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Old 05-13-2019, 10:01 PM   #1
23window
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3 speed interchange question

Hello all,
After hours of internet research I have a handful of random information about transmissions that I'd like to clarify.

I want to put a 67-68ish 3 speed trans behind a 235 Chevy in a 55 sedan.
Can it be as simple as just finding a 67 Saginaw and bolting it up?
I was told the Muncie 318 behind the 235 could not be rebuilt due to obsolete parts.
Guidance and clarity would be appreciated.

I want to keep it as simple as possible so no 4-speeds or T5 swaps thanks.
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Old 05-13-2019, 11:09 PM   #2
geezer#99
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Re: 3 speed interchange question

67-68 was an sm318 just like the one you have.
Here’s a link with some good info.
http://67-72chevytrucks.com/vboard/s...=414555&page=2
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Old 05-13-2019, 11:33 PM   #3
23window
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Re: 3 speed interchange question

Great link,
I'll keep my eyes out for a good trans.
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Old 05-13-2019, 11:37 PM   #4
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Re: 3 speed interchange question

What obsolete parts do you need.
There are rebuild kits available.
https://www.ebay.com/itm/GMC-Chevy-M...ty!98225!US!-1
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Old 05-14-2019, 12:04 AM   #5
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Re: 3 speed interchange question

The second gear idler is supposedly not available new.
To be clear, in not a trans builder. I'd love to have my transmission rebuilt locally but I wanted to do my research before I pull the trans out.
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Old 05-14-2019, 12:22 AM   #6
geezer#99
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Re: 3 speed interchange question

Maybe these guys might have one or know where to find one.
http://www.garagemotorsports.com/muncie.htm
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Old 05-14-2019, 06:06 AM   #7
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Re: 3 speed interchange question

My friend put a '72 C/10 Saginaw and rear in his '55 1st. I can pick his brain, but pretty sure it went right in and it took some effort to get the linkage right. Very road worthy... as in interstate hiways. I have driven it on long runs and it rolls right along smooth as silk. A bone stock truck other than those two components. Full synchro is nice
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Old 05-14-2019, 03:37 PM   #8
weim55
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Re: 3 speed interchange question

A1 Transmissions here in Denver Colorado can completely rebuild your original 55 SM318. They have a complete stock of new and used parts for these transmissions and techs that know this old stuff really well.

Steve weim55 Colorado
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Old 05-14-2019, 03:51 PM   #9
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Re: 3 speed interchange question

But to answer your original question : the 7 bolt Side to cover fully synchronized Saginaw three speed was used in various GM cars 65 and up and light duty trucks as the standard transmission from 69 up. The most important thing you will have to match is the input retainer diameter at the front of the transmission. This is the large 4 to 5 inch pilot hole in the bell housing. The seven bolt Saginaw has two different sizes for this. Measure your original 235 bell housing hole to match. Speedometer cable can attach to left or right depending on the transmission, another thing to match the same as your Original. The transmission output yolk Will have to be changed for the proper fine spline unit on your driveshaft and the driveshaft length may have to be changed as well. You will have to do some fabrication for the column shift linkage so make sure the arms are still attached on the transmission that you purchased, the arms from your original transmission are not the same. Other than that the transmission is a bolt in. It’s a significant upgrade from your original transmission, synchromesh first gear, smoother operation overall and quieter.

Steve weim55 Colorado
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Old 05-14-2019, 09:12 PM   #10
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Re: 3 speed interchange question

Perfect thanks much!!
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