Whats this part on my speedo cable (NP205) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

suburban99 · 11-20-2016, 02:22 PM

Looks to be some kind of a conversion unit..truck is in MPH and I am in Canada. Could it be that this is an old school MPH/KMH convertor? Truck has 35's and at 100KMH speedo says 50 mph..at 120 KMH it reads 60 MPH on speedo...It's leaking that's why I ask. (72 K10)

**Stocker** · 11-20-2016, 02:39 PM

I forget what it's called but yes, that is to correct the speedometer reading. They can also be used to correct the speedo when changing tire size (height) or changing differential gear ratios.

Andy4639 · 11-20-2016, 02:40 PM

Inline-Gear reduction is what I think it is from my old memory.

**jocko** · 11-20-2016, 04:02 PM

stewart warner made them among others. primary purpose is to correct the speedo due to a change in something - tires size as pointed out, etc. But you posed something I hadn't thought of before - wonder if that was common piece for an oconus truck for kmph. There weren't any kmph speedo faces were there? I've got one of these lying around somewhere, but it leaks like crazy, ha.

Orange Crate · 11-20-2016, 04:39 PM

You can still purchase those here if you need to:

https://transmissioncenter.net/?swoo...edometer-gears

Bigdav160 · 11-20-2016, 06:53 PM

Speedo ratio adapter

Orange Crate · 11-21-2016, 12:45 PM

If you take a look at the link I posted there is a speed adapter that is made for converting a MPH speedo to a KPH. It is a 61% ratio so that your speedo needle will be at 100 when driving at 100 KPH (62 MPH). 120 KPH would look cool in a video because the label would still be the same (MPH). Who has ever done 120 MPH in our trucks?

**Dieselwrencher** · 11-21-2016, 04:43 PM

I'm pretty sure all the 4x4 67-72s had these on them to correct the speedo readings. There for a while they were really hard to a hold of.

MagmaJct · 12-16-2016, 09:05 PM

I know this thread is getting up there in age... ...but.

My 71 C10 has one of these on it. The truck belonged to my grandparents until they eventually passed away. From there it was passed down to my uncle who put large balloon-like tires on it.

When he passed away, the truck was passed down to me and I put standard size (according to Discount Tire's computer) radials on it. The Speedometer is off, I forget to what degree.

When I found this device, I'd assumed my uncle had installed it because of the large tires he was running. I removed the device, and found my speedometer/odometer to be off by 20%! Didn't take long before I put it back on.

I used a GPS trip tracker to compare the odometer and speedometer values. This is in the land of MPH!

68 50th · 12-18-2016, 04:32 AM

Those adapters are sold marketed here in Sweden as MPH/KPH adapters. I see they also come in many different gear ratios for other purposes. There are many cars and trucks here imported from US that use them for the MPH/KPH purpose. Trucks that were sold new by GM here did in fact have a KPH speedo from factory, you can see one in my avatar.

100%Chevy · 12-18-2016, 11:05 AM

Yes,they were made and installed by GM.
I have a couple of them NOS in the original boxes.
Mike.

11-20-2016, 02:22 PM	#1
suburban99 Registered User Join Date: May 2014 Location: Mission BC Posts: 452	Whats this part on my speedo cable (NP205) Looks to be some kind of a conversion unit..truck is in MPH and I am in Canada. Could it be that this is an old school MPH/KMH convertor? Truck has 35's and at 100KMH speedo says 50 mph..at 120 KMH it reads 60 MPH on speedo...It's leaking that's why I ask. (72 K10) Attached Images __________________ 1962 C10 Longbox LS 5.3 4L60E----Sold$$ 2014 Ram 4x4 3500 Laramie Diesel..Momma's truck 2015 Ram 4x4 1500 1997 Boxster. 1972 K10 Custom Deluxe LS 6.0 1950 GMC 3100 S10 & LS swapped

11-20-2016, 02:39 PM	#2
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,694	Re: Whats this part on my speedo cable (NP205) I forget what it's called but yes, that is to correct the speedometer reading. They can also be used to correct the speedo when changing tire size (height) or changing differential gear ratios. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

11-20-2016, 02:40 PM	#3
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Whats this part on my speedo cable (NP205) Inline-Gear reduction is what I think it is from my old memory. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

11-20-2016, 04:02 PM	#4
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,976	Re: Whats this part on my speedo cable (NP205) stewart warner made them among others. primary purpose is to correct the speedo due to a change in something - tires size as pointed out, etc. But you posed something I hadn't thought of before - wonder if that was common piece for an oconus truck for kmph. There weren't any kmph speedo faces were there? I've got one of these lying around somewhere, but it leaks like crazy, ha.

