4107 thoughts

[RoyJ]

Roy -

Perhaps this will help you visualize the GMC V-Drive.  It is "flopped" from the actual orientation, but you'll get the idea.  (I actually got it oriented correctly in my photo editing software, but you couldn't read the notations!)  In your mind, "roll" the engine assembly over the rear axle so that the transmission bevel gear is in the lower RH corner, and you'll have the proper layout.

Thanks for the info RJ. That's one crazy looking setup for sure! Clever way of packaging though.

This will definitely increase torque/power loss over a regular transmission; it has two extra bevel gears.


The typical rule is, you can make a driveshaft as long as you want, and you'll loose zero power, whether static or moving. Same applies for u-joints near zero angle. The reason is, a drive shaft has no moving components, and therefore, cannot dissipate any power, except for the minute amount of elastic deformation of metal.

As soon as you put a bevel gear, straight gear, or pulley, it becomes a moving system. Gears have to mesh, and rubber belts have to constantly roll along a metal ridge, both of which create rolling friction. And again, since static friction > rolling friction, the greatest torque loss of a moving system occurs at zero rpm / velocity.

[artvonne]

  Lets just agree to disagree on torque loss, Ive read too many books by engineers that contradict each other I dont know if anyone really knows. Even automotive manufactures disagree on HP measurements and how to accurately measure it.

  I drove down and met Rick and his wife and family yesterday and checked out his Bus. It was an absolutely beautiful day through very beautiful country, that was only surpassed by the breathtaking view from Ricks own back yard of