Bouncing Tach?

Tidybuoy · 10-13-2011, 10:09 AM

My car is new to me - 1974 911

The tach bounces about 2000-3000 rpm between shifts, without the engine actually reving. I know there was a thred about this on the 914 board but I cannot find it.

Any advice would be appreciated.

Driver_X · Driver_X's Garage

Could be a few things, voltage spikes (check VR), short in wiring (check wire from distributor), but it my case it was a worn set of points. I would start there....

gwmac · 10-13-2011, 10:46 AM

Same problem with a Pertronix ingnitor. Distributer clean and lube fixed it. Probably a grounding issue.

72T · 10-13-2011, 11:12 AM

In my case, a bouncing tack has always meant the points were failing. Does the tach bounce while at a set rpm?

tobluforu · tobluforu's Garage

Points, grounds, tach. Don't forget to pull the tach and clean all connections if points are ok.

Tidybuoy · 10-13-2011, 12:37 PM

Quote:

Originally Posted by 72T

In my case, a bouncing tack has always meant the points were failing. Does the tach bounce while at a set rpm?

The tach is stable at idle and while driving. It only bounces between shifts.

I will take all the advice and cleant things up. I've only had the car for two weeks and althouh it's very clean (inside & out), I have yet to fiddle with anything in the engine compartment.

Putting on a new roof on my house has given me no time for cars, this week.

Scott R · Scott R's Garage

I've got a newer alternator and electrical system thanks to a fire mishap and my tach still does this even after the rebuild. I would seem that based on posts here that the damper fluid/damper something inside the tach is worn out. There are some success stories here about sending it out to be repaired and then no more bounce.

Hodgey · Hodgey's Garage

..not to hijack this thread but what about on an 87? Mine flickers at around 3400 rpm when cruising...no other rpm, just this one......I have no points see?