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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
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| | | | Joined: Nov 2006 Posts: 2,544 Shop Shark | | Shop Shark Joined: Nov 2006 Posts: 2,544 | I think that the big GMC trucks with diesels used those | | | | | Joined: Oct 2006 Posts: 1,847 'Bolter | | 'Bolter Joined: Oct 2006 Posts: 1,847 | I heard they did, in the larger trucks, sure would be a generous gesture if you were to let me have that there tach, ya got. (I have been looking for a while) | | | | | Joined: Jun 2009 Posts: 2,201 Shop Shark | | Shop Shark Joined: Jun 2009 Posts: 2,201 | Where did the speedometer cables go to? Wondering why the miles are so far apart. I'm guessing the tach ran off the PTO somehow, that would explain the difference in the odometer readings. | | | | | Joined: Mar 2005 Posts: 1,636 'Bolter | | 'Bolter Joined: Mar 2005 Posts: 1,636 | The motor miles on the tach are different than the miles on the speedometer because many of the pumps were run while the transmission was in neutral.
A few fire trucks ran their pumps while the transmission was in gear. Even then the speedometer cable may have been farther back in the drive line so that it didn't work while the pump was engaged so they added motor miles to the tach to keep up with how much mileage the engine actually had. | | | | | Joined: Aug 2011 Posts: 835 Shop Shark | | Shop Shark Joined: Aug 2011 Posts: 835 | Looks to me like this tach probably is a speedometer, except it has a different scale on the face. So I think you could probably make one pretty easily using a speedometer. The issue would be where to hook it up. I think they were usually connected to the distributor which had a takeoff for the tach.
Kurt | | | | | Joined: Oct 2006 Posts: 40 Wrench Fetcher | | Wrench Fetcher Joined: Oct 2006 Posts: 40 | Most of the gasoline powered fire trucks were dual ignition and have a place on the distributor for a tachometer. The speedometer was attached to the PUMP transmission. When the truck is pumping, the transmission is in high gear unless it is an overdrive trans, then it is pumped with the trans in 1 to 1 gear. There is a large PUMP transmission that is linked in behind the conventional trans. To engage the pump, the pump transmission is engaged and it throws the drive shaft that goes to the rear axle into neutral and it turns a short drive shaft that turns the pump. While the truck is pumping, the speedometer is at idle, but the tachometer is still going. The engines are running pretty hard when the truck is pumping. Never judge a pumper truck by its road miles!
Last edited by c Jason Barnett; 09/02/2012 3:41 PM.
| | | | | Joined: Dec 2001 Posts: 14,522 Moderator: Welcome Centre, Southern Bolters, Legion Hall | | Moderator: Welcome Centre, Southern Bolters, Legion Hall Joined: Dec 2001 Posts: 14,522 | Its been a loooong time but I remember the question of the "AD" guages being in a LaFrance firetruck....yep sure nuff. | | |
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