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  #1  
Old 21-11-18, 00:57
ahleeds's Avatar
ahleeds ahleeds is offline
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Location: moosomin sask.
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Default HUP restore in Sask

Hello
Im knee deep in this new vehicle , ive hit a road block with the transmission . It was full of water so im wondering if anybody has any gears for this
1943 Hup Pers-1
Chev sm420 trans
casting 590474
Thanks Anthony

and if anyone is wondering on a transmission color there is a lot of original kakki olive paint all over this one.
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File Type: jpg IMG_2773.JPG (126.0 KB, 11 views)
File Type: jpg IMG_2772.JPG (125.5 KB, 6 views)
File Type: jpg IMG_2774.JPG (130.3 KB, 7 views)
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  #2  
Old 21-11-18, 03:24
Grant Bowker Grant Bowker is offline
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Are you sure that you have a SM420 transmission?
I have understood that the SM420 had synchromesh 2nd to 4th and I usually think of synchromesh as having helical, constant mesh gears rather than the straight cut gears in your photo.
Some online sources give the part number 590474 as being a 4 speed transmission as early as 1931 which feels early for a truck to have synchromesh.
Some characteristics of your photos resemble standard 4 speed of the CMP era but I don't find the part number 590474 in the CMP manuals I checked. The "retainer, clutch gear bearing" 591327 does appear in CMP manuals and is listed as 1938-46 in a Master Parts Catalog. (590474 doesn't appear in the same master parts catalog applying to 1929-48 so may be a later than '48 number).
I think that GM basically assigned part numbers sequentially so early parts have lower numbers, parts designed at the same period have similar numbers etc.
I hope I'm not making you as confused as I feel.

Looking at your photos, I wouldn't give up on the gears. I suspect a good wirebrushing or scotchbrite pad buff would make them usable (subject to inspection after cleanup). Some simple old mechanisms are remarkably tolerant of imperfections.
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  #3  
Old 21-11-18, 03:33
Harry Moon Harry Moon is offline
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Location: Burnaby B.C. Canada
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Default Looks good

Unless there is some damage I don’t see it looks pretty good. I recommend getting a new from input shaft bearing a sealed version and pull out the neoprene seal on the inside. Check the cage bearing and I often see the rear seal on eBay.
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  #4  
Old 21-11-18, 05:29
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ahleeds ahleeds is offline
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Default Rotten teeth

So it isn't a sm420 but the earlier 31-48 predecessor.
Normally I would buff up the gears and carry on ,but the rust ate 3 teeth off third and the rest don't look much better.
If I was to run this pitted up gear set it would be so loud in the cab you'd need good ear plugs .
Anthony
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1954 GMC 211 , Restored
1941 F8, Restored
1942 F15A , needs box and restore
1944 C15A , needs box and restore
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  #5  
Old 21-11-18, 07:51
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Tony Smith Tony Smith is offline
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Default

Although the CMP parts books list the transmission casing as being Pn 590524, it seems that 590474 is a common alternative.

I have 2 Chev CMP gearboxes with the casing number 590474.

The mainshaft 3rd gear is pn 590493, while the countershaft 3rd gear is pn 590502, both available NOS from a variety of sources.
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File Type: jpg Original-1.JPG (93.6 KB, 2 views)
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  #6  
Old 21-11-18, 15:13
Phil Waterman Phil Waterman is offline
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Default I would not give up on this box

Hi Anthony

I would not give up on this box, rust on gears often looks far worse than it is. Two of my CMPs had transmissions as bad or worse than this, and they both clean up and have many thousands of miles on them after going back on the road.

I started by removing the bearings then polishing each gear tooth with 3M rowloc pads, used old wheels with most of the abrasive worn off, with a very light touch, object remove and smooth the surface. I didn't try polish out the pits, leave the pits alone.

Take a look at the photos http://canadianmilitarypattern.com/C...ansmission.htm it shows, primarily, the transmission in my C60S as I started 1990 and then 2008 and 12000 miles later. When the main shaft got noisy and had to be replaced, new shaft and it ran for another 10,000 miles before breaking a tooth. http://canadianmilitarypattern.com/3...ansmission.htm

That time I got lucky and found a NOS gear box, can we say scarce as hens teeth. Yes, I did find a replacement gear and rebuilt the first transmission, which with three CMPs on the road sits on the shelf full of gear lube ready to go in.

Back to my point, if the gears and bearings areas clean up it will probably give many thousands of miles.

Keep us posted on your progress.

Cheers Phil

PS I'll look to see which of my photos need to be moved to MLU.
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  #7  
Old 21-11-18, 17:57
Harry Moon Harry Moon is offline
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Quote:
Originally Posted by ahleeds View Post
So it isn't a sm420 but the earlier 31-48 predecessor.
Normally I would buff up the gears and carry on ,but the rust ate 3 teeth off third and the rest don't look much better.
If I was to run this pitted up gear set it would be so loud in the cab you'd need good ear plugs .
Anthony
Loud is normal, at highway speed I use a com set just to talk to the passenger. Straight cut gears in the transmission and transfer case will do that!
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  #8  
Old 21-11-18, 18:50
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ahleeds ahleeds is offline
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Default Gear closeup

Looks like this gear was on the meth pipe
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1954 GMC 211 , Restored
1941 F8, Restored
1942 F15A , needs box and restore
1944 C15A , needs box and restore
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