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Torque tube to open shaft conversion
#1342516 Fri Jan 17 2020 01:47 AM
Joined: Nov 2012
Posts: 17
4
New Guy
Hi . My buddy has a 2 ton 53 with a sm420 trans. and an open drive shaft. I have a sm420 set up for a torque tube. Can we change the rear bearing retainer and use my trans as a replacement? His has a parking drum on the rear of the box. Are the output splines the same? Will the PTO bolt up? I guess i'll find out when it gets warm enough to pull his out. His won't stay in 2nd gear . Thanks, Chip

Re: Torque tube to open shaft conversion
47fivewindow #1342567 Fri Jan 17 2020 03:14 PM
Joined: Jun 2011
Posts: 3,455
E
Shop Shark
Novak has 420 rebuild kits.

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.
Re: Torque tube to open shaft conversion
47fivewindow #1342568 Fri Jan 17 2020 03:46 PM
Joined: Feb 2004
Posts: 20,401
H
Boltergeist
Yes, everything ahead of the bearing retainer is the same. I got involved in the conversion recently, but the other way- - - -changing an open driveline 420 to torque tube drive. Do not discard the front universal joint yoke used with the torque tube- - - -it's unique to the 420 transmission, and it's very scarce! The joint cross and the rear yoke are the same as a 1/2 ton, but not the front!
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Torque tube to open shaft conversion
47fivewindow #1342575 Fri Jan 17 2020 05:29 PM
Joined: Jan 2013
Posts: 1,643
S
Shop Shark
Good info to pass on Jerry, I might add that if he plans to retain the parking drum and related appurtenances, of his bigbolt he will need the top loader off the original transmission unless the donor trans has the shaft for the brake handle. I have never seen a fine spline sm420 but a couple late models have them.Also even the sm420s found in 1/2 ton had a side cover pto provision that is identical. Basically sm420 from 1/2 tons on up to 2 tons are identical sans the rear bearing cover and ujoint for the enclosed driveshaft, and top cover for the hand brake.

Like Jerry says save the yoke and bell type rear bearing cover found in 1/2 and 3/4 ton trucks pre 55, getting hard to find.

Last edited by sstock; Fri Jan 17 2020 05:36 PM.

1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
https://www.youtube.com/watch?v=Bli...n05i04t1aokgm4p04jiwgffwhyyih5xbk0h00410
1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration
Re: Torque tube to open shaft conversion
47fivewindow #1342732 Sat Jan 18 2020 05:49 PM
Joined: Nov 2012
Posts: 17
4
New Guy
Thanks for the replies. I'll keep you posted when we get into it . Baby it's cold outside! Snowing in Maryland

Re: Torque tube to open shaft conversion
47fivewindow #1342742 Sat Jan 18 2020 07:34 PM
Joined: Feb 2016
Posts: 376
7
Shop Shark
It got cold here for a couple of days, eight inches last night now raining, too sloppy to get the truck out of the barn.


1957 Chevrolet 5700 LCF 283 SM420 single speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto

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