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

Sounds like the brass synchro's to me. 2nd gear is a will shifted location and that makes sense to me that this synchro would wear first. Take a good look at them.

Thats all I know.

Kman

It sounds like a syncro ring. I'm no expert though. Second gear is often the most abused gear (although maybe not on a tranny with a granny).

Does it look like the shift lever has been altered?

All the synchros are fine. That was the first thing I checked. In fact only 3rd and 4th have brass synchros. 2nd uses a steel gear and a spring. Kinda wierd but Oh well.
Keep the ideas coming guys.

Matt H.

Perhaps a worn shift fork or shifting dog (the thing with the female teeth that meshes with the synchros and collar on 2nd gear; or else bushing on 2nd and it gets crooked. Does it pop out under load or deceleration, or in between (transition)? Is the input bearing retainer indexed properly to the bellhousing (4.686")?
Charlie

Originally posted by Charles Aarons
Perhaps a worn shift fork or shifting dog (the thing with the female teeth that meshes with the synchros and collar on 2nd gear; or else bushing on 2nd and it gets crooked. Does it pop out under load or deceleration, or in between (transition)? Is the input bearing retainer indexed properly to the bellhousing (4.686")?
Charlie

I checked the forks and they are fine. A little wear but not much. Better than I would expect for a 45 year old tranny. If I end up having to pull the tranny I'll check that dog but it feels fine. no excessive slack in it or anything like that. It pops out at different times. Sometime when I try to take off, sometimes only when i let off. Sometimes you can shift it 15-20 times and it never jumps out then you won't get it to grab at all. Also If i take the shifter housing completly off and move the dog manually into gear. it works fine. It seems that the forks are moving it far enough to completly engage the gears. I've been thinking that maybe I got a mixmatched tranny with a earlyier model shifter housing and that mayby they were different. Any ideas on if that is possible?Thanks for all the help.

Matt H.

I suspect the shift forks too... I remember one of the guys on the Ultimate Adventure (i think rick pewe) had that problem, and it turned out that he had shift forks from different year 420's. There is a 3/16" difference in them. I will try to dig up that article and confirm this.


Updated:

Oct 2001 4WOR: Rick Pewe had a problem with the 420 sticking in 3rd gear during the ultimate adventure.

In the Dec 2001 4wor, there is the article on the Ultimate A1 rehash. They find the problem with the 420's gear sticking.
From dec 2001 4wor (pg 118):


The SM420 trans had the wrong shift fork installed on the 3-4 rail, which caused the trans to stick in Third gear if the stick was shifted too far. Two forks were used, Series One from 1947 to 1961, and Series Two from 1962 to 1967, and there is only 3/16" difference between them.


Maybe the wrong shift fork is on the 1-2 rail? Your guess is better than mine, I just wanted to pass along some potentially useful info.

Thanks Fullreversal, That confirms that there are two different forks. Thanks for the input. Keep it coming.

Matt H.

According to the owner of the trans shop I used to work at this is caused by an in correct shift fork. He said he *thinks* you need the early style if it won't fully engage but he could be wrong on that.

The syncros are the problem if it pops out under power, my 465 was doing that a while ago.....fawkin' thing would about bust your hand when it shot out of gear!!!

For some reason I thought the 420 did not have a syncronized 2nd gear....but I could bey WAAAAYYYYY off on that.

I agree with the wrong fork diagnosis. BTW Dug, the 420's 2nd is synchro'd. 1st and reverse arent.

You could call M.I.T. in El Cajon CA. They rebuild and stock parts for the SM420. Their number is 619-579-7727

Thanks for all the help guys. Once again POR saves the day. I'll give them a call first thing in the morning.
Free :beer: :beer: :beer: for everyone.
If anyone has anymore ideas let me know.
Thanks again.

Matt H.

First of all why the hell would the synchro cause it to pop out of gear? As already established there are different covers/shifters. 2nd gear is synchro'd and the synchro sits inside 1st gear. My buddy who had his own tranny shop before he retired had told me that the 420's did have a problem with 1 of the gears popping out, I think it was 3/4 with the shift collar and after time it would wear a slight taper which allowed it out of gear. This can be fixed by machining the taper the other direction. Nevermind that, just FYI. I think its in your cover/shifter. Shouldn't have to pull tranny.

Ok, for all you that think a synchro might be causing this guys problems. Don't rebuild your trannys. At this point I firmed up with Yoda my tranny master and he said, the shift forks aren't even the issue. 2nd gear as far as the covers are concerned should be the same. 3 &4 are different for the different versions. First off, is there any noise/vibration coming from the tranny? 2nd. Take the lid off and make sure 2nd gear isn't loose for any reason (Broken Clip or something)

Next, Yoda feels that this is just due to wear on the tranny, he would recommend before pulling the tranny to make sure 2nd gear doesn't have any play. Now if everything is A-OK......You should do some grinding on the detent hole for 2nd gear. If you make this deeper it will hold the gear better. You have to grind the cavity evenly in the shape of the detent ball, use a dremel or something, be careful and keep checking the shape and depth. Don't go deeper than 1/2 the ball or it won't come out of gear. Lastly, change or use a slightly stronger detent spring.
Might be useful to check and try these things before pulling and buying parts or a new tranny.
GoodLuck and let us know.