I just swaped a SM420 into a 79 crusier for codeman's brother and now it keeps popping out of 2nd gear. Everything looks fine and I even had a tranny builder come take a look at it and he said it looked fine . It just doesn't seem to be going all the way into 2nd. If I take the shifter housing off i can shift the gear in manually and it stays but if i put the housing on and then shift it into 2nd and then pull it off it's not all the way in gear. Iv'e tried using the 420 shifter and the stock 3speed toy shifter. The toy shifter actually fits better and feels better but it still won't go into 2nd. I've inspected the housing and everything seems fine. The forks move fine and seat into the detents well but still it doesn't work.
What am i doing wrong? Somebody please help.

Matt H

Take the top cover off and look at the shifting forks. There may be excessive wear. Also check to make sure that the shafts that the forks hang on are locking into their detents.

It's also possible that you might have a stray shifting fork in there from a different year. It may look fine but it might not be the right one. I never seen this but I've heard that an early one can be a little bit different from a later model one.

I would also look even a bit deeper and and make sure that you don't have a broken clutch key spring.

If you'd like a shop manual I have a dealers truck service manual from 1959 that has an excellent chaptor on the SM420. I'd be happy to send you a copy if you want.

Mine had a similar problem... turned out to be the second speed syncronizer ring, it's different than the 3-4th brass syncros (the big cone shaped ring with the two tabs) , it goes into the back of the big first and reverse gear. One of the tabs was broken off and it had broken off so cleanly I did not see it. It would not go all the way into 2nd gear.
I thought I had broken it off during the rebuild. PO had dropped it and broken it. PO Failed to tell me. $ 88 fix. I also found out that all sm 420 syncros are not the same. Earlier years are different than later years. Found that out the hard way too. The thickness of the syncros were different by .0125. Make sure your syncro in the back of that largest gear is not worn too badly. I was told that pulling your finger across it diagonally it should feel sharp and grab your skin. That won't address the pop out problem but is worth looking at while your back in there.
Post your results when you find the problem as I would be interested.
If you get frustrated e-mail me and I know a fellow that has worked on 420s for 50 years . I could call or get you a toll free # and you could ask direct.
good luck.........
Bennett


Do you have the link to that sm 420 rebuild manual that was posted days ago? It is located halfway down on this sm 420 site.
http://www.kinzers.com/don/landcruiser/transmissions/sm420/doc/300x300/


http://members.home.net/cglabe1/sm420/sm420.html

Reddog- I've looked at the forks and they are fine and the shift rail detents engage very firmly.
Iv'e also cosidered that maybe I have the wrong shifter housing. I've also heard that the early models were different from the later models but wasn't sure.
I'm not sure what the clutch spring key is but I can't find anything else brocken or out of wack.
I may take you up on the manual if I can't figure anything else out.
Thanks Alot.

Bennett-I've checked that ring and both tabs are there. It will go all the way into gear and not pop out of gear as long as the housing is removed. But with the housing on, the shifter fork holds the gear far enough out that it just barely grabs a gear. Some times it holds and then sometimes it doesn't.
That's the third time I've heard that there are two different vertions of the 420. I'm thinking more and more that i got a pieced together tranny. Thanks for the help. If ya'll have any more ideas PLEASE let me know.

Matt H.

make sure you get a good look at the shifter itself. does the end show excessive wear? how are the pins in the topcoverthat lovate the shifter on both sides. how are the keyways on the shifetr for the roll pins? sounds like a linkage problem to me.

Matt,
My sm420 pops out of third gear when I decelerate. however I can hold it in. There was a change in the shifter cover between years.
However on mine it is because the third gear synchros are bad

They are really easy to take apart and replace though. PM or give me a call

Jason

p.s. the steering box is BEAUTIFUL!!!!!


:D

Thanks

orangefj45- I'm not sure what keyway and roll pins your talking about but everything looks good and tight. The only thing that I've found is that the upper pins for the shifter are a little loose, but once the locking ring is twisted in they seem to hold tight. But when I remove the shifter and move the forks manually they still travel the same amount. Thanks for the help, if you have any more ideas please let me know.

Jason M-All the synchros look good in this tranny. That was the first thing I tought of. Do you happen to know what the diferences are in the two different models? any info would help.
Glad you like the box, let me know how it works for you. I'm always looking for feedback.
Thanks for the Ideas, Keep them coming.

