Mercedes-Benz Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter #1
So I'm trying to weed out some small problems and this one I have not found an answer for:

Whenever the transmission shifts, the tach bounces about wildly and will steady out to actual RPM's. I can live with it but it is somewhat irritating, and I have not found an answer anywhere for what it could be besides replace it.

Any thoughts?
 

·
Registered
Joined
·
16,695 Posts
Make sure those replacements are copper core ceramic types such as those made by Flosser. Do not use the generic plastic ones, as you risk melting down your fusebox.
 

·
Registered
Joined
·
38 Posts
Discussion Starter #5
Make sure those replacements are copper core ceramic types such as those made by Flosser. Do not use the generic plastic ones, as you risk melting down your fusebox.
I ordered MB replacements via ECSTuning, I don't intend on messing about trying to save a few pennies.
 

·
Premium Member
Joined
·
982 Posts
Seems like it might be flaky capacitors in the tach unit itself. Tachometers have a frequency to current conversion circuit that usually involves charging a capacitor. There is also usually a low pass filter filter on the tach input. If any of those caps go bad or develop a bad solder joint (as all W124 electronics seem to be prone to at this age), the current through the meter movement may get erratic when the input frequency changes at the time the transmission shifts. The erratic current causes the movement to "bounce" until the current stabilizes. Another possibility is that that bearings (jewels) are going bad in the meter movement. This is a common issue that I have seen in old British tachs.
 
1 - 6 of 6 Posts
About this Discussion
5 Replies
4 Participants
Floobydust
Mercedes-Benz Forum
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!
Full Forum Listing
Top