The Stovebolt Site Forums The Parking Lot Big Bolts Old 4 speed trannies

I have a question about the old 4 speed transmissions used in the big bolts. I have a old 1947 with full sliding gear shifting. The thing shifts fine when the trucks cold but get the gear lub hot it starts grinding every time I shift and double clutching don't even help some of the time. And more importantly the tranny makes insane amounts of noise in 1st second and third gears. (And yes I realize it's the way it's designed.) Once in 4th the noise is considerably reduced, but I installed a overdrive that required the truck to be in 3rd gear. The engine can't handle fourth and 3rd about will drive you crazy.
Anyway the question. I acquired a 1954 4-speed transmission a while back and can get a 1980's transmission for $100. I know they changed the 4speed in 1949 to helical cut constant mesh for gears 2,3,4. And I hear both tyrannies should bolt right up. but I was wondering if this cuts down the noise much and improves the shifting performance? The helical cut is at a fairly small angle compared to newer units so I'm not sure if it will help. If not I may opt to get the 1980's tranny.
Another issue, I need a PTO and don't think my 47' will fit on either newer tyranny cause the gears it has to run from are helical and mine a straight. Is this correct?

I've got a question. Did the trans get worse since you installed the Overdrive? Riding around in 3rd a lot more than usual may be what's heating up your gear oil.

main problem is 60 years of abuse, it's been driven away with the PTO still engaged way too many times .... when cold things are a bit more snugged up - as the gear oil heats up things can move around more

the SM465 [1968+] will be smoother than the SM420, but any used trans, especially one that's had a long life with a PTO could be noisey .... either newer trans might bolt to your bellhouse, but either may have different input and/or output shafts than your current one

Bill

C10-C90 Bill-
Nope the OD didn't make it worse, it's been like that since I bought it I'm afraid and been doing it for years before I bot it. About 1/4 of the teeth are ground down where it's been forced in gear. (another reason why I kinda want to change it.)

squeeze-
I kinda figured anyway you look at it the 80's unit would work better than the 54', less age, less abuse, better tolerances etc. But I'm not sure if the SM465 will take the hand brake system, and I like the drive shaft parking break the 1954 has hince why I'm considering the 1954.
I've drove several trucks with SM 465's very good trannies. Even with wear they still shift easy and noise is minimal compared to my 47's tranny.
I haven't had the pleasure of driving a truck with a SM420 (other than the sliding gear job) before so I don't know how they are.
So my question though not phrased properly before is: How much better will the constant mesh 1954 SM420 be to shift and how much less noise will it make than the 1947 tranny with sliding gears? And how much worse is it than the SM465 assuming all three are actually in relatively the same shape?
I know having helical cuts will kill some noise but with the small angle how much is my question.
According to what I've heard and read the input shafts on both these tyrannies are exactly the same. Length spline and diameters, only output shaft changed. But I guess I'll find out. What I do know for a fact is my 1947 tranny is currently hooked to a 1959 engine. So I assume at least the 1954 will fit.

Put heavier grease in it like 85/140.

If the gears are already ground down It will likely fail at some point. That point is usually when it's most inconvient.( Thats also the point where the stories start as well.) Heavier oil or stabilzer such as lucas products may help quiet the noise some. If you deide to keep running transmission you may want to flush transmission to get rid of sludge and metal filings.That would leave a bit more room for new lube which may help with noise and heat issues.

I love the trans in my '49 6400. Truck is all original so I assume it has the sm420. Very quiet transmission in all gears except granny low. You can't rush the shifts, but I rarely "grind 'em". I hear the sm420 is a popular upgrade in older Jeeps. My buddy bought some kind of conversion kit for his old Jeep a few weeks ago. From what he saying, those old four speeds aren't nearly as easy to find as they used to be.

I put a rebuild kit in my sm420 and have been pleased with it. As said - you cant rush it but it shift's fine and is pretty quite. Good luck.

Just for future reference to anyone. I dropped the tranny out of my truck this past weekend and tried to put in the SM420. However it don't fit. Input shaft goes right in, same length, same splines, same size journals for throwout and pilate bearings. However the bolt pattern is different, I need the bell housing for the SM420 tranny which I don't have. Guess I'll have to deal with the noise when using the OD.

Can you redrill your bell housing for the SM420?

Mike B

Mike B, If I remember correctly the holes are about a half a hole off which would make it difficult to redrill. I went through all that over 50 years ago.

1947farmer, you refer to an overdrive. What kind of overdrive did you install?

Go to a truck trans shop they can tell you what you have.
Your trans has some bad gears in it----Take the cover off it you will see the bad gears. Eather get it rebuilt or find a used one.
If yoy let it run 7 worm up the old grease & drain it there will be metal shavings in there.

Nope the holes are way too off. The top set of bolts are too high and offset from center is in the opposite direction of the old sliding gear tranny. It would need an adapter plate, which may mean the tranny splines and piolate bearing wouldn't work.
What I need is the original bell housing for the tranny. My cousin's trying to get me the bell housing for the tranny I have... maybe. It will match my engine with no problems, if I can get it.
Actually what I really need is the yahoo over on the next road to sell me his 1951 2-ton that is utterly shot (no cab floor front post rotted off etc). It has the right bell housing and the rear-end I need, but the guys a jerk. I tried to get a hold of him to buy it for 2 years, but he never returned my calls. Tried to stop in three times once got his wife the next time no one was home, the third time he spent 5 minutes balling me out for interrupting him from bailing, when in that 5 minutes he could have made $300-500.
So I've quit trying on that one, I don't deal with jerks if I don't have to.

The over drive is a new process 205 transfer case mounted backward. So it has a .5 OD in high range. Take a look.
http://s1133.photobucket.com/albums/m596/acmandrk/

What I really need is the original 2-speed rear axle for the same year truck. The 8.10 low gears would give me about a .7 to .8 OD (I forget exactly what it was) when I put the transfer case in high range. instead of the .5 OD plus I'd have a 16 speed!! But again one that is close, owner is a pain...