Jump to content


Photo

LX Tacho Gradually reads higher and higher


  • Please log in to reply
7 replies to this topic

#1 CI 0308

CI 0308

    Forum Fixture

  • Members
  • PipPipPipPipPip
  • 708 posts
  • Name:Brett
  • Location:Perth W.A
  • Car:77 LX SS, VX SS
  • Joined: 19-January 06
Garage View Garage

Posted 01 June 2017 - 05:59 PM

This has been asked before but there was never an answer given. My Original LX SS Tacho starts off reading ok but after about half an hour starts to read higher and higher until it sits around 6000rpm at idle. park it up over night start up the next day all is fine for half an hour of driving then the same thing happens.

I have replaced the voltage regulator with the Jaycar DC to DC regulator and set at 5 volts, soldered a wire bridge across where the selector switch usually goes. checked all wiring and all other gauges read fine. no the needle hasnt been painted etc. checked wiring through to negative side of standard style coil. runs an old school SBC with standard distributor.

anyone have any ideas as there isn't much more I can think of.

 

cheers Brett 


Edited by CI 0308, 01 June 2017 - 06:00 PM.


#2 VDO

VDO

    Forum Member

  • Members
  • PipPipPip
  • 154 posts
  • Name:Chris Curtis
  • Location:Brisbane QLD
  • Joined: 17-September 14

Posted 02 June 2017 - 07:48 AM

Circuit board is dying.  The components are changing values as the circuit warms.  Usually the resistors are fattening (increasing value) and the capacitors.



#3 CI 0308

CI 0308

    Forum Fixture

  • Members
  • PipPipPipPipPip
  • 708 posts
  • Name:Brett
  • Location:Perth W.A
  • Car:77 LX SS, VX SS
  • Joined: 19-January 06
Garage View Garage

Posted 02 June 2017 - 08:06 AM

Thanks VDO. I'll pull it out and check it. Hopefully I can change out the components with a bit of luck. Or is there a better way.

Sent from my Redmi Note 4 using Tapatalk

#4 VDO

VDO

    Forum Member

  • Members
  • PipPipPip
  • 154 posts
  • Name:Chris Curtis
  • Location:Brisbane QLD
  • Joined: 17-September 14

Posted 02 June 2017 - 09:55 AM

Replacement circuit boards can be bought.  Or the internals can be replaced with the same from another particular vehicle.



#5 deauville

deauville

    Forum Participant

  • Members
  • PipPip
  • 12 posts
  • Joined: 11-January 08

Posted 16 September 2021 - 07:55 AM

 Dads  original untouched Feb75 built LH SLR/5000 did this  exact thing  "Gradually the tacho would read 1000rpm high then idle would be at 3500 then finally at idle 6000rpm showing and at the same time the neddle would be "EXTRA BOUNCY" .   It was a build up of HEAT that seemed to affect the tachos movement.

 

We put a coduit black plastic tube around the tan tacho wire near where it ran past  the wiper motor.This really didn't help much.

 

Often wondered why ,No one ever explained it to me.



#6 VDO

VDO

    Forum Member

  • Members
  • PipPipPip
  • 154 posts
  • Name:Chris Curtis
  • Location:Brisbane QLD
  • Joined: 17-September 14

Posted 16 September 2021 - 08:28 AM

Replacement circuit boards can be bought.  Or the internals can be replaced with the same from another particular vehicle.

You can try re-working the solder joints on the tacho circuit board, but it probably won't make much difference in this case.  The most common culprit is the choke (on the circuit board) which often becomes intermittent due to flimsy wiring and eventually just falls off the board.  It looks like a small puck.



#7 Rockoz

Rockoz

    Lotsa Posts!

  • Members
  • PipPipPipPipPipPip
  • 3,422 posts
  • Name:Rob
  • Location:Bargo NSW
  • Joined: 21-September 08

Posted 16 September 2021 - 02:57 PM

I went through about 4 tachos about 10 years ago.

The choke had fallen off on all of them.

I did find a replacement choke from I think VDO in Western Australia.

But to be honest I reckon a replacement circuit board would be better than trying to fix the old one.

 

I think you do this dont you Chris?

 

I know there was someone doing it anyway.

 

Cheers

 

Rob



#8 VDO

VDO

    Forum Member

  • Members
  • PipPipPip
  • 154 posts
  • Name:Chris Curtis
  • Location:Brisbane QLD
  • Joined: 17-September 14

Posted 16 September 2021 - 03:02 PM

I went through about 4 tachos about 10 years ago.

The choke had fallen off on all of them.

I did find a replacement choke from I think VDO in Western Australia.

But to be honest I reckon a replacement circuit board would be better than trying to fix the old one.

 

I think you do this dont you Chris?

 

I know there was someone doing it anyway.

 

Cheers

 

Rob

Hi Rob.

Yes I do.  In my opinion, it's best to replace the circuit board.

I'm in QLD.






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users