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RockEater Gears for the D18/D20 Transfer Case

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Rick G View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rick G Quote  Post ReplyReply Direct Link To This Post Topic: RockEater Gears for the D18/D20 Transfer Case
    Posted: 18 Nov. 2017 at 7:33pm
I am going to be replacing the 2.46:1 gear set in my stock Dana 18 transfer case over the winter.  We all are familiar with the Tera-low gear set that is 3.15:1 for the large hole D18 or D20 case.  This set will also work with the Saturn (or other type) overdrive.  I need (want) to run an overdrive also.  There are lots and lots of members here that have made this modification.  I think the general consensus is that it all works very well.  However, with stock driveline components (T90C, D41&D25), the lowest FDR you can achieve is 56:1.  This is much better than original, but I want more without going to a different transmission, e.g. T18.  

I had talked with jpet a while back and he indicated there was a lower set available and I think Bob W is running a set, but they are pricey.  I followed up on his lead here (http://www.mycarpro.org/Auto-Supply/Jack-Brien-Briens-Wheel-West/) and gave Jack a call.

There are indeed four options available from Jack O'Brien, aka RockEaters.  There are 3.0, 3.6, 4.05, and 4.86:1 sets available.  The 3.0 and the 3.6 will work with the Saturn OD with their special bowl gear.  The two lower sets will not accommodate an overdrive.  Jack indicated that it was best suited for the large hole, 1.25" intermediate shaft case and they use the tapered bearing shaft arrangement most of the time, but, it could be used as original also.

Jack began making these gear sets for the Ford racing team in the early days of the Baja races.  He said he as been doing  this since 1972.   He spoke of how they cut the gear teeth (in 120 passes vs 6 or 10 or whatever), how they are slightly larger, and how they are heat treated and then cryogenically treated, and a lot of other stuff that really exceeded the needs of my Willys.  I believe he said his gears are designed to withstand 185% more torque than the stock gears.  Probably not going to get there with my L134, no matter what I do to it. There were also alot of other influential motorsport names and credentials casually tossed around during our 1 1/2 hour conversation that have, had, and are using these gears.  From just the mention of these names, I would believe that these gears are of the highest quality.  

That high quality also comes at a high price as you might expect.  I don't have the price sheet or literature yet, but Jack indicated that his gear sets run anywhere from $1700 to $2,000 to ~$2,200 for the Saturn OD setup, and then I think you start tacking on the case prep work, other parts, etc.  Adds up quickly.  There is alot of modification required to the case for the 4.05 and 4.86 gear set.  Jack said the 3.0 and 3.6 gear sets are in stock but the others are not.  He indicated that there are litigation issues pending with the sublet manufactures and production may not resume any time soon (my interpretation).

Anyway, my question is:  Does anyone have these gears and if so, tell us how you like them?  Did you install them or did Jack build it for you?  Are they installed behind stock transmission, motor, axles, etc?  Pics?  Was it worth it?  Is the 4.86 too low?  

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oilleaker1 Quote  Post ReplyReply Direct Link To This Post Posted: 18 Nov. 2017 at 9:32pm
Just some added info. , Advance adaptors (Saturn) does not recommend using their overdrives for off roading, especially in severe torque type application. They were designed more for adding final output ratio for extra speed and possibly splitting between 2nd and 3rd on a highway steep climb. I have one installed on my '51 M38 with the T90 C like you have. I love what it does, but after seeing the inside of Split Personality's when it made a "Bang" noise, and Ryan Murdock's in Maine's detonation, I'm a believer in the warning. If your OD starts to shift differently, immediately pull the rear overdrive extension and check the funky snap ring to see if it's popped out of it's groove and let the bowl gear nut begin backing off the mainshaft. If a piece of the snap ring gets between the planetary gears and the inside bowl gear-----------------------------expensive noises will soon follow. Shocked  If you go with a OD, Joe Friday recommended blue lock tite on the threads when you install the bowl gear, and also as the manual states torque it to 120 foot pounds. No air wrench is to be used. Make sure you have the correct fitting funky snap ring. If it's older stock with holes in each end, it's too small. They tooled up and made a better fitting slightly wider diameter one. 

i'm glad to hear you are gearing your Jeep down more. It will save your starter a bunch. Wink John
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 18 Nov. 2017 at 11:40pm
Yeah Rick later in the day Jack told me that some guy from Texas called.
I got a big smile cause I figured that was you. Ha Ha Ha !

