a real tach

[Rabbit on Roids]

Thanks for that info..  Might just be easier to stick with my a/c pulses than try to calibrate everything to work with anything..   Not to mention I have get to find a complete working Benz diesel tach in the boneyards around here...


Burn, take a look at the housing for the IP gear on your truck..   There should be a plug either at the 12 o clock or 2 oclock postion..   That's where they screwed in a magnetic pickup for the factory tach....Although I can;t remeber for sure if there were specfic teeth to trigger it, or if it just used the teeth on the IP gear... If it used the teeth on the gear it would probably be easier to trigger it off the crank for calibration sake...

no.

vw never put a tach there.
they used the w term on the alt.
and for the people who build the photo eye tach,
theres a disk of metal on the front of the injection pump pulley. 2 quadrants are painted black, and 2 are left un painted.
they never used a magnetic pickup on the teeth of the pulley.
plus, most of the older engines dont even have the hole next to the ip in the cover.

[maxfax]

Most mag pickup tachs I've seen triggers on one tooth (that 's one per rev) of the crankshaft.

Yeah most diesel setup I have seen used one tooth on the crank and some variety of electronics to convert the signal..  I used a standard ole Sunpro gasser tach set to 4 cyl.. So for calibration 2 teeth were much easier..   One rotation of a distributor = 2 crank revolutions..  So 2 teeth on the crank would give the same result... 
Finally I got my hands on a factory gasser tach so I swapped that in with no mods required to the tach (plus I have no W terminal on my Alt)..   But of course the Tach itself took a poo recently, so it's back to the dorkey 5" sunpro tach for now..

no.
vw never put a tach there.

No they didn;t...  But I was referring to the diesel in his Ford..  

[92EcoDiesel Jetta]

While I certainly commend your ingenuity and resourcefulness, I have to mention that the Merz 300 series tachometers are notoriously unreliable.  I've fixed them before because they fit in the Merz cluster, but there is no way I'd use any parts from one on a VW.  I am most fond of the Ford probe method that Jimbote outlined in the FAQ.  Similar or possibly less complicated install, uses a stock gas VW tach, inexpensive, fits the cluster perfectly, etc...

I just read Jimbote's method. Thanks for pointing out that thread, Andrew. Certainly having a VW tach that fits in the cluster without modification is the way to go. When I saw the "Ford probe method" in your post I thought it was a tach from a Ford Probe car at first lol. But it's actually a magnetic pickup from a Ford, the same type of pickup as used in the Mercedes and many other diesels with a tach. Magnetic pickups are easy to make. All you need is a short 1/8 dia. iron bar core , magnet wire, epoxy and an electric drill. Just wind the wires over the iron core with the drill and bring the leads out and encapsulate it with epoxy. I had to make one once and it worked fine.

I will look for a VW gasser tach and use the Mercedes mag pickup which is already installed which I think will work but won't know for sure till I try it. I just have to add another tooth 180 degree from the tooth that's already there.

As far as the Mercedes tach being unreliable. Are you referring to the tach amp? If so I agree. I've repaired a few of them. But once repaired properly, it is as reliable as any other tach.

[92EcoDiesel Jetta]

The problems I've seen with the Merz tach have been either the amp or the large multi-pin connector in the engine bay.

I like that the magnetic pickup when used with the VW tach doesn't need any amplifier at all.

Andrew

The location of the Mercedes tach amp high up in the engine compartment and its circuitry being potted certainly does not help. Heat and poor solder joints is what causes them to fail. The second video I posted is a self contained tach, but it probably won't physically fit into the VW cluster without modification. Would you know if Mark II gasser tachs works the same as the one Jimbote used (I think his came from an 83 GTI )?

[JerryGTD]

All you need is to find the cluster from a mk2 diesel with a tach. Match up the wiring style, CE1 or CE2 and that's about it. I've always thought that no calibration was needed but I could be wrong.

