Sm420 in 54 gmc ,found at the bottom ,any idea what caused this tranny was working okay . 3rd picture is from another tranny showing the parts that were sheared off.
Moderator for Tons o' Fun , Co-Moderator Driveline Forum
Kevinski , I'm curious as well. That looks like the energizing lugs off of the 2nd speed gear synchronizer cone. Hopefully one of our experts will chime in and I can learn something too.
GM Group 4.383 , part number 591566
Ron - - Dusty53 "you can't dance with the Devil and then wonder why you're still in Hell" " They will forget what you've said, and they will forget what you have done but they will never forget the way you made them feel"
Moderator for Tons o' Fun , Co-Moderator Driveline Forum
FYI, if your thinking of rebuilding / repairing there are two new / nos 2nd speed synchronizer cones on Ebay, not over-priced. Search for GM# 591566 on Ebay. Good luck and hoping to hear what could have caused this type of damage.
Ron - - Dusty53 "you can't dance with the Devil and then wonder why you're still in Hell" " They will forget what you've said, and they will forget what you have done but they will never forget the way you made them feel"
Not a problem had a extra one from a 67 pickup with the back up switch that I saved from the mid 80,s .I am going to use that one and was just curious as to what happened as the lugs are quite thick.I was using the truck up to a few years ago and it had a few issues but it still worked okay ,I think after pushing the clutch in it would make a noise then if I put it in neutral let the clutch out and pushed it back in and into gear the noise would stop (not a grinding just a rolling noise like something was still spinning).
Moderator for Tons o' Fun , Co-Moderator Driveline Forum
Agreed on the thick lugs, its a mystery to me for sure.
Ron - - Dusty53 "you can't dance with the Devil and then wonder why you're still in Hell" " They will forget what you've said, and they will forget what you have done but they will never forget the way you made them feel"
Save the good parts. Some parts are no longer available new, like main drive gears, I think. I learned this from buying parts from Novac 4x4 in Utah. Also some 2nd gear syncros for the earlier boxes, I think. We used to think these SM420s were indestructible but the last of them were made almost 60 years ago. Fortunately there are still lots of good used parts and complete boxes around.
1951 3800 1-ton '62 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971. In the DITY Gallery
