The Stovebolt Site Forums The Shop Area Driveline 1947 chevy 4 speed unsyncronized transmission question about rebuilding

Have my original 47 chevy 4 speed. This is not the SM420 that was available in 48 and latter. It's a GKT-134. I am having issues finding a rebuild kit for it. Do any of you know of anyone making this kit or if a can send the parts to somebody and have one made for it? I'm not looking for the gasket kit I'm looking for the gears and everything. I have not torn into this transmission yet but I would like to know what I can do about it before I do.

I would guess maybe Hemmings Motor News in services may be a place to start. If it was me I would try to find a good used trans. Post an ad in the Swap Meet section. I think rebuild parts (most likely NOS) are going to be very expensive and rare.

Rarity is why I want to use this transmission. It has a lever on the side of the shifter to engage reverse.

eBay is a good place to look.
I have a 1st-rev slider on there right now for one of those transmissions.

I get the rarity, I said source a good used crash box. It will be a lot easier then assembling 25 original NOS rebuild pieces.

Ok sorry about that.

Have you done an overhaul on a transmission before?

If you can't find any advice online like Novak or other supplier, than you will be having to find each part on your own, which is what they did in order to create their packages.

Teardown the entire transmission. There are many videos and resources to guide you. The gears themselves if not damaged, can be reused. Bearings, shims, and synchros (if applicable) are the parts replaced. Each will have part numbers on them.

Shop around for the parts and reassemble! Now I make it sound so easy, but ask many questions here and take LOTS of photos.

Heck, do a write up along the way and post it in our technical articles and help others who want to do your exact overhaul in the future.

Just a thought and I do not know if they are the same or not but my 1946 2 ton truck has the tranny fitting your description with the reverse lock out lever on the side. Maybe the same? Maybe not?? There a quite a few of those around if you "Beat the Bushes"
Jerry

It was 41 to 47 production tranny. I'm actualy looking for parts not a compleat tranny. Just wounding where I may find gears. There is an art to shifting those things from what I am told and most have not survived because people did no learn how to do it.

it was out before 41. i have the same thing and i took the tail piece from a 46 and put it on my 40 to open the driveline.

its not an art. its a procedure. people learned how to to do it and so will you. the reason they went away is because they came out with something better called the sm420.

if its bound up or not drain the oi, pull the stick out of it and pop the top and look inside. its a very simple transmission with straight cut sliding gears. depending where it was stored all it may need is a good flushing and new oil. until you open it up your just guessing

Called double clutching......

Ok thanks. I have always been told there is an art to it so went with what have been told. It's been In under my cab and hood so it was protected to some degree all this time. I can't pull it out because my dad pulled a boat in the shop so I'm sortof stuck for the moment.

I agree with the others that have said it is easier to source a complete transmission than individual parts. People are still replacing them with newer, synchromesh transmissions so the original 4 speeds are available.
But - you probably don't need more than bearings to get it good unless someone let it fill with water and rust up. If you have a decent bearing supply shop in your area, take any of the old bearings that you don't trust to them, let them measure (or read the old numbers) and get replacements. This worked well for me.

Ok thanks. This thread has taught me more than most of my research through google.

Greetings from New Jersey, I like the idea of finding NOS parts for a complete rebuild of your 1947 crashbox 4 speed transmission.
Maybe just finding a good used box is a viable option ?
How do you know what actual condition it is in ?
Maybe just replacing bearings would get your old crashbox
working well ?

My method of restoration would be to replace everything inside the tranny case if possible.
It's had 40 - 50 or more years of use.
Isn't it about time to refresh the old trans ?

My 1954 Chevy truck has a SM 420 4 speed trans.
It took me ( 7 ) month's of searching to find EVERY SINGLE
PART GM NOS inside the gearbox case.
The only parts I will re-use are: The case - Top Cover - PTO Cover - Drain & Fill plugs.
Everything else is GM NOS !!!!!!!!!!

NOVAK wants over $1,500.00 for a used SM 420 4 speed trans with a $215.00 rebuild kit installed.

So, I ask, What's my SM 420 worth with ALL NEW PARTS 100% ???

I personally would not want a 1947 crash box trans.
But.....it interests me that you would like to keep it & find parts to rebuild it.

I looked on ebay, and I was surprised to find a number of 1947 crashbox parts for sale: see my 1947 Chevy Transmission ebay parts album on photobucket below.

http://s669.photobucket.com/user/glp0329/library/1947%20Chevy%204%20Speed%20Transmission

I've taken a little more than an hour to check out people that sell new GM NOS parts.

I have found the following parts GM NOS.
Albeit, you could find nearly every single part for a rebuild.

Here's what I found that's available.

