With modern tachs not fitting the original tach mount location in GMC(not Chevy) trucks, an adapter is easily made with a suitable size piece of plastic pipe, most are white, easily painted to match other instruments, lots of options are available, inexpensive.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires. '47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle. '54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed. '55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
....... or, if your 55.2-59 GMC has a factory V8 like mine did you can do it this way.
Get a Sun Supertach II. I found mine at a swap meet for $15 (in 1992).
Remove the chrome bezel from the front of the tach and use a dremmel tool, hand held sander, etc to remove about 1/16" of the OD of the open end of the tach case where you removed the bezel so the tach will slip into the stock GMC bezel. Buy a decal kit for GMC instruments. Use a sharp Xacto knife to cut out the numbers to reface the tach to 4000 rpm (you won't turn the stock GMC [Pontiac] V8 any faster than that). Get some paint from a hobby shop and paint the red tach needle to match the GMC needle color.
The trick is to switch the tach to 4 cylinder mode before installing. 8000 rpm (full scale) in the 4 cylinder mode is the same as 4000 rpm (new full scale) in 8 cylinder mode.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Guys, I have moved this conversation over to the Interiors forum as I think that may be the best place for the topic and further discussion. Both are interesting modernization options. Thanks for sharing.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
