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RockEater Gears for the D18/D20 Transfer Case

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oldtime View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb. 2018 at 5:15pm
Bob, that's a pretty interesting drive train configuration.
All ratios with the transfer case shifted to low range are slower than the slowest speeds available iwhen it's in high range. 
Just not very many jeeps set up that way.
I crunched some numbers and it looks like your available ratios without OD unit are
HIGH RANGE   5.38  - 10.1  -  17.9  
SLOW RANGE   22    -  41    -  74

Is 74/1 slow enough for you ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nothing Special Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb. 2018 at 5:55pm
Originally posted by oldtime oldtime wrote:

....Is 74/1 slow enough for you ?
 
I'm not the Bob W you were asking (although that is my name and last initial!), and my experience is in a much different vehicle, so it's comparing apples and kumquats...
 
Stock my '71 Bronco had a final drive ratio of 34:1.  When rock crawling the engine would tend to stall out if I let it get below about 1200 rpm.  So with 33" tires I was going 3.4 mph.
 
After changing the trans (NV3550) and transfer case (Atlas 4.3:1) my final drive ratio is 71:1.  With the lower gearing I find I can idle the engine down to about 800 rpm without stalling too much in the rocks, giving me a speed of 1.1 mph.
 
The eye-opening thing to me was when I looked at it as energy.  Energy is proportional to the speed squared, so dropping the speed by 1.1/3.4=0.32 means that I'm hitting rocks with 0.32^2 = 0.10 times as much energy.
 
Hitting rocks only 1/10 as hard as I used to is HUGE!  It's very noticeable, and as I mentioned before, it's the best change I've made to my Bronco.
 
Is 71:1 the "right" crawl ratio?  All I can say is that it feels pretty good.  There might be a few times that going even slower would be good, but I haven't found them yet.  Obviously projects like this creep, and I'm sure some day I'll start to wish I had even lower gears.  But I really don't see that being soon.
Bob

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rick G Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb. 2018 at 8:14pm
Originally posted by Nothing Special Nothing Special wrote:

Originally posted by oldtime oldtime wrote:

....Is 74/1 slow enough for you ?
 
Stock my '71 Bronco had a final drive ratio of 34:1.  
 
After changing the trans (NV3550) and transfer case (Atlas 4.3:1) my final drive ratio is 71:1. 

Is 71:1 the "right" crawl ratio?  All I can say is that it feels pretty good.  

Bronco Bob, this is good info for me.  This is the real world experience I was seeking when I started this thread, albeit not exact Rockeater gear experience.  Experience with different crawl ratios within the same vehicle is good comparative data and is very useful to me.  

Our flatties have the stock crawl ratio of 37:1.  My dilemma was whether I needed to go all the way to 87:1 with the 4.86 Rockeaters or stop at 65:1 with the 3.6 set (and the T90C).  I have seen jpet and his 77:1 (and variants thereof) navigate obstacles with relative ease.  I want that, but I wasn’t sure that I was willing to go all the way to 87 to get it (because there is no OD option after 3.6).  I’m pretty sure I would like the 4.1 or even the 4.86 better, but I’m compromising for the OD capability.  The 65:1 will give me a 75% increase in crawl over stock and a 14% increase over the Teralow set.  This crawl will be pretty close to your 71:1, so I’m anxious to see how happy I will be with them.

Here are the gear ratios from which I made my decision.  With the Rockeater 3.6 and the Saturn OD I can mimic the original low-range gear ratios, plus get the low crawl ratio of 65:1.  The only down side is I wont have 87:1 (except in Rev). But will I need it?  We shall see........

T90a with 2.46 (original)
1st.          36.93
2nd          20.51
3rd          13.23
Rev          50.16


T90c with 3.15 Teralows
1st          56.60
2nd         31.35
3rd         16.95
Rev.        76.77



T90c with 3.6 rockeaters & OD
1st            64.69
1st OD      48.52
2nd          35.83
2nd OD     26.87
3rd          19.37
3rd OD     14.53
Rev          87.74
Rev OD    65.80



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Post Options Post Options   Thanks (0) Thanks(0)   Quote flatfender47 Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb. 2018 at 8:54pm
7.00 SM420, D18 2.46, 5.38 = low
1947 CJ2A 225V6 SM420 D30 PLok/D44 D/Locker Warn OD 5:38s
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nothing Special Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb. 2018 at 10:47pm
One thing I have going for me as well is a wide spread in my transmission.  My NV3550 does from 4:1 in 1st to 0.78:1 in 5th (overdrive).  The fact that it's an overdrive isn't significant, changing the axle gears would make it the equivalent of 5.1:1 in 1st with 1:1 in high gear.  With my setup I can go up to about 18 mph in low range, so I don't need to hunt between low and high too often.
 
With your T90a you only have 2.79(?) between your low and high tranny gears, so you can't go as much faster than your crawl speed without shifting into high range.  That could get old.  The T30C is a little better at 3.34(?), but still not very close to my 5.1.
 
Adding the OD does get you pretty close, with a gear spread of 4.45 (by your numbers) between 1st and 3-OD.
 
