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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 December 15th, 2022, 02:14 AM
Harleyq Harleyq is offline
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Default '66 1500 slipping out of second gear

Looking at past threads, I can only assume I have a bad synchro. Just how tragic is this, and what is the difficulty rating between I got this and oh s#%* what have I done. Fairly well experienced with fixin' and rebuildin', just haven't had the mispleasure of having to break one of these trannys open. Any advice, warning, or cautionary tales would be greatly appreciated. Thanks, Dastardly Dave
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  #2  
Old December 15th, 2022, 12:06 PM
George Bongert George Bongert is offline
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Default Re: '66 1500 slipping out of second gear

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Originally Posted by Harleyq View Post
Looking at past threads, I can only assume I have a bad synchro. Just how tragic is this, and what is the difficulty rating between I got this and oh s#%* what have I done. Fairly well experienced with fixin' and rebuildin', just haven't had the mispleasure of having to break one of these trannys open. Any advice, warning, or cautionary tales would be greatly appreciated. Thanks, Dastardly Dave

Greetings Dave!

I take it your tranny is a SM318 three speed. This is a very simple transmission, and repairs are pretty straight forward. Anyone with a degree of mechanical acumen can fix one of these transmissions. The SM420 four speed is just as easy to fix except for the fact that it is bulkier, heavier, and more clumsy to work with. And to answer your question, your diagnosis of a bad snychro would be pretty accurate. It's not really tragic, it's just an annoyance of popping out of second gear.
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Old December 15th, 2022, 02:59 PM
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Default Re: '66 1500 slipping out of second gear

if your trans is jumping out of gear on a load, it means the gear is worn not the synchronizer. also shift fork could be worn, not fully engaging gear. synchronizer is used to engage gear, generaly grinds when shifting, or is hard to engage into gear.
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Old December 15th, 2022, 06:03 PM
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Default Re: '66 1500 slipping out of second gear

Isn't the Sm318 (three speed) non-synchro? Like, there's no synchro at all.
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Old December 15th, 2022, 06:57 PM
George Bongert George Bongert is offline
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Default Re: '66 1500 slipping out of second gear

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Originally Posted by ilvracn View Post
if your trans is jumping out of gear on a load, it means the gear is worn not the synchronizer. also shift fork could be worn, not fully engaging gear. synchronizer is used to engage gear, generaly grinds when shifting, or is hard to engage into gear.
You would be correct on the worn gear and shift fork diagnosis. I misspoke. While he's at replacing worn parts, it certainly would do no harm to replace the synchronizer as well.
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Old December 15th, 2022, 07:02 PM
George Bongert George Bongert is offline
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Default Re: '66 1500 slipping out of second gear

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Originally Posted by FetchMeAPepsi View Post
Isn't the Sm318 (three speed) non-synchro? Like, there's no synchro at all.
Greetings, Fetch!

The SM318 is non synchro in first gear only. Second and third gears are synchronized. While I am right here, Merry Christmas and Happy New Year to you and your Family!
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Old December 15th, 2022, 07:18 PM
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Default Re: '66 1500 slipping out of second gear

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Greetings, Fetch!

The SM318 is non synchro in first gear only. Second and third gears are synchronized. While I am right here, Merry Christmas and Happy New Year to you and your Family!
Thanks George! And Merry Christmas and Happy New Year to you too!
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Old December 16th, 2022, 03:11 PM
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Default Re: '66 1500 slipping out of second gear

merry christmas
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Old December 16th, 2022, 09:35 PM
Harleyq Harleyq is offline
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Default Re: '66 1500 slipping out of second gear

I'm rather new to the forum but have spent a lot of time reading posts on here and totally impressed with the level of knowledge here, for most things either so.eone has been through it or knows someone. Not sure on exact numbers on tyranny although it is a 4 speed, or 3 discounting 2nd. It goes I to gear just fine, tends to pop out under load. I agree with the worn gear and changing the synchros while there...thanks for enlightening.

Dave
Medford, Or.
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Old December 16th, 2022, 11:25 PM
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Default Re: '66 1500 slipping out of second gear

Lets get back to first base - is your shifter lever on the steering column or does it come out of the floor? A 3 speed is a whole different animal that a 4 speed when it comes to repairing. So is it a 3 speed column speed or 4 speed floor shift transmission - then we can begin to help you.
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