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Old 02-16-2007, 07:44 PM   #1
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Driveline Gear box/transfer case?

Hey guys. I know many of you have been really helpful before and may know I am looking for better gear ratio solution.

Three years ago I was pointed toward an overdrive transfer case in which the drive shaft would have to be shortened. I was told about $2000 for the job.
Of course at the time I wasn't ready to spend 2k on a transfer case and then have a tranny randomly go out on me that I could possibly have replaced with a 5 or 6 spd. Anyway. My AT545 is in great shape, shifts like a cadillac(or any other model you thinks shifts great
I just received some info that I have yet to follow up on directly, but I heard that I could have the drive shaft shortened and get the gear box and install it for less than I would spend on getting gears changed. The information comes from an good friend who is a retired railroad engineer and former professional sprint car driver. he knows his stuff but I haven't talked to him personally about this yet.

Anyway My tranny is good. Tools for the installation are no problem. I think it would be ideal because I have low end gears and an overdrive on open highway. I guess I am just asking for info and opinions from anyone who has done it or checked into it themselves etc.. Is having a bus size drive shaft shortened expensive? Do you have any idea who makes these units and where to look for them?

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Old 02-16-2007, 08:39 PM   #2
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Auxiliary transmissions, both over and underdrives, are pretty common from Jeeps all the way up to to big rigs. As to whether or not it's going to be cheaper for you...well....that depends on how expensive the unit itself is for you. I'm thinking you would be getting a junkyard unit. I really don't know if a divorced or married type woulbe be cheaper to be perfectly honest. A married unit would simply require that you shorten your existing driveshaft, but you would have to mate it to the tailshaft of the transmission which can sometimes mean a bit of work. It would also likely need another crossmember. A divorced unit wouldn't require transmission surgery, but would require that your existing driveshaft be shortened and a new one made up for between the transmission and the overdrive unit itself. You would also need a crossmember for it. Do you have more information on the specific unit you're looking at?
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Old 02-18-2007, 08:35 AM   #3
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i've also contemplated adding an auxillary trans/overdrive unit.

i think another consideration is how fast you spin the drive shaft. ie: you woulnd't want to double the top end speed of the bus, but a small increase should be fine. Spinning teh drive shaft faster also spins the gears inside the differential faster.

I think the aux overdrive unit is a great idea. One idea i toyed around with is finding an aux trans out of an old logging truck. These transmissions were divorced and were used to lower the gear ratio of the trucks, and many had 4 speeds. The input/output shafts are the same size which allows the unit to be turned around and used to increase the gear ratio ie: make the truck go faster. You could even set up a small air cylinder to move between gears. (I don't think it would be easy to move to all 4 gears that way, but you could choose between 2 gears that are straight up/down from each other) I also thought that a small trap door in the floor would be a good idea so you could manually move the gear selector in case the air shifter didn't work.
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Old 02-18-2007, 06:03 PM   #4
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married? divorced?

I am still single so I don't fully get the metaphor I don't have a specific unit in mind. I have a high mechanical aptitude with a medium amount of experience. Based on hat i've heard I visualized what I think is a married unit but didn't anticipate any surgery to my tranny. Is married one that connects directly to the tranny on the front end and the other side it connects to the shortened drive shaft? I guess I imagine that a short shaft could be used between unit and tranny. ???

I am not really concerned about high speeds. I just want to reduce RPMs(and engine noise/fuel consumption) at 55mph without permenantly giving up my low gear power. Also it would be great to go 65 steady for a few hours when the interstate is the only option.
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Old 02-18-2007, 09:16 PM   #5
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You've got it on the married versus divorced set up, Joe. Married attaches to the tailshaft of the transmission and usually requires a different output shaft/housing. A divorced unit mounts aft of the transmission and is connected with a small "spud shaft."
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Old 02-19-2007, 06:21 PM   #6
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Thanks

Thanks guys. Yeah, I am going to look for a used unit, but I want to find out who makes them new etc..
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Old 03-01-2007, 07:18 PM   #7
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google gear vendors, i think they make the product you are looking for
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Old 04-24-2011, 07:04 PM   #8
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Re: Driveline Gear box/transfer case?

just found this site, they have a good Q&A section, they say that they have a married gear splitter that can match up to almost any tranny to give under / overdrive, just thought id pass it along
www.gearvendors.com
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