SM 420 questions

couple questions here. I read that that 1st, not low, is synchronized. I "should" be able to downshift from 2nd to 1st without spinning up the transmission to get it into gear, right? I should also not need to double clutch it so that it does not grind going into 3rd, or high gear?

These are the issues I have with this transmission. They really aren't a problem at all and I could live with it forever. I assume the synchronizers are going bad. I also see that there is not a lot of suppliers for any parts.

Iknow these issues are not going to get better and i am just thinking ahead to when i blow it up.

 

I believe you are correct. However, I think you're calling 2nd gear 1st gear and 4th gear 3rd gear. I usually call it a 4 speed with 1st being the granny low, 2-3-4. Just semantics I guess. But, yes, you should be able to downshift from (in my terminology) from 3rd to 2nd but 2nd to 1st is not synchronized.

Parts. Hmmmm. Herm might be of some help. Perhaps R&P as well. Or, when it's done blowed up, consider a T18 or SM465. Plenty of stuff still available for them.

 

What wheelie said,

the old 65 Chevy I had, I would always shift neutral then put into second. Solved a lot of problems, by doing the shifting into neutral.
That old transmission didn't like going in unless I was practically stopped, it would sometimes without doing that or stopping but yeah.

Is your SM-420 might do a rebuild, if you want to be able to down shift into second.

 

Yes guys. 1st i call low because some ancient chevy I learned to drive stick in said low instead of first on the shifter knob. This knob says nothing on it. It IS a 4 speed. I know that its not synchronized in 1st or low... I have seen bearings and small parts for sm420 but the synchronizer rings seem to be difficult to find.

I have seen a bunch of sm465 for sale but I bought the 500 buck Novak adapter for the d18/sm420. Thats my only attachment to this particular transmission. Other than the quirky shifting that isn't really a problem so far, this transmission is pretty good. It shifts like all the old 50's farm trucks did.

 

While they aren't as plentiful as the T18/NP435(my personal fav)/465 there are still rebuild parts available, and they're worth holding on to.
A couple of things to look for- if yours was made before 1953 it will not have a seal in the input bearing retainer, and they were notorious for leaking gear lube out the retainer and onto the clutch. Novak makes a replacement bearing retainer with a seal to alleviate that issue for good if yours is an earlier model. The other issue is that the shifter pin in the top cover where the shifter fits in usually needs some attention to alleviate the shifter slop. They're old school noisy compared to newer granny trannies, but with a good rebuild they will last and I haven't seen anyone break one. Another plus to them, like the 435 and the 465, but unlike the T18 is that they have a lower 2nd gear, a 3.54 which is an added benefit for everyday street driving.

FWIW,
MIke

 

I made new shift tower pins. http://www.earlycj5.net/forums/show...shifter-pin-rebuild&highlight=420+shifter+pin
they helped immensely with the shifter slop. With the 225 V6, 5.38 gears and 35" tires, the gear ratios on this transmission are great. I want for nothing really. I NEVER use 1st/low. The Novak adapter is so great that I have not had to think about it. Just works.

What I really need is some synchro rings for this thing I guess. No one lists them besides Novak and they are " in production". I think if I found them, I would just buy them and hold on to them until it was winter to install.

 

First I know nothing about these suppliers but both appear to have parts including synchros available and in stock. You might want to call and verify.

http://www.drivetrain.com/parts_cat...ual_transmission_overhaul_kit.html#PartNumber

http://www.americanpowertrainwareho...ual-transmission-3-4-synchro-ring-fits-59-67/

 

Awesome! you found them. Only problem is that i think mine is 1953. Their numbers state they start at 1954. I will call them. Thanks.

this place http://www.obschevy.com/Pages/1929-72_Trucks_2014.pdf says they have it too.

 

Chris -- When I was a kid my dad had a 1950 GMC 3/4 ton 'Carryall' 2WD with an SM420. We used it for camping hunting trips. Even though it only had 2WD that thing could CLIMB! I have a '52 or '53 SM420 sitting on a coaster in the shop right now that I might use with my 225 Dauntless in a planned CJ6 build. If I ever finish my 2A.

Mike

 

On the farm we had running and used regularly in the fields and on the roads when i was a kid, chevy 2 ton 1948, 1949, 58, 59, 64 and a couple 70's versions. We also had a GMC detroit powerd 10 wheeler with a 2 speed rear that I learned to drive when I was 11. 13 speed transmission with 2 speed rear. We also had a 10 wheeler 58 chevy that we made into a potato bulk loader. The chevy I learned to drive in was a 1975 or so 3/4 ton with the sm465 i guess. Granny gear makes the clutch operation a lot easier to learn. First tractor I drove was a 1969 john deere 4020. I had to stand with both feet on the clutch and push on the steering wheel to stop. second was a 1964 oliver 1650 gas job.

there were also so many other trucks and tractors, road tractors too. Maybe a dozen different trucks and equal number of all running tractors? 38 dodge dump truck... so much junk. Everything got used until it was useless.

late 50's chevy trucks are my favorite body style of all time.