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pvfahrer
Samba Member
Joined: July 28, 2016
Posts: 11
Location: New York
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 Posted: Mon Apr 18, 2022 6:19 am Post subject: Re: Gas tachometer to diesel conversion |
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| ?Waldo? wrote: |
Probably. The similar era VW tachometers all followed the same general schematic and parts list. The image is specifically regarding the Vanagon tachometer, though. You'll have to map out your board to identify which components to change.
There might be a schematic to your specific tach here: http://vwdiesel.net/forum/index.php/topic,3741.0.html |
Quick follow up, i indeed found the schematics at the vwdiesel forum, my 7k tachomter has an almost identical circuit to the first posted one, although the physical appearance is different, the circuit is the same. I have ordered the parts as per list in the post at vwdiesel.net. Waiting for them to come in. Once i have them in place, i'd like to test and calibrate the tachometer using a function generator and was wondering what the input wave form looks like. I am assuming the signal is a 0-12V square wave or pulse with a frequency related to the rpm? Does anybody know the alternator rpm to engine rpm ratio?
Also since i have a golf tachometer, the rear plate is different to the one needed to fit the Vanagon instrument cluster. In case somebody has some left-over parts please let me know, this woudl make the project a lot easier.
edit thesamba for the rescue, i found the information on calibration using a wave from generator in https://www.thesamba.com/vw/forum/viewtopic.php?t=430888 an older topic
It is in german, the part on the calibration translates to:
"Calibration; if you own a wave form generator: Use sine wave with 10-15V amplitude, at a frequency of 1320hz the tachometer should show 6000rpm. This is for Diesel engines with a V-belt between alternator and water pump."
(Abgleich, wenn man einen Frequenzgenerator hat: Mit einem Sinussignal mit einer Amplitude von etwa 10-15 V wird der DZM so eingestellt, dass er bei einer f=1320 Hz 6000 1/min anzeigt. Dieser Wert gilt für alle Dieselmotoren mit einem Keilriemen für Lichtmaschine und Wasserpumpe.)
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RolandD
Samba Member
Joined: January 15, 2017
Posts: 283
Location: Menomonee Falls, Wis
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| Posted: Wed Apr 06, 2022 3:46 pm Post subject: Re: Gas tachometer to diesel conversion |
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Waldo, would it be on topic if no modifications where needed for it to drive a gas tach?
Roland |
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?Waldo?
Samba Member
Joined: February 22, 2006
Posts: 10156
Location: Where?
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| Posted: Wed Apr 06, 2022 8:26 am Post subject: Re: Gas tachometer to diesel conversion |
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| It is commonly known as a possibility, but not actually on-topic for this thread. |
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RolandD
Samba Member
Joined: January 15, 2017
Posts: 283
Location: Menomonee Falls, Wis
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| Posted: Tue Apr 05, 2022 4:57 pm Post subject: Re: Gas tachometer to diesel conversion |
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Is it not common knowledge to put an industrial proximity sensor on the injection pump pulley?
Roland |
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Zeitgeist 13
Samba Member
Joined: March 05, 2009
Posts: 12177
Location: Port Manteau
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| Posted: Mon Apr 04, 2022 8:07 am Post subject: Re: Gas tachometer to diesel conversion |
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I've tried this mod on two different WBX tachs, but I couldn't get either to function correctly. I'll strike that up to user error. I just finished up converting an AHU alternator to send a W signal to a Speedhut tach and it works excellent.
_________________
Casey--
'89 Bluestar ALH
'01 Weekender --> full camper
NEAT, no ICE. |
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chrismsnt
Samba Member
Joined: March 06, 2018
Posts: 259
Location: Cumming, GA
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| Posted: Mon Apr 04, 2022 7:53 am Post subject: Re: Gas tachometer to diesel conversion |
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From what I've found.... the HARDEST part is finding an alternator with a W terminal anymore! 
_________________
Chris
1989 T3 Vanagon 16" Syncro
1967 Squareback
https://vwvandiesel.com
Instagram @VW_VanDiesel |
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pvfahrer
Samba Member
Joined: July 28, 2016
Posts: 11
Location: New York
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| Posted: Sun Apr 03, 2022 5:15 pm Post subject: Re: Gas tachometer to diesel conversion |
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| ?Waldo? wrote: |
Probably. The similar era VW tachometers all followed the same general schematic and parts list. The image is specifically regarding the Vanagon tachometer, though. You'll have to map out your board to identify which components to change.
There might be a schematic to your specific tach here: http://vwdiesel.net/forum/index.php/topic,3741.0.html |
great! thanks for the link, i'll have a look and see if i can find a comparable one. |
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?Waldo?
Samba Member
Joined: February 22, 2006
Posts: 10156
Location: Where?
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| Posted: Sun Apr 03, 2022 4:47 pm Post subject: Re: Gas tachometer to diesel conversion |
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Probably. The similar era VW tachometers all followed the same general schematic and parts list. The image is specifically regarding the Vanagon tachometer, though. You'll have to map out your board to identify which components to change.
