SM 420 / SM 465 Difference - The 1947 - Present Chevrolet & GMC Truck Message Board Network

72Bob · 12-30-2003, 02:59 AM

I have a 4 speed from a 68 Chev 4x4 I am going to sell, but I don't know what kind of tranny it is. How can I tell? And what tranny is better?

1969 GMC · 12-30-2003, 05:00 AM

SM420 has reverse toward the driver and down.
SM465 has reverse toward the passenger and down.

Parts availability is most likely better for the 465 because it was used until the early 90's in trucks. 420 has a bit lower of a creeper gear, and the unit itself is a little smaller than the 465. both are strong.

HeavyK20 · 12-30-2003, 09:06 AM

SM420 has one PTO Cover
SM465 has two PTO Covers

These covers are about 4"x4" and are located towards the bottom of the housing.

**kwmech** · 12-30-2003, 11:50 PM

Quote:

Originally posted by HeavyK20
SM420 has one PTO Cover
SM465 has two PTO Covers

These covers are about 4"x4" and are located towards the bottom of the housing.

Also the 420 is about 10'' long and the 465 is about 12'' long but the pto covers are a dead give away.

blink32 · 12-31-2003, 09:59 AM

I have an add-on question to this. After reading this thread I figure I most likely have an SM465 tranny (I'll check for dual covers tonight). I've got a 76 K10 with 4spd , reverse being back and towards the passenger. My question is, how can I used this information to purchase an aftermarket shifter setup? I did some research (thanks www.73-87.com ) and I was pretty sure that the Trans is a Muncie M20 (or MM4). But I haven't found any specific shifters for this. I did find (for an example) ClassicIndustries lists a shifter "for GM Muncie trannies from 69 and later" but I'm not going to order something that might not work. Thanks for the help. This site is proving to be a great resource.

Mike C · 01-01-2004, 12:59 AM

There are no aftermarket shifters for the SM465. M20 is GM's code for a wide ratio 4 speed transmission. In the passenger cars, it could have either been a Saginaw iron case box or a Muncie aluminum case. Either way they are external shifter type transmissions vs. the trucks internal rail shifter. There is no need for a performance shifter on the truck trans as its internal mass and design prevent it from being driven like one! 1967 was (supposedly) the only year for the married SM420 box, but some 68's may have had it. Regardless, 69 and up 4 speed 4x4 should be the SM465. I don't think the close ration NP435 could be had in 4x4 configuration.

blink32 · 01-01-2004, 06:51 PM

I was just looking for something to tighten up the shifts, not nessicarly (sp?) for "perfomance".

72Bob · 01-02-2004, 12:56 AM

Thanks ya'll for the help, looks like I got a SM465.

12-30-2003, 02:59 AM	#1
72Bob Registered User Join Date: Sep 2002 Location: Burlington, WA Posts: 298	SM 420 / SM 465 Difference I have a 4 speed from a 68 Chev 4x4 I am going to sell, but I don't know what kind of tranny it is. How can I tell? And what tranny is better? __________________ 1971 GMC Sierra 3/4 Ton 4x4 1972 Chevrolet SWB 4x4 RIP LeRoy

12-30-2003, 05:00 AM	#2
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	SM420 has reverse toward the driver and down. SM465 has reverse toward the passenger and down. Parts availability is most likely better for the 465 because it was used until the early 90's in trucks. 420 has a bit lower of a creeper gear, and the unit itself is a little smaller than the 465. both are strong. __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

12-30-2003, 09:06 AM	#3
HeavyK20 Registered User Join Date: Dec 2001 Location: New Richmond, WI Posts: 547	SM420 has one PTO Cover SM465 has two PTO Covers These covers are about 4"x4" and are located towards the bottom of the housing. __________________ Eric 1969 K20, 465/205 package

01-01-2004, 12:59 AM	#6
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,727	There are no aftermarket shifters for the SM465. M20 is GM's code for a wide ratio 4 speed transmission. In the passenger cars, it could have either been a Saginaw iron case box or a Muncie aluminum case. Either way they are external shifter type transmissions vs. the trucks internal rail shifter. There is no need for a performance shifter on the truck trans as its internal mass and design prevent it from being driven like one! 1967 was (supposedly) the only year for the married SM420 box, but some 68's may have had it. Regardless, 69 and up 4 speed 4x4 should be the SM465. I don't think the close ration NP435 could be had in 4x4 configuration. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

01-02-2004, 12:56 AM	#8
72Bob Registered User Join Date: Sep 2002 Location: Burlington, WA Posts: 298	Thanks ya'll for the help, looks like I got a SM465. __________________ 1971 GMC Sierra 3/4 Ton 4x4 1972 Chevrolet SWB 4x4 RIP LeRoy

12-31-2003, 09:59 AM	#5
blink32 Registered User Join Date: Dec 2003 Location: OTR Posts: 338	I have an add-on question to this. After reading this thread I figure I most likely have an SM465 tranny (I'll check for dual covers tonight). I've got a 76 K10 with 4spd , reverse being back and towards the passenger. My question is, how can I used this information to purchase an aftermarket shifter setup? I did some research (thanks www.73-87.com ) and I was pretty sure that the Trans is a Muncie M20 (or MM4). But I haven't found any specific shifters for this. I did find (for an example) ClassicIndustries lists a shifter "for GM Muncie trannies from 69 and later" but I'm not going to order something that might not work. Thanks for the help. This site is proving to be a great resource.

01-01-2004, 06:51 PM	#7
blink32 Registered User Join Date: Dec 2003 Location: OTR Posts: 338	I was just looking for something to tighten up the shifts, not nessicarly (sp?) for "perfomance".

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