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#1 |
Registered User
Join Date: Jun 2012
Location: 30 miles east of nowhere
Posts: 70
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Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
Well the title says it all guys. Im was told a c-30 driveshaft would work but id like an exact fit. Its a fleetside bed too. So what other transmissions would work?? Thanks a ton guys!!!!!
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#2 |
Registered User
Join Date: Aug 2011
Location: Six-Mile, SC
Posts: 153
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
if i were you i'd find a good overdrive transmission to swap in, and have the driveshaft you have cut and balanced at a driveline shop. i swapped a t5 to my 250 and not a single regret getting rid of the sm420. the only thing about the sm420 is you can't break it and if you haul heavy the granny is nice.
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#3 |
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Join Date: Jun 2012
Location: 30 miles east of nowhere
Posts: 70
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
This truck is a heavy hauler. Thats why i need to keep the 420. So what would ypu reccomend for a driveshaft?? I would like to avoid custom making one but if i have to its a last resort. Thanks!!!
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#4 |
Registered User
Join Date: Aug 2011
Location: Six-Mile, SC
Posts: 153
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
i'd go digging through junknyards honestly. measure from the center of the length you'll need and start crawling under some truck to measure. i'd start with 70s and 80s chevy trucks because i believe its the same u-joint.
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#5 |
Senior Member
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Location: Tucson, AZ USA
Posts: 7,268
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
Are you sure you have a 420? Their last year was '67.The SM465 came into production in 1968. They are very similar -- both bombproof, but the 420 is some few inches shorter. Both have the Granny gear. On the 420, Reverse is toward the driver, on the 465 Reverse is on the other side toward the passenger. Gearing on the 420 is slightly lower in 1-2-and 3rd gears. 4th is 1:1.
A PO may have put in an SM 420, but it's not usual for a '69. A straight drive shaft should work in a C/10 application. What length is your truck?
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
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#6 |
Registered User
Join Date: Jun 2012
Location: 30 miles east of nowhere
Posts: 70
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
Im replacing my Saginaw 3 speed with the 420 my truck is a fleet side so it has the 8 ft box on. So will a driveshaft from a C-30 work??
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#7 |
Registered User
Join Date: Aug 2011
Location: Six-Mile, SC
Posts: 153
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
if yours is a longbed you have the two piece drive shaft. put the transmission in and bolt the rear half of the driveshaft you have in and measure center of u joint on the trans to the center of the u joint on the rear driveshaft. any difference should probably be made up with the slip yoke.
oh and sm420 granny gear is lower than the sm465, also the sm420 doesn't have a synchroed first
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#8 |
Senior Member
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Location: Tucson, AZ USA
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
The 465 doesn't have Synchro in 1st either.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
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#9 | |
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Join Date: Jun 2012
Location: 30 miles east of nowhere
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
Quote:
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#10 |
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Join Date: Jun 2012
Location: 30 miles east of nowhere
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
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#11 |
Registered User
Join Date: Jun 2012
Location: 30 miles east of nowhere
Posts: 70
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
Ok so the c-30 drive shaft won't work? If not where Springer abstinence drive shaft and how much do the run?? Thanks! - Sam
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#12 |
Registered User
Join Date: Jun 2012
Location: 30 miles east of nowhere
Posts: 70
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
Stupid auto correct lol cant stand that phone sometimes. Meant to say if the c-30 drive shaft wont work where do I get one that does?
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#13 | |
Senior Member
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Location: Tucson, AZ USA
Posts: 7,268
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
Quote:
Anyway good luck.
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Every 25 years I like to rebuild that 292, whether it needs it or not. |
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#14 |
Junior Member
Join Date: Dec 2006
Location: Southeast Missouri
Posts: 2,436
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
I hope you got the bell housing with the SM-420 since the hole in the bell housing for a SM-420 is the correct size to re-enforce the front of the SM-420 tranny.
I think the bell housing hole for a SM-420 is smaller than a bell housing for later manual transmissions.
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'67 Chevy C-20 short stepper - build complete, 454/SM-465. '75 C-30 Single Cab DRW-350 small block/NP-435. '77 GMC-6500 Dump Truck, 427 Tall Deck. '92 GMC K-3500 Duallie, 454/4L80E. |
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#15 | |
Senior Member
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Location: Tucson, AZ USA
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
Quote:
The later bellhousing: [GM5] p/n:3925505, has an I.D. of 5-1/8" and works with the SM465, and perhaps other later transmissions. 1968, I think, is possibly the start of the timeline for 3925505, with 3815891 being used thru the '67 model year run. Exceptions being Canada and GMC where they tended to use up the older parts until changing out.
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Every 25 years I like to rebuild that 292, whether it needs it or not. Last edited by '68OrangeSunshine; 07-02-2013 at 06:51 PM. |
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#16 |
Registered User
Join Date: Jun 2012
Location: 30 miles east of nowhere
Posts: 70
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Re: Puttin a SM 420 transmission behind a 1969 gmc 292 2wd what driveshaft to use??
I looked at the bellhousing and it checked out to fit the SM420. Ok so what do I need to use for a driveshaft???? Im on a deadline to get a drive shaft. What will work??? Thanks!!!
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