4500 RPM tachometer in a 4.9L gasoline truck?

[Jon M]

Good morning folks and Happy Sunday!

I came into possession of an instrument cluster with a tachometer which I was pretty excited about before I realized it had a lower RPM count because it was from a diesel truck. It's definitely not the correct factory configuration for my truck, but it came pretty cheap and I'd rather not spend $200 (plus shipping) on ebay. So I suppose my questions is, will the tach (and printed circuit) fit and work on my 1984 4.9 i6. I probably will not purchase one (unless it's really cheap), but I have this one so if it functions in my truck, I might just throw it in there. You know, just 'cause.



(I suppose it's obvious but, the top one the donor, bottom one is mine)

I suppose I'll throw in the backstory: I got it from a local yard that specializes in bullnoses for pretty cheap in order to take the ammeter and convert it to a voltmeter in advance of pulling off a 3G conversion. I saw the tach and figured, "why not?" I do not know the year of the donor truck, just that it was a diesel F250.

(Additional question, do you guys repaint the needles in your instrument clusters? if so, what sort of paints or markers do you recommend?)

[viven44]

Not sure diesel and gas clusters are compatible as the Tachometer signals come from different sources.

About needle paint, I have used the one below and it "works for me" and my amateur needs. That bottle will last me a lifetime.

Go real easy on the paint. A little bit on the brush goes a long way before you potentially cause a drip.

https://www.michaels.com/product/testors-fluorescent-enamel-paint-10226505?cm_mmc=PLASearch-_-google-_-MICH_Shopping_US_N_Craft+%26+Hobbies_N_PMAX_LocalOnly_N-_-&Kenshoo_ida=&kpid=go_cmp-18514199957_adg-_ad-__dev-c_ext-_prd-10226505&gad_source=1&gclid=CjwKCAjw7s20BhBFEiwABVIMrdjcU5Q3bgeOivcbKv-ldx5PBo_l1c7ohhMgRa4JUSMEIKvdjanE-RoCOMkQAvD_BwE

If you are looking for something more professional.. I have seen this recommended before here and I think Gary did some extensive testing
https://www.hipoparts.com/fluorescent-speedo-gauge-needle-restoration-paint/

I found the thread below helpful

https://forum.garysgaragemahal.com/Instrument-Lighting-Paint-Testing-tp52526.html

[Jon M]

So I was going to merge the two, I was going to keep the original gauge cluster and install the tach into it with it the tach's printed circuit board. At a glance it looks physically compatible. But I don't know if the internals calculate the inputs in the same way.

[Ford F834]

The diesel tach absolutely will not work with a gas engine. I plugged one in by mistake on my I-6 truck and it shuts off the ignition instantly.

The circuit films are the same (gas vs. diesel), only the 1980 year with the green circuit film or the late F600/F700 with the electric speedometer are different.

That diesel tach for the 6.9 is fairly desirable. You might very well find someone willing to trade you a gas one for it, or be able to sell it and buy one for a gas engine.

Just as a side note, there are low rpm gas tachs from F600/F700 trucks (I am running one on my I-6) but they are very rare. The one you have with the red and yellow warning zones is definitely from a 6.9 diesel and definitely won’t work in a gas truck 😞

[Jon M]

Thanks for this. I suspected as much but felt obligated to be sure. I'll see if I can post it somewhere and get any interest in a trade.

[ArdWrknTrk]

You could probably start with the marketplace here on the forum.

Have a look at completed auctions on eBay for an idea on pricing.

[viven44]

I have a neighbor who had asked me once about installing a diesel tach in his dad's one owner truck. He has a spare tach but I don't know if it is a diesel tach. It might be a gasoline one possibly, and he could use that diesel one if so...

[1986F150Six]

Here is some beneficial reading for the OP:

https://www.garysgaragemahal.com/tachometers.html