sm 420 problems

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Jun 30, 2008
cheshire CT.
Ok to start with I split my oem 3 speed tc, bought an Orion 4-1 tc, bolted it up to my sm420 and start driving, everything was ok (i thouht) started making a lot of grinding noise,tore it out and bought a rebuild kit and rebuilt it with a transmission guy ( owner of a transmission shop). put it back in and it started poping out of fourth gear, he said the main shaft needed to go forward about 60 thousands, If the main shaft is on the shoulder of the rear bearing I cant see how to move it forward. if there is anyone that knows how to make these adjustments please help, Thanks capt.
I do believe there is a thrust washer that goes between the shoulder on the shaft and the inner race.
A key piece of information is what adapter are you using ? Reason is that the older A/A adapters used a replacement output shaft for the sm420 and when that was installed there would be a chance that it was not correct. Although any issues at that stage likely would have showed while using stock tcase.
I think the previous post was in reference to the details regarding installing an Orion behind the sm420.
In the thread linked there is details about a certain spacer that must be used or it could cause issues with input bearing and gear on Orion and the rear output bearing on the 420. Again , that spacer should have been used wether mounting Orion or stock tcase so why would it only effect trans after Orion install is a ?
Is it possible that the gear does not need to go forward but that the entire output is pushing back ? This happened to me on an old ford bronco 3spd. The rear bearing began to fail (barely) and that was enough play to let the entire output to push back letting the synchro that sits right on the end of the input to drop off.
Are you sure the proper bearing was used on the output?
I purchased a rebuild kit from novak and it was the same bearing as the one removed. the problem lies in the main shaft has .105 of play . Im adding a .100 shim on the shoulder of main shaft and the inner race , that should solve the problem , I hope
Not sure what adapter was used , its about 3/4in possibly a EBI
I will measure a thrust washer I have for that application, I do believe you are on the right path. Be sure that the spacer between the output bearing of sm420 and the input gear on the tcase is installed, otherwise the input gear of orion will walk forward, bad idea. IIRC the spacer is approx. 3/4 " and must be a hardened piece. It should already be there, just trying to catch all the things people sometimes miss. Godd luck, sucks when cruiser doesn't run.

Hey Rick,
You never had the problem prior to the Orion t/c case?
That should be a direct bolt in.
John has plenty of experience w/ Orions/ popping out of gear on a downhill coast. haha
The adaptor could be a Danny Wardens/ same as mine 3/4" aluminum plate.
This w/b prior to EBI..
Hey Rick, I know someone in New Hampsha that could help, he's real good.
Send me a pm if you want the contact info.
Hey John, that thrust washer comes in 3 sizes, I've only been able to get it through Mudraks,is this the one you speak of?

Good Luck ;)

(hey peesabunch how ya been?) :cheers:
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'I'm good.
That would be it. used in 2places as the main output is assembled.
my sm420 adapter is an old one that replaces the output shaft of the sm420 with a longer one that goes all the way thru the tcase like the oem design, no cut and thread. I found another old school adapter kit on eBay and it had some of the washers/spacers with it.
Well finished up yesterday,, this is what I came up with. I had to use a shim on the shoulder of the rear of the main shaft and the inner race. What i did was use the inner race of the old bearing ( same size, no cutting) and cut it down with a cutoff wheel and ground it down on a surface grinder . Had to try a few different sizes till .070 worked. I also had to us a spacer on the inside shoulder of the adapter plate where the shoulder holds the split ring against the back of the case (to deep on mine and no different thickness's on the split rings). With everything tightened I ended up with about .08 play between the brass block rings. Back in the truck now I started the engine and said a prayer to the cruiser gods, let the clutch out ,,,and nothing !! I thought something was wrong (no noise), So I put it in 1st gear and wow it moved forward, The trans was always so noisy and now quiet, so off the trailer and drove it down the road and it was quiet, smooth, did not pop out of fourth, and shifted smooth again, I dont know what happened to the trans and why it needed to be shimmed, I think it had to do with the adapter plate when the bearing slipped back into the shoulder deeper when I bolted the new output gear on... thanks for all the input , Capt
PS; the ORION case is not to blame for this
so you are all set for tomorrow?

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