The Stovebolt Site Forums The Shop Area Driveline SM420 Removal (and clutch question)

I have seen several people recommend removing an SM420 by bringing a cherry picker in from the cab and lowering it with a chain.

Is that just a recommendation if you don't have a transmission jack? Or is there a reason to do that instead of using a tranny jack?

As far as I can tell, I have the original clutch installed and it is super grabby. I am getting ready to teach my daughter to drive it and I want to put in something newer/more forgiving.

All of the old documentation I see says it should have had a 10" clutch. People say the 10" replacements now are 10.4".

Fair enough. But if I go to Autozone or Rockauto, they list 11" and 12" clutches as being standard.

I see 10.4" clutch sets from various racing houses, but they are both more expensive and tend to be the grabbier ceramic material.

I am looking at a kevlar clutch to be a bit smoother experience.

Are the 12" clutches interchangeable onto the stock flywheel?

Follow the recommendation to use the cherry picker. I tried the floor jack method and it was not a good experience. The SM420 has a round bottom and it's top heavy. It wants to tip over and fall off the jack even with wood wedges installed in an attempt to keep it vertical. Best thing I can say that nobody was physically injured.

Before removing the transmission I suggest that you make some measurements so that when you go to reinstall it you can be close when you are trying to get the thing to go into the pilot bushing. It seemed like it took forever to do this wiggling it up and down and left and right. Great feeling when it finally when home!

I understand about the floor jack, but I have a proper transmission jack with the adjustable fingers and chains.

I am not insisting that is better than the cherry picker, but I do want to draw a distinction between the types of jacks.

Can you elaborate on what measurements you mean? Like pitch angle and such? It should index to the bellhousing right?

It has been 20+ years since I swapped a manual.

If you've got a true transmission jack, I would use that. I have not had the opportunity to pull an AD transmission using a cherry picker, but I recall my dad repairing the transmission in his 51 GMC with four speed. I was just a kid and wasn't involved with it but I don't recall he used any kind of jack, but bench pressed it out and in. I wouldn't even attempt that with the 3-speed in my AD. Dad was in way better shape then than I am now.
But I've used a transmission jack on a 6-speed manual transmission in my Ford diesel. That sucker weighs about 200 lb. Still a tough job.

As far as reinstalling, build a couple of guide pins (just bolts with the heads cut off) that will thread into the bell housing to guide it back in place.

Clutches, per the Vehicle Info Kit for 1958 trucks were either standard 10 inch or optional 11 inch (based on disk OD.) They each take different flywheels with different bolt pattern (6 bolt for 10" and 9 bolt for 11") for the pressure plate. The 11 inch clutch/flywheel combo is pretty rare and clutch kits are hard to come by.

I use all-thread and grind some of the thread off as you get towards the end that the tranny first slips over. Also, use a hacksaw to cut a slot in the tapered-down end so you can back these guide pins out with a screwdriver.

Something like a Perfection Clutch 30005 is a 10.4" disc with a 6 bolt pressure plate.

The Sachs K190902 is listed as a 12" disc that claims to be compatible and has a 6 bolt pressure plate as well.

The Sachs says it interchanges up to a 95, while the Perfection is listed as 58 compatible, but the interchange stops at 57.

From the pictures, it seems plausible that they have the same bolt pattern but I can't find that spec listed anywhere.

Think there is a better option than just ordering one and seeing if the bolt pattern matches what I have?

I found the adjustable fingers and chains useless. Floor jacks seem to be designed for automatics with their nice flat pans. Apparently, it's just me as others think they are OK.

I would measure from the output yoke to the frame and to the cab floor. (maybe put a chalk mark to replicate the measurements). The issue is that when the transmission on the guide pins, it can still move around quite a bit making it hard to align it to the pilot bearing so it can be shoved home.

Only thing I can suggest about the clutch is to buy it locally to save shipping costs in case it has to go back. Turns out my '54 uses a '53 clutch.

I have removed and reinstalled small trans. like 420 by sitting on the seat with a chain or rope around the trans. and lifting up and back, helps to have a helper. Make sure the trans in in direct gear so one can turn it be hand to engage the clutch splines.

Ed

I recall someone here saying to place a sturdy board (4x4?) through the windows (rolled down) and using that as the lifting/lowering point.

