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Double Trannys

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by pcorssmit, Feb 9, 2001.

  1. pcorssmit

    pcorssmit 1/2 ton status

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    Is anyone out there running a double tranny setup using an auto in front of a manual? I know I've read of a couple double sm465 setups, but I prefer an auto. I need a new tranny pretty bad, but don't want to do it until I figure out the t-case scenareo. The new ORD gen2 doubler looks promising, but I'd rather have an extra trans in between. Ideally I'd like to have something that I can run in direct gear with the 35's, and one gear down with the 39.5s. Anyone tried this or got any ideas? I'd like to run a 205, and not have it much longer than my current slip yoke 208.

    For the guys with the double sm465s, how'd you do it? Are the input and output splines the same, or did you have to get custom shafts made?

    Thanks,

    Pete


    '83 K5, 350 TBI (ex 6.2), Dana 60/14 bolt, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  2. pcorssmit

    pcorssmit 1/2 ton status

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    Some of you guys must have at least thought about this.

    Pete

    '83 K5, 350 TBI (ex 6.2), Dana 60/14 bolt, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  3. HarryH3

    HarryH3 1 ton status Author

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    Years ago, when I lived in Florida, there were lots of guys that did this on custom, off-road only, swamp buggies. (Real swamp buggies, not those things they race on ESPN). These things had tractor tires mounted on truck axles, so they had to gear way down to compensate for the tall tires. As far as I know, they were all home made.

    Seems to me that it would be tough to get both trannies and a t-case to fit under a K5. Don't the trannies have male shafts at both ends? If so, you would need some pretty long adapters and couplers to fit them together. If you could figure out a way to convert a tranny input shaft to a female spline, then the combined length would be a lot shorter.

    I've often thought it would be a cool thing to have. Splitting the gears between the two trannies would give you a bunch of gear ratio options!

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  4. pcorssmit

    pcorssmit 1/2 ton status

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    One thought I had was that Advance Adapters sells some female output shafts for autos. Another issue is which manual tranny to use. It seems the truck trannies are stronger, but the gear ratios of a car trans would work out better. I'm assuming a 205 would be the best t-case to use. I had also thought about the potential length problem. Ideally the gear below direct (ie 3rd in a 3 spd) would be in the 1.3-1.5 range. A granny gear in the manual would be pretty much useless. However if a more compact, single speed t-case were used it would work out, but I don't think I'll find anything strong enough thats much smaller than a 205. A divorce mount might be feasable in a long bed, but certainly not in a Blazer. I'd really like to be able to gear it down a bit with the Swampers on the street, since I'm vibration limited to around 60 mph, but this may become less of an issue as I've begun looking for a trailer.

    Do you know if the swamp buggies were running an auto and a manual or just two manuals?

    Pete

    '83 K5, 350 TBI (ex 6.2), Dana 60/14 bolt, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  5. HarryH3

    HarryH3 1 ton status Author

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    The female output shaft would certainly shorten things. Are they splined to mate with a tranny input shaft or a t-case input shaft? I don't know if you could find a match on the splines. Car trannies typically have closer spaced ratios, but few are rated to take the torque you'd be putting into them. A 465 could probably take the abuse, but since it's really a 3-speed, the ratio spread is pretty big. It's earlier cousin, from the 60's GM trucks, has a different ratio spread. It's also pretty noisy. It sounds like it might have straight-cut gears. [​IMG]

    Clark 5-speeds, which came in zillions of school buses, have lots of different ratio options, but adapting one could be a challenge.

    The Gear Vendors overdrive will do what you want, but it ain't cheap. But then, neither is adapting 2 trannies together. [​IMG]

    Advance Adapters has their Ranger Torque Splitter <A target="_blank" HREF=http://www.advanceadapters.com/BUYERSGUIDE/acrobat/ranger.pdf>http://www.advanceadapters.com/BUYERSGUIDE/acrobat/ranger.pdf</A> but it doesn't appear to fit with an auto tranny. It looks like it will only work with a 4-speed manual.

    The swamp buggy guys run dual manual trannies. Simple and effective. You don't want to have to walk out of the Everglades! [​IMG] Of course, their rigs are not even remotely street legal, so top speed, comfort or asthetics don't really weigh into the equation! [​IMG] They LOOK home made! [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  6. ftn96

    ftn96 1/2 ton status

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    What in the hell would you wanna do this for? you planning on building a home made Grave-Digger or something? For that kinda length you outta be looking at a suburban. I just cant see how that will all fit under a Blazer.

    No offence on the opening sentence. Just seems a little too bizarre. But hey, its all good. Just wondering what the hell your planning on doing, thats all.

    Will work for beer, parts and tools.
    90 Jimi,350/700R4/241/10bolts/4.10's/33's/4"
    <A target="_blank" HREF=http://www.nashvillek5.freeservers.com>http://www.nashvillek5.freeservers.com</A>
     
  7. HarryH3

    HarryH3 1 ton status Author

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    So he'll always have the right gear ratio. Leave the 2nd tranny in 4th gear (direct drive) with his short tires, on the highway. Then run the 2nd tranny in 3rd gear when he's running his tall tires on the highway. Of course, the possibilities off-road get pretty interesting as well. Imagine granny low in the 2nd tranny, 1st gear in the main tranny and low range in the transfer case. Can you say CRAWL??? [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  8. Butch

    Butch 1/2 ton status

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    Maybe this overly simplistic but why dont you just twin stick the 205 and run it in 2lo on the road with your big tires and let the RPM's run up a little

    I thought I was wrong once,
    but I was mistaken
     
  9. pcorssmit

    pcorssmit 1/2 ton status

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    ftn96, no offense taken. Actually, I thought it was kind of funny. Harry pretty much summed up what I want it for. I really need a new trans, but I hate to have one built with a 208 output shaft for the current t-case and then swap it out. I like the doubler, but it would be nice to have the extra gear choices.

