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Author Topic: Two speed rearend???  (Read 1814 times)
OneLapper
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« on: February 28, 2010, 05:25:59 PM »

I could have sworn a couple years ago I read about a two speed rearend in a 4106.  I searched the forum but came up dry.

I'm preparing to pull out my "7V71" and install a fresh(er) 8V71 from NIMCO.  I have a spare rear axle from a 4106 I scrapped last fall (Rockwell 58 series, 4.13:1, mfg date of 4-64) that looks to be in really nice shape.  At least it's not leaking fluid like the one in my bus!

I would LOVE to install an underdrive to split the gear ratios, but if I recall the issue is the short drive shaft length, or was is the angle drive on the pumkin?  Is it at all possible?

I'm sorry if this a re-hash of an old topic!

Mark
1964 4106-2853
4 spd Spicer
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OneLapper
1964 PD4106-2853
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TomC
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« Reply #1 on: February 28, 2010, 11:10:00 PM »

I too have a V drive on my AMGeneral transit (with a V730).  My rear overhang is long enough to use a T drive (in fact the Canadian versions did have T drives).  I looked into getting a two speed rear end, and Meritor (new name for Rockwell) doesn't make one.  It would be great to put a three spd Browning in, but manufacturing the mounts and trying to make it work would just plainly be daunting.  The 4106 has a higher then most horsepower to weight ratio-it is considered to be the hot rod of buses.  The easiest is to increase the injectors from 55 to 65 for more horsepower, but of course will probably get worse fuel mileage.  How fast do you have to go?  If startability with the 4 spd manual is an issue, installing an Allison V730 will alleviate all that-but again you'll loose fuel mileage.  But what a joy to drive!  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Len Silva
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« Reply #2 on: March 01, 2010, 05:46:14 AM »

There was a guy in California who developed a two-speed rear for the V-Drives.  I got a little info on them and published it here: http://autos.groups.yahoo.com/group/gmc-busnuts/files/GM%20Two%20Speed/

Not a lot to go on.
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« Reply #3 on: March 01, 2010, 09:36:31 AM »

I asked a lot of truck drivers, wreckers and tranny guys about two speed rear ends for my bus.  There were a few who either had them or had used them successfully, but for the most part the feedback I got was that they are rare because it turns out it's too easy to miss a split with them when coming down a grade, and if you do you're out of luck until/unless you stop the vehicle to re-engage them.  Evidently they don't easily re-engage when things are spinning... resulting in the first stages of a runaway...
  So for that reason, most people I talked to did not recommend messing with them...
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1962 Crown
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gus
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« Reply #4 on: March 01, 2010, 06:46:44 PM »

4104s, and probably 4106s, had an option of a two-speed clutch but nothing about a two-speed rear.

I've never seen one but would sure like to have one even if a couple of the ratios are almost the same.
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PD4107-152
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Ash Flat, AR
buswarrior
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« Reply #5 on: March 01, 2010, 07:10:18 PM »

Some one in the Great Lakes area has one of those rare factory 4104 transmissions that lets you split each gear.

Well executed, and the engine room could be used as a dinner table when i saw it some 6-7 years ago at a rally.

Who knows who?

happy coaching!
buswarrior
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Frozen North, Greater Toronto Area
Hard Headed Ken
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« Reply #6 on: March 01, 2010, 07:38:14 PM »

The transmission with the splitter built in was the Hydra-Shift I had one in my 4104. I don't think it was available in the 4106 because it has a slightly differently drive angle than the 04. The Hydra-Shift does what it's supposed to do, but it's not easy to shift. Splitting ever gear was not easy. I usually just used it as a 5 speed. It did work good in the hills, there was a gear for most ever situation. For anyone who has one or finds one, the Hydra-Shift has two clutch packs and planetary gears like an automatic. There was a factory update for the high side clutch where the thickness of the metal plates was reduced enough to allow an extra fiber plate. If the trans doesn't have this update it's not dependable.

Ken
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« Reply #7 on: March 02, 2010, 03:17:32 PM »

It must not have been very popular since they are so rare but it sounds good in the book.
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PD4107-152
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Ash Flat, AR
OneLapper
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« Reply #8 on: March 02, 2010, 05:48:05 PM »

I'm not looking to go faster.  It'll go 85 all day long, even on seven cylinders!  I'm really looking for a lower first gear.  I live in New England.  We have some serious hills, and getting going on a hill with my car trailer behind can be a real clutch chattering experience!  And then there's always the slight grade when you don't need third but can't pull it in 4th, unless the engine is screaming at 75 - 80 mph.  If I try to pull a hill at 65 in fourth, forget it.

I've never heard or read about the cluth planetary gear setup.  Sounds like the TA on my '58 McCormick International crawler.  That things works great, but when they break, forget it.  Toss the tractor away.

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OneLapper
1964 PD4106-2853
www.markdavia.com
buswarrior
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« Reply #9 on: March 02, 2010, 07:15:37 PM »

Welcome to the limitations of the V-drive.

With all the ingenuity of the busnut community to date...

There are a couple of ZF V-drive automatic set-ups that were competitors to the Allison.

And there's the Bill Teal overdrive for the V730...

Otherwise, we haven't heard on these boards of anything else you can do.

happy coaching!
buswarrior
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Frozen North, Greater Toronto Area
RJ
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« Reply #10 on: March 02, 2010, 07:27:04 PM »

One -

I seem to remember having a conversation with either a fellow busnut who no longer posts on this bbs, or maybe it was with Tom Campbell, the GM guru in Williams, CA, that the Suburban transits delivered with a manual gearbox have different ratios in them than the Parlor cars.

IIRC, first three are lower, with a big gap between 3rd & 4th.

Makes some sense, when you consider the revenue service application - one's running around town, the other is running down the highway.

Dunno if you can mix/match to come up with something "perfect" for RV applications.

It's too bad GM never built these with a well-spaced five-speed!

FWIW & HTH. . .

 Wink
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RJ Long
PD4106-2784 No More
Fresno CA
buswarrior
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« Reply #11 on: March 02, 2010, 07:35:16 PM »

If ever there was time for a v-drive renaissance...

The horrible loss of interior space to the low floor transit designs, a return to a modern v-drive would give us back some seating capacity down the back...

Trouble is, no player is in a position to make it happen.

No financial return big enough to pay for it.

Perhaps the conditions that GM encountered in the beginning?

Or, the conditions that drove them out of it?

happy coaching!
buswarrior
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Frozen North, Greater Toronto Area
OneLapper
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« Reply #12 on: March 02, 2010, 09:12:58 PM »

The problem with "wanting" a better transmission option in my 4106 is that the ROI (Return On Investment) would never happen!  I'm sure I could spend $15-20k on a solution, and the bus would be worth less because I tinkered with it!!! 

I can see why the transmission options are limited.  I have a transmission sitting on my driveway.  It really isn't all that big!  Dimensionally a gearbox with more speed probable just wouldn't fit.  That's why I though someone put a two speed rear end in a 4106.  Too bad a GearVendor underdrive wouldn't fit.

Hmmm..  Since I have the entire drive train to a 4106 sitting in my driveway, I figured I would mock the whole setup together and see what options come to mind!
 
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OneLapper
1964 PD4106-2853
www.markdavia.com
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