(By the way, going to a granny 4 speed is actually better than my NV3550, with a gear spread somewhere between 6 and 7.)
 
So what does this mean?  I don't know.  If with your current setup you can go 15 mph in low range (just a guess, and maybe not a good one), with 3.15 gears you'd be down to 12 mph, and with 3.60 gears and no OD you'd be at 10 mph (but at about 14 mph with OD by your numbers).
 
So in addition to looking at what your crawl ratio is you also need to look at how often you'll need to stop and put it in high range.  You need to decide for yourself what you'll be happy with.  I'm just trying to help frame the questions a little.
Bob

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bob W Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb. 2018 at 11:49pm
Originally posted by oldtime oldtime wrote:

Is 74/1 slow enough for you ?

It is almost slow enough. I really wanted the Rockeater 4.86 gears but when I was finally ready to purchase them they were out of stock. Then the sub-contractor gear problem arose, so I went with 4.1 before they ran out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 12:37am
Yeah Bob, I heard about quality control problems Jack O' was having with  his 4.86 gear sets.
I've long time  considered 75 /1 crawl ratio to be the point where true rock crawling begins.
Your valid experience seems to agree with my idea concerning that.

Quote
T90c with 3.6 rockeaters & OD
1st            64.69
1st OD      48.52
2nd          35.83
2nd OD     26.87
3rd          19.37
3rd OD     14.53
Rev          87.74
Rev OD    65.80
 

Rick G your ist gear in O.D. is going to be a real handy ratio. 
It's no doubt too fast for the big rocks but
I figure 50/1 is a great ratio for running between obstacles when your on the slow trails.

I agree the O.D. is a real bonus especially with the meager powered  134 engines.
Seemed to me that Jacks OD bowl gears were way cheaper than the Tera Flex O.D. bowl gears.

These drive train choices are all really good ideas guys  ! 
But I got something different up my sleeve ....
Currently building my final F-134 powered 3B .
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chasendeer Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 1:59am
Spent my 45 minutes on the phone with Jack today. Looks like I will have a set for the Rubicon this summer. Trying to decide if I want to keep the OD.
Jay

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 2:47am
Originally posted by oldtime oldtime wrote:

......Is 74/1 slow enough for you ?
Here is X98 Rockeating in granny low:



.... I officially pulled the trigger on my TC today. Jack is not going to make it to EJS but he should have it done in plenty of time for me to have it installed for Moab. This will put BAM BAMs basement at 107.5:1 and 1/low at 59:1

Edited by jpet - 22 Feb. 2018 at 2:59am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rick G Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 3:27am
Originally posted by Nothing Special Nothing Special wrote:


 So in addition to looking at what your crawl ratio is you also need to look at how often you'll need to stop and put it in high range.  You need to decide for yourself what you'll be happy with.  I'm just trying to help frame the questions a little.

It’s kinda a fixed question, because my build requirements are:  Original T90, original D18 (both with lower gears, obviously), and original D41/D25 with 5.38.  I would certainly like to not have to shift between High/Low 4wd, but that’s what I live with now, so no big change there.  

I’ve put off installing an OD, but with these 34” tires in high altitudes, I really need a gear between 2nd and 3rd.  In addition the OD will give me stock gearing when in low range with the Rockeaters.  I hoping this will be near perfect for me.  If not, it’s going to be expensive for the next mod.

If I were to build another flatfender...no telling what I might build, but it would definitely CRAWL and RUN 75 mph.  Kinda sounds like Bam Bam and Blueberry, huh????
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 5:19am
A few thoughts. My flatty is a heavy mod.....225 V6, T18, D18, 5.38s, 35" tires. I can't think of many, if any, cases where I have wanted or needed lower gearing than that and I am at 83:1 


A few notes...

-With a 4cyl engine with less bottom end torque I could see the need for a bit lower gearing. I think this is kinda the 'toyota' problem. Smaller motors need deeper gearing generally. The problem becomes that this is really difficult to fit in a short wheelbase like a flat fender. If you gear the t-case extra deep you will lose useful middle range gearing. I think an overdrive COULD help with this, but I am still hesitant of the overall durability. Being able to shift the overdrive on the fly in low range would give you some extra speed which would be nice to avoid the hi-low-hi shuffle on mild sections of trail. 

-Having an engine that will lug down and be able to recover will stretch out your gearing. The ol' Buick 225 odd-fire is really good at this because of the VERY heavy flywheel. My engine will lug down below 200rpm under a load. I have watched the tach bottom out on zero and had the engine recover. I think running a slightly richer idle mixture can help also. There is also something with being able to play with idle speed to find a happy medium between no load speed and speed under a heavy load while off the throttle. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 11:49am
I've said this in other threads but I'll throw it in here as well. I spent a lot of time wheeling with sonoblast77, smfulle, and Rick G last year. Watching these locker stockers convinced me that in a small tire short flatty, a 55-60:1 ratio is one that you want in your arsenal. More than once, I failed at 77:1 trying to walk something where they succeeded on the first try. I contribute it to momentum. I think the rules change a little with 80" wheelbase and NDT tires. I really think that T-90C/with Teraflex is a sweet combo for flattys with 30-31" tires.

