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Joined: Nov 2005
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'Bolter
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Has there ever been a Back up light swich for sm420 4 speed? Asking for my 58 Viking 60. Thanks for any knowledge or sources.


The 1958 TRI-FECTA
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'Bolter
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yes the last year of production 196? and or http://kinzers.com/don/landcruiser/sm420rev_switch/

1


1953 Chevy 3100
261 and SM420
53Chevy 3100
1953 Mack Firetruck
1972 Porsche 911
1986 Honda Goldwing
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There was a kit with a switch and some little parts that attached to the shifter and top of the tower of the older models. I remember seeing pictures and discussion here or the old GMC forum.


1951 GMC 250 in the Project Journals
1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup
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Here is a link explaining how to add a back-up switch to an SM420. I had one of the factory kits, but like the set up described in the link much better.

http://s844.photobucket.com/user/ma...20PM_zpsfsnbzrj6.png.html?sort=2&o=0

Matt

Last edited by Maybellene; 11/15/2016 4:45 AM.
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I just bought a rebuilt sm420 tranny that came out of a '65 pickup that has the backup light switch attachment.


1949 Dodge Coronet
1955 2nd Chevy 4400 1.5 ton
1955 2nd Chevy 3100 1/2 ton
1955 2nd Chevy 3100 1/2 ton
1957 Chevy 5400 LCF 2 ton
1966 Dodge D100 Sweptline
1968 Chevy P20 stepvan
1969 GMC LWB pickup
1972 GMC Sprint
1974 CP30 shorty bus

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Bubba - Curmudgeon
Bubba - Curmudgeon
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"The last year of the SM420 (1967) had a backup light switch installed in the top cover to meet that year's federal mandates." ( From Novak Transmission GM Muncie SM420 Transmission page )

Another retro-fit description.

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Big Bolt Forum Moderator
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I drilled the top of mine and installed one like Maybellene suggested. Works great! The only thing I am going to add is a 2nd switch somewhere so I can turn them on and leave it running with the park brake on. That way, I can have them on when hooking up a trailer or working back there behind the truck.


Mike
1955 Chevy 6400 ex-flatbed (no bed now!) sold September 2023
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1958 Chevy 6400 flatbed W/dump
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1959 Chevy Suburban Owned for almost 20 years, Daily Driver -- sold May 2016
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Wire in a timer to the bypass switch so you don't forget and leave it on to annoy drivers behind you- - - -maybe 10 minutes or so before switching off automatically.
Jerry


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If you use a 7 wire connector for your trailer, you can get a work light that plugs into the connector.


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1954 1/2 ton 235 4 speed
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The set up Grigg is talking about shows up in my 1957 Chevrolet Accessory Installation Manual. The switch attaches to a new gear shift lever retaining cap and the light switch lever attaches to the gear shift shaft. When the trans is put in reverse the switch lever pushes down on the switch button turning on the lights. The part number is 987454. I'm not sure what year it was introduced, but it would work on ALL SM-420 transmissions.

Mike B smile


Mike Boteler

1956 Chevy 3100 Resto Rod
1956 8400 Wrecker w/Holmes 525
1956 9200 Tractor w/Allison Automatic
1952 Willys M38 Army Jeep
1953 Willys M38A1 Fire Jeep
1978 Jeep CJ-5 Navy Jeep
1984 Jeep CJ7
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Thanks guys. Now I need to locate one. ( down the list now til I get brakes working better ) pete


The 1958 TRI-FECTA
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Crusing in the Passing Lane
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Great photos, when tapping the hole, might want to test fit the switch occasionally, since if too deep, the rigid part of the switch will rest on the shift rail, negating the switch function.

ED


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.

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