| |
Click on image for the lowdown. 
====
| | | Forums66 Topics128,087 Posts1,056,377 Members48,442 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | 
#73624 02/20/2007 6:00 AM | Joined: Oct 2005 Posts: 11 New Guy | | New Guy Joined: Oct 2005 Posts: 11 | SM420 4speed is difficult to shift into and out of 2nd gear. It does not 'pop' out of gear, however. Shifting into all other gears is easy enough. No grinding sound is noted. It takes a 'double throw' to get it into 2nd.
Thanks for your brain power!
1951 AD 3100. 216 with sm420 floor shift.
'51 Chevy 3100
| | |
#73625 02/20/2007 3:57 PM | Joined: Jul 2004 Posts: 5,708 'Bolter | | 'Bolter Joined: Jul 2004 Posts: 5,708 | Oldcreek,
Are you indicating you are starting out in first gear, which is 'grandmother' and shifting to second gear, and this is the difficult one.
I don't think the normal, everyday drill would be to start in 1st gear...this is usually reserved for climbing trees.
As I recall, this shift from granny to 2nd is stiffer than most because of the drastic ratio change involved.
If this is not the case, then the second gear synchro would be the obvious next choice.
Have you verified that the transmission is full of the proper lube.
I was absent the day they taught "SM-420's" so I might be all wet.
Stuart | | |
#73626 02/20/2007 9:10 PM | Joined: Jul 2004 Posts: 5,708 'Bolter | | 'Bolter Joined: Jul 2004 Posts: 5,708 | Oldcreek,
My incessant need for info turned up something that might be of interest. I found it on the wonderful Novak Transmission site...it is a quote!
"About SM420 Synchros:
The SM420 has a 1st-2nd gear synchro ring that is integrated into the 1st gear hub. As such, this ring does not come with our standard rebuild kit as does the 2nd-3rd & 3rd-4th rings. However, unless the transmission has seen a great deal of shifting from the compound 1st to 2nd, this ring should not see excessive wear".
Stuart | | |
#73627 02/21/2007 1:45 AM | Joined: Feb 2005 Posts: 469 Shop Shark | | Shop Shark Joined: Feb 2005 Posts: 469 | If the motor is over wound in second gear and a quick shift is tried the tranny tends to hang in gear till things slow down to normal speeds. You could have a slight clutch drag that would make it hard to shift out of the lower gears. | | |
#73628 02/21/2007 1:55 AM | Joined: Jun 2005 Posts: 422 Shop Shark | | Shop Shark Joined: Jun 2005 Posts: 422 | OldCreek, I had my SM420 rebuilt and I was having the same problem, hard to get in and out of 2nd (this was starting off in 2nd). After about three hundred miles it loosened up and is now just fine. | | |
#73629 02/21/2007 5:51 AM | Joined: Oct 2005 Posts: 11 New Guy | | New Guy Joined: Oct 2005 Posts: 11 | Thanks for the replies.
Shifting into (and out of) 2nd is difficult at ANY time. Starting off in second from neutral, downshifting to second, upshifting from 1st. Hot/cold... no matter.
Thanks again. Obviously, I'm trying to get a heads up before I decide to get into the tranny. I don't know if the tranny has ever been rebuilt... I doubt it.
'51 Chevy 3100
| | |
#73630 02/21/2007 5:55 AM | Joined: Jul 2004 Posts: 5,708 'Bolter | | 'Bolter Joined: Jul 2004 Posts: 5,708 | OldCreek,
It wouldn't take much to pull the transmission cover and remove the shift tower. Maybe that particular rail or fork has been tweeked somehow.
Stuart | | |
|
|
| |