.... This is why I changed pumpkin gears. It wasn't to get 100:1 crawl ratio, it was to get my next gear into the 55-60:1 range. Before, my next choice was 42:1 (32" tires)

I don't feel like I need a gear lower than 77:1, but I like having it simply because it allows me more time to think. Sometimes the adrenaline gets pumpin' and my brain don't work too good.

.... lets also not forget to add tire size to the equation.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 12:05pm
Originally posted by Metcalf Metcalf wrote:

....-Having an engine that will lug down and be able to recover will stretch out your gearing. The ol' Buick 225 odd-fire is really good at this because of the VERY heavy flywheel. My engine will lug down below 200rpm under a load. I have watched the tach bottom out on zero and had the engine recover. I think running a slightly richer idle mixture can help also. There is also something with being able to play with idle speed to find a happy medium between no load speed and speed under a heavy load while off the throttle. .....
This is the one disadvantage I have found to TBI, at least my stock setup. The 4.3 will lug down quite a bit, but at a certain point, when the computer feels a stall coming on, it will try to compensate with a 5 second fuel burst. . Even if it were just a second would not be as bad, but I'm stuck with a 5 second high idle. ... or, at least, I think that is what's happening.

Edited by jpet - 22 Feb. 2018 at 12:07pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 2:23pm
Originally posted by jpet jpet wrote:

I've said this in other threads but I'll throw it in here as well. I spent a lot of time wheeling with sonoblast77, smfulle, and Rick G last year. Watching these locker stockers convinced me that in a small tire short flatty, a 55-60:1 ratio is one that you want in your arsenal. More than once, I failed at 77:1 trying to walk something where they succeeded on the first try. I contribute it to momentum. I think the rules change a little with 80" wheelbase and NDT tires. I really think that T-90C/with Teraflex is a sweet combo for flattys with 30-31" tires.

.... This is why I changed pumpkin gears. It wasn't to get 100:1 crawl ratio, it was to get my next gear into the 55-60:1 range. Before, my next choice was 42:1 (32" tires)

I don't feel like I need a gear lower than 77:1, but I like having it simply because it allows me more time to think. Sometimes the adrenaline gets pumpin' and my brain don't work too good.

.... lets also not forget to add tire size to the equation.

Yup. There are certain ranges that are going to work better to balance things out. I wouldn't mind a gear between 1st and 2nd sometimes. I currently drive a LOT of stuff in 1st high or 2nd low, both which are pretty similar. Those gears also work very good for when you need to carry a little momentum for steep long climbs. I for sure can't crawl everything. I don't have NDT tires :)


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 2:26pm
Originally posted by jpet jpet wrote:

Originally posted by Metcalf Metcalf wrote:

....-Having an engine that will lug down and be able to recover will stretch out your gearing. The ol' Buick 225 odd-fire is really good at this because of the VERY heavy flywheel. My engine will lug down below 200rpm under a load. I have watched the tach bottom out on zero and had the engine recover. I think running a slightly richer idle mixture can help also. There is also something with being able to play with idle speed to find a happy medium between no load speed and speed under a heavy load while off the throttle. .....
This is the one disadvantage I have found to TBI, at least my stock setup. The 4.3 will lug down quite a bit, but at a certain point, when the computer feels a stall coming on, it will try to compensate with a 5 second fuel burst. . Even if it were just a second would not be as bad, but I'm stuck with a 5 second high idle. ... or, at least, I think that is what's happening.

Should have just done a carb ;) 

Did you read through that build thread I posted a link to in your build? That had a bit of info about deleting/modifying the 'stall saver' feature in the programming. That sounds like JUST what you need. Finding someone that knows about that might be a little challenging. From what I remember the guy with that build thread was very helpful on PMs. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote smfulle Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 2:45pm
Originally posted by Metcalf Metcalf wrote:

I don't have NDT tires :)


I spite of this one flaw, Rango is still pretty cool. Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 4:25pm
Originally posted by smfulle smfulle wrote:

Originally posted by Metcalf Metcalf wrote:

I don't have NDT tires :)


I spite of this one flaw, Rango is still pretty cool. Wink

Thanks. It gets around ok. Ouch
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb. 2018 at 4:53pm
Quote  Spent my 45 minutes on the phone with Jack today.
Wow you got off pretty easy. Ha Ha Ha !

Quote  If I were to build another flatfender...no telling what I might build, but it would definitely CRAWL and RUN 75 mph.
Note: Has not installed his Rockeaters yet and he's already got plans to upgrade.

Quote  My flatty is a heavy mod.....225 V6, T18, D18, 5.38s, 35" tires. I can't think of many, if any, cases where I have wanted or needed lower gearing than that and I am at 83:1 

Right, with proper engine that's about as slow as most ever need to go. 

On a side note: 
Willys Motors was never officially credited with the development of the modern Rock Crawler.
The terms "Rock Crawler" never existed but it became a reality in 1956 with the installation of the T98-A @ 84/1 crawl ratio.
That said IMHO the T98-A / F-134 combo was not geared low enough for all situations due to lack of power.
Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963)
Zero aftermarket parts

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