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Short: one of the three is available; super deep gears (5.86), doubler, or tcase gears. Why would you pick one over the other?

Long:
Setup: Big block cady(472), SM465, and 34mm split case in FJ55. Axles are Dana 60s with 3.54 gearing and rear steer. Front is getting Spartan locker, rear will get selectable locker(leaning toward OX) Tires are 35" and may go 37". Virtually zero highway miles. ~35 miles of Wentworth Springs to get to Rubicon(windy mountain roads).

I have a single set of 5.86 gears and an open carrier to go with them. I have to buy a selectable locker for the rear so cost of 'carrier split' will be a wash.

Use: Rubicon rock crawling. Snow plowing the yard. From previous wheeling with similar drivetrain(5.0L TBI, SM465, one piece case, 4.1 axle gears, and 35" tires), I found it not to be geared low enough. :(

In actuality, the doubler is off the plate since I've already got the SM465 to split case adapter but I would like to hear some logic on picking that. Last time I priced the Blackbox for split case, it was ~$1800. Not 100% certain it is available for 35 spline SM465. Which possibly puts getting another SM465. Length in an FJ55 isn't a concern nor is there a gas tank in the way issue ;)

The 'super deep' gear of 5.86 puts a pretty good limit on top speed; 3000 rpm gets me to about 55mph. But if I call the locker a 'wash' cost, I have to setup gears(~$300 each end) and cost of quality gears(~$250). So relatively speaking, it is a cheap fix to gearing. But it is a 'lot' of up front costs.

Going to AA gears takes out one gear setup and cost of gears. But it adds in cost of tcase gears(~$1k) and requires a new split case housing($300) plus machining of case(~$300 I think). The requirement of a new case is based upon the thinner casting of the 34mm case being a strength concern(transmission guy recommends 38mm) Side benefit is it gives a 10% underdrive so it brings the 3.54 gears to similar 'feel' as 4.1 gears.

I will temporarily run the 3.54 gears since they are setup but looking for some opinions.
With you using the 465 transmission, I personally would go transfer case gears, and the 5.86's. I'm not a huge fan of doublers (although, if it's the only option, I would take it) and prefer the deep single case gears.
I would also plan a larger tire with dana 60's. I found 37's to not have enough clearance in the rocks.
 
I have run Dana 60, 5.86 gear sets for a number of years (15 actually), early with a doubler (203-205) and then lately with a TH400 and Atlas 3.8. As I am sure you know, the down side of the D60 5.86 is the incredibly small size of the pinion gear and the resulting minimum gear-tooth contact with the ring gear. After going through 5 R&P sets in 10 years in the rear, I finally gave up and switched to a GearWorks 10 in the rear. The original 5.86 in my front finally gave up last spring and has been replaced with a fresh 5.86.

If your goal is running the Rubicon and similar trails on 37's you should be able to keep the Ring & Pinion intact for a number of years. My driving style is, should we say, a tad bit more aggressive, and I use larger sticky tires:cool: As long as you realize the weakness in the 5.86 gears, that might be your best option.

And if you choose to go with the 5.86 gear sets, it is extremely important to have them set up correctly, with minimum backlash.
 
Cruiser Outfitters shows gear sets for the 34mm split case. Problem solved!?
 
I personally like dual cases for the gearing options it provides, which is why one is going in my current rig over deep axle gearing and the stock case. With the old rig, it was easy with Marlin dual cases and 4.7’s in the rear case. Stupid amounts of gear and low range options, but necessary with the little 4 bangers. When I ran the rubicon, I usually just used the 4.7 low range and left the first case/rangebox in 1:1. Cruise around in 2nd or 3rd, slow stuff used 1st. Anything more was just too slow for most of the trail. But at Johnson Valley, there were a lot of times when that real deep gearing came in handy.

With my current junk, i’m keeping the 3.73’s I have and running duals with an SM465, which should give highway-ish speeds and still a good crawl 1st gear with the small block. When I first got the truck, it had an SM465 with a 3 speed FJ40 case, and I felt like it wasn’t slow enough for what I wanted to eventually do with it. I then found a one-off Np203 - 19 spline split case adapter, so I got lucky but they’re still out there used if you look around and are patient.

Sounds like in your case the highway speed need isn’t there, so i’d go with the low geared axles since you’re already gonna be in them for lockers. If thats no bueno, look for the doubler or t-case gears.
 
Interesting on your experience with the split case doublers, good info to know. My NP203-Split case adapter came with a spare input shaft, spare case & internals, almost a spare of everything save the billet adapter itself. I also have a 2nd SM465 complete. I'll keep an eye on it all as the rig gets running, thanks for the pointers.
 
When you machine out the 34mm case for 4:1 gears, it gets very thin or will peek thru :( My transmission guy doesn't recommend doing it at all.

You’ve posted this before but it makes zero sense as to why it would be an issue on a 34mm idler shaft case vs 38. I’ve never seen anyone actually show the casting is “thinner”
There’s plenty of people wheeling 80-87 Land Cruisers out there

Other comments:
You don’t need to spend $300 to machine the case, you could spend 20 minutes with an angle grinder
Why do you need to spend $300 a diff to setup gears when you are just driving it an hour to the trail and home? Set them up yourself, it’s not hard
There, $1200 saved.
 
