Sm420 Swap In Progress

Didn't want to resurrect old threads on this, so I have a quick question. There is a small portion of the top cover on the SM420 I have that protrudes past the machined surface where the bell housing mates up, preventing the two surfaces from making full contact. Can I just use a cutoff wheel to notch the aluminum bell housing for clearance? It would be a small notch, I don't think it would weaken anything. Have others done this?

 

What engine/ bell housing?
Can you post a picture?

 

Sorry...Buick 225 V6. I'll try to post a photo.

 

If you’re talking about the shifter rail plug that protrudes on the front of the 420 I’d say yup you gotta cut the bell. But I also wouldn’t “cut it” you should try and relieve it maybe use you a burr grinder? Aluminum is pretty soft so be careful. I’d think if you used an angle grinder any score marks you put in might be prone to cracking.

 

I milled mine out on a Bridgeport.

 

I'ld use a palm router myself.

 

Hahahaha. Bridgeport > any other suggestion.

You could probably use a piece of plywood to make a nice jig that indexes on the bolt holes and set the plunge to the right depth and get a nice close stress free pocket.

 

Good idea, thanks! I've done very little metal work, but have routered aluminum before. I didn't think about causing stress cracks...glad I asked. Thank you!

 

I don't remember having this issue when I put mine in. But then again, that's been 20 years ago so yeah. If I did, I would have just hit it with a burr bit and moved on.

 

What I did

 

My brother had a die grinder and burr bits...it was easy and quick...rounded everything off to prevent cracks. I got the bottom holes of the bell housing drilled out, the old pilot bearing out (not easy), the Novak pilot bushing for this swap installed, and new clutch disc and pressure plate on. Maybe should've resurfaced the flywheel, but didn't. Waiting on a clutch release bearing, then I'll hoist it up into place. Seems like I'll need a custom crossmember--I'll see more when the transmission & transfer case are in. The transfer case is a Dana 20 and the adapter mating the two together is, I'm assuming, an Advance Adaptor...it's aluminum and 4 1/2" long. That makes this setup around 25" long from the back of the bell housing to the inside of the yoke for the rear drive shaft. My rear drive shaft has a double cardan joint and a slip joint (I'm sure there's a name for that). I don't know if I need to shorten the shaft yet...

 

Seems like a dumb question, probably is, but do these units share oil? I want to put the proper oil in them at this point. Thanks.

 

May I why a you are using a dana20 and what rear axle? Centered or offset?

 

Rear axle is a centered Dana 44. Why the Dana 20? I purchased this transmission and transfer case combination already assembled, from a guy that seemed very knowledgeable about Jeeps, and had several of them, in Modesto, CA. I had a Dana 20 behind a T-86, prior to this swap, and it always worked fine, so I never really thought about anything different.

The transmission is in! Front driveshaft will clear the webbing on the SM420 case! Front shaft needs lengthened, rear needs shortened. I got a quote of $325 to do both. In a stroke of luck, and with a little grinding, I was able to reuse the bracket that mounted on the T86 for my clutch slave cylinder. The existing crossmember needs to be modified, but it's not going to be as bad as I envisioned.

 

I'm measuring for my modified driveshafts. I also checked the angles on all 4 yokes. The front yoke on the transfer case points up 5° and the rear yoke points down 5°. The front differential yoke points down 4° and the rear differential points up around 25°. I'm sure the front differential points downward because of how I set the caster a few years back (using McRuff's shims) to stop the Jeep from wandering. Should I raise the rear of the drive train slightly, to get to zero degrees on the front and rear yokes of the transfer case, or are my numbers acceptable? Now would be the time to do it, while I'm working on the crossmember. I'm mainly asking because the transfer case is so close to being "level", that it made me wonder if it's supposed to actually be level...

 

the front angle is less critical as the front shaft is rarely spun as fast as the rear the rear. the rear with a cv should look like this
Driveline Geometry 101 – Tom Wood's Custom Drive Shafts (4xshaft.com)

 

Thank you, Sterlclan...good video. Lots of info on Tom Woods site. I got my driveshafts back on Friday. They look good! I got them from Adam's here in Vegas. I wound up getting 2 new shafts, as the center pin on the CV was badly worn and the front shaft was thin-walled. These shafts are beefy. It's hard to believe, but this SM420 had been sitting in my garage for 10 years! I'm retired now, and finally getting it in process. The whole time it sat, I never saw any oil under it but, now that I've been spinning the yokes, shifting linkage, etc., it's leaking at the front output shaft. I pulled the seal out and am waiting for a replacement. I ordered an SKF from Rock Auto. In the meantime, I checked some driveline angles. Using Shawn Woods preferred method of holding the angle finder (my phone) on 2 vertical bolt heads on the rear differential cover, I got a reading of 73 degrees for the rear pinion angle. I subtracted that from 90, so 17 degrees. Holding my phone on the driveshaft, I got a reading of 163. Subtracting that from 180, also gives me 17 degrees of shaft slope. So, I might try driving it like that and see if there are any vibrations. My springs are super stiff. But if it vibrates, I'll shim the axle to get the pinion to 15 degrees. Does this sound reasonable? Any mistakes with the way I got the angles? Also, I got a new boot for my clutch fork opening from a company called Rubber Done Right. Perfect fit on the fork and in the hole! PN 09-007X. They're out of San Diego.

Also, got the crossmember done.

 

Been meaning to update. SM420 has been in for a while now. Everything is working well. No major issues with the swap...didn't need to grind the case at all and didn't even need to shim the rear axle for the pinion angle. Had the shafts done by Adam's Driveshaft. They seem well done, but the front shaft doesn't have much engagement where the splined male and female shafts slide together. I questioned whether they read the measurement i provided correctly, but the shop manager says it's "perfect". There is some blue paint on the splines as if to indicate how deep it should engage...half that blue paint is showing. But, what do I know? I'm not the expert. Anyway, I really like the transmission. It's old school for sure...slow-shifting, like others here have said. I've had it out in the desert a little. The granny gear is awesome! She'll climb like a goat, but also, no more squirrelly moments braking on steep, loose downhill trails...just put it in first and creep down. Street driving isn't as carefree as with the T86AA, but that's a tradeoff im happy with. Thanks everyone for your advice!

 

I have used Adam’s for 20 plus years (probably 15 ds) and have always been pleased. I sent one to shorten that they built last year and they did it for free and didn’t even charge me shipping. Oh, just to get it in here in case someone doesn’t know use a bar of soap with the die grinder burr to keep the aluminum from sticking. Just recoat everything couple minutes.