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New Process NP435 Versus Muncie SM465 Noise


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I don't doubt that there have been umpteen NP435 vs SM465 comparisons, and I've read quite a few this last few days while trying to Google up the answer to this question. I've also posted the question on a number of truck forums, all with no luck. I'm hoping that someone who's had experience with both might be able to offer some insight. Given the choice between the NP435 and the SM465, both in good working order, is one or the other typically noisier? Old-style truck transmissions aren't the quietest on the highway, I know, but I'm just wondering if there tends to be any difference in noise level between the two.

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  • Moses Ludel changed the title to New Process NP435 Versus Muncie SM465 Noise
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vykkagur...I've run an NP435 in a Jeep CJ-5 (4.2L Jeep engine with a Dodge truck transmission) and stock SM465 transmissions in GM full-size trucks with V-8 engines and an FJ40 Land Cruiser with a stroker Chevy 383 V-8 and SM465.  In my experience, the NP435 and SM465 produce similar and not highly objectionable noise levels. 

"Noise", of course, is subjective, it depends upon just how quiet you expect a cast iron, large gear set transmission to be.  The Older SM420 Muncie, especially with a compound 1st gear ratio of 7.05:1, was noisier all around.  The NP435 or SM465 is generally picked for its compound first gear ratio, superior stamina and longevity—not the noise level.

Arguably, having rebuilt these transmissions to factory specifications, I would say that higher noise levels usually have more to do with bearing and gear tooth wear.  Neither the NP435 nor the SM465, each with helical 2-3-4 speed synchromesh gears, is characteristically a "whiner".  Each of these transmissions was "modern era" with synchronizers.  (The NP units use a unique synchromesh hub assembly design.)  Vintage truck transmissions with straight cut gear teeth (Clark and other "spur gear" designs) make plenty of noise.

Are you running this transmission in a Jeep CJ?  Here, I would base my choice on the length of the transmission, weight and the cost of adaptation to the transfer case.  Weight can be a deal breaker on some transmission conversions although I have swapped hefty NV4500 units into an AMC/Jeep eighties CJ and an FJ40.  It all depends upon the ratios desired and whether you want or need a "bulletproof" transmission.

I am partial to the SM465.  GM used these units with great success in 1/2-ton through 1-ton capacity trucks.  The NP435 also has a high load capacity or "torque rating" although I have never seen torque figures for these units.  Each is iron cased with a PTO outlet.  4th is direct, compound low is non-synchromesh and requires stopping for a proper downshift.  Most ratio combinations allow starting off in synchromesh 2nd gear when the vehicle is unloaded...Ratios may influence your choice, compare them and know the ratios of a donor transmission.

Here is a snapshot of ratios and details for all three transmissions (data courtesy of Novak Adapters). Each transmission has an iron case.  Note that the SM465 is heavier and "beefier".  Ratios are correct for most recycled transmissions that you will find.  Before buying a unit, test the transmission to see what ratios are in place:

The Novak Guide to the New Process 435 Transmission The Novak Guide to the GM Muncie SM420 TransmissionThe Novak Guide to the GM Muncie SM465 Transmission

If noise is a large concern, an HD NV4500 or NV5600 would be "noisier" than these three transmissions.  All of these transmissions are heavier duty units with larger gear mass.  This is a recipe for noise.

To offset the noise, you have many options for insulating above and below the floorboard...

Moses 

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This is exactly the info I've been looking for, Moses. Many thanks!

Weight, length, ratios, parts availability and price, adapters available, all these things I could find out online, but this one question has eluded me for weeks, until now. With nothing to chose between the two for noise, my decision can focus on other factors. Both these boxes are relatively bullet-proof, both will fit within the length restrictions, and both are generally available at reasonable prices in my area. The decision may come down simply to which one I can find in the best condition for the best price at the time.

The background here, is that I'm planning out my new project, a replacement for my current vehicle. This to be my sole daily driver, not a weekend hobby. Our climate, my location, and my work responsibilities make a 4WD pretty much a necessity, but year-round it will do many hours of pavement driving, so I needed to consider noise, if there was a clear-cut difference. You've removed that concern for me. Thank you again!

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You're welcome, vykkagur...Since you won't have overdrive with either transmission (4th is 1:1 ratio), select your axle ratios and tire diameter accordingly.  If you're sold on the NP435 and SM465 rather than an NV4500, which has overdrive, you do have the compound low reduction 1st gear.  This enables somewhat "taller" (numerically lower) axle ratios. 

What is the model/chassis, tire diameter, axle ratio(s) and engine?  If you plan to daily drive, fuel efficiency is important.  Engine rpm at highway cruise speed will directly impact fuel efficiency.

Moses

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