Author Topic: Need confirmation on rear end ratio  (Read 2448 times)

Offline jfkelley

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Re: NEED Confirmation of rear gear ratio
« Reply #15 on: December 11, 2020, 12:41:27 AM »
Thanks everyone I’m gonna work on addressing the issues you guys have posted ..I truly appreciate all the help ..This one thing I enjoy about this site is everyone is helpful ..Happy Holiday’s!
1976 Chevrolet 4x4 ,K10,Stepside, 400/350/NP203, 35” BF Goodrich All-Terrain, Factory A/C

Offline JohnnyPopper

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Re: NEED Confirmation of rear gear ratio
« Reply #16 on: December 12, 2020, 03:07:15 PM »
UN-couple your full time 4x4 with a miles marker part-time kit and locking hubs.

Take out the Gunther mechanical fan and install two electrics.

You'll pick up a noticeable amount of horsepower= mileage

I have the same rig, '78
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline jfkelley

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Re: NEED Confirmation of rear gear ratio
« Reply #17 on: December 17, 2020, 03:09:42 PM »
Good Looking truck ! Been looking at the following Mile Marker kit to install ...Thoughts ?

https://milemarker.com/wp-content/uploads/2018/04/503-instructions.pdf

1976 Chevrolet 4x4 ,K10,Stepside, 400/350/NP203, 35” BF Goodrich All-Terrain, Factory A/C

Offline SilverMiner

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Re: NEED Confirmation of rear gear ratio
« Reply #18 on: December 17, 2020, 07:30:45 PM »
Good Looking truck ! Been looking at the following Mile Marker kit to install ...Thoughts ?

https://milemarker.com/wp-content/uploads/2018/04/503-instructions.pdf

Well, you asked -

Converting the NP203 to part-time has had no clear or quantifiable benefits since 1974 when the kits were first introduced. If the 1973 oil embargo had never occurred nobody would have given the NP203 a second thought, and the technology may have even benefited from a second generation of research and improvement. The magazine Pickup Van & 4WD ran repeated tests over the years until their untimely demise in 1983 and could barely measure an increase in fuel mileage using their sophisticated flow meters and meticulous methodology. By 1982 they were explicitly advising readers via the letters column that NP203 conversion kits didn't make economic sense - the rest of the drivetrain would be undriveable long before the gas savings even paid for the kit. Not a way to make advertisers like Doug Nash, MileMarker and others very happy which no doubt contributed to the magazine ceasing in 1983.

And PV4 wasn't alone in pointing out that the emperor had no clothes. Four Wheeler magazine by the late 70's explicitly stated that the maximum mileage gain after the part-time conversion that they could measure was inconsistent but always less than 10%, and even that small amount was difficult to repeat.

The kits themselves are fine and will cause no harm or be unreliable. Older kits like the Doug Nash version required 4WD to be engaged on a regular basis or lubrication issues would cause failure, but the modern kits don't seem to have that problem. Or at least they don't mention it in their instructions.

In my opinion, the NP203 was and is a technological marvel that should be celebrated for what it was designed to do and managed to achieve. The friction loss of the additional drivetrain movement is utterly inconsequential when compared to adding the mass of just two additional passengers. But keep in mind, I'm also an admitted fan of the engineering excellence of Quadrajet carburetors (also hated in the 1970's), so take what I say with a healthy dose of salt.

Online zieg85

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Re: NEED Confirmation of rear gear ratio
« Reply #19 on: December 17, 2020, 07:43:19 PM »
I agree and converted one back in the 80's and found no measurable increase in MPG
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline ehjorten

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Re: NEED Confirmation of rear gear ratio
« Reply #20 on: December 18, 2020, 09:46:39 AM »
Main problem with running a NP203 in its natural form is that you have U-joint half shafts on the front axle and running and turning those front tires on the street all of the time adds a lot of wear and tear to the front end. U-joints run at an angle have an acceleration and deceleration profile that is typical of a U-Joint, so turning isn't smooth on the pavement even with an open front differential. It is fine at small turn angles, but you will feel it jerking around on the pavement at even moderate turn angles.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline jfkelley

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Re: NEED Confirmation of rear gear ratio
« Reply #21 on: December 18, 2020, 02:34:12 PM »
I have an 15” electric fan I had on my 77 Trans Am ..Will that work for the truck ? Or do I need Dual fans ? ..Thanks everyone !

