4106 Drive train choices

[Len Silva]

I am looking at two different 4106's.  One has the stock 8V-71 with a VS2-8 and the other has a 6V-92 Turbo with a V-730.

All things being equal in amenities, condition etc. what are your views on either combination.  To me, fuel economy is a bigger factor than performance.

Thanks,

Len

[Barn Owl]

Len,

What type of driving do you mostly do? Hills or flatland? There are pluses and minuses to both I believe, but those factors depend on where you will mostly use it. From what I have read (No real world experience) I think the 6V-92 w/ V730 would be a better combination. But, if fuel mileage is what you want then I have read the VS2-8 would be better. If I have time I will try to find the old post that supports those statements if you don't get the responses that you need. I'm sure there are many who will respond that will know a whole lot more about this than I do. I love my auto (8V71 w/V730), it allows me to go places that would burn up a clutch.

Laryn

[Buffalo SpaceShip]

Laryn's dead on about the MPG. The VS2-8 was a high-OD model used on GM's Suburban New Look transits and often coupled with a very high rear-end to allow the transits to run at highway speeds. On a 4-1/8 rear end typical of 35' parlor coaches, the DD will turn very slowly at speed compared to even the 4-speed Spicer. The V730, by nature of it's higher bevel gear ratio, will spin rev the DD even faster than the stock stick. On a flat road, the VS2-8 would sloooowly walk away from the V730... and get better MPG doing it.

It's when things get hilly, the V730 becomes much better-suited. It's a true torque-converter lockup three-speed tranny, and almost bulletproof. The VS2-8 is technically a two-speed OD tranny, and can really heat up when stuck climbing in hydraulic mode. Also, in stock config the VS2-8 will shift up at a given rpm... making them dangerous on downgrades. I'm told that this limitation can be resolved with some "plumbing".

I've had coaches with both trannies... and I prefer the V730, even with the MPG hit. Others may not agree, and that's fine. I know that I won't go back to a 4 speed coach. The high-geared 1st and reverse make them untenable in our camping lifestyle. Now... if I ever get a t-drive coach (or toterhome, etc.), I'd pick a 13-speed RoadRanger over a slushbox.

Then, there's the turbo motor. If you ever drive anywhere above 3,000 feet, you'll appreciate the boost. I've taken my normally-aspirated 8v71 over 10,000 feet... and it sux. Even here at mile-high elevations, it's really struggling.

Bear in mind, neither installation is stock. So take a long, hard look at the rear bulkheads on each coach. The auto tranny requires opening up the bulkhead, and major reinforcing would be necessary.

HTH,
Brian B.

[Barn Owl]

Brian,

How hard is it to get VS-2 parts or service? It has been a while since they were made, right? Very good point about the turbo. I learned alot reading TomC's posts about them.

[Utahclaimjumper]

Len, I have the VS2-8 in my 06, I live at 5600 ft. and travel the west, I wish I had the 6V92 TA as a buddy has. I installed a 5:55 rear end to bring down the gearing, so I basicly have a three speed slightly overdriven in top gear( tops out at 85 MPH @ 2300RPM) This unit climbs well with propane injection use for the hills.  the VS2-8 does NOT require a mod to the bulk head on the 06, the drive shaft is shortened to 17 inches and thats it. I never get any overheating issues, but this combination can be challenging when decending long twisty hills that require speeds less then 18 to 20 MPH, it will shift into free-wheeling and leave you with only service brakes( sometimes 18 is faster than you want to go down a mountain) All in all I like my setup but a guy can wish cant he?>>>Dan 4106-1261

[TomC]

I have the V730 and for a three speed, really works well.  I have 4.625 (4 5/8) gearing so my 65 mph cruise is at 2100rpm and tops out at 73 at 2350.  I like the full control you can have with this transmission.  If you pull it down to first (shifter is R-N-3-2-1), I can get torque converter lockup down to 15 mph.  And going up a long hill can get lockup by just pulling up on the gas pedal by about an inch, so the trans doesn't burn up like it would on a VS2-8 at the same speed.  Parts are readily available since there are alot of commercial buses still in service using this transmission.  The main part of the transmission is basically a HT740 without first gear.  Very dependable, although it would be nice to have one more gear. Good Luck, TomC

[RJ]

Len -

Brian did a very decent job of describing the differences between the two powertrains, so I won't go into that.

However, let me add a few points:

The stock bevel gear ratio in an OEM 4-spd 4106 is 0.808.  The bevel gear ratio in the V-730 is 0.875, somewhat lower, so, as Brian mentioned, slightly higher RPM at the same road speed.

There is, however, a way around this to bring the V-730 back to almost the same rpm at speed as the stick, and that's going to 11R24.5 tires - but you have to shop very carefully for ones that turn 470 - 475 revs/mile.

Why?, he asks. . .

A quick background - the OEM powertrain for both your 4104 and the 4106 was designed around tires that turn 495 revs/mile.  If you do the math, you'll see that the 11R24.5 I mentioned above turns about 5% less rpm than OEM - which, again if you do the math - is almost identical to the difference between the OEM stick bevel gear ratio and the V-730's. 

Bingo!  You've got some of your fuel mileage at cruise back!

One final point, and that is that your fuel mileage will still suffer somewhat when you use your coach more around town, like most automatics.  But, with the tires I mentioned above, your highway mileage will be very close to that of a stick.

Still less than a stock 4104, but close to a stock 4106.

Between the two coaches you're looking at, the 6V92TA/V-730 is the more modern powertrain.

FWIW & HTH





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