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Old 15th January 2015, 02:16   #1
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Default Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

This question is for all of you who rebuild CJ Jeeps. Has anyone tried using two T-18 gearboxes one behind the other in a "Brownie auxiliary transmission" fashion to get a overdrive final output, in a CJ 500 3 speed. The 3 speed gear boxes are extremely popular for a dual gearbox option. One way of doing it is having the second gearbox between the transfer case and the rear propeller shaft.

My understanding is this (no one tells you on any of the forums), the second gear box I guess is mounted reverse and is usually kept in the 3rd gear to take off from stand still. This is because the third has 1:1 ratio. Please correct me if I am wrong.

First Gear box: 1 gear + Second gear box (reversed): 3 gear = 1 gear
First Gear box: 2 gear + Second gear box (reversed): 3 gear= 2 gear
First Gear box: 3 gear + Second gear box (reverse): 3 gear= 3 gear (1:1)
First Gear box: 3 gear + Second gear box ( reversed): 2 gear= overdrive

[First Gear box: 3 gear + Second gear box ( reversed):1 gear= extreme overdrive may not be practical]

If anyone has tried this please give us your valuable input. If I have to shift the second gear box stick just from 3 to 2 back and forth, then it looks like a nice working option for a overdrive. I would even permanently remove the reverse gear in the second gear box.

Ideas needed.

Last edited by GTO : 15th January 2015 at 14:45. Reason: Typo
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Old 15th January 2015, 18:36   #2
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Gulps! Are you planning this on CJ? Am not very sure there would be enough space for two GB to sit on that chassis? Should be a very interesting thread to watch

Do keep us posted, and i don't think we have any documented of this being implemented in Team BHP.
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Old 15th January 2015, 21:52   #3
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

I don't have any experience with Jeeps, but subscribed to this thread as the subject seems very interesting for a Mechanical engineer.
I have a simple question here, if Overdrive is the requirement why not couple another GB with such drive ratio instead of adding 2nd GB (added mass, reduced efficiency, etc)? Is there any specific advantage of using 2 GBs?
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Old 16th January 2015, 04:35   #4
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Quote:
Originally Posted by drsamuelk View Post
This question is for all of you who rebuild CJ Jeeps. Has anyone tried using two T-18 gearboxes one behind the other in a "Brownie auxiliary transmission" fashion to get a overdrive final output, in a CJ 500 3 speed. The 3 speed gear boxes are extremely popular for a dual gearbox option. One way of doing it is having the second gearbox between the transfer case and the rear propeller shaft.

My understanding is this (no one tells you on any of the forums), the second gear box I guess is mounted reverse and is usually kept in the 3rd gear to take off from stand still. This is because the third has 1:1 ratio. Please correct me if I am wrong.

First Gear box: 1 gear + Second gear box (reversed): 3 gear = 1 gear
First Gear box: 2 gear + Second gear box (reversed): 3 gear= 2 gear
First Gear box: 3 gear + Second gear box (reverse): 3 gear= 3 gear (1:1)
First Gear box: 3 gear + Second gear box ( reversed): 2 gear= overdrive

[First Gear box: 3 gear + Second gear box ( reversed):1 gear= extreme overdrive may not be practical]

If anyone has tried this please give us your valuable input. If I have to shift the second gear box stick just from 3 to 2 back and forth, then it looks like a nice working option for a overdrive. I would even permanently remove the reverse gear in the second gear box.

Ideas needed.
Hi drsamuelk,

I have extensively looked into this as a alternative to changing the axle ratios on a Jeep and you can read about it in the below thread:

http://www.team-bhp.com/forum/4x4-te...ml#post3543143 (Mahindra Transfer Cases)

But that being said, even if this is something that can be achieved in India with the available gearbox/trasfer case combinations, the biggest problem in your case would be the additional length of the gearbox. Things are tight in CJ to being with and the added length of the gearbox would leave you with a very short rear propeller shaft and a rather long front propeller shaft.

In case you are interested in calculating the real final gear ratio for your application do let me know. There is a quick tool to help with it.

