Driveline & rear spring setup sanity check

To recap, I'm using 2/3A rear springs (Superlift 1" and Crowns) for front and rear.  I want to take a page out of Metcalf's book and raise my driveline to keep everything as near to, or above, the frame rails as possible.  The SM465's output shaft centerline to the bottom of the transmission case is about 3" deeper than the T90's and adding in the D18 looks like it will take 5" to get the bottom of the case to the frame rails.  I haven't explored any clocking options for the D18 on the 465 so that is an unknown for now.  The 5" likely represents my nominal drivetrain lift.  The centerline of the crank to bottom of the oil pan on the V6 and the L134 are about 8" so very close to the trans/TC combo.  That tells me the engine trans combo would have to be installed in the frame parallel to the ground with no rearward tilt.  I also picked up some Hardox 2" x .25" steel strip I am planning to use to armor the bottom of the frame rails so that will give me an extra quarter to hide under. 

Once I started laying out how that will work, the next thing I noticed was the rear axle spring hanger brackets.  I figure that if I went to 2.5" lift Rancho rear springs, I could french in the brackets and eliminate them as a hang point and have the fixed eye of the spring buried in the frame.  Just looking at it, it doesn't look like there are any show stoppers but has anybody gone down this road already?  I don't know what this will do, if anything, to my driveline angles.

As always, any input on any of the above is much appreciated.

You probably won't be able to get the belly of an SM465 completely above the frame rail. Getting the D18 above the frame rail could happen. The rear output of the D18 will be just peaking above the floor of the tub....it is also going to end up right where one of the hat channels is located.

The SM465 shifter will be getting really close to the dash at this point also. The shifter cane will need a hard right coming out of the tower. You might be able to find a late model SM465 shift tower which had the shifter positioned back a decent amount ( they also shifted better in my opinion.

I would use the plate style D18/20 adapter. You really won't be able to clock things much because the D18 shift tower will be hard into the side of the transmission. That extra few inches of driveline length is really nice though.

The engine will also be wanting to poke through the hood and the bellhousing will be up high on the firewall. It is best to get the powertrain slightly forward to move the bellhousing out of the tunnel a bit more. The tunnel ( and toolbox if you have a civi jeep ) will need completely rebuilt.

I would shoot for having the t-case above the frame, and then have the SM465 belly hang down a wee bit with a skidplate over it. Make the new transmission crossmember mount to the INSIDE of the frame, not under it. Your thinking right to plate the bottom of the frame with material. I would try to avoid any fasteners for the crossmember of skidplates pointing down. Make it all as smooth as possible. The stock pedal pivot under the frame needs to go too.

Getting the rear spring hangers up out of the way is a great idea. I would be nervous about taking out that much material from a stock frame however. An alternative idea would be to outboard the rear spring mounts and move them up. Then move the shack mounts outboard on the bumper to match. I would take a careful look at where you want the rear axle position for your chosen tire size. With a 35" tire having the rear axle back about 1.5" from stock works well.

The stock front spring hangers are not nearly as annoying falling 'onto' them usually VS trying to drag the vehicle UP onto the rear hangers.

It will make the driveline angles steeper, but not critical if you keep the overall lift conservative. It will pull the driveshafts up in the chassis which is nice in the rocks.

The final question will be how high you can push the engine up under the hood. Reducing the height of the engine is tough. You will likely be on the verge of needing to poke something through on a low hood flatty. That is the line in the sand for many.

I hope that helps. Devil is in the details.

Thank you.  Do you have a part number on that shift tower?  Or a picture?  Be interested in pursuing that.  I had planned on using this Advance Adapter kit: https://www.advanceadapters.com/products/50-4703--gm-sm465-4-speed-transmission--to-jeep--dana-18-or-20-transfer-case-adapters-short-style/

I wonder if or how much a SM465 could be shaved?  I have a spare case to experiment with.  That could be a fun project.

I'll look hard at outboarding the rear springs.  On recessing the rear spring brackets, my thinking was just to plate the outside of the frame rail, box in the mount, then box the inside of the rail.  Run a bolt through the whole section and spring eye.  The springs are only 1.75" so it seems to me like it'd be an easy mod and in the end, no strength lost.  I'd lose material on the lower flange where the spring travels, but would add material with the new inner web, plate over the outer web, plus the bracket boxing.  I'll look at it hard before I commit either way.

I had planned on moving my rear axle back an 1" anyways.  I'll go to 1.5"  I've also planned on moving my front axle forward 2.5-3".  I've already built new tube bumpers for it anyway so that's easy.

I have a couple of spare hoods.  Hopefully I won't need them!

Thanks again for the assistance.

Yes, that's exactly what I'm planning to do.

Jay

I looked pretty hard at swapping to YJ springs.  I might still.  I'd have to replace all my springs, shackles, and other assorted hardware I've already accumulated.  I haven't even finished the first CJ and I probably already have parts for two more.  I'm down hard in my back today so I'll have plenty of time to consider it.  In for a penny, in for a pound and all that...

What springs did you end up getting?

But like I said removing it does you no good toward additional clearance if your TC has standard Jeep drop.

The T18 four speed transmission will set the exact same depth as the internal expanding park drum and your 465 will set even lower.

So when building with any deep four speed I see no reason to remove the drum concerning belly clearance.

I do agree you can gain right at 1” propeller shaft length when switching from a companion flange is to a yoke.