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Discussion Starter · #1 ·
I have a Chevy 350, TH400, and LC 3speed tcase and am going to do a swap. I want to change the tranny to a 4spd. I have a LC4spd but everyone says don't waste my time and go with an SM420. I have also seen SM465's I believe was the number. What type of vehicle do I pull the tranny out of, and is there a 2 and 4wd version? I'd also appreciate it if anyone could give me a list of parts that I'll need for the job.
 

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I run the SM465, but it is MUCH easier to mate a 420 to your drivetrain.

There is only one plate adapter available on the market for the SM465 and it is expensive to make work.

If you us this, you must have a 4wd version w/10 spline output shaft.

As for the SM420. All models are the same, even the rare 4x4 case. They are bombproof and they are common.

Plate adapters are a dime a dozen out there for around $300

I recommend the Extreme Bends adapter kit and a SM420.
 

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I'm gonna disagree with Nolen, cause I can. <IMG SRC="smilies/biggrin.gif" border="0">

SM420's were last produced in 1967, and yes they are nearly indestructible. However, they are also AT BEST 34 years old already. SM420's are an easy swap since the output splines match the early transfer case input splines. 7.01:1 first gear, non-synchro.

SM465 is what I went with, mostly cause of availability. These were found in Chevy's from 1968 until the late 80's. You'll need the 4wd version since it has the 10-spline output shaft. 6.55:1 first gear, non synchro.

There are a couple plate adapters available...I run a Classic Cruisers plate which I had few problems with but I know others had some alignment issues. A quick check thru the archives here ought to turn up a couple other sources.

The Plate adapters are nice since they keep your rear drive line longer. However, if you are running a factory PTO winch, you must use the Advance Adapters adapter since it keeps the factory PTO gear in the transfer case.

Check my site for numerous writeups.
 

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I went with a SM420 due to the availability of plate adapters and the lowest possible 1st gear. Plus they are cheap - I got 2 in good shape for the same price as the boneyard wanted for the SM465.

Just my opinion - get the 420 - you will be very happy.
 

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the 420 is probably the way to go. they were produced from 1958(i think) until 1967. stay away from the really early units because some of the parts are hard to find. besides that, they are a great little unit that will hold up well. also with the plate adapter, your rear driveline will be much longer and at a flatter angle than with the 465.
even though the 420 is at least 30 something years old by now, all the internal parts including gears and everything else is readily available brand new.
i think the 465 is overkill, but it's easier to find one in good shape.
you can find both these units in just about any chevy p-u ever made from 1958 to 1990. a 4x4 420 is not very common, but the 2wd version will do just fine.
good luck, georg
 

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I believe the SM420 was available from '47 to '68. The SM465 was from '68 till '88.

Just added info.
 

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Originally posted by woody:
<STRONG>I'm gonna disagree with Nolen, cause I can. <IMG SRC="smilies/biggrin.gif" border="0">

SM420's were last produced in 1967, and yes they are nearly indestructible. However, they are also AT BEST 34 years old already. SM420's are an easy swap since the output splines match the early transfer case input splines. 7.01:1 first gear, non-synchro.

.</STRONG>
The deal is though, they rarely ever have problems, especially in a low milaege trail rig. If they do, get another $50 tranny

<IMG SRC="smilies/biggrin.gif" border="0">

The reason I went with the 4654 is the same as why Woody did, however, if I had it to do over....
 

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Discussion Starter · #8 ·
Thanks for all of the info, it really helped. Now the only thing is I checked the IH8MUD article and woh, I felt all turned around and confused. I have done all of the work on my cruiser and used to be an aircraft mechanic so I feel that I have some knowledge, but all of the input/output shaft/spline this/that -- I felt like a complete idiot. I have pulled my tcase apart before and changed out gears, and at this point I am still wondering if something is different because I had the TH400 hooked up to it? I don't think length will be an issue because the TH400 was real long and my rear shaft was really really short. Is the 465 comparable in length to the TH400 setup? I have to move the rear tcase support anyway so the only real concern now is cost. I want to stay fairly low in cost, but I don't want to be displeased and want to change somewhere down the road. I imagine pretty much any manual tranny will suit me better than the stupid automatic.
Thanks again for all the help.
 

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Discussion Starter · #9 ·
I'm going to make my trip to the junk yards tomorrow so I need some last minute info. The 420 should be about $50 bucks? And the adapter for it is around $300? How much should I expect to pay for a 465, and how much is the adapter for it? <IMG SRC="smilies/question.gif" border="0">
 

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Just an added note. You can go with a SM465 2wd or 4wd tranny. On the 2wd tranny you need to cut the output shaft which is a pain in the ass.
 

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I did the exact same thing you are doing this last winter. I converted from 350, TH400, 3 speed case to 350, SM420, 3 speed case.

Regarding transmission choice, I agree with everything above. I went to the SM420 because I was doing this I wanted the absolute lowest.

Regarding tranny price. SM420 are cheap if you can find one that has not been opened in the rain for 20 years. I paid a $100 for one was in very good working order...low miles or the syncro's were replaced. (ohio).

Regarding the plate adapter. I am dissappointed with mine. I will not flame anybody here. It is a steel plate adapter only...no bearing. My drive gear in the tcase does not line up at all. Check out the for sale section in the Ppost. Mike Smythe aka spaceghost has fabbed some plates cheap. I am probably going to upgade to his.

