Click on image for the lowdown. 
====
| | | Forums66 Topics128,080 Posts1,055,953 Members48,430 | | 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!
| | | | Joined: Apr 2013 Posts: 18 'Bolter | | 'Bolter Joined: Apr 2013 Posts: 18 | Hello i am thinking of changing the non syncro 1934 gearbox for a gearbox from a 1948 chev i am told they should just bolt straight in and the 48 box would have syncro in 2nd 3rd and 4 gear my question is what is the make and model of the gearbox for the 48
1934 1-1/2 ton truck (Australia)
| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | I believe the early gearbox has a slightly smaller bolt pattern, bottom right not offset like 420 has. Drill new mounting hole in bellhousing. Verify first of course.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Nov 2005 Posts: 6,100 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,100 | Hy psmith1954, the 1948 four speed truck transmission is referred to as the SM420. I am a little confused, (situation normal) are you intending to try and install this transmission in a 1934 chassis? As Ed has said the earlier transmissions had a different bolt pattern and the bellhousing may require modification to allow the SM420 to bolt up. More research is required, good luck. | | | | | Joined: Sep 2009 Posts: 5,844 Gearhead, Stovebolt Tech and Parts Tracker, Mod for Swap Meet and GTT | | Gearhead, Stovebolt Tech and Parts Tracker, Mod for Swap Meet and GTT Joined: Sep 2009 Posts: 5,844 | psmith1954, Another impediment to using the SM420 transmission in place of the '34 non-synchro "crashbox" is the difference in the front main shaft bearing retainers used on the different transmissions. Your original '34 will have an opening in the bell housing for the 4-3/16" diameter front main bearing retainer on the "crashbox". The SM420 front main bearing retainer has a larger 4-11/16" diameter bearing retainer that won't just slide into place into the existing bell housing hole without opening that up to match the larger diameter. If you do go the route of opening up that hole, extra attention is needed to make sure the change keeps the SM420 input shaft alignment correct to the crankshaft bearing where you input shaft will ride. While others come along to chime in with more info, check out this earlier conversation about the conversion you are talking about. Dan
~ Dan 1951 Chevy 3 window 3100Follow this story in the DITY Gallery"My Grandpa Carl's Truck and How it Became Mine"1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
| | | | | Joined: Apr 2013 Posts: 18 'Bolter | | 'Bolter Joined: Apr 2013 Posts: 18 | thanks for the info everyone ill let you know how it goes
1934 1-1/2 ton truck (Australia)
| | |
|
|