Thanks.

Regards,

L.o.R
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Old 16th January 2015, 09:54   #5
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Quote:
Originally Posted by drsamuelk View Post
no one tells you on any of the forums
I think there is a reason for this. The 2nd gearbox - if you ever manage to make it work properly - brings unnecessary complexity, cost, weight & inconvenience.

End of the day, why would you? For 'overdrive'? The old CJs are as badly suited to high-speed cruising as a Tata Indica is to offroading. With the CJ's poor dynamics, handling, steering, braking capability & safety at speed, lower engine rpm should be the least of your concerns.

Nevertheless, there are simpler ways to accomplish cruisability:

- Should be easier to fit a 5-speed gearbox in the CJ500 (than the CJ340 where length is an issue).

- Taller final drive ratio (at the cost of low end torque).

- A ready solution like the Warn Overdrive. Related posts:

Quote:
Originally Posted by RedMM340 View Post
The Warn overdrive is a simple 2 speed gearbox that mates to the Jeep's transfer case and provides a 25% drop in engine rpm when engaged. It is a very old design that has been around for decades.
Quote:
Originally Posted by trammway View Post
Instead of creating the final gear as overdrive, the Warn overdrive model introduced new gear ratio between each gears. Hence a transmission in which the highest gear ratio is less than a one-to-one ratio. This means the drive shaft turns faster than the engine crankshaft. The overdrive feature saves fuel and, because the engine runs slower, engine wear and noise are reduced.

What I have got is the same Warn Design reproduced by ATV Mfg. for Mahindra Jeep transmission/transfer case specification. What makes the Mahindra Jeep different from its American cousins is that of Tooth and Spline counts in the transfer case, hence the regular or used Warn Overdrives will not fit directly into Mahindra Jeeps. Herm Till ford reproduced the gear with 29tooth and 15 spline count to suite the Mahindra Jeeps. The same is what I have got and going to be placed into my Jeep.

Instead of the normal 5speed gearbox with overdrive that provides an additional gear to rotate faster than the engine(crankshaft) RPM, The warn overdrive actually sits on the PTO port of Dana/Spicer T-19 transfer case and takes the input from transfer case main gear shaft and converts into different gearing ration and sends it back to the actual transmission. Because of this particular model, the warn model overdrive can introduce as much as double the number of existing transmission gears.

Currently my Jeep equipped with KMT-90 4 forward and 1 Reverse transmission, hence I'm running the Jeep with 10 gearing ratios including the 4 wheel drive Low mode. By installing the Warn Overdrive I will get 20nos of gearing ratio that will enable to choose huge range of gearing ratio according to my need.

The moment I enable the Overdrive all the gear ratio will be on the higher side, hence going to give me a smoother noiseless ride. Whenever I need to do Offroad the overdrive will be temporarily disabled by pulling the Overdrive lever back to the driver side position. Practically the overdrive will be left in engaged mode all the time as most of the time the jeep is driven on the road.

Now I will let the pictures talk about what are the items came with the Herm Tillford supplied overdrive baggage(Who brought this baggage all the way from USA?).
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Old 16th January 2015, 18:32   #6
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Thank you all for the valuable suggestions. I agree space is a big issue. Me and my friend have turbocharged his CJ500, (pics will be posted by him soon), now the the real use of a turbo is lost without an overdrive. We were looking for cost ideas for overdrive.
Warn costs $1100 and $950 for a used one.
and then I came across this video on youtube


and a lot of other videos with 2 and 3 stick shifts ( not ideal in Indian traffic),

which inspired me to read up more.

I guess for now, we have little choice but to use a 5 speed.
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Old 16th January 2015, 22:49   #7
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Quote:
Originally Posted by drsamuelk View Post
...Me and my friend have turbocharged his CJ500, (pics will be posted by him soon), now the the real use of a turbo is lost without an overdrive. ..
Could you please share on how you have managed the fueling?

