SM420 crossmember mount part #?

[slickrock]

Edit: AA sm420 adapter to dana 18. Uses standard Gm Tranny mount. Does anyone know the standard GM part number (or aftermarket/generic) for an SM420 crossmember mount? The parts guys are useless looking up part numbers and they don't have any on the floor at either of the parts stores in town that i can measure to see if it will fit. Thanks, Dan

 

[Downey]

Rear Mount

Any interest in a transfer-case crossmember??? I still have 3 or 4 left.

 

[Pin_Head]

I have never seen a "standard" GM crossmember mount for a sm420. The Tranny itself doesn't have a mount for a crossmember, so if there is one, it must be part of the rear extension, which you would throw away to use on a cruiser. The Advanced Adaptors adaptor has a cross member mount IIRC.

 

[RAYJON]

Sm420's used belhousing mounts, are you looking for a bottom mount with a 3 speed case? All the swaps I have seen used the propeller rear mount..

 

[slickrock]

It's a standard GM tranny mount that is on the old AA adapter. I wasn't clear.

Edit: adapter is to a Dana 18, not the LC case.

 

[lcwizard]

I'm not a fan of the AA transfer case mount. Under hard use it tended to tear tear up the t-case. You're better off having a GOOD fab guy do a mount off the adapter like the pic by slickrock. it will best be done on the truck for the best fit

 

[slickrock]

I'm not a fan of the AA transfer case mount. Under hard use it tended to tear tear up the t-case. You're better off having a GOOD fab guy do a mount off the adapter like the pic by slickrock. it will best be done on the truck for the best fit

Figuring this setup was behind a healthy V8 since the first few years if this adapter creation (now its behind an F), I think it will handle the job for my purposes. I don't necessarily need to mount the adapter to a crossmember, but I'm modifying the stock skid plate to go back in place and it is easy enough to modify that to adapt the SM420/Dana18 to that as added insurance under heavy loads climbing.

 

[lcwizard]

The problem with the AA style crossmember that bolts to the back of the t-case is that it can pull the bolts or studs right out of the case under twisting loads. If you wheel like the pic in your own avatar. your frame is twisting. The cast iron block and cast iron tranny won't give but the soft aluminum case will. The 40 case doesn't twist a lot but a little bit x 100 takes it's toll. Mounting with your flex point at the center, like off the adapter, lets the tranny and t-case roll with the engine with no twisting loads on the bell housing or t-case

 

[Downey]

Transfer-case twist

Well, here's what happen back in the day: A Landcruiser transfer-case is a "side thruster" design (i.e. power enters, makes an immediate left turn, tries to spin the transfer-case around in a circle behind the tranny). Originally Chevotas were cracking bellhousings all day long. The cracks were not around the circumference (like a cracked egg shell), which would be cracks from an un-supported long span (i.e. the Golden Gate Bridge). The cracks were fore and aft, starting at a mounting bolt hole. These cracks were from torque twist. Three companies all made transfer-case crossmembers at about the same time. Downey's was the only crossmember that was 1/2" thick, the other two were thinner and could be bent. These crossmembers brought an immediate stop to cracked bellhousings because they were grabbing the torque twist right at it's center and locking it into the frame. Knowbody was cracking 6 cylinder bellhousings because they are 3/8" thick minimum (qualifies as a scatter shield). Chevy bellhousings are only about 3/16" thick. Back when folks were cracking bellhousings 33's were gigantic tires, I got laughed at first time I showed up with 33's. Today 33's are about a minimum - - -more grab and twist on the transfer-case???
Three Point Mounting: back in the day those who three point mounted (engine, bell housing, transfer-case) broke motor mounts. The Landcruiser has a hot riveted frame, it twist like wet spaghetti. Because of that, three point mounting is too rigid and won't let the drivetrain "float" inside the frame, consequently the motor mounts break when the frame twist!!!.

 

[slickrock]

Wow! That was impressive. Long story short...if it ain't broke, don't fix it. I thought an additional support to the drivetrain would help, but it appears it will actually cause problems I don't need. Thanks for the responses. I won't bother mounting the adapter.

 

[user42]

The problem with the AA style crossmember that bolts to the back of the t-case is that it can pull the bolts or studs right out of the case under twisting loads. If you wheel like the pic in your own avatar. your frame is twisting. The cast iron block and cast iron tranny won't give but the soft aluminum case will. The 40 case doesn't twist a lot but a little bit x 100 takes it's toll. Mounting with your flex point at the center, like off the adapter, lets the tranny and t-case roll with the engine with no twisting loads on the bell housing or t-case

Thread Jack - but on the same subject.