But I don’t remember what they were using to lower. A smallish chain hoist might do it.

i have used 2x4s across the hole in the floor and ratchet straps around the ends to get the trans off the floor and onto a jack. Unless I jack the truck way up, I can't roll the jack and trans under the truck. If I do that it's too high for the jack to raise. With two guys and a floor jack it's doable, only just. Not fun. Once you get the trans raised with the straps, put the shift lever back on so the inside man can use it for a lever to hold the trans straight up and down while perched on the jack. In the heavy truck world there are trans jacks that have arms useful for holding big, tall gearboxes but I don't know where you might rent one.

Before you start trans installation, IT IS IMPERATIVE that you use a GOOD alignment tool or an old clutch-gear shaft to line up the clutch with the pilot bearing BEFORE you tighten the clutch bolts. There are also plastic reproductions for this purpose. Use one or the other to grease the clutch splines and the pilot nose but not so much that grease flings off the shaft when you start it up. Also if you use too much on the nose of the pilot, you risk forcing the bushing out of the crank when you cinch the bolts down. That's one method for getting pilot bushings out.

If you have taken the clutch out or have a new one, grease the splines and work the disc back and forth on the input shaft (clutch-gear) to spread the grease before you install the clutch. If there is an existing clutch in place use the alignment tool to spread the grease.

Hook up the clutch linkage and do an approximate adjustment of the throw-out bearing,
a) so the bearing stays in place and
b) so you can release the clutch if you need the trans to move one way or another for that final push into the pilot bearing.

Insert the guide pins you made. Grease them too. Remember not to make them too long or you cant get the left upper one out. Likewise the bottom ones that have to clear the clutch. for the bottom you may just want to use longer bolts but remember if they're too long you can't get them out.

One you get the trans raised the and straps off, roll the whole shebang forward to engage the clutch and guide pins. Now you're on your own It's just brute force mixed with finesse till the trans is home and you can remove the guide pins and install the bolts. Do not let the trans hang from the clutch at any point or you will bend the disc and have to start all over with a new one.

Have also used ratchet straps underneath to remove and install. One end hooked to battery box floor opening and the other to parking brake post. Kept a floor jack underneath to control the drop because ratchet release can be kinda sudden and imprecise.

Taking out not so bad ,jack and a few boards.Going in using a jack not very stable as bottom of trans is round but if you have the trans out for as long as mine was out and move the sm420 around then you can just bench it up .lol

Here's a couple old pics of my cherry picker earning it's keep. Once I pull the gearbox out, I would lower it to the ground, disconnect the chain and slide the gearbox out from under the truck. Install is just the reverse.

Is the chain bolted to the sides? Or wrapped around?

I was planning to do the swap today, but the UPS man lost my bellhousing mounts and I want to do it all at one time.

Next week, I guess. Seems like a good use of superb owl Sunday.

The chain is bolted to a couple of the top cover bolts. Not wrapped around.

And once you got it out from under, you need to get out your gearbox support stand, etc

Why not just lift it up and roll the crane back and remove the transmission out through the door?

There was a reason which I do not remember. Probably the overall length of the gearbox vs the floor hole depth having had to tilt the gearbox way up, to bring it up thru the floor? Hey! I'm only 1 year younger than my truck......

The seat is going to be in the way as well. The front of the seat frame is forward of the floor opening, even if the seat is out. Then there's the possibility of drooling gear oil on the interior.

I took my Sm 420 out with a floor jack and Trany adapter. Very easy

BD,
Were you able to slide the floor jack with the tranny attached, out from under without having to raise your truck? Would love to see any pics of the setup if you have any.

I don`t have any pics. I have lifted the truck on one side to remove a 4 speed.
I think with the SM 420 ,I rolled it off the jack onto a cardboard box and slid the whole thing out.

That's what I do with the cherry picker. Lower the gearbox down to the floor, disconnect the chain, roll it on its side onto a piece of cardboard or a large piece of plastic sheeting and slide it out from under.

I can see that. I`d rather not have anything swinging on a chain on install. With the jack I can line it up and slide it in at the right height.
But whatever works. I improvise best I can with what I have.

Looks like transmission was much lighter for the install!