    Harry, as for the '60s tranny, you're probably thinking of the SM420, used until '68. Its actually geared lower than the SM265 (its got a 7.05:1 first).

    I remember one of the four by mags a few years ago had a gear box that looked pretty cool, I think it had about 4 gears in it and was pretty small. I think it was called something like the Bradnob Mountain Box. It was a custom case using 18 wheeler gears and was air shifted. It would probably work really well for me, but it was like $3500.

    As for running the 205 in low, it would be too much reduction. It also wouldn't be enough reduction off road. They aren't really designed to be run all the time in low, either.

    I figured that with a 700R4, SM420, NP205, and 4.56s, the crawl ratio would be almost 200:1. Completely useless, unless you're running a Toyota 22R.

    Pete

    '83 K5, 350 TBI (ex 6.2), Dana 60/14 bolt, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  10. HarryH3

    HarryH3 1 ton status Author

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    SM 420 sounds right. The ol' grey matter couldn't come up with that yesterday! I think it has a different gap between 3rd and 4th than the 465. Maybe it was between 2nd and 3rd. Been a lot of years!

    Yeah, you wouldn't want to accidentally blip the throttle on a healthy V8 with a 200:1 reduction. KaBoom! [​IMG] Something would come apart for sure. Just a 300 lb/ft engine would be putting 60,000 lb/ft to the axles! [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  11. pcorssmit

    pcorssmit 1/2 ton status

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    Trans: 1st 2nd 3rd 4th 5th
    SM420 7.05 3.57 1.70 1.00
    SM465 6.58 3.58 1.57 1.00
    NV4500 6.34 3.44 1.71 1.00 .79 (93-94 Chevy)
    NV4500 5.61 3.04 1.67 1.00 .79 (95+ Chevy, Dodge)

    Of the above, the SM465 looks best (highest 3rd gear)

    Pete


    '83 K5, 350 TBI (ex 6.2), Dana 60/14 bolt, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  12. HarryH3

    HarryH3 1 ton status Author

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    Actually, just the NV4500 all by itself looks the best to me. Run 4th gear on the highway with the tall tires and 5th with the short tires. You still have a granny low first for the trails. Of course, you lose the torque converter. [​IMG] It's certainly a lot shorter than any 2 trannies combined. And certainly easier to install! [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  13. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    I think you're going to be length prohibited from messing with 2 trannies. The 465 case along is 12" long, and the 205 is about 12.5", so with no adapters you're as long as you want to be.
    Personally, I'd say buy a Doubler for the low range, and then get a trailer. That's about the simplest way to solve the highway/offroad problem! What if you (gasp wheeze) switched to TH700? Then you have overdrive with the small tires, direct with the big'uns and a lower first to boot. Keep in mind that even a decent big block will struggle to put out over 400 lb ft at our altitude.
    What axle gears do you have?
    BTW, we're working on an adapter configuration that will allow you to use the TH400/208 (2.5" stickout) output shaft with a 203, that way you don't have to swap the output shaft. It adds a little length, but it's still shorter than the 208 overall.

    Making the world better, one truck at a time.
    [​IMG]
    SW-ORD
     
  14. Bigd

    Bigd 1/2 ton status

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    I was just looking into this same thing.Just for your info.There is a machine shop in Utah that stacks two NP435's.These where used in i think 60's chevys and ford used them for a long time i think.It is a granny low tranny like the sm465.The setup adds 12 inchs too the tranny length.The brochure states it can handle 45,000 Gvw.THe only problem is the price.He wants 3000 for the setup.I believe he changes the input and output the trannies then mates them with a one inch adapter.Just though you would like too know.
     
  15. pcorssmit

    pcorssmit 1/2 ton status

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    OK, first off I edited my signature. Thought I had the trans listed, but I guess not. I'm running a 700R4, NP208, and 4.56s. The gearing works out great with the 35s, around 3000 rpm at 95 mph. Second gear slips bad, and I'd buy a new tranny before Moab but I don't have time to do any custom stuff before then (ie Doubler). Probably this summer. Can't wait to finally be rid of that diesel torque converter! I had thought about a 4L80E, but I don't see ever getting around to putting a big block in it, so the 700 should work, and the 1st gear is better. My 350 isn't exactly a powerhouse, I'll probably add a cam at some point but I don't see it ever getting too crazy. I was gonna convert the 208 to a short shaft, I think I have all the parts I need except for the yoke, but I'd like a little more gearing and mostly be able to quit worrying about the 208. I am pretty good at changing range forks, though (I now carry a spare).

    Funny you should mention it, I actually started looking for a trailer over the weekend. Been wanting one for a while (that was half the reason I bought the Dodge), but storage was a problem, solved now. Problem is, most of the used ones I see are 16', 7000 lb. GVW, and I want an 18', 10,000 lb GVW.

    By the way Stephen, not sure if you remember me or not, but I've met you in Moab a couple times, the first time in the City Market parking lot back when the shackle flip was still in the prototype stages.

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     

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