I've an AA style propeller T-case mount (SBC - SM420 - 3speeed Tcase) and I have been looking into alternatives. I was initially thinking I would go with something like what pardion (hopefully he will produce some for sale hint hint ;p) came up with in the orion thread https://forum.ih8mud.com/showpost.php?p=8564034&postcount=510 However I happen to have the truck bellhousing, the one with provisions to mount to the frame.

Which would be better? 4 point mount engine and bellhousing, leaving the trans and t-case hanging. OR a three point mount engine and t-case using a less rigid tcase mount?

Thanks

 

[lcwizard]

You're best off with conventional motor mount and a single flexible mount between the t-case and the transmission as in the position most of the adapters have built in. That way your engine, trans and transfer roll as one piece . Locking the transfer solid to a separate position on the frame as in the AA style mount, transmits the frame twist to your transfer case..
FJ60's used a single, centered, rubber mount off the bottom of the transmission. Only the t-case is hanging free. Since there's mo provision on the 420 for a mount the adapter point is next best

 

[user42]

You're best off with conventional motor mount and a single flexible mount between the t-case and the transmission as in the position most of the adapters have built in. That way your engine, trans and transfer roll as one piece . Locking the transfer solid to a separate position on the frame as in the AA style mount, transmits the frame twist to your transfer case..
FJ60's used a single, centered, rubber mount off the bottom of the transmission. Only the t-case is hanging free. Since there's mo provision on the 420 for a mount the adapter point is next best

Thanks

 

[pb4ugo]

Hey Slickrock, I ran the set up your running b4 I went to a dana 20 tcase. I made my own crossmember to attach to the Novak 420/18 adapter. The trans mount is just a standard mount for say a 1/2 ton chev pickup. GM used it on just about every rear wheel drive vehicle they made. I found the stk mount was crap & the rubber would separate from the metal. Energy suspensions makes a better mount & can be found @ autozone & the like. I also had a snubber mounted on the 18 case on the pass side. There should be a cast mounting boss at an angle on the pass side where a rubber donut bolted to, to asorb engine torque.

http://static.summitracing.com/global/images/prod/mediumlarge/ens-3-1108r_bk_ml.jpg

 

[slickrock]

Experts say let them free float or the frame twist will destroy the adapter.

Did yours ever crack? Maybe that's why the runner mounts were splitting.

I ran it hard last weekend. I was more concerned about building an anti wrap bar than my tranny. I did notice my stock engine mounts are looking a bit worn down so gonna swap those out. Just add to the list...

I really like my set-up. Bit of a pain to adapt everything and my front driveline looks more like a child's building blocks but it works fine. The low gear is perfect. Just drive up to a ledge, take foot off the clutch, and up she crawls.

 

[pb4ugo]

I've had no problems w/the adapter. The Stk GM $5 mount wouldn't last, A poly mount last yrs longer. B4 I went to the model 18, I split several 1 piece toy cases, then cracked a couple of model 18 cases. Then I realized offset rear outputs suck. The model 20 case w/18gears(2.41:1) hasn't let me down & it has true front dig. It's twin sticked, 1 for the frt & 1 for the rear.

 

[pbgbottle]

i have my sm465 long AA adapter to 3spd case mounted up using the adapter mount also .
i have had no issues , but i don't wheel it very hard .
that mount is used on all the turbo 350's ,turbo 400's it can be found at any parts store.

 

[lcwizard]

The side winder cases have there good and bad points. I haven't used a 40 case in any 40's I drive in
over twenty years. I have used the Split case from the 60 in everything since the mid nineties. It's far stronger case. I've used Dana 300's a couple times but with an automatic and 4" lift the rear driveline angle becomes an issue. The rear driveline works out better with offset rear case.

 

[slickrock]

Are the 18 and 20 the exact same physically on the outside and bolting pattern? If I could swap I'm a 20 and not have to repdo my driveline, floorboard, etc I'd do the swap. Did you have to make any changes when you swapped?

 

[jimkyser]

The late model Dana 18s used essentially the same case as the Dana 20. The real issue is the opening that indexes on the output bearing of the transmission adapter. There are two diameters, the early 'small hole' that most Jeeps and Scouts with Dana 18s used into the mid '60s, and the 'large hole' that later Dana 18s and ALL Dana 20s used. If you have a 'small hole' Dana 18 you'll need a new adapter to go to the Dana 20. If you have a 'large hole' Dana 18 the Dana 20 will bolt right up.

Some people have had luck putting all of the guts of a Dana 20 into a Dana 18 case, they are that similar.

You will end up with a centered rear output if you go to a Dana 20. You'll also go from a 2.6:1 low range to a 2:1 low range. TeraFlex makes a 3.15:1 gear set for the Dana 20 (AA sells it, too) and there is also an old-school way to combine Dana 20 and 18 parts and end up with a Dana 20 with the low range of 2.6:1 like the Dana 18.