Either way though, I like what you've done and my truck will probably get something like that

Does anyone know if its possible to swap the tach from a CE1 turbo diesel cluster into a CE2 diesel cluster with the clock in it? I have a spare CE1 TD cluster but it won't work in a CE2 car.

[Rabbit on Roids]

All you need is to find the cluster from a mk2 diesel with a tach. Match up the wiring style, CE1 or CE2 and that's about it. I've always thought that no calibration was needed but I could be wrong.

Either way though, I like what you've done and my truck will probably get something like that

Does anyone know if its possible to swap the tach from a CE1 turbo diesel cluster into a CE2 diesel cluster with the clock in it? I have a spare CE1 TD cluster but it won't work in a CE2 car.

time for a wiring harness swap! CE2 has 1 plug and CE1 has 2 plugs. its kinda a *** to pull the whole dash to swap the wiring.

[JerryGTD]

All you need is to find the cluster from a mk2 diesel with a tach. Match up the wiring style, CE1 or CE2 and that's about it. I've always thought that no calibration was needed but I could be wrong.

Either way though, I like what you've done and my truck will probably get something like that

Does anyone know if its possible to swap the tach from a CE1 turbo diesel cluster into a CE2 diesel cluster with the clock in it? I have a spare CE1 TD cluster but it won't work in a CE2 car.

time for a wiring harness swap! CE2 has 1 plug and CE1 has 2 plugs. its kinda a *** to pull the whole dash to swap the wiring.

I'm not looking to do a whole dash wiring harness swap. To clarify, all I was asking was can you use the tachometer from a CE1 cluster in place of the clock on a CE2 cluster. Maybe someone would WTT a CE1 for a CE2 tach or whole cluster.

[lovinthedeez]

man, i've been looking for a ce1 cluster for awhile now.  all I got is a ce1 gasser cluster(in the car now) with tach.

[92EcoDiesel Jetta]

What year & model MK II diesels came with a tach? What is CE1 and CE2? Please explain.

[jack's lack]

How do they read RPM when they dyno A diesel? Seems like that would need to be pretty accurate.
Also is there any concern with the weight of the magnet throwing the already fragile crank pulley off balance? Especially since it is located as far as possible from the center causing the greatest moment? Or is it so small that the effect is negligible? Since we expect hundreds of thousands of miles from these engines I can't help but ask

[92EcoDiesel Jetta]

The problems I've seen with the Merz tach have been either the amp or the large multi-pin connector in the engine bay.

I like that the magnetic pickup when used with the VW tach doesn't need any amplifier at all.

Andrew

Andrew, have you successfully duplicated jimbote's method? I got hold of a MKI gasoline tach and did a bench test with it and was not able to get a reading from it. I didn't have a Ford probe and that may be the problem. The magnetic pickup I was using was putting out only 300 milivolts and that may not be enough for the SAK215 chip in the VW tach. I'll keep working on it.

The bench test setup was a 1725 rpm AC motor that I added 1 or 2 trigger "tooths" to. I used this same setup to check the calibration of the Mecedes tach and it was spot on.

[92EcoDiesel Jetta]

Andrew, I read on another forum you found a Ford probe for $15. Where can I get one for that?

[Rabbit on Roids]

the same place you can get running driving cars for $250 bucks.. craigslist!

[Smokey Eddy]

if anyone can find a probe such as the one mentioned i'd be interested. I have a dead tach in my dash that does nothing.

[92EcoDiesel Jetta]

Anyone know if this tach originally ran off the ignition coil or the W terminal of the alternator? Per the data sheet, the SAK215 needs 0.5 volt minimum to trigger, max 20 v. I tried bypassing the RC network at the input and wired the pickup direct to pin 2 and it still wouldn't work. So I momentarily touched pin 2 direct to +12V and got the needle to jump slightly, which confirms the tach is not dead, just need the proper amplitude to trigger it. I found a pickup from a CIS distributor which puts out just around 0.5 v per my measurement. If I can set a small enough gap, maybe it will put out enough voltage to trigger.