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| | | | Joined: Sep 2010 Posts: 1,714 back yard wrench turner | | back yard wrench turner Joined: Sep 2010 Posts: 1,714 | 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
Wayne1938 1-Ton Farm TruckStovebolt Gallery Forums1989 Silverado 1996 Mustang GT convertible When I die, I hope she doesn't sell everything for what I told her I paid for it! | | | | | Joined: Apr 2005 Posts: 2,101 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,101 | 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
| | | | | Joined: May 2015 Posts: 11,120 Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums | | Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums Joined: May 2015 Posts: 11,120 | 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 1951 Chevy 3100 work truckFollow this saga in Project JournalPhotos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) 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. | | | | | Joined: Feb 2004 Posts: 29,841 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,841 | 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
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| | | | | Joined: Mar 2002 Posts: 9,115 'Bolter | | 'Bolter Joined: Mar 2002 Posts: 9,115 | I remember years ago , having this problem. It is one of the most annoying problems that one can have.!! | | | | | Joined: Apr 2005 Posts: 2,832 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,832 | 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
| | | | | Joined: Mar 2010 Posts: 1,660 Curmudgeon | | Curmudgeon Joined: Mar 2010 Posts: 1,660 | Wayne is this the same transmission with floor mount shifter from you previous post? https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/765630/1.html
"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."
| | | | | Joined: Sep 2010 Posts: 1,714 back yard wrench turner | | back yard wrench turner Joined: Sep 2010 Posts: 1,714 | Yes it's the same. I'm using a Hurst shifter with it
Wayne1938 1-Ton Farm TruckStovebolt Gallery Forums1989 Silverado 1996 Mustang GT convertible When I die, I hope she doesn't sell everything for what I told her I paid for it! | | | | | Joined: Mar 2010 Posts: 1,660 Curmudgeon | | Curmudgeon Joined: Mar 2010 Posts: 1,660 | 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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