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Jan 21st, 2020
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Joined: Sep 2010
Posts: 1,913
OP
back yard wrench turner
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I have a 55 GMC 3 speed trans in my truck. It started jumping out of 3rd gear the other day. It hasn't been doing this until now.
What do I need to look at to make a determination how to repair?
Thanks
Wayne When I die, I hope she doesn't sell everything for what I told her I paid for it! 1938 1-Ton Farm Truck-30- Stovebolt Gallery Forums
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Joined: Apr 2005
Posts: 2,020
'Bolter
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Unfortunately it's a fairly common event with 3 speed transmissions both in the early transmissions with a torque tube and the later open driveline version. I would start with the shift linkage and make sure it fully engages and doesn't have a lot of slop.
Next check the universal joint which can cause a vibration effect and cause it to jump out of gear. It could possibly be a worn 2-3 shift fork and/or weak springs on the shift fork detent balls. Worn bearings can also cause an issue similar to the u-joint problem. And of course the good old syncronizer assembly which is a common wear part.
Or it could be a combination of all of the above.
Fred
1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine
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Joined: May 2015
Posts: 6,671
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
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Could be the input shaft pilot bearing in the flywheel also. A worn one will allow the input shaft to be out of alignment and at a slight angle to the mainshaft which can cause the engaging clutch teeth to walk out of engagement.
Kevin Newest Project - 51 Chevy 3100 work truck. Photos [ flickr.com] #2 - '29 Ford pickup restored from the ground up. First car '29 Ford Special Coupe Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
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Joined: Feb 2004
Posts: 25,692
Kettle Custodian (pot stirrer)
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Do't forget to check the transmission case to bellhousing bolts for tightness. I've cured several jumping out of gear problems by simply tightening the bellhouding bolts.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!"
Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self.
Ernest Hemingway
Love your enemies and drive 'em nuts!
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Joined: Mar 2002
Posts: 9,185
'Bolter
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I remember years ago , having this problem. It is one of the most annoying problems that one can have.!!
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Joined: Apr 2005
Posts: 3,105
'Bolter
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You don't say if it is a 55.1 or a 55.2. Either way there is a good chance the syncro drum is worn and no new ones offered. It should have an open driveshaft so it is not a hard swap to put in a fully synchronized 67 or newer 3sp trans.
Evan
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Joined: Sep 2010
Posts: 1,913
OP
back yard wrench turner
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Yes it's the same. I'm using a Hurst shifter with it
Wayne When I die, I hope she doesn't sell everything for what I told her I paid for it! 1938 1-Ton Farm Truck-30- Stovebolt Gallery Forums
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Joined: Mar 2010
Posts: 1,782
Curmudgeon
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Unknown used transmissions can used transmission problems. Things you get into resurrecting old trucks.
#1 thing to check, does the transmission have lubricant or has it all leaked out?
If I remember correctly the 3 speed can have wear issues with the shift shaft bushings and synchronizers.
It wouldn't hurt to check the previous mentions and external things before going internal.
"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."
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