Tach on a 6.2 Diesel??

[67_C-30]

Did any 6.2 trucks come from the factory with an optional tach. If not, can and how would one be wired up? I am currently putting a 6.2 in a '67 C-30, and I have a dash cluster w/ tach that I want to use in the truck. If anybody has any info on this, please let me know. Thanks in advance!!

[draino76]

I had an aftermarket tach in my 6.2. I can't say that I ever saw a factory one, but they may exist.

[67_C-30]

How was your tach hooked up? Thanks!

[draino76]

It actually connected to the alternator, and would be accurate as long as you use the stock size pulleys on the crank and alt. I bought it through JC Whitney, and it worked great, I think they still sell them. Always good to see some other diesel fans on the site.

[ElGracho]

You can also use a vacuum pump for a California 6.2 that had the signal generator on the top. I have the schematic for a signal conditioner to make that signal into a square wave that a regular gas tach will use.

GM offered a dealer accessory tach for 6.2 equipped trucks. It was a combined tach and fuel gage. I had a line on a kit, but the dealer that had it wouldn't sell it. Wierd. Anyhow, it triggered off the alternator like the aftermarket ones.

Isspro sells aftermarket tachs for diesels.

[crossy]

this is what I was told from our resident diesel head ,Arveetek[Casey]. the factory mid 80's ones were 4K tachs. DAVE
Getting a tach signal on a diesel is not easy. As you know, there is no electrical signal to tap into.
There are three ways to get a tach signal: one is to locate a vacuum pump with a tach drive built into it. These are rare. On a 6.2L diesel engine, there is a spot in the back of the motor in the same place as a distributor on a gasser. The vacuum pump sits in this hole, and is driven by the camshaft. The vacuum pump then drives the oil pump, just like a distributor. Diesels produce no vacuum, so you have to have a pump in order to operate your A/C controls, cruise control, etc. Some pumps had a built in sensor for a tach, but they're hard to come by.
The other and more common way to get a tach signal is to glue a magnet onto the harmonic balancer, and a sensor onto the engine block. If you buy a tach made for a diesel, it usually comes with this type of setup.
The final way to get a signal is off the alternator. The late model factory Chevy tachs use this method. They are wired directly into the alternator to derive rpms. It's critical in this case to get a proper sized alternator pulley with a replacement alternator. Most aftermarket alternators slap on any old pulley then can use, and even a mm in size difference can throw off the readings. A few aftermarket tachs do use this method, but most use the crank sensor style.
If I were to get a 4000 rpm tach like we've been talking about, I would have to rig up a crankshaft sensor.
Casey

[67_C-30]

Thanks for help once again guys. I am installing the 6.2 in my '67 C-30 as I said before, and I have gauge cluster out of a big 2 tin truck. This cluster has the factory tach and air pressure gauge for the air brakes. I might to have to use aftermarket5 unit, but use a custom face that wiull look factory in my dash. I want to add a turbo to my 6.2 like Arveetek and Grape, so I also want to modify the air pressure gauge to read boost. I think this will be a super trick looking mod on an old truck. Check out pic below. I think it would look pretty good.