Regarding the conversion from an auto.
You will need to weld new rear frame supports.
You will need a new crossmember (possibly) due to the "clocking" of the tcase.
You are going to have to modify your cowl.
You will need custom tcase linkage.

I would be happy to tell you all of my mistakes in more detail..email me direct so I don't bore everybody like I just did.

Karl
 

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Originally posted by crawlin:
<STRONG>I'm going to make my trip to the junk yards tomorrow so I need some last minute info. The 420 should be about $50 bucks? <IMG SRC="smilies/question.gif" border="0"></STRONG>
If you get a good running Transmission for $50, I'd sure like to know where ???

I've got about 5 or 6 SM420 trannys out in my garage and one in my Cruiser. They are tough and you can't beat that low first gear.
I wouldn't run anything else for the kind of trails I run.

But as mentionioned above these trannys have been around awhile and anything you get for $50 is going to need a rebuild. Plan on buying seals, bearings, and start looking for who's got the synchros. If you need to replace a shaft you are S.O.L. unless you've got a parts transmission laying around.
Needless to say that's why I've got 5 or 6 of em layin around.
BTW the most I ever paid for one was $100 and I still ended up going thru it.
 

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Discussion Starter · #13 ·
So since I am going to have to fork out some cash anyway, how much should I expect to pay to have the tranny gone through? If it is a lot wouldn't it be cheaper and make more sense to get a fairly new 465? That way I would not have to have it gone through and could spend the money on the adapter? As for clocking the tranny what's up? I have done lots of stuff and everything on my cruiser so far but I must say that I am a manual tranny virgin <IMG SRC="smilies/eek.gif" border="0"> <IMG SRC="smilies/biggrin.gif" border="0"> Rear driveshaft length I think no matter what is going to be better than that TH400. It made the rear shaft super short.
 

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I did a sm465 tranny about 3 years ago now and love it .. I went with the 465 as it is quieter on the road and 6.55 was low enough for me. I would recommend that you put a rear cross member under the adapter and not on the back of the t-case, AA adapter has this option and some plate adapters also, as it puts less stress on the t-case. I paid 185 to have my 465 R&Red but I only paid 30 bucks and it came with a parts tranny. Clocking the t-case is a clearance issue with your auto, but not everyone does this so when you do your 4 sp. swap don't worry about it. you'll love the 4sp and I would say look at the kinda wheeling you do and chose your tranny based on that and what you can find for cheep <IMG SRC="smilies/biggrin.gif" border="0"> Good luck
 

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hey! why is everybody here capping on autos?
either way, it's personal preferance.
<IMG SRC="smilies/bounce2.gif" border="0"> <IMG SRC="smilies/bounce2.gif" border="0"> <IMG SRC="smilies/bounce2.gif" border="0">
i am looking for a rebuildable 4x4 th400 if anybody has one kicking around. PM me.
 

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Discussion Starter · #16 ·
Well, I went to 3 junk yards yesterday and they all wanted at least $225 for an SM420. There were 2 420's and the cheapest was $225. There were only 4 465's and the yards were awfully proud of them because they ranged from $250 all the way up to $325. <IMG SRC="smilies/flipoff.gif" border="0"> If there is somebody in my area-even within 3-4 hours- help me out. I need a tranny and there has to be someone that has one or knows where one is that is under $150. I keep hearing stories of people getting them for $50-$100 so what's up?
So much for staying cheap on this one. <IMG SRC="smilies/puke.gif" border="0">
<IMG SRC="smilies/crybaby2.gif" border="0">

OrangeFJ45wagon- I have a rebuildable TH400 if you have a housing. This one is cracked pretty much from side to side on the bellhousing area. It was even mated to a 3spd LC tcase. So you could get mine with all the necessary adapters and shafts to put it on a 3spd tcase and just need a housing.

David <IMG SRC="smilies/usa.gif" border="0">
 

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David... Yea, the salvage yards in our neck of the woods are usually overly fond of their junk <IMG SRC="smilies/pissed.gif" border="0">

I have a 2WD SM465 that you can have for $100. As far as I know it is in very good shape. PM me if you are interested and we can dicker.
 

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Discussion Starter · #18 ·
Medusa as far as I can gather if I go with the 2wd 465 there is cutting involved and I have no idea of what or where. Plus it seems that the 465 adapter is more costly and I have to stay as low as possible on this one. If you have any other suggestions or ideas I would really appreciate it. It just seems that for this one I am best off going with a 420 due to my lack of knowledge on manual trannies and this type of conversion.

David <IMG SRC="smilies/usa.gif" border="0">
 

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hey david! thanks for the offer on the 400 trans. i have a couple of cores but i need a 400 4X4 case that's in good shape. the guts are pretty much the same on all of them, chevy, gm (even cad and pontiac, buick..) and even jeep 400's.
besides, it would cost too much to ship.
good luck with the 420. call my buddy mike at lebanon auto and salvage (i think) in lebanon OR. tell him you're a buddy of georg's from CA and see what he's got. he's been pretty fair to me in the past.
<IMG SRC="smilies/bounce2.gif" border="0"> <IMG SRC="smilies/bounce2.gif" border="0"> <IMG SRC="smilies/bounce2.gif" border="0">
 

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correction: mike is at cascade auto and truck! i just talked to him today but forgot to jot down the digits for ya. 411!
<IMG SRC="smilies/bounce2.gif" border="0"> <IMG SRC="smilies/bounce2.gif" border="0"> <IMG SRC="smilies/bounce2.gif" border="0">
 
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