NP205 speedometer gearing - The 1947 - Present Chevrolet & GMC Truck Message Board Network

87Skier · 01-27-2016, 02:55 AM

Need help with my NP205 transfer case. It's in a 1972 GMC Jimmy and the speedometer reads about 42 mph when I'm actually going 60 mph.

Do I need to buy just gear on the end of the cable or do I need to buy the gear on the output shaft as well? Thanks.

Orange Crate · 01-27-2016, 08:46 PM

That's a big discrepancy, how did it get like that? Here are two combo's that I have. Notice that the red gear has splines on the inside so make sure your replacement matches what you have. To change the ratio I am pretty sure you need to change both as a set, maybe someone can chime in here to confirm that. Also the red gear is taller and does not need a spacer shown in the second pic. The red gear does not rely on the torque of the output yoke to hold it in place either. One of these is an "H" gear set and one is an "M" gear set but I just don't have that written down which is which. I did write down the ratio as 3.1:1 for the red and 2.6:1 for the white. Anyway, it's just information.....

87Skier · 01-27-2016, 10:55 PM

That's what I thought. I figured both had to be replaced but I had heard a lot of talk about just the metal gear on the outside.

Not really sure how it came to be that way. As far as I can tell it has factory 3.07 gears and the original NP205. I am running a significantly bigger tire than stock, but I don't think that would change it that much.

'63GENIII · 01-28-2016, 12:17 AM

It may be easier to get a speedometer correcting "box" for lack of the proper terminology. There are speedometer companies that make the correction "boxes that attach in between your T case and speedometer cable and adjust for the error. I have the same issue with my 35s and the speed being off by 15 or so MPH.
If Im not mistaken, the steel drive gear is a Dodge unit and is kinda hard to find. The plastic gear was used on GM and Dodge and can be found fairly easy. The driven gears were like trying to find hen's teeth though. I had to buy a complete output housing just to get the driven gear for the 205.

'63GENIII · 01-28-2016, 12:25 AM

So I think I stand corrected. I just looked up driven gear and theres a few on evil bay 19t and 20t. For reasonable $. Theres also a few different drive gears as well. Lastly, theres one of those "correction boxes" too.

I saw a listing for a steel GM no spline drive gear too.

In other words, just disregard my first post. LOL

Orange Crate · 01-28-2016, 04:20 PM

There are some good parts and such here:

http://www.transmissioncenter.net/sp...n_______va.htm

01-27-2016, 02:55 AM	#1
87Skier Registered User Join Date: Mar 2014 Location: Corvallis, OR Posts: 715	NP205 speedometer gearing Need help with my NP205 transfer case. It's in a 1972 GMC Jimmy and the speedometer reads about 42 mph when I'm actually going 60 mph. Do I need to buy just gear on the end of the cable or do I need to buy the gear on the output shaft as well? Thanks. __________________ 1972 GMC Jimmy Custom 4.8L (L20)/6L90E/NP205 1989 Chevy Suburban V2500 350/Turbo 400/4.11 gears 1996 Chevy Suburban K1500 350/4L60E

01-27-2016, 08:46 PM	#2
Orange Crate Registered User Join Date: Feb 2011 Location: Under the Truck Dreaming Posts: 759	Re: NP205 speedometer gearing That's a big discrepancy, how did it get like that? Here are two combo's that I have. Notice that the red gear has splines on the inside so make sure your replacement matches what you have. To change the ratio I am pretty sure you need to change both as a set, maybe someone can chime in here to confirm that. Also the red gear is taller and does not need a spacer shown in the second pic. The red gear does not rely on the torque of the output yoke to hold it in place either. One of these is an "H" gear set and one is an "M" gear set but I just don't have that written down which is which. I did write down the ratio as 3.1:1 for the red and 2.6:1 for the white. Anyway, it's just information..... Attached Images __________________ 72 K20 Custom Camper, D60, 14BFF, full roller 406 TPI w custom built ECU and yes..it has tow hooks...and a 5 speed

01-27-2016, 10:55 PM	#3
87Skier Registered User Join Date: Mar 2014 Location: Corvallis, OR Posts: 715	Re: NP205 speedometer gearing That's what I thought. I figured both had to be replaced but I had heard a lot of talk about just the metal gear on the outside. Not really sure how it came to be that way. As far as I can tell it has factory 3.07 gears and the original NP205. I am running a significantly bigger tire than stock, but I don't think that would change it that much. __________________ 1972 GMC Jimmy Custom 4.8L (L20)/6L90E/NP205 1989 Chevy Suburban V2500 350/Turbo 400/4.11 gears 1996 Chevy Suburban K1500 350/4L60E

01-28-2016, 12:17 AM	#4
'63GENIII Registered User Join Date: Sep 2008 Location: San Carlos, Ca. Posts: 3,048	Re: NP205 speedometer gearing It may be easier to get a speedometer correcting "box" for lack of the proper terminology. There are speedometer companies that make the correction "boxes that attach in between your T case and speedometer cable and adjust for the error. I have the same issue with my 35s and the speed being off by 15 or so MPH. If Im not mistaken, the steel drive gear is a Dodge unit and is kinda hard to find. The plastic gear was used on GM and Dodge and can be found fairly easy. The driven gears were like trying to find hen's teeth though. I had to buy a complete output housing just to get the driven gear for the 205. __________________ Chris '63 k15 long step Vortec 7.4 - L29 Blackbear tune, Five 0 Motorsports injectors, Chris Straub Cam, NV4500, divorced 205 52" front and 63" rear spring swap D44 / 14bff - disc axles Milemarker 9K and 10.5K hydraulic winches 63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29

01-28-2016, 12:25 AM	#5
'63GENIII Registered User Join Date: Sep 2008 Location: San Carlos, Ca. Posts: 3,048	Re: NP205 speedometer gearing So I think I stand corrected. I just looked up driven gear and theres a few on evil bay 19t and 20t. For reasonable $. Theres also a few different drive gears as well. Lastly, theres one of those "correction boxes" too. I saw a listing for a steel GM no spline drive gear too. In other words, just disregard my first post. LOL __________________ Chris '63 k15 long step Vortec 7.4 - L29 Blackbear tune, Five 0 Motorsports injectors, Chris Straub Cam, NV4500, divorced 205 52" front and 63" rear spring swap D44 / 14bff - disc axles Milemarker 9K and 10.5K hydraulic winches 63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29

01-28-2016, 04:20 PM	#6
Orange Crate Registered User Join Date: Feb 2011 Location: Under the Truck Dreaming Posts: 759	Re: NP205 speedometer gearing There are some good parts and such here: http://www.transmissioncenter.net/sp...n_______va.htm __________________ 72 K20 Custom Camper, D60, 14BFF, full roller 406 TPI w custom built ECU and yes..it has tow hooks...and a 5 speed



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