11-20-2016, 04:39 PM	#5
Orange Crate Registered User Join Date: Feb 2011 Location: Under the Truck Dreaming Posts: 724	Re: Whats this part on my speedo cable (NP205) You can still purchase those here if you need to: https://transmissioncenter.net/?swoo...edometer-gears __________________ 72 K20 Custom Camper, D60, 14BFF, full roller 406 TPI w custom built ECU and yes..it has tow hooks...

11-20-2016, 06:53 PM	#6
Bigdav160 Registered User Join Date: Apr 2011 Location: Klein Texas Posts: 3,852	Re: Whats this part on my speedo cable (NP205) Speedo ratio adapter __________________ My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe

11-21-2016, 12:45 PM	#7
Orange Crate Registered User Join Date: Feb 2011 Location: Under the Truck Dreaming Posts: 724	Re: Whats this part on my speedo cable (NP205) If you take a look at the link I posted there is a speed adapter that is made for converting a MPH speedo to a KPH. It is a 61% ratio so that your speedo needle will be at 100 when driving at 100 KPH (62 MPH). 120 KPH would look cool in a video because the label would still be the same (MPH). Who has ever done 120 MPH in our trucks? __________________ 72 K20 Custom Camper, D60, 14BFF, full roller 406 TPI w custom built ECU and yes..it has tow hooks...

11-21-2016, 04:43 PM	#8
Dieselwrencher 6>8 Plugless........ Join Date: Sep 2007 Location: Prairie City, Ia Posts: 17,139	Re: Whats this part on my speedo cable (NP205) I'm pretty sure all the 4x4 67-72s had these on them to correct the speedo readings. There for a while they were really hard to a hold of. __________________ Ryan 1972 Chevy Longhorn K30 Cheyenne Super, 359 Inline 6 cylinder, Auto Trans, Tilt, Diesel Tach/Vach, Buckets, Rare Rear 4-link and air ride option Build Thread 1972 GMC Sierra Grande Longhorn 4x4 1972 Chevy Cheyenne Super K20 Long Step side tilt, tach, tow hooks, AC, 350 4 speed 1972 C10 Suburban Custom Deluxe 1969 Chevy milk truck 1971 Camaro RS 5.3 BTR STG3 Cam Super T10 1940 Ford 354 Hemi 46RH Ford 9" on air ride huge project *Tired of spark plugs? Check this out.*

12-16-2016, 09:05 PM	#9
MagmaJct Registered User Join Date: May 2008 Location: Mesa, AZ Posts: 281	Re: Whats this part on my speedo cable (NP205) I know this thread is getting up there in age... ...but. My 71 C10 has one of these on it. The truck belonged to my grandparents until they eventually passed away. From there it was passed down to my uncle who put large balloon-like tires on it. When he passed away, the truck was passed down to me and I put standard size (according to Discount Tire's computer) radials on it. The Speedometer is off, I forget to what degree. When I found this device, I'd assumed my uncle had installed it because of the large tires he was running. I removed the device, and found my speedometer/odometer to be off by 20%! Didn't take long before I put it back on. I used a GPS trip tracker to compare the odometer and speedometer values. This is in the land of MPH! __________________ I own 3 classic vehicles. 1971 LWB C10 Deluxe. 1974 VW Super Beetle. 1971 VW Fastback. The C10 and the Super Beetle run, the Fastback is just not there yet! Please visit my Super Beetle and Fastback profile on TheSamba.

12-18-2016, 04:32 AM	#10
68 50th Senior Member Join Date: Jul 2004 Location: Sweden Posts: 833	Re: Whats this part on my speedo cable (NP205) Those adapters are sold marketed here in Sweden as MPH/KPH adapters. I see they also come in many different gear ratios for other purposes. There are many cars and trucks here imported from US that use them for the MPH/KPH purpose. Trucks that were sold new by GM here did in fact have a KPH speedo from factory, you can see one in my avatar. __________________ Mats.. ---------------------------------------------------- 1971 Cheyenne Super Custom Camper 475CBB/TH400/AC 1992 Silverado Sport Truck 1988 Silverado 2500 Ext Longbed 4x4 2001 GMC Sierra SLT 4x4 1990 Chevrolet K3500 1965 Pontiac Grand Prix 1980 Z 28 350/4-speed/AC/T-top 1980 Camaro Coupe V6/3-speed 1979 Buick Century Wagon

12-18-2016, 11:05 AM	#11
100%Chevy Registered User Join Date: Jun 2008 Location: Moss Point,Ms. Posts: 1,439	Re: Whats this part on my speedo cable (NP205) Yes,they were made and installed by GM. I have a couple of them NOS in the original boxes. Mike.



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