Quote  However, with stock driveline components (T90C, D41&D25), the lowest FDR you can achieve is 56:1.

Yeah T90-C has the lowest gearing considering all of the Borg Warner 3 speeds.

Just my opinion but I think most 134 Jeeps will find the TeraFlex to be more practical than Jacks gear sets.
The exceptions would be .... those who are wanting lower gear ratios than 3.15 permits, also those wanting a super quiet case operation or those with huge amounts of available torque.

So Rick looks like your only options are the  lower gear sets or else locate a T98-A.
There were a very few underdrives  made to fit Willys Jeeps but those are exceptionally rare.
I have only ever seen 1 myself and they and would not be O.D. compatible.

Quote  Did he explain why his gears are superior to Teraflex other than more choices?  Is it just metallurgy, or is the design of the teeth better? 


Lots of reasons why they would be superior. 
Basically its much better quality of metal for starters. 
If I recall correctly he said 4120 or was it 4130 ?? chromoly billets are used.

More accurate machining via hobbing the gears means much tighter tolerances as opposed to other indexing and cutting processes. 
Sounded to me like his tolerances are maybe 10X ?? the Spicer standard.

He says the tooth cuts are made to allow for increased change during the hardening process.
I believe the helical angle was increased to provide more surface contact for increased strength.
Also the tooth faces are wider providing max strength for the given space.

Quote I wonder why you would have to machine the case for tapered intermediate bearings.

His design is much different than the AA (Jack called them Warn) tapered intermediate shafts.
His is a two part shaft. 
The cones and rollers are much larger diameter than AA/Warn intermediate bearings.
He claimed that the bearing contact area of the original intermediate 48 bearing rollers is greater than that of the AA/Warn design.
The 2 piece design is such that it put no stress into the case as the Warn intermediates shaft does when it's pre loaded.
I'm guessing that the Spicer case intermediate thrust faces need to be widened and made to accept a bearing cup or something ???

Anyway Jeff I'm sure your figuring out that the right combination of gearing has everything to do with arranging of the gears. 
I have spent the last couple years crunching numbers and developing the science of RANGING.
I figured it was much cheaper to think it through carefully than to go by way of the trial and error method. Ha Ha Ha !
Currently building my final F-134 powered 3B .
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Zero aftermarket parts

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rick G Quote  Post ReplyReply Direct Link To This Post Posted: 18 Nov. 2017 at 11:59pm
John, was Jeff and/or Ryan running the OD with Tera low gears or just stock? Stock engine?  I certainly worry about the potential of exploding an OD unit.  I’d like to think I would be judicious enough to not overpower one, but you never know...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 7:42pm
I just got off the phone with Jack. 55 minutes. Every minute interesting. Here is some pricing for Dana 20:

The DIY kit for 3.06 gears is $1549.99
The DIY kit for 3.6 gears is $1659.99

Jack's Tapered bearing intermediate kit is $409

He also sells a shift rail for twin sticking a D20 which will give you front wheel drive low but NOT front wheel drive hi. it is $150. This requires some machining and shimming of the front output housing.

He quoted me to do the whole thing. I would send him my TC and he does all the machine work:

3.6 low range
Tapered intermediate bearing kit
twin stick shift rail

$2629.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oilleaker1 Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 8:14pm
Originally posted by Rick G Rick G wrote:

John, was Jeff and/or Ryan running the OD with Tera low gears or just stock? Stock engine?  I certainly worry about the potential of exploding an OD unit.  I’d like to think I would be judicious enough to not overpower one, but you never know...

Rick space, I just saw your question. Duh, I may be slow, but I'm ahead of someone. Big smile The answer is: I am not sure if Split had terra flex at that time. No idea about Ryan either, but my guess is neither had them when you asked. 

