I hope I'm posting in the right area, I wanna participate. My sweetheart(1964 C-30 Suburban) So it kept popping out of 2nd gear even if I held the shifter down, it seemed like it was gear related as opposed to Syncro related. I have 2 of them and Pop had one he didn't need. Internals Look brand new in there, and it feels beautiful. It's the older model and it didn't have the hand brake. So I swapped out the yoke and rear cover assembly and between the two I had I was able to recreate/build the propeller shaft hand parking brake. Which I had to have the band relined(I hate paying to have stuff done. I don't call a plumber, electrician, or carpenter....ever! But brake lining is difficult because materials and procedures are top secret). Anyhow a tranny swap turned into a clutch, rear main seal, the pilot bearing was stuck like chuck and I had to cut it & chisel it out in pieces. Found out I have a 1980-85' 350ci power plant with all of the 1964 attachments and housings. The person in there before me didn't know there's a pin hole in the crank and flywheel for a reason which causes me some concern. This covid thing has hit us financially and since I hate to have stuff done by someone else I decided to resurface the flywheel myself......go ahead and breath everyone I have a max runout of .003(pretty darn good if you ask me). I mounted the bell housing and followed my 1963 Chev truck shop manual(supposed to be a chev factory shop manual??🤬) Which I find a little confusing. I think they pull engine/tranny when they do a clutch because there doesn't seem to be a procedure for engine in truck. Although there's reference to "use transmission section to remove tranny" in the clutch section?(I accidentally ordered the 1964 shop supplemental for cars and not trucks so maybe it's in there?) By far the most in depth procedure for a clutch I've ever done(on an Automobile. I'm getting to finish driving the pilot bearing home and see if I can squeeze the pressure plate and disc between the crossmember and bellhousing.'m gonna have to rebuild another sm-420 probably end up with 1out of the 2 I have. Does anyone know if syncros are available yet as an aftermarket item? or have any other advice or knowledge regarding the procedure?
.003" runout on a flywheel is huge- - - - -get ready for lots of clutch chatter. I hope you used a tool post grinder to get the right surface finish, also. There are complete overhaul kits for the SM 420 on Ebay with bearings, gaskets, and other small parts, along with plenty of gears, synchronizers, and other hard parts. Those transmissions are so bulletproof that rock crawlers install them in virtually everything. If you're having clearance problems with the crossmember while installing the clutch, unbolt the rear motor mounts and jack up the bellhousing a little, and/or install mounts that aren't worn out and collapsed. I've installed dozens of those clutches with no problems whatsoever. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
My SM420 pops out of second when under deceleration. Plus, I can only shift into second from third while moving very slowly. Maybe it's a common problem with these units.
I just now noticed that this topic is about the "infamous SM420".
"infamous" = adjective. having an extremely bad reputation: an infamous city. deserving of or causing an evil reputation; shamefully malign; detestable: an infamous deed. Law. deprived of certain rights as a citizen, as a consequence of conviction of certain offenses.
I do not think of that transmission as having a bad reputation?
I think of it as the famous and favored SM420 transmission.
"The SM420 has proven to be one of the best transmissions ever built." (see the Novak Conversions links, in two prior posts, above)
Novac kits have both 3 & 4 syncros for the later transmissions that use the same size. As of last summer they did not have the one that is different on the earlier trans. I don't remember which one that is. I lucked out and had enough good syncros to finish the job. I don't remember if the kit contained the 2nd gear syncro. In any case I didn't replace it.
One thing I noticed was that the clutch-gear bearing supplied with the kit has fewer, larger balls than I have seen before on that part number bearing. I have a new bearing of the same size with more balls but no snap-ring groove which is probably why I still have it. Be careful installing the 2nd gear detent springs and shoes. If you don't get them positioned correctly the trans will jump out of 2nd gear. Jumping out of 3rd gear is usually because of worn clutch-gear or rear mainshaft bearing or both. This was the first SM420 I had worked on in about 10 years so my memory for the details is a little fuzzy.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
Ok sorry everyone my device was stolen off the fender of my 64' while I was working on her and I just flat boycotted the whole thing for a while so now I'm back on here. Novak did not have Synchros when I checked, however I did find an additional in perfect condition 3rd sm420 in the corner of my garage(I'm buying Pops house and they moved out of town) because of covid BS most of his stuff is here still including the tranny that's in my truck right now! Score! I was able to rebuild the propeller shaft brake and had it re- lined. Cost 50 bucks so after I rebuilt the carb and had her running beautiful I didn't notice the Brake on and I drove right through it for 2 blocks. So now I have a really used brake and I'm setting up an ignition switched circuit normally open brake switch with a detent going up to an indicating red light. I happen to have an unused knob position right next to the ignition key. So my dumb [censored] can't do that again!!
