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Transmissions and Rear Ends Three on the tree or four in the floor? Shift it all here.

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  #1  
Old April 28th, 2020, 02:46 AM
GreenStreak GreenStreak is offline
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Default Transmission Identification + Clutch Replacement

Hey folks,

I'm working on restoring a 1966 GMC C1000 with a 305E which belonged to my late grandfather. One of the things on my list is addressing any issues with the transmission. My family mentioned to me that the clutch needs replacing, which is the reason the truck has sat in a shed since ~2003, but I'm unsure if the clutch actually needs replacing and even what size clutch it takes.

It's a 3 speed manual which was originally a column shifter then converted to a floor shifter to circumvent the supposedly untrustworthy column linkage. I suspect it's a SM318 transmission, but I'm not sure how to verify that. Does anyone know a good way to determine which transmission is in the vehicle? Perhaps a model or serial number scribed onto it?

Secondly, the 65-66 GMC Maintenance Manual says it can be either a 10.5", 11", or 12" clutch. I've found replacement 10", 11", and 12" clutches readily available on RockAuto, LMC truck, etc, but no 10.5". If a 10.5" clutch is the one I need, any ideas where I could pick one up?

I plan to inspect the trans either this upcoming weekend or the next, but I figured I'd ask y'all so I could go into the situation armed with some more informaton.

Thanks for the help!
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Old April 28th, 2020, 09:45 PM
James James is offline
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Default Re: Transmission Identification + Clutch Replacement

If you have a picture of the transmission, linkage side, would help to identify. There a lot of resourceful folks on this forum to help you with this and any other problems.

Pictures of the truck would also be nice.
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Old April 29th, 2020, 12:15 AM
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Quigley Quigley is offline
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Default Re: Transmission Identification + Clutch Replacement

If the side cover with the shifting arms is held on to the main transmission with 4 bolts it is a SM318. As far as the clutch is concerned you will know what size it is when you remove it. Hope you have better luck finding a clutch than I did. Ended up having the original rebuilt. Dave
l
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Old April 30th, 2020, 01:54 AM
GreenStreak GreenStreak is offline
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Default Re: Transmission Identification + Clutch Replacement

Thanks for the info! I'll keep that in mind. I plan to do the brakes this weekend, and should have time to take a peek at the trans. I'll take some photos of the linkage, but in the meantime, here's some photos of when I picked the truck up back in March.

https://drive.google.com/open?id=14B...mkt9yrid5mS94n
https://drive.google.com/open?id=144...Nmu3XAt4MF2UAJ
https://drive.google.com/open?id=14D...uybvG4Yprn7H6V

I plan to start a thread under the "Builds and Journals" section to document my progress, just haven't gotten around to it, yet.

I'll update this thread when I get a good feel for the transmission.
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Old May 19th, 2020, 11:27 PM
GreenStreak GreenStreak is offline
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Default Re: Transmission Identification + Clutch Replacement

Updating this for the sake of documentation: finished the brakes and got around to checking out the transmission.

Turns out it's the SM318 that I suspected. Additionally, it looks like the clutch size is a non-issue for now. Opened up the inspection cover and the clutch seemed to have a good amount of life left on it, and the throw out bearing turned smooth as butter. We'll see how well the transmission likes to work when I get to take the truck on a test drive.

Thanks again to Quigley and James.



^(Not sure if above photo will display properly or not, so apologies if it's just a broken mess.)
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