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Driveline identification
#1232762 Thu Aug 31 2017 03:44 PM
Joined: Jan 2014
Posts: 1,373
J
JW51 Offline OP
Shop Shark
My 1951 3100 has an open driveshaft....which means the torque tube was swapped for something else in the distant past. Not sure where the rear end came from, but it's 6 bolt and it appears to be pretty early.

The rear U-joint definitely needs replaced, so I got the rear shaft pulled this week. I figure we might just have to measure at the parts store to find the correct U-joint.

I would like to know what I am working with for future parts needs:

1) Am I right in thinking the transmission (4 speed) would also not be original to the truck? I have in my head that the torque tube version of the tranny was different than the open driveline. If so, where do I go about finding numbers to help me identify it? Everything is covered in a thick, protective layer of petrified grease and dirt....so need some idea where to start digging.

2) How about the rear end? Count bolts on the cover? Other numbers I need to look for?

Re: Driveline identification
JW51 #1232784 Thu Aug 31 2017 06:10 PM
Joined: Jun 2011
Posts: 3,441
E
Shop Shark
Both open and torque tube would have had SM-420 trans'.

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: Driveline identification
JW51 #1232787 Thu Aug 31 2017 06:16 PM
Joined: Sep 2001
Posts: 30,014
ace skiver


Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
Z-series (54/55) GMC 350 (2-ton) COE [1954advance-design.com] - now part of Dave's family
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engine are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: Driveline identification
JW51 #1233002 Sat Sep 02 2017 11:09 AM
Joined: Aug 2004
Posts: 1,391
ODSS Lawman
First thing is to put the truck on a diet and get the years of preserving muck off the truck. I know when I did mine the first time I wasn't sure I would ever get it all off. Thankfully that muck also kept things nice underneath. Once you are cleaned up find the casting numbers to help ID the parts you have. The transmission casting numbers will be easy to see, likely to start with 59xxxxx as mentioned in Tim's link above. The rear ID numbers if a GM axle will be on the passenger side near the pinion or U-joint.

The SM-420, the stock transmission used in these trucks, came both in closed and open versions. They also have conversion kits, so it is possible the transmission you have is the original.


SWEET
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Old Dominion Stovebolt Society

BUNS?!?!?! Where we're going, we don't need no buns.....

1950 GMC 450 (25% owner)
1951 Chevy 1/2-Ton
The GreenMachine
In the Stovebolt Gallery [stovebolt.com]
Re: Driveline identification
JW51 #1233031 Sat Sep 02 2017 02:46 PM
Joined: Jan 2014
Posts: 1,373
J
JW51 Offline OP
Shop Shark
Exactly what I needed! Thanks, SWEET!

Re: Driveline identification
JW51 #1233268 Mon Sep 04 2017 01:59 AM
Joined: Jan 2014
Posts: 1,373
J
JW51 Offline OP
Shop Shark
Is it a sin to replace the rear u joint and not the front? Crawled back under the truck this evening and the front joint seems ok to my untrained senses.

Re: Driveline identification
JW51 #1233294 Mon Sep 04 2017 05:22 AM
Joined: Mar 2013
Posts: 176
Q
Shop Shark
Yes you can replace just one,but remove the drive shaft and check the front joint by moving the yoke side to side and up and down. This makes the ujoint cross pivot in the bearing caps. Do it slow and if you feel any roughness or tight spots then change it.

Re: Driveline identification
JW51 #1233298 Mon Sep 04 2017 11:30 AM
Joined: Jan 2014
Posts: 1,373
J
JW51 Offline OP
Shop Shark
Thanks!

Dumb question: Does the front one have some sort of spring action? It always returns to center when you move it to one side or the other.

Last edited by JW51; Mon Sep 04 2017 11:30 AM.
Re: Driveline identification
JW51 #1233331 Mon Sep 04 2017 02:59 PM
Joined: Jan 2014
Posts: 1,373
J
JW51 Offline OP
Shop Shark
Now that I've messed with it some more, my spring action comment isn't really accurate. But it definitely does feel like there are some fairly positive "stop" positions at center, right, and left as you move it around.

Re: Driveline identification
JW51 #1233484 Tue Sep 05 2017 03:03 AM
Joined: Mar 2013
Posts: 176
Q
Shop Shark
Yeah that's a good sign it's on its way to being done...change it...as far as what kind of u-joints to get,if they are gm,they should be easy to match up at a parts store. GM is good at using standardized u-joints.as well as making cross over u-joints.it won't be hard to find something to fit.

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