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| | | | Joined: Nov 2005 Posts: 1,554 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 1,554 | I looked at the instrument group of my 41 gmc coe yesterday. Something unusual to me was a fixture attached to the speedo group, I was thinking it must be some sort of speed limiter because I thought a Governor would be associated with the carburetor. This device is attached directly to the back of the speedo fitting then the speedo cable hooks to it. It has a cable departing the device going who knows where, maybe the carb. When I got this truck I only got the cab so a lot is unknown.
1941 Chevy"First rebuild - complete!"Follow the story in the DITY1941 GMC resting peacefully 1946/1947 Chevy Street rod on s10 frame complete 1945 GMC panel truck in line for restoration 1941 Plymouth stock complete 1941 GMC COE in restoration processRead his Project Journal1941 Chevy Coe uncertain future resting now
| | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | Sounds like the 2-speed rear gear ratio adaptor, used to keep the speedometer in calibration when shifting between the two different rear gear ranges. I've only see vacuum or electrically shifted units... Mike B 
Last edited by Mike B; 08/18/2024 7:00 PM. Reason: spelling
| | | | | Joined: Feb 2004 Posts: 29,773 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,773 | Yes, that's a ratio changer for the speedometer. If you watch the speedo during a rear end shift, you'll see the needle change positions as soon as you move the splitter knob- - - -even before the differential actually makes the shift.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Feb 2016 Posts: 1,985 'Bolter | | 'Bolter Joined: Feb 2016 Posts: 1,985 | The mechanical ratio gearbox was connected to the dash mounted rear axle range knob. On my truck, the range selector is mounted on the gearshift lever and a cable runs down to the vacuum switch on the transmission. The speedo ratio gearbox is vacuum operated from that vacuum switch.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
| | | | | Joined: Oct 2023 Posts: 74 'Bolter | | 'Bolter Joined: Oct 2023 Posts: 74 | Vacuum-operated ratio changer for a two speed axle. Sometimes removed or plugged off because the actuator diaphragm rots away and causes a vacuum leak. I repaired mine by replacing the actuator with a carbureator choke actuator from a Honda generator.
Last edited by Puffie40; 08/23/2024 5:42 PM.
| | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | Vacuum-operated ratio changer for a two speed axle. Sometimes removed or plugged off because the actuator diaphragm rots away and causes a vacuum leak. I repaired mine by replacing the actuator with a carbureator choke actuator from a Honda generator. Can you share the Honda part number? Pictures of the repaired unit would be nice also!  Mike B | | | | | Joined: Nov 2005 Posts: 1,554 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 1,554 | Thanks folks, I won't be using this so if anyone wants it, just pay shipping and it's yours. Dave
1941 Chevy"First rebuild - complete!"Follow the story in the DITY1941 GMC resting peacefully 1946/1947 Chevy Street rod on s10 frame complete 1945 GMC panel truck in line for restoration 1941 Plymouth stock complete 1941 GMC COE in restoration processRead his Project Journal1941 Chevy Coe uncertain future resting now
| | | | | Joined: Sep 2009 Posts: 5,825 Gearhead, Stovebolt Tech and Parts Tracker, Mod for Swap Meet and GTT | | Gearhead, Stovebolt Tech and Parts Tracker, Mod for Swap Meet and GTT Joined: Sep 2009 Posts: 5,825 | Dave - Post an ad in the Swap Meet Freebies forum to offer this 2 speed gear ratio speedometer adapter to fellow Bolters. Shipping costs don't affect its "Freebie" status! If you need a little help with that, send me a PM and I can try and assist. 
~ Dan 1951 Chevy 3 window 3100Follow 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)
| | | | | Joined: Oct 2023 Posts: 74 'Bolter | | 'Bolter Joined: Oct 2023 Posts: 74 | Can you share the Honda part number?
Pictures of the repaired unit would be nice also! pix The part number I found was Honda 16400-ZE2-704, But you can get Chinese clones of the entire choke assembly for a fraction of the cost of OEM if you are willing to strip off the extra parts. I made a new thread showing some pictures of the inside of one of these gearboxes as well as some pictures of the actuator repair.
Last edited by Peggy M; 08/25/2024 2:45 PM. Reason: edit quote
| | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | Thanks Puffie! Mike B | | |
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