1.) 4.309 - 590518 - Reverse Shaft

2.) 4.421 - 590501 - Countershaft 2nd. Gear

3.) 4.421 - 590502 - Countershaft 3rd. Gear

4.) 4.421 - 590503 - Countershaft Reverse Gear

5.) 4.421 - 590504 - Countershaft Driven Gear

6.) 4.409 - 590486 - Pilot Bearing Spacer

7.) 4.433 - 590496 - Reverse Idler Shaft

8.) 4.429 - 590333 - Countershaft Keys

9.) 4.303 - 590515 - Reverse Shifter Yoke

10.) 4.309 - 590516 - 3rd. & 4th. Gear Shift Shaft

11.) 4.431 - 590236 - Idler Gear Bushings

12.) 4.309 - 590517 - 1st. & Reverse Gear Shift Shaft

13.) 4.351 - 3847311 - Main Drive Gear

14.) 4.355 - 954373 - Bearing

15.) 4.374 - 590479 - Maindrive Gear Bearing Retainer

16.) 4.422 - 121888 - Bearing

17.) 4.423 - 590496 - Washer

18.) 4.408 - 954390 - Bearing

19.) 4.409 - 590483 - Inner Rear Bearing

20.) 4.415 - 590484 - High Speed Sliding Gear

21.) 4.417 - 605555 - 1st. & 2nd. Sliding Gear

22.) 4.422 - 142260 - Countershaft Front Bearing

23.) 4.422 - 121856 - Countershaft Rear Bearing

24.) 4.374 - 590479 - Oil Slinger

25.) 4.403 - 605023 - Mainshaft

My guess that another 10 - 15 parts would give you a very substantial rebuild.

I personally like all new nos bearings & all new nos shafts.
All new gears are a bonus.
I'm sure hunting down some of the small parts will nearly drive you nutty !

You've got to check ebay nearly every day for parts.
When you see it .....grab it !

Make a list of what you need with part #'s.
Get a blow up diagram of your crashbox.

My SM 420 cost me a $1,000.00 in NOS Parts.

But.....I now have a new NOS gearbox 100% .
This is nearly unheard of !!!!!!!

My SM 420 is not some used SM 420 box with new bearings & a few small parts like I would get from NOVAK. No knock on Novak intended. They serve a purpose & need to make a profit. I'm glad they are out there doing what they do.
You can be sure if Novak was selling my SM 420 the price would be $$$ astronomical $$$.

I'd be glad to let you know where & who has the parts listed above. Just email me.

Hope this gives you some inspiration.

I do believe this 60 plus year old gearbox can be rebuilt.

I think it's going to cost probably around $1,000.00 , maybe a little less maybe a little more.

I'd checkout the gear pre 68 Dave has before it's gone.

It sounds like a nice rare part.

Whatever you do good luck.

George
in
New Jersey

I have the same tranny GKT 134. I have to double clutch on up shift and down shift to prevent grinding the gears but this tranny is been very good to me. Just FYI when I say dbl clutch on the up shift I mean when I shift from 1 to 2 or 2 to 3 etc I pull the shifter to neutral, let out the clutch (without any rev to the motor)push the clutch back in and shift. It is so much easier that way and just makes you feel more involved in the driving experience.
Also I have the hotchkiss tail yoke. There is a speedo gear behind the yoke seal. To take the bearing cover off the tranny I found that you have to unbolt the perimiter bolts, I think there are 6 or 7 and the unit will come off. Just FYI

Rick....

I think that there is a bit more to properly double clutching than an extra in and out of the clutch pedal

Great!! Please explain. I'm always willing to learn.

Ah, Mike Reese (51 ashton) has tried to educate me on double clutching gear-shifting. I had first tried to learn this double de-clutching in Britain almost 40 years ago. If/when I put a Clark 5-speed (w/overdrive 5th gear) in my COE, I'll have to learn/master the technique.

I'll be interested in reading how people try to describe this supposedly simple procedure (simple once you have learnt it).

I called Blumenthal's in Oklahoma City a few months back about some driveline parts. I was transferred to the elder Blumenthal (owner-I can't recall his name) since it was for a vintage truck. He was curious about what I was working on and after discussing it he stated that they have the capability to rebuild these older transmissions. I know you're not necessarily asking to go this route and I can't vouch for them at this point except for their name and longevity in the community, but since you'll probably have shipping even on an old one, you might want to call them and just see what the rebuild would cost (405-212-3065).

tim that was split shifting with a two speed rear not double clutching. even with the clark you will still need to split shift the rear shifting with the clark will be simlpler since it has syncro's its just like the one in your burb but with one more gear.

I'll take a crack at it....LOL.

What double clutching is mainly about is equalizing the rpm going into the transmission with the rpm going out. When downshifting, you let up on the throttle,push in the clutch, shift into neutral, then speed up the engine in rpm, push in the clutch and shift into the next lowest gear. It takes a lot of practice, and knowing your truck.
Shifting up isn't as hard as down. Because you need to let the rpms drop to shift into the next highest gear.
The need to shift to neutral first is to allow you to speed up or slow down the input shaft of the transmission to allow the speed of the gears to match, for a grindless shift....
How'd I do Tim?? :-)

John

Well said.

Sounds good to me, John. Thanks

Personally Tim, I'd rather have your Hydramatic... I only ever tried double clutching once, didn't do to well at. It was in a friend's 1940 Crosley.