There might be a schematic to your specific tach here: http://vwdiesel.net/forum/index.php/topic,3741.0.html |
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pvfahrer
Samba Member
Joined: July 28, 2016
Posts: 11
Location: New York
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| Posted: Sun Apr 03, 2022 4:10 pm Post subject: Re: Gas tachometer to diesel conversion |
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Looking into doing a Tachometer conversion for my diesel van, I scored a gold mk2 instrument cluster with a tachometer to 7k. If I replace the components of this Tacho with the ones on the list, will this change the rpm range to the diesel range?
| ?Waldo? wrote: |
Red = Keep
White = Remove
Green = Replace/Add
3.3uF cap: 445-8294-ND
10K ohm res: MFR5-10KFI
0.047uF cap: 399-C410C473K5R5TA-ND
71.5 ohm res: MFR-25FBF52-71R5
0.01uF cap: CS14-F2GA103MYGKA
15K ohm res: MBA02040C1502FRP00 |
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alexgb
Samba Member
Joined: July 24, 2020
Posts: 1
Location: BC
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?Waldo?
Samba Member
Joined: February 22, 2006
Posts: 10156
Location: Where?
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| Posted: Wed Mar 16, 2022 1:43 pm Post subject: Re: Gas tachometer to diesel conversion |
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What is the value and part # for the yellow rectangular capacitor?
When you say "As far as I know it worked well," tell me more. Do you have any firsthand evidence that it worked well prior to the conversion? Did you see it working properly on a gas engine? |
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VanTransylvania
Samba Member
Joined: March 16, 2022
Posts: 5
Location: Transylvania, Romania
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| Posted: Wed Mar 16, 2022 1:33 pm Post subject: Re: Gas tachometer to diesel conversion |
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| sorry Waldo, just saw your questions after posting the details of accelerating ~500 rpm and the needle jumped more then that... |
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VanTransylvania
Samba Member
Joined: March 16, 2022
Posts: 5
Location: Transylvania, Romania
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| Posted: Wed Mar 16, 2022 1:25 pm Post subject: Re: Gas tachometer to diesel conversion |
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Did the tach work properly as a gas tach prior to attempting the conversion?
- As far as i know, it worked well
Do you have the polarity backwards on the 3.3uF Cap?
- I checked and made sure the polarity on this cap is as it should be
What happens when you adjust the potentiometer?
- nothing happens, i even checked the potentiometer with a multimeter and it works |
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?Waldo?
Samba Member
Joined: February 22, 2006
Posts: 10156
Location: Where?
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| Posted: Wed Mar 16, 2022 1:24 pm Post subject: Re: Gas tachometer to diesel conversion |
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I saw the video.
Answering the specific questions I asked might help the diagnosis. |
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VanTransylvania
Samba Member
Joined: March 16, 2022
Posts: 5
Location: Transylvania, Romania
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| Posted: Wed Mar 16, 2022 1:22 pm Post subject: Re: Gas tachometer to diesel conversion |
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| when i accelerated (as seen in the video) it shouldn't have gone that high up, from 5k rpm to above 6k rpm, the acceleration should have measured around 1.5k rpm |
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?Waldo?
Samba Member
Joined: February 22, 2006
Posts: 10156
Location: Where?
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| Posted: Wed Mar 16, 2022 1:21 pm Post subject: Re: Gas tachometer to diesel conversion |
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Did the tach work properly as a gas tach prior to attempting the conversion?
Do you have the polarity backwards on the 3.3uF Cap?
What happens when you adjust the potentiometer? |
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VanTransylvania
Samba Member
Joined: March 16, 2022
Posts: 5
Location: Transylvania, Romania
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| Posted: Wed Mar 16, 2022 1:19 pm Post subject: Re: Gas tachometer to diesel conversion |
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| when i shut it off, it goes to 0 |
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?Waldo?
Samba Member
Joined: February 22, 2006
Posts: 10156
Location: Where?
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| Posted: Wed Mar 16, 2022 1:14 pm Post subject: Re: Gas tachometer to diesel conversion |
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| Where does the needle go when you shut it off? |
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VanTransylvania
Samba Member
Joined: March 16, 2022
Posts: 5
Location: Transylvania, Romania
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| Posted: Wed Mar 16, 2022 12:51 pm Post subject: Re: Gas tachometer to diesel conversion |
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hi there,
thank you for the useful information from this thread. Unfortunately, the result in converting to fit a diesel (jx) engine has been frustrating me for the past week.
here is a video that shows what the rev counter does after double and triple-checking each and every resistor and capacitor. I've also checked them with a multimeter to make sure they meet the above mentioned criteria.
Video >> https://youtu.be/dhN51G8pvok
I also checked the the wire (+ - and W) all good. The alternator has a W by default, i didn't have to change anything.
I am at my wits end and was hoping someone could point me in the right direction.
Thank you in advance for any helpful info. |
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Achilles3588
Samba Member
Joined: February 11, 2005
Posts: 640
Location: Bradenton, Florida, USA
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| Posted: Sat Sep 11, 2021 1:49 pm Post subject: Re: Gas tachometer to diesel conversion |
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I've just done this mod using the parts from Digikey as listed above (with thanks) by Gnarlodious to a gasser tach PCB.
Initially I got no readout. I went back and checked the continuity on the circuits on the reverse side of the PCB node by node and everything checked out OK. In the process of doing that I realized I had installed the D1 replacement bridge in the wrong location!
Removed and reinstalled the link in the correct place, reinstalled the tach in the rig and sure enough it worked! One tweek of the potentiometer and the readout was accurate, too! Fantastic!
_________________
Larry V.~
'91 Syncro Doka 1.9L TDI 'AFN' |
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