For your Jeep, if you had a large 1 1/4 intermediate shaft D 18, or D 20, you can do the install yourself like I did. The road ratio remains the same for highway speed. If you want overdrive, you have to special order the bowl gear to match the terra flex. Add about 550.00 I think to the 1200.00 for the OD. The tapered bearing kit to quiet down the intermediate shaft is more bucks. John
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rocnroll Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 8:45pm
Head shaking emoticon.....sure does cost alot of money to go slower than everybody else.

Guess I'll never be able to go slow, guess I'll just have to keep driving fast.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 9:36pm
Much cheaper to put smaller diameter tires on the thing. Does the same to the gear ratio LOL.

With my 66 Chevelle for street drag racing I always ran G-50-14's they were barely 25" tall and almost 10" wide. Other guys especially the Mopar guys always had taller tires. With my 2.88 first gear (Borg Warner Super T-10) and 4.11's those short tires launched me as well as if I was running 4.56's
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rick G Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 9:39pm
I ordered my Rockeater 3.6:1 gear set last week.  I also ordered Jack’s bowl gear (in addition to the regular output gear) to run with the Saturn OD as well as a large hole index ring to mate up the T90 and D20 case (I’m building it as a D18).  According to the USPS tracking number, it should be delivered tomorrow.😁

Now, back to pulling the tub off😏
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Post Options Post Options   Thanks (0) Thanks(0)   Quote flatfender47 Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 9:51pm
Originally posted by Mark W. Mark W. wrote:

Much cheaper to put smaller diameter tires on the thing. Does the same to the gear ratio LOL.

But then you'd be banging and bouncing off the boulders.....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nothing Special Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 10:06pm
A couple years ago I put an Atlas 4.3:1 transfer case in my Bronco.  Not cheap either (and no, I'm not recommending anyone put an Atlas in their flatfender).  But I will say that the super low low range is the best modification I've made to any trail rig for rock crawling.  Yes it's expensive to go slow, but it's also really fun!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rick G Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 10:17pm
Originally posted by Oilleaker1 Oilleaker1 wrote:

i'm glad to hear you are gearing your Jeep down more. It will save your starter a bunch. Wink John

Oily, I don’t think my gears had a lot to do with my motor dying all the time.  That has been a persistent pain in the butt.  I believe I have found the culprit.  I have made a modification and will be making another to verify that was the problem.  I’ll report in another thread once I get Gus all put back together.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 19 Feb. 2018 at 10:51pm
I was close to pulling the trigger and sending Jack my case, but I couldn’t chance not having it back by EJS. I need to dig up another D20 to send him. He convinced me that his build will last forever and be much quieter. With a 3.6:1 TC, I would go to 4.11 pumpkin gears and get my road gear noise down.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb. 2018 at 2:56am
Aaron Holdaway built a auxillary low range box that bolted into the PTO port. It has its own 2.6 low range. You can read about it here. Rumor from EJS last year was that he was working on offering it to the public. 


Kinda a neat option if you don't HAVE to have the overdrive. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb. 2018 at 3:21am
I love that kinda stuff
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Post Options Post Options   Thanks (1) Thanks(1)   Quote smfulle Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb. 2018 at 3:21am
Will non Rock Eaters still be able to hange out with you guys? Are you getting big Rock Eater Equiped stickers for your cowls so that we all know not to mess with you? Will there be a new class added called Locker Stockers are Last Year’s News?  If my transfer case still whines will you not let me play any rock crawling games, like all the other reindeer did with Rudolph? 
This is very concerning to me. Oilly won’t come play on the rocks with me. My Utah friend with a new Rubicon JK only bought it cuz he can take the doors off in the summer. He doesn’t want to endanger it by going on Chicken Corners with me. I may be left driving my rig to the local show and shine by myself where they will ridicule me for the little dent in the hood that I couldn’t quite get straight by running over it with my pickup, and for having too many shifters. Wacko
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb. 2018 at 3:26am
.... huh?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Unkamonkey Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb. 2018 at 3:28am
I have a Terra low unit for a D20 but They all expect me to install it as well.
Sorry.
My brother wanted it until he looked up the prices for the new gears needed with the OD.
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