I'm in Australia and I've sourced parts from Tim Tygarts OBSCHEVY
PARTS in Nashville GA phone 229/686-5812 talk to Teresa

Thanks guys. This is all useful info. I'm surprised at the actual availability in parts for my tranny. Maybe it's because I'm going the less popular route it may even be easy to find NOS parts for it than the sm420.

Zach, I found some more available parts your 1947 Chevy truck 4 speed trans. I have nothing to sell to you. I've become quite efficient in my humble opinion in searching down old time nos parts. I had to go thru your old posts on stovebolt & in one of your posts you say, you have a '47 half ton. In my previous post concerning your transmission . I listed a mainshaft part GM # 4.403-GM # 605023...this mainshaft is only for one ton trucks. According to my 1954 parts manual you need this mainshaft...which I can't find. GM # 4.403 - GM # 364160 ...10 & 1/2" long, fits '41 to '47 (4-sp.) except 1 ton.

I also located the following parts for you '47 crashbox:

1.) 4.431 - GM # 590236 - reverse gear idler bushings

2.) 4.008 - GM # 590282 - fulcrum pins

3.) 4.015 - GM # 590387 - shifter cap

4.) 4.303 - GM # 590854 - 2nd/3rd shift shaft

5.) 4.303 - GM # 590852 - 1st/rev shift shaft

6.) 4.303 - GM # 590854 - 2nd/3rd shift yoke

7.) 4.317 - GM # 591356 - Rear Bearing retainer housing

8.) 4.309 - GM # 590518 - reverse shaft

9.) 4.311 - GM # 551946 - springs, fork lock ball

10.) 4.421 - GM # 591263 - Countershaft - must be used with 1st/2nd gear # 605555

11.) 4.426 - GM # 590506 - countershaft spacer

12.) 4.311 - GM # 147489 - detent yoke balls 3/8th "

13.) 4.356 - GM # 591605 - maindrive retainer

14.) 4.095 - GM # 4.095 - shifter interlock

15.) 4.095 - GM # 590513 - interlock guide

Add these parts to my previous list of found parts.

Your now looking at ( 40 plus ) GM NOS parts for your transmission.

email me for all details.
I'll give you the sellers: name, address, phone # & email address.

Actually, it's easier if you to give me your phone number & best time to call. Have pen & paper ready. I'll give you all the info from my 3&1/2" x 5" file cards.

How's that.

Good Luck,
George
in
New Jersey

Zach, I've located the MAINSHAFT...GM # 4.421 - GM # 364160.
Seller says, he has lot's of parts for your transmission.

Regards,
George
in
New Jersey

54 3600/ George,
Thank you for the research you have done, I myself have a non syncroed trans and the lift reverse lock out that I am considering opening up and see whats groaning in it and this parts list should be in a stovebolt archive some where.

saving to my favorites!
Thanks!
Skip

OK, I'll take a shot at describing the technique of double clutching. I've got the same crashbox 4-speed in my '46 - been driving it for 28 years. Ex long-haul trucker as well.

It's correct that you're basically trying match the speed of the gears before making them mesh. On an upshift (1st to 2nd for example - which is really 2nd to 3rd since you don't use "granny 1st" for driving), you run the truck up to its shift point in 2nd, clutch in, shift to neutral, clutch out. Now when the engine spins down to the RPM it will be running when engaged in 3rd gear, clutch in and shift to third. Upshifts are easier then downshifts. 3rd to 4th is easier than 2nd to 3rd.

On a downshift run the truck to the point it needs a lower gear, clutch in, shift to neutral, clutch out. On downshifts you need to spin the engine up to the RPM it will be running when engaged in the lower gear. Rev the engine up to this point, clutch in and downshift. On an over-the-road diesel you can use the tach to figure your shift point, but that's not an option on our older trucks. It's a touchy-feely thing. It seems impossible at first, but it's like anything else - pretty simple when you get the hang of it. That said, I still miss an occasional downshift and grind gears.

The good news is that those "gear jammer," "rock crusher," "crash box" gearboxes(pick your favorite term) are pretty darned stout. That same 4-speed was used in WWII in the 1 1/2 ton truck (looked like a deuce and a quarter, but with 6 wheels instead of 10). Whole generations of farm boys learned to drive on them and had a hard time tearing them up. That trans is super heavy duty in a 1/2 or 3/4 ton truck - it can take a heck of a beating and come back for more.

Hope that helps,

David

Good tutorial, David! What I love to watch is somebody who's really good at it work their way through the gears on a two-crashbox setup like a 5X3 or a 4X4 arrangement. Back when Diesel engines had a very narrow power band like 1750-2150 RPM, I learned to drive a big rig on a B-73 Mack with a 262 Cummins and a Tri-Plex system. The guy who tutored me only used the clutch once in 15 shifts- - - -to get the rig moving!
Jerry

George - I am just starting on this project but with at '46 4-speed. Can I contact you to obtain your sources?

Thanks - Peter