Good Looking truck ! Been looking at the following Mile Marker kit to install ...Thoughts ?

https://milemarker.com/wp-content/uploads/2018/04/503-instructions.pdf
1976 Chevrolet 4x4 ,K10,Stepside, 400/350/NP203, 35” BF Goodrich All-Terrain, Factory A/C

Offline SilverMiner

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Re: NEED Confirmation of rear gear ratio
« Reply #22 on: December 18, 2020, 10:16:47 PM »
I have an 15” electric fan I had on my 77 Trans Am ..Will that work for the truck ? Or do I need Dual fans ? ..Thanks everyone !


As long as your 15" fan worked fine in the Pontiac I'd suspect it will work just as well in the truck. Both had similarly sized engines and radiators. Unless you intend to spend hour upon hour in stop and go desert traffic pulling an overweight trailer, and then I'd suggest something more robust such as the dual fans covering more of the radiator surface area.

Offline VileZambonie

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Re: NEED Confirmation of rear gear ratio
« Reply #23 on: December 19, 2020, 06:00:07 PM »
Main problem with running a NP203 in its natural form is that you have U-joint half shafts on the front axle and running and turning those front tires on the street all of the time adds a lot of wear and tear to the front end. U-joints run at an angle have an acceleration and deceleration profile that is typical of a U-Joint, so turning isn't smooth on the pavement even with an open front differential. It is fine at small turn angles, but you will feel it jerking around on the pavement at even moderate turn angles.

This
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline jfkelley

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Re: NEED Confirmation of rear gear ratio
« Reply #24 on: December 20, 2020, 08:32:08 PM »
I was doing some maintenance routine stuff on the truck today and pulled the thermostat housing and there was Not a thermostat in it , I just Soum the gauge was broken because it never really got hot ..So I put the correct thermostat in it and once it got up to temperature It ran a whole lot better… Adjusted the real drum brakes now stopping a whole lot better also..No hopping in the rear when I brake ..
1976 Chevrolet 4x4 ,K10,Stepside, 400/350/NP203, 35” BF Goodrich All-Terrain, Factory A/C

Offline JohnnyPopper

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Re: NEED Confirmation of rear gear ratio
« Reply #25 on: December 20, 2020, 09:00:34 PM »
Okay, I'll jump in...

Did the NP203 conversion to MM last year, (don't forget the spacers/bearings PULESSSE)

Ditched the mechanical fan, huge difference.

Changed out my read diff from a 3.73:1 to a 3.41:1.

Ditched (for now) my front drive shaft

A

1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline JohnnyPopper

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Re: NEED Confirmation of rear gear ratio
« Reply #26 on: December 20, 2020, 09:19:47 PM »

At 2500 RPM "max torque", I get 15 MPG, going over a 800' hill between my office and home.

I'll post more data when I have a straight shot on level road.

Pretty good for an old box?  I think so... 8)
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline SilverMiner

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Re: NEED Confirmation of rear gear ratio
« Reply #27 on: December 20, 2020, 09:39:00 PM »
I was doing some maintenance routine stuff on the truck today and pulled the thermostat housing and there was Not a thermostat in it , I just Soum the gauge was broken because it never really got hot ..So I put the correct thermostat in it and once it got up to temperature It ran a whole lot better… Adjusted the real drum brakes now stopping a whole lot better also..No hopping in the rear when I brake ..

Good catch on the thermostat - proper operating temperature is a key element in how the GM engineers attempted to achieve the contradictory goals of trying to maximize peak performance for the customer and optimum emissions to keep the government happy.

Knowing that the thermostat had been eliminated suggests the previous owner probably made some other questionable changes as well. You would be well advised to double check the timing, mechanical and vacuum advance as well as the general health and operating condition of the carburetor too. To achieve maximum mileage as stated in your original post these components are critical. Setting the best overall tune of the engine cannot be understated and is generally far cheaper parts wise than messing with transfer cases or axle gearing.

Offline jfkelley

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Re: NEED Confirmation of rear gear ratio
« Reply #28 on: December 21, 2020, 04:53:46 PM »
I’m going to install an electric fan ..What size do you all suggest for everyday driving ?
1976 Chevrolet 4x4 ,K10,Stepside, 400/350/NP203, 35” BF Goodrich All-Terrain, Factory A/C

Offline VileZambonie

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Re: What Size of electric fan should I use for everyday driving
« Reply #29 on: December 22, 2020, 04:18:35 AM »
Did you really edit your original post instead of making a new one?  ::)
,                           ___ 
                         /  _ _ _\_
              ⌠¯¯¯¯¯'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10