Matt H.

Matt,

Shit-can that POS SM420 and install another one!

I would NEVER want that much labor tied up in an SM420...they are cheap enough to buy, just ditch it and start over.

Matt:

I've got the technical sheet scans for GM stick shifts on my website. (http://www.ih8mud.com/tech/gm-trans.html direct) Includes the SM420. There is also a writeup on disassembly on there from Charlie Glabe.

That outta show you where all the parts are!

Maybe your shifter is not long enough to fully enguage the gear?

Originally posted by TheLakeRat
orangefj45- I'm not sure what keyway and roll pins your talking about but everything looks good and tight. The only thing that I've found is that the upper pins for the shifter are a little loose, but once the locking ring is twisted in they seem to hold tight. But when I remove the shifter and move the forks manually they still travel the same amount. Thanks for the help, if you have any more ideas please let me know.

Jason M-All the synchros look good in this tranny. That was the first thing I tought of. Do you happen to know what the diferences are in the two different models? any info would help.
Glad you like the box, let me know how it works for you. I'm always looking for feedback.
Thanks for the Ideas, Keep them coming.

Matt H.

All of the synchros look good in my tranny too. But it still pops out of third gear.
And if the little beads on the shifter fork are worn it will pop out of gear too. Grab the shift forks and wiggle them to see if there is any play in them...
I agree with Nolen, You can get these trannys for super cheap. By the time you get this one fixed you could hav bought two good used ones.. I just have been to lazy to get to the Junkyard and replace mine... There were some small differences between models. Some of them had odd ribs on the case. The older models did not have a seal on the front bearing retainer (who needs a front seal on a two wheel drive truck!) And the 67 top piece actually has a reverse switch.
Hope some of this helps!!!


I did have one question for you though. Do you happen to know if on the Cheif Rams you can take the front (closest to the actual "ram" section) plate off and shift it 90 deg? If it is possible It would make running the lines a bit easier....

Thanks man, the steering will be in this weekend and I will try ti out!!!

I had that exact problem with an SM420. It would hold every gear fine but second. It would pop out if I stopped on the gas or let off. Sometimes it wouldn't go in at all. Tried a different shift housing and it was a litttle better. I had 3 different tranny shops look at it and they all said it was fine.

So you know what I did?? I pulled fawking POS, rolled it in the back yard, gave it a :flipoff2: for good measure...and went to pic-n-pull on half price day and bought me another one for $40 and change. Works freaking killer, WILL NOT POP OUTTA GEAR...even if you try. My clutch slave went out and I had to get towed home because I couldn't get the tranny to pop out and rev-shift it. :o

So my advice, stop wasting time on it. I wasted 3 months on mine and for $40 fixed it with a new tranny. Why put $88 into it? Just get another and save yourself some trouble.

Since you guys are giving up on these trannys, and "rolling them into the back yard", why not give them to me ? I collect them, I have never passed on a 420 no matter what shape it's in.
I don't know what it's like where you guys live but around here those trannies are getting hard to come by.

Hell, I'll even give you a few bucks for them.

Glo-N-Dark, If you still have it let me know, I'll come and get it. I don't think you're too awful far away from where I'm at.

Have to agree with Reddog.........around here the wrecking yards are proud of those 420s. From what I found at wrecking yards $100 was minimum for a 420 that needs attention and $150 and up for one out of a 60 or newer model. Three yards I went to said they did not have them and I pointed out that they did in fact have them, then the price went up.
I have looked at a bunch and they all had real rust problems. I finally found 2 sm420s from two seperate individuals and they both had PTOs on them- $ 50 bucks each , one needed about $100 worth of parts.

Now a PTO would be pretty cool, I knew they were out there but I've never run across one that I could purchase. I did see one on a workbench at a local machine shop and like the tranny, it looked heavy duty.

I guess they used those in like dump truck type applications or somthing simular to that, eh ?

