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Old 03-01-2019, 03:23 AM   #1 (permalink)
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NP203 Speedo Driven Gear

New to the forum. In the middle of restoring a 77 Chevy K10 to factory specs. The NP203 was converted to part-time with an Offroad Marketing kit some years ago (see pic below for those not familiar with this style conversion). Converting it back to full-time 4WD. I obtained a partial NP203 (from differential out including tailhousing and spindle). I was simply going to swap in the diff and reassemble, but decided to take the tailhousing apart to see what kind of condition the oil pump & speedo gears were in - and to check the driven gear tooth count. I will be running 33 inch tires with the TH350 trans and 3.73 rearend. So I really need a 16T driven gear (vs 18T that I have stock). It seems driven gears for the 203 are available from 17T up to 22T, but nothing less than 17T. Very frustrating. I was convinced I will need to add an external converter.

Well upon tearing into the tailhousing I found that the internals are different and also the orientation clocked about 15 degrees different. In the pic the original in on the left (red drive gear) and the new one on the right (yellow drive gear). The most obvious difference is with the speedo driven gear. And guess what? This driven gear is 14T.

Talking to the guys at Offroad Design (where I purchased this part) they tell me the difference in these tailhousing is between a very early design 203 (likely pre-74) and a new design. Seemed logical to me.

So now I went on a search to see if there are 16T driven gears available for this 'early' design 203. After a ton of searching I did actually find a 16T used driven gear. I also found the exact 14T gear in this case with the same part number stamped on it. But it is listed as the part for a 72-93 Dodge NP205. So now I questioning the info I received about the early vs late 203 design. Is the difference really 203 vs 205? GM vs Dodge? Any help is appreciated.
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Last edited by dhenderz; 03-01-2019 at 08:39 AM.
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Old 03-01-2019, 07:57 AM   #2 (permalink)
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A lot of that shit is interchangeable but my have only been used in a particular applicayion.

Afaik, early 203 (73-75) had cast iron tail housings not alum
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Old 03-01-2019, 01:23 PM   #3 (permalink)
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I've spent a fair amount of times in 203s do yourself a favor and just put in a 205, it was an option and a good one .

You can do it now or later, but mark my words, IF YOU KEEP THAT TRUCK, you will do eventually .
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Old 03-01-2019, 02:24 PM   #4 (permalink)
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I've spent a fair amount of times in 203s do yourself a favor and just put in a 205, it was an option and a good one .

You can do it now or later, but mark my words, IF YOU KEEP THAT TRUCK, you will do eventually .
Already in the plan that eventually it will be switched out for a 205. In the meantime this 203 is in good shape and will work fine for the intended purpose. This truck is my daughter's. It's a father, daughter resto project. It will only be used as a fun, weekend cruiser. Doubt it will see more than a few thousand miles per year. But when the day comes that the chain finally goes, I'll swap in a 205 for her.
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Old 03-01-2019, 02:43 PM   #5 (permalink)
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Dodge does use the same speedometer pinions for both the NP203 and NP205. Dodge also only used one of 4 pinions with the NP203 and NP205 but also typically used a converter to match gearing and tire options.

2225026 - 14 Th.
2225027 - 15 Th.
2225028 - 16 Th.
2225029 - 17 Th.
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Old 03-01-2019, 03:28 PM   #6 (permalink)
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I saved a bunch of old weird 203 stuff years ago and threw it in a box, let me see if there is a 16 tooth driven in there .



EDIT: Looked, all I could find is a 17, which is weird considering how many of these I have taken apart for doubler conversions, but it would be easier to buy one than for me to look and maybe never find one that I'm not sure I have .

Last edited by Valley Rock; 03-01-2019 at 03:49 PM. Reason: findings
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Old 03-01-2019, 04:58 PM   #7 (permalink)
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Dodge does use the same speedometer pinions for both the NP203 and NP205. Dodge also only used one of 4 pinions with the NP203 and NP205 but also typically used a converter to match gearing and tire options.

2225026 - 14 Th.
2225027 - 15 Th.
2225028 - 16 Th.
2225029 - 17 Th.
Thanks. Do you recognize the one in the pic I posted as being a Dodge 203 case/speedo? I am still trying to determine exactly what I have. Your part listing does match (14T) exactly what is in the 'new' one (yellow drive gear). This would suggest that the difference is the new one is actually a Dodge 203 vs a GM 203?
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Old 03-01-2019, 05:01 PM   #8 (permalink)
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I saved a bunch of old weird 203 stuff years ago and threw it in a box, let me see if there is a 16 tooth driven in there .



EDIT: Looked, all I could find is a 17, which is weird considering how many of these I have taken apart for doubler conversions, but it would be easier to buy one than for me to look and maybe never find one that I'm not sure I have .
Thanks for taking the time to look. I was able to locate a Dodge 16T used online. Kinda expensive, but I did find one. Now I need to decide exactly what this tailhousing is from and confirm putting on this GM case will be OK. Need to check the speedo cable attachment nut to insure it is the right size/thread. Otherwise I won't be able to attach the GM speedo cable.
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Old 03-01-2019, 06:10 PM   #9 (permalink)
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I know i have 1 203 tail out back and maybe 1 inside. Ill lok in the am. (Leaving work now)
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