912 Tach => works only from 900 to 1600rpm?

[Peter - Belgium]

Goodmorning all!

Yesterday I hooked up my 912 electical tach to a 1600cc beetle engine, and it is not working as I hoped for…
It seems to work fine up to 1600rpm… then it is stuck. At first I thought is was hung up on the little screw which is there since it is stuck at perfect level, but at closer inspection I doubt the screw is sticking out bit too far. It does not seem like the needle touches the screw?
Also once it was as the 1600rpm position and I release the throttle, the needle stays there until I lightly tap the glass. Then it drops again and works between the 900 and 1600rpm range.

gets stuck here:

(sorry for the sidewards pics... taken w the iPhone and for some reason they always turn even after I saved them after rotating??)

Connections I made are the
• earth
• the 1 that goes to the coil
• the +12V connection



Also, I hooked up all the little lights into all the gauges, but you hardly see any light showing through! I really need to look very closely before I actually see the lights are on? Driving in the dark I will never be able to see at which speed I’m with that poor lighting (lights are hooked up to the 58b and the switch all turned to the right for max voltage). Checked by hooking it up at the 58 for a full voltage, but no change.

Any thoughts?
Thanks!
Peter
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356 Outlaw built: https://www.thesamba.com/vw/forum/viewtopic.php?t=430774&highlight=

[Mike Hamrick]

Hello, Peter -
You are having problems associated with all the (old) 60's-era VDO gauges, which I have also had on 912's in the past. Keep in mind your tachometer is approaching 50-years in age and likely hasn't ever been serviced/restored. The sticking needle is a result of dead lubricant in the mechanism and very likely a worn-out bearing on the needle shaft. It needs to be rebuilt and calibrated by a VDO Authorized Shop.
As for the very "dim" lighting, this is caused by several age-related problems, all working against you. Lighting in these old gauges is all reflected light. From the lamp, the light reflects onto the inside of the rusted outer "can", then enters the space between the "can" and the gauge face, where it then is reflected on the black dial face, then reflected again through the build-up of dust on the inside of the scratched gauge glass. I've had moderate success with the following:
1) The Osram lamps used in the VDO gauges are/were available in 4.5, 6, 7.5, 9 and 12-volt versions. These may still be available in Europe. Installing the 9-volt lamp gives you more lumen output to reflect; the 7.5 was even brighter, but being operated at 12-13 volts, died prematurely.
2) Check all the wiring for the instrument light circuit, starting at the fuse panel. Clean all the connectors to a shiny-bright finish with 600-grit wet/dry sandpaper, including the sockets for the lamps. With a volt-ohm meter, check the wiring to make sure you have 12-volts (13.2 volts from a fully-charged battery) at the connection points. Check your light switch for the same voltage output; when the dimmer is turned all the way to bright, are you getting full-voltage out to the instrument lights? If not, years of dirt and corrosion are the problem. You can take the light switch apart, clean and re-lube it with special grease made for electro-mechanical components.
3) Have your tachometer rebuilt by an approved VDO Shop. Request they clean the rust out of the inside of the outer "can" (it was once shiny metal) and paint the inside white, with an appropriate paint product. This will reflect all the light possible through the light slot and onto the gauge face. I use Palo Alto Speedometer, here in California. "Harmut" is great to work with and will give you personal service (by phone). Your tachometer will come back looking and working as new (paloaltospeedo.com.us). They can put a new face on your gauge which is identical and has sharp, clean numerals, green and red stripes. The gauge glass will be cleaned and all scratches polished-out, so that light from the lamp isn't reflected back onto the black gauge face. You will be a happier person once this is done, believe me! Good Luck!

[Peter - Belgium]

Thanks for the reply! Was also fearing that the tach had to be opened for mechanical overhaul (opened again… since I already did that to clean the glass and repaint the black ring). Just need to check for a VDO shop in the area then, no idea where we would have one.

As for the lights… all is new so bad connections should not really be the cause. All wiring is new wiring, the bulb holders are new, lamps are new and all grounds are properly set and redone. I indeed checked the voltage output at the switch which was close to 12V when fully open, and I also connected the lights straight to the battery and that did not make a major difference.
I did open all the gauges to clean the glasses and repaint the black outer rings, did not really see a rusty/dusty inside?


Will check again when I/they reopen the tachometer.

THANKS!
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356 Outlaw built: https://www.thesamba.com/vw/forum/viewtopic.php?t=430774&highlight=

[Peter - Belgium]

opened the tacho yesterday and quickly saw the issue:

one of these little metal tabs was bent in wards preventing the copper winding to pass. just pushed it outwards a bit and all moved freely again:-)

quick check outside of the car

all OK!



Now for that issue with the lights... these tacho can not be better. On the inside it all looks new

all grounds etc have been checked + all wiring is new. I think I might order some of these:
http://www.thesamba.com/vw/classifieds/detail.php?id=1574215

anyone has any experience with these LED lights?

Thanks!
Peter
_________________
356 Outlaw built: https://www.thesamba.com/vw/forum/viewtopic.php?t=430774&highlight=