mark Lindley
Mark Lindley's picture
Offline
Joined: 17.11.2003
Location: Plymouth
rev counter

Folks,
I had the same issue with my 1988 300GD - the rev counter didn't work at all. It turned out to be a faulty multi-pin plug and socket assembly. This looks like a large (about 3cm) diameter black screw cap attached to a plate on the left hand inner wing - about half-way between front and back. I've no idea what other functions this thing has - probably somewhere to plug in diagnostic equipment. Anyhow, this was replaced and the rev counter now works perfectly. The part numbers marked on this device is 0015455932 and VDO 415 202/1/1. I remember it wasn't cheap (about £50)

buckalec
buckalec's picture
Offline
Joined: 30.03.2004
Location: Belfast
GWOA Groups: Members
Rev counter

Just adding my tuppence worth!!

1989 300GD, worked perfectly for the last 4 months, now doing exactly what is described above.

My more knowledgable mechanic pal says it is almost certainly a contaminated socket, taken from the back of the alternator.

I'll giggle it and let you know.

Cheers

Hunting-G
Hunting-G's picture
Offline
Joined: 14.08.2004
Location: Perth, Western Australia
Tacho Frustration

Guys,
I have the exact same problem as Mark Lindley, model with magnetic pick up pulse generator on the front of the crankshaft pulley.
VDO checked tacho (A$100), I replaced pulse generator and wiring (A$170), and the tacho still has a mind of it's own.
The diagnostic plug as mentioned appears to be the solution, short of an engine change.
The part numbers are the same, 0015455932 and VDO 415 202/1/1.
MB Aust want (A$640), can any one help me with a part from the UK (approx A$120), as stated by Mark.
Mal

Hunting-G
Hunting-G's picture
Offline
Joined: 14.08.2004
Location: Perth, Western Australia
Tacho impulse sender

Got a replacement part from the US at $70.

http://www.germanstar.net/116el.htm

Same part as on the MB 116 Chasis
RPM Sensor
0015455932
All 300SD
$69.00

Hunting-G