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Gas Tacho / Revcounter Conversion to Diesel W terminal

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regcheeseman:
Originally dealt with in this thread http://www.vwdiesel.net/forum/index.php?topic=3096.0, now condensed into the various solutions to convert all type of VW gas type revcounters to work from the W terminal on VW fitment altenators.

The original gasser schematic



Re-worked into diesel w terminal version


First up the VDO unit...

The gasser board before

replace R1 with 100 ohm
leave R2  
replace R3 with wire link
replace R4 with 191 ohm
replace R5 with wire link
replace R6 with 10K
replace R7 with 15K

 
replace C1 with 10nF
remove C2
leave C3
remove C4
replace C5 with 47nF
fit C6 3.3uF in vacant spaces next to tacho motor (red and blue) wires or desolder wires from board, fit cap and then solder wires to cap wires/board.

adjust RV1 to mid range

The final working board.


Note the two resistors joined together are because I could not find a 191 ohm resistor so joined a 180 and a 10.

C6's value is not critical, I used a 2.7 instead of a 3.3, it works fine without this cap altogether and I believe is only there to stop needle flutter (I didn't have a problem with or without this fitted)


Mods for westmoreland clocks...

First the schematic as is..


The annotated board..


A lot of similarities with the original VDO circuit, I'll wager the SAK chip is the same and converting to the diesel tacho circuit should work..

Make R1 = 100ohm
replace R2 with 72ohm
replace R3 with wire link
replace R4 with 191ohm
replace R5 with wire link
replace R6 with 10K
replace R7 with 15K

replace C1 with 10nF
leave C3
remove C4
remove C?


make RV1 = 22K
remove RV2 and replace with 47nF cap

If you can get a 3.3uF across the needle output wires then do so....it's not critical though.



Now the Motometer clocks...







Swap R1 for 15K
Remove R2
Remove R3
Swap R4 for 191 ohm
Swap R5 for 72 ohm
Swap R6 for 100 ohm
Swap R7 for 10K

Replace zener with wire link

Swap C1 for 10nF
Swap C2 for 47nF (nanofarad)
Swap C3 for 47uF (microfarad)
Swap C4 for 3.3uF

If replacing C3 or C4 with electrolytics then observe polarity as marked on board.

Leave the terminal marked ZA disconnected where appropriate.

RabbitJockey:
this should help anyone doing a gti tach:


--- Quote from: fatmobile ---That is a very nice tiltisorie ... bad spelling I'm sure but it tilts the car up on it's side nicely. I've been eyeing a few on the vortex and this one looks great compared to some of them.
 I was messing with the '83 westmoreland tach, figuring what parts I need to source.
 It looks like there are a few resistors that can be moved from one spot to another.
 R6 is a 15K resistor and can be moved down to where R7 is. Then a 10K is used in the R6 spot.
 R3 needs to be a wire link and is a 100 ohm now. On the diesel tach, R1 needs a 100 ohm resistor so that can be used there.
  Actually I'm thinking the R1 resistor determines how far the needle swings so I might put a variable resistor in there and see if I can get it to work with the stock gas tach face and go to 7000RPM.
 The stock R1 resistor in the gasser tach is about 10ohm (it was 15ohm in my '91 Golf gasser tach) so I might even keep that one in there.

 ...so the parts list looks like:
10K resistor
 72ohm resistor
191ohm resistor
 and a 10nf cap (the '91 Golf already has a 10nf cap that is getting removed)
 4 little pieces
--- End quote ---

Black Smokin' Diesel:
If I were to use a CE1 golf/jetta MK2 8v gasser tach to convert to diesel use, which schematic would I use?

RabbitJockey:
try to find the one thats closest to the board you have, they are all so different and there are so many of them

Black Smokin' Diesel:
Allright I'll grab one from the junker and go from there. Maybe I'll bring a print of these with me and try to get one as close to the ones in this thread.

Thanks a lot.

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