Tech Tip #55: Cummins B Series Tachometers

Dr. Diesel
Written by Dr. Diesel


Helpful guide to installing a tachometer in your Cummins B series Diesel

Got a Cummins B series diesel but no tach? Surprisingly, lots of these B Series come out of the factory in truck and industrial applications without tachs. Our Dr. Diesel™ says that running a diesel without a tachometer is like driving at night without headlights. Sure, you can do it, but why? So here’s the skinny:

Parts List

First, pick up the following parts from Cummins:

Description Part No.
Tach Drive DF 9013
Valve Cover, 6 Cylinder 3902605
Valve Cover Gasket 3902666
Filler Cap 3901895
Seal Ring 3902363

From a Stewart Warner dealer, you’ll need:

Tach, 3500 RPM 9CWB994C
Drive Tang B821870
Tach Sender 9CWB106AW

From a speedometer shop, buy a standard speedo cable with .104 drive ends.

Installing Your Tach

Remove the oil filler tube assembly and install the plastic drive unit on the now exposed nut in the gear cover. Install the new valve cover, gasket, filler cap, and seal ring in place of the old filler hole-less valve cover. Hook the speedo drive cable to the drive and the tach sender unit (which can be mounted anywhere). Hook the wiring up between the sending unit and the tack, remembering always that the drive ratio is 0.5:1.

Please call with any questions and of course, we stock Cummins B Series Service Manuals that can be shipped out same-day or e-mailed.


Dr. Diesel
Written by Dr. Diesel
Knowledge is power. Power to build ties to engine users. To build a relationship with our customers, we share with you our 105 years of knowledge in many ways. We have this special section called “Ask Dr. Diesel™” where you can pose questions about engines, transmissions, industrial hand clutches, exhaust scrubbers, etc.