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doing the tacho boogie
Posted: Wed Aug 31, 2016 9:18 am
by Joelipol
I have a 71 911T sporto with rebuilt gauges from Hollywood and a temperamental tacho.
The tacho swings wildly from nothing to redline+ when it is started, regardless as to if the car is hot or cold.
However if the car is 'hot' it takes very little time to settle down and read accurately - if it is cold it takes a bit longer.
It seems the car needs to be 'hot' to be reading accurately.
No idea what could be going on here but would be grateful for some advice.
Re: doing the tacho boogie
Posted: Wed Aug 31, 2016 3:46 pm
by Joelipol
Oh I have:
- new voltage regulator (problem was there with old one as well)
- new batteries
- rebuilt alternator
- I've checked that the alternator is earthed properly
- I haven't checked the starter
- I haven't checked the connections to the tacho
Re: doing the tacho boogie
Posted: Wed Aug 31, 2016 4:02 pm
by jb
Maybe check the points gap as they seem to affect the rev counter sometimes.
Re: doing the tacho boogie
Posted: Wed Aug 31, 2016 4:09 pm
by Joelipol
Points gap checked and a-ok - new points as well... the question is why would it work once the engine has been running for a bit... seems odd.
Re: doing the tacho boogie
Posted: Wed Aug 31, 2016 4:18 pm
by Mike Smith
Why not speak to Hollywood Speedo ?
Re: doing the tacho boogie
Posted: Mon Sep 19, 2016 6:35 pm
by Joelipol
It seems there were multiple problems just to round off the thread:
1) There is a tacho 'deadening' capacitor on the cdi electrical board that had gone. Apparently as it heated up the resistance in the unit changed and it would start to work again... when bypassing it, bam - tacho worked.
2) alternator output is down and has likely been damaged by overcharging
3) multiple earths needed redoing...
anyway - now some things to replace and mystery solved
Re: doing the tacho boogie
Posted: Mon Sep 19, 2016 6:47 pm
by MT
Nothing to add technically, but thanks to Joel for rounding out the thread. Not so much here, but on Pelican and 991S I have been frustrated in the past when after being thrilled at finding a thread that describes my very problem, to then be frustrated when the OP never posts the end of the story about what fixed it!
Re: doing the tacho boogie
Posted: Tue Sep 20, 2016 10:27 am
by Barry
MT wrote:Nothing to add technically, but thanks to Joel for rounding out the thread. Not so much here, but on Pelican and 991S I have been frustrated in the past when after being thrilled at finding a thread that describes my very problem, to then be frustrated when the OP never posts the end of the story about what fixed it!
Too right! How annoying is that, not to mention discourteous.
Good thread, excellent reference for the future
.