These PTOs came off 3/4 ton pickups. I can't determine what they were used for because each had been flipped and used out the rear for some type of set up. The PTOs were were off early fifties Chev trucks. Before I pulled them I was looking at the cradle that the rear of the engine sat in and it would eliminate the use of a forward mounted PTO. ( IMHO)
I have seen forward mounted ptos in 60 and later chevys. I would assume the rear engine trans mount change to facilitate the use of a forward mounted pto in the early 60s.
One of the trans I got was off a 53 but ID on the side of the case puts it as a1956 version. I believe at some point it had been swapped. These truck had the Frantz oil filter systems on them from years ago. I remember seeing those years ago. They were sort of a Kidney dyalisis sytem for oil systems and they use a toilet paper type filter clean the oil. I saw a demo on those once and they would take black dirty oil and feed it into the filter system and out the other end was incredible clean oil...cool factor of 10 there!!
http://www.wefilterit.com/frantz_facts.htm

here s link to a 420 pto from the web. My ptos are
smaller than the one pictured and can be flipped internally for forward or reverse output.
http://www.geocities.com/yj3qtr_ton/sm420.html

I'll take a pic of the pto and send it to you and you can post it if you want. Headed out to a crusier meeting this AM so I'll catch ya later.

bennett

Thanks, very interesting.

Originally posted by Reddog
Since you guys are giving up on these trannys, and "rolling them into the back yard", why not give them to me ? I collect them, I have never passed on a 420 no matter what shape it's in.
I don't know what it's like where you guys live but around here those trannies are getting hard to come by.

Hell, I'll even give you a few bucks for them.

Glo-N-Dark, If you still have it let me know, I'll come and get it. I don't think you're too awful far away from where I'm at.

I have 4 in my backyard. 2 that are good, 1 that has a bad 3rd gear synchro, and 1 that has a cracked case. As you can see I never pass them up either!! :D:D I am working on taking the internals from the cracked one and putting it into the good case. My brother has called one of them, I am keeping one as a spare, and if I let the last one go, You will be the first to know. :D:D:D

REDDOG: do you know the p/n of the input shaft seal? I need to replace mine, it's leaking pretty bad.

We'll I've looked into every thing that I can think of and everything that ya'll have suggested and talked it over with the customer today and just decided to find another one. SO, all you guys with a backyard full of them need to help a new Young Wheeler out and hook him up with another 420. PLEASE!!!
Hope to hear from yall soon. Thanks for the help!!!

Originally posted by Aggro
REDDOG: do you know the p/n of the input shaft seal? I need to replace mine, it's leaking pretty bad.

When I get to work tomarrow I'll look it up. I've got a current SKF bearings and seals catalog that gives all the part numbers.

The shop manual I have here at home doesn't show a seal....It shows a gasket , an oil slinger and a deflector.

Post the seal part number when you get the time
cause I need one too!

thanks

There are two different SM420 older one has the "slinger" and the newer one has the seal it should not be hard to find here in Sac I was able to get a gasket set for under 20 dollars witch included the seal and I didn't need it (I have the older one) but before you ask its already spoken for.

Originally posted by Aggro
REDDOG: do you know the p/n of the input shaft seal? I need to replace mine, it's leaking pretty bad.

Here's what I got out of the SKF catalog of seals and bearings;

They only show the front having a seal in SM420s from 1958 thru 1972 ( yes I did say 1972 ) ( and yes GM did make the SM420 thru 1972 ) The famous date of 1967 that we all hear about came about because it was the last years Chevy or GMC used the SM420 in the common off the lot pick-up truck. GM continued to use the transmission for several other applications up thru 1972.

They don't list anything prior to 1958 which probably explains why my GM Truck shop manual does not show a seal but instead shows a gasket and an oil slinger arrangement in place of the seal. ( But don't quote me on that, it's my guess )

There's a difference to make note of in the later model SM420 trannys. 1958 thru 1972 for the most part had a shaft diameter of 1.250. Those had seal # CR12363.

There were some built from 1963 thru 1972 that had a shaft diameter of 1.625. Those used seal # CR16054.
I can only assume that the transmission with the larger shaft dia was built for an extra heavy duty application. ( another guess on my part )

I also have the speedi sleeve part numbers if you are interested. These are still availible parts and can be gotten thru any good bearng supply house.

Aggro, the best way to tell what kind of seal you have to replace is take it out and clean it. There should still be some numbers on it. It'll be a common, easy to get seal, whichever one it is.

For the seals I have always just gone to the parts store and asked for a seal for a mid sixties chevy four speed. They usually have them in stock. As for the different shaft diameters, I've seen the version of the 420 with the larger input shaft. It was used in some of the 2 ton trucks, and it's input is obviously larger, but the internals appear to be the same.