1966 4sp vs 1975 ? sp differences. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

vince1 · 04-29-2015, 04:02 PM

I saw a transmission in a 75 P/U with the gear shift stick missing so couldn't tell the number of gears or shift pattern. Looking underneath it looked to me that the transmission, as well as the bell housing might be different. It was cast iron case with the PTO plates, one on each side. Any chance they had 5 sp back then, or what would any other differences be to the original one that came as OE in the 66? Thanks.

'63GENIII · 04-29-2015, 04:23 PM

If you are able to post a pic, it could probably be identified here within minutes. It could be a bunch of different transmissions. Yes there were 5 speeds then. The Clark 5 and the NP540 come to mind. Some of the harder to find ones had OD for 5th.

1963c-10 · 04-29-2015, 04:42 PM

I think the SM420 & SM465 were both available with PTO's also.....

padresag · 04-29-2015, 10:32 PM

the main difference is the input bearing cover is larger in dia on the sm365(75) vs the one on the sm420(66) and will not fit into the earlier bell housing without enlarging the hole or using the later bell housing which means that you will have to install a rear trans cross member to mount the trans.
believe the sm365 is also synchromesh in first
ron

**Captainfab** · 04-30-2015, 12:59 AM

The SM420 4 speed was used up thru the '67 model year. Then starting in '68 the SM465 was used into the 90's I believe in some applications. Padresag is correct in the front bearing retainer. The SM420 has a front bearing retainer that measures 4-13/16" OD whereas the SM465 front bearing retainer measures 5-1/8" OD. Consequently a '68-'72 bellhousing would be needed to upgrade from a SM420 to a SM465. Or you could go with a '73+ bellhousing and add a trans crossmember.

The '75 truck you saw more than likely had the SM465 4 speed.

vince1 · 04-30-2015, 01:35 PM

I might go back and take another look. With the stick out there was only a hose clamp left so probably had some problems there. It's behind a 292 that I would also like but don't think I can afford the time to bring all that stuff home and rebuild it.

04-29-2015, 04:02 PM	#1
vince1 Registered User Join Date: Jan 2013 Location: Calgary Alberta Posts: 1,170	1966 4sp vs 1975 ? sp differences. I saw a transmission in a 75 P/U with the gear shift stick missing so couldn't tell the number of gears or shift pattern. Looking underneath it looked to me that the transmission, as well as the bell housing might be different. It was cast iron case with the PTO plates, one on each side. Any chance they had 5 sp back then, or what would any other differences be to the original one that came as OE in the 66? Thanks.

04-29-2015, 04:23 PM	#2
'63GENIII Registered User Join Date: Sep 2008 Location: San Carlos, Ca. Posts: 3,048	Re: 1966 4sp vs 1975 ? sp differences. If you are able to post a pic, it could probably be identified here within minutes. It could be a bunch of different transmissions. Yes there were 5 speeds then. The Clark 5 and the NP540 come to mind. Some of the harder to find ones had OD for 5th. __________________ Chris '63 k15 long step Vortec 7.4 - L29 Blackbear tune, Five 0 Motorsports injectors, Chris Straub Cam, NV4500, divorced 205 52" front and 63" rear spring swap D44 / 14bff - disc axles Milemarker 9K and 10.5K hydraulic winches 63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29

04-29-2015, 04:42 PM	#3
1963c-10 Registered User Join Date: Nov 2011 Location: fayetteville nc Posts: 10,338	Re: 1966 4sp vs 1975 ? sp differences. I think the SM420 & SM465 were both available with PTO's also..... __________________ 1963 Short bed step side SBW 427 big block and borg warner T-16 HD 3 speed manual http://67-72chevytrucks.com/vboard/s...d.php?t=519869 1963 Short bed fleetside BBW 348 1st gen big block w/Powerglide http://67-72chevytrucks.com/vboard/s...d.php?t=619024 1964 Short bed trailer

04-29-2015, 10:32 PM	#4
padresag Registered User Join Date: Feb 2008 Location: Sidney,b.c. Posts: 4,425	Re: 1966 4sp vs 1975 ? sp differences. the main difference is the input bearing cover is larger in dia on the sm365(75) vs the one on the sm420(66) and will not fit into the earlier bell housing without enlarging the hole or using the later bell housing which means that you will have to install a rear trans cross member to mount the trans. believe the sm365 is also synchromesh in first ron

04-30-2015, 12:59 AM	#5
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,252	Re: 1966 4sp vs 1975 ? sp differences. The SM420 4 speed was used up thru the '67 model year. Then starting in '68 the SM465 was used into the 90's I believe in some applications. Padresag is correct in the front bearing retainer. The SM420 has a front bearing retainer that measures 4-13/16" OD whereas the SM465 front bearing retainer measures 5-1/8" OD. Consequently a '68-'72 bellhousing would be needed to upgrade from a SM420 to a SM465. Or you could go with a '73+ bellhousing and add a trans crossmember. The '75 truck you saw more than likely had the SM465 4 speed. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

04-30-2015, 01:35 PM	#6
vince1 Registered User Join Date: Jan 2013 Location: Calgary Alberta Posts: 1,170	Re: 1966 4sp vs 1975 ? sp differences. I might go back and take another look. With the stick out there was only a hose clamp left so probably had some problems there. It's behind a 292 that I would also like but don't think I can afford the time to bring all that stuff home and rebuild it.



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