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

roger0080 · 12-13-2022, 12:32 PM

Attached are two pages from the parts manual for a 1972 T350/NP205.

You could have two different driven-gear/adaptor combinations for the 3.07 depending on which H78 tires you had (Highway or On/Off-Road).

In your picture showing the "1.3000J" stamped in the adaptor, I presume that the "J" refers to code "J", Adaptor 3950350 as shown in the parts table?

It would have been helpful if they had a column in the table listing the ratio for each adaptor, i.e. 1.3000

After seeing this, I have to go back and look at my 71 K20 that I swapped out my T350/NP205 w/4.10 from a '77 SWB CH465/NP205 gear ratio of ?. I put an adaptor on that and got it back to pretty close but the speedo is still off. I should be able to use the old T350/NP205 speedo gear w/o the adapter according to the parts manual table. It's winter here now so I'll have to look at that in the spring.

Summary: One needs the correct driven-gear -and- correct adaptor (if necessary) for your gear ratio. Sigh. See attached pic's.

Attachment 2238214

12-13-2022, 12:32 PM	#6
roger0080 Registered User Join Date: Nov 2000 Location: Carver County, Minnesota, USA Posts: 627	Re: Factory NP205 speedometer setup Attached are two pages from the parts manual for a 1972 T350/NP205. You could have two different driven-gear/adaptor combinations for the 3.07 depending on which H78 tires you had (Highway or On/Off-Road). In your picture showing the "1.3000J" stamped in the adaptor, I presume that the "J" refers to code "J", Adaptor 3950350 as shown in the parts table? It would have been helpful if they had a column in the table listing the ratio for each adaptor, i.e. 1.3000 After seeing this, I have to go back and look at my 71 K20 that I swapped out my T350/NP205 w/4.10 from a '77 SWB CH465/NP205 gear ratio of ?. I put an adaptor on that and got it back to pretty close but the speedo is still off. I should be able to use the old T350/NP205 speedo gear w/o the adapter according to the parts manual table. It's winter here now so I'll have to look at that in the spring. Summary: One needs the correct driven-gear -and- correct adaptor (if necessary) for your gear ratio. Sigh. See attached pic's. Attachment 2238214 Attached Images __________________ 72 Chev C-10 90% restored (former AZ truck) ... 71 Chev K-20 Cheyenne my vacation crusier... 72 Chev C-10 Now retired and striped after many faithful miles... 72 GMC 1500 Retired to the junk yard after bought new in '71... Last edited by roger0080; 12-13-2022 at 01:18 PM.



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