Also, re: your gearbox issue, sell the 3+1 gearbox and get a 4+1 KMT90 from scrap. You get KMT90's starting from 7k.
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Old 18th January 2015, 00:28   #8
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

But still KMT-90 doesn't have overdrive ratio.
Quote:
Originally Posted by dhanushs View Post
Could you please share on how you have managed the fueling?

Also, re: your gearbox issue, sell the 3+1 gearbox and get a 4+1 KMT90 from scrap. You get KMT90's starting from 7k.
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Old 18th January 2015, 04:29   #9
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Yes 'dracul' is right the 3rd gear of T-18 and 4th gear of the KMT-90 is 1:1; no real advantage in swapping.
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Old 18th January 2015, 12:48   #10
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Quote:
Originally Posted by drsamuelk View Post
Yes 'dracul' is right the 3rd gear of T-18 and 4th gear of the KMT-90 is 1:1; no real advantage in swapping.
4+1 (KMT-90) with a suitable rear axle (lower ratio) should give an advantage of over drive compared with the current 3+1

PS: I'm repeating, I'm very much new to the world of Jeeps. Please pardon me if I'm blabbering something that isn't a practical solution.
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Old 18th January 2015, 16:07   #11
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Quote:
Originally Posted by dracul View Post
But still KMT-90 doesn't have overdrive ratio.
Quote:
Originally Posted by drsamuelk View Post
Yes 'dracul' is right the 3rd gear of T-18 and 4th gear of the KMT-90 is 1:1; no real advantage in swapping.
Ah, right. Well, you can also go for the 5+1 GB's (BA10, NGT520, 530 etc). I know a short wheelbase vehicle is short to fit these long gearbox's but, I know vehicles done so, and running properly. The rear drive shaft will look funny though.
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Old 19th January 2015, 12:48   #12
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Quote:
Originally Posted by drsamuelk View Post
This question is for all of you who rebuild CJ Jeeps. Has anyone tried using two T-18 gearboxes one behind the other in a "Brownie auxiliary transmission" fashion to get a overdrive final output, in a CJ 500 3 speed. The 3 speed gear boxes are extremely popular for a dual gearbox option. One way of doing it is having the second gearbox between the transfer case and the rear propeller shaft.

My understanding is this (no one tells you on any of the forums), the second gear box I guess is mounted reverse and is usually kept in the 3rd gear to take off from stand still. This is because the third has 1:1 ratio. Please correct me if I am wrong.
Hi Dr. Samuel,

Nice Idea.

Correct me if I'm wrong.

But to get the t90 to function as an overdrive, the gearbox will be driven up the rear output, and the top gear shaft will be the new output shaft for the t-Case or Rear Diff.

2.73:1 will become 1:2.73. (0.36)
1.51:1 will become 1: 1.51 (0.66)
1:1 will remain the Same.

http://www.werewoof.com/beast/drivetrain/drivetrain.htm

If the Auxiliary Gearbox (2nd T90) changes orientation, how will you mount a T-Case.

Regards,

Arka
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Old 19th January 2015, 22:02   #13
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

I assume he is not interested in running in four wheel drive while in overdrive, at any time?
If so, he can keep the TC linked to tranny #1, 'ay?
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Old 26th January 2015, 21:59   #14
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Whoa This *needs* to be tried out - if only for the super-crawl ratios possible (opposite of drsamuelk's stated req) before the TC.

[Thinking aloud] this with 5.89:1 on the axles, and 35 inch tires?
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Old 4th February 2015, 07:36   #15
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Default Re: Brownie Auxiliary Transmission as Overdrive (using two gearboxes)

Thanks everyone, its been a good food for thought and stretch of imagination, if not anything else.
For crawling there are videos on youtube where chaps have put a manual transmission behind an auto transmission in pickups, without reversing.


Mind you the second gearbox is non-clutched and will be a mother of all misery to shift. In the original Brown-Lipe-Watson type the rear propeller was split in two and the Brown -Lipe spicer was between the 2 pieces of the rear propeller shaft. Then again its without a clutch !!!.
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