I'm a big fan of a doubler. For a long time I had 4:1 case gears and I found it was either too slow for rolling around on easy trails, or too fast for the big rock gardens. I bought the ecobox and NP205 from @mr jits and I'm a huge fan of of the options I have. I really like 2:1 low for buzzing around on the trails, and double-low is perfect with my 3.73 diff gears in any of the east coast rocks I've encountered. Keeping 3.73 diff gears retains my highway drivability.

There's no special equipment needed to set up gears, unless you don't already have a dial indicator on a mag base. If you don't want to do it yourself, that's fine, no excuses needed, but then the cost of paying someone else can't really be a negative.
 
I guess sockets, a beam torque wrench, and a big vise are special tools if you don't already have them :lol:
 
If Georg says the 34mm case is weaker I’ll believe it
 
Cost can absolutely be a negative... I saw more than just a dial indicator from several videos. It is also time that I don't care to spend. As I noted, it is something I'd rather have 100% done correct and not a concern. The $300 is also a guestimate that I've seen thrown around.

I always looked at it as an opportunity to learn something. Yeah you'll spend money on the tools if you don't have them and yes you'll likely have to do it a few times to get it right. However, it isn't rocket science and when you figure out how to set your own gears and differentials up you'll never have to pay anyone again to do it. Over the past 35 years I'm not sure how many I have done. Still use the same equipment i originally purchased to do it the first time. Knowledge and experience are what a lot of people are lacking these days. All they know is what someone else has told them or they have seen online. Go get the tools, figure it out and you'll be much better off for it.
 
I guess sockets, a beam torque wrench, and a big vise are special tools if you don't already have them :lol:
What is this "Torque wrench" you speak of? Hahahahahahaaaaaa.... just zap it tight with the big impact. :rofl::rofl::rofl:
 
I didn't mean to distract too much from the original question.

Which gearing solution depends on the intended use, and most importantly your transmission choice IMO. Want highway and big time rock crawling ability with a manual transmission? I think a doubler is the only way to do that. Auto? 4:1 transfer case with or without a doubler. Don't care about highway speeds at all? Super deep diff gears.

They all cost money. In my truck, a doubler is the way to go.
 
I'm building a lightweight rig with a small diesel and I'm going doubler, transfer case gears and a 5 speed with 4.88 gears in the axle.
 
500 Caddy has, even in swill compression (7.9:1) 525 ft lbs torque, then you put a granny gear 435 behind it, then no overdrive..... my opinion is you'll never drive this on the highway? while this would be peaches in crawl, hp is how fast you can accelerate the motor and with those gears you will constantly be floating valves.... on a motor that HATES rpm because the bottom end is both heavy (the crank) and weak (the windowed mains). Not just that but the caddy motor uses T pedestals for the rockers - and they are not happy above about 4k rpm.

Add the comments above about weak pinion and I think you're asking for trouble - all that torque in that tiny contact patch.... which brings me to the doublers - it would be stronger than the pinion by several factors.

with the gearing and the doubler and the 435 - you'd be far happier with a big bore, short stroke motor like the 302....

I'm building a lightweight rig with a small diesel and I'm going doubler, transfer case gears and a 5 speed with 4.88 gears in the axle.

the more gears the better when you have the narrow power band of the diesel... good choice.

 
Good info... keep in mind that the ~500 ft-lbs of torque that is usually thrown around about cadillacs is related to the early 1970s and earlier numbers where they did a LOT of fudging. I forget when they normalized to SAE(???) but the more realistic number I've seen dyno'd stock was ~380 ft-lbs for a 500.

I haven't heard of any inherit weakness in the cady crank except that the 472 lends itself to be stronger that a 500 because of larger overlap between mains and rod locations on the crank. I 100% agree that the crank is a heavy MFer... my back still hurts from the one I played with 20 years ago :rofl:

The engine I'm using has had a Compcam 268H swapped in plus the valves are taken care of:
View attachment 2165536
I forget my book crunching numbers but I think I came up with my low compression 472 coming in at a bit under 300hp but close to 450ft-lbs(cam+edl intake+sanderson header).

As noted, in my particular case, a doubler is off the table because I have the SM465 adapter already... I doubt I will find a buyer for the adapter where I'm not giving it away. I haven't talked to Northwest fab but I'm not sure they do a 35 spline version of their box. This means I'd have to get rid of the 2wd SM465 I have. But I would agree with the assessment that a FJ55 platform lends itself VERY well to doubler: equal length driveshafts is a benefit. One of my 55s does have a Blackbox in it. ;)
I love the 472/500 motors - I ran a 472 in 2 different jet boats and a 500 almost landed in my '40. The only difference between the 472/500 is stroke even the blocks are the same with the same numbers on the outside. I never dynoed them, but comparatively, even the low-compression versions outrun 454s of similar vintage. Fun fact, the ports are close enough to a BBC that you can cut the BBC flange off headers and weld the caddy flange on - which really helps when it's trying to fit one of these beasts in something other than a caddy. That said, outside of the valve-float deal, oiling (or lack thereof) is what kills them - to the point that I'd run a low pressure kill switch.
Good luck with your build!
 
Combo that worked great for me, (fj45) bbc 402, nv4500, 203/205 and 4 .10 open 60, locked 14 bolt, 40” boggers Could drive up to rubicon, drive through and drive home. 65 mph one hand on the wheel! Only neg was 8 mpg and a 15 gallon tank! Never broke anything, front 60 was all stock( built this in 2000). I did drive with common sense most of the time. I switched to 5.13 later on and it helped with street drivability and I could use 5 th gear a lot more often. I stayed with 4.10’s because of the big pinions, and a built bbc doesn’t really care!
 

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