Just Curious...

[doubleclutchinweasel]

Curious. Was looking around at tachometers (and cables). Noticed some older mechanical tachometers on other trucks and even on farm tractors. Seemed to be made by the same folks who made the broken one in my R. Maybe Stewart-Warner???

Does anybody know for certain what the ratio is on the OEM tach that would be found on these old Rs or even Bs? 1:1? .5:1? Something else?

[doubleclutchinweasel]

Looks like the tachometer drive is turning 1/2 the speed of the engine. The only tachometers I can find are either 1:1 ratio or .5:1 ratio. So, I'm guessing this is the .5:1! I've found the PAI FTA-0550, as well as the Stewart-Warner 82688 & 82689. I know the S-W units are .5:1ratio. I think the PAI is. None of these has the cool, old-style needle.

My empty tachometer cable sheath is 96" long. But, I can tell it is not original. There are multiple places where a different cable has rubbed various things over the years. And, this sheath has been spliced on the drive end. I guess someone had the wrong threads?

The build sheet shows an 80 or 88" cable. But, there's no way that would work. Looks like the 96 will work, as routed. Or, a 92 might work, if routed to the other side of the intake pipe.

Sure like to see how an original was routed, and the original length. Anybody ever pulled an original cable off an R611?

[thomastractorsvc]

I replaced mine except the gauge I had to add tach drive and a new cable ordered mine from Ballard mack with the fuel transfer pump as mine was incorporated together mine runs up and over the engine along the Radiator support into the fire wall above the steering wheel boot.

[doubleclutchinweasel]

I replaced mine except the gauge I had to add tach drive and a new cable ordered mine from Ballard mack with the fuel transfer pump as mine was incorporated together mine runs up and over the engine along the Radiator support into the fire wall above the steering wheel boot.

What model? How long was the cable?

[thomastractorsvc]

I never measured it but at least 6-7 ft mine is R686ST tack drive just below the injector pump and towards the front.

This is before I changed it

[doubleclutchinweasel]

According to Mack, this truck should use an 88" tachometer cable. I still don't see how. But, I guess I'll measure it out again, and see if it would reach.

[doubleclutchinweasel]

Okay. Put on a new 88" PAI cable (FCC-2975-088) & a new Stewart-Warner 0.5:1 ratio tach (82689).

It's nice to know how fast the old Dog is turning!

It's also nice to know that, whenever I need a speedo, S-W has one that matches this tach. In fact, they have a whole series.

[j hancock]

Looks good!

By the way, you need to put some fuel in the tank. You are running on E.

[doubleclutchinweasel]

Looks good!

By the way, you need to put some fuel in the tank. You are running on E.

Nah. Just another problem! Always reads there. Tried swapping the gage wires, thinking they had not been done when it was switched from pos to neg ground. But, it didn't work at all that way.

I have a precision visual fuel level indicator under the seat!!!

[Maddog13407]

my gauge works and I still have one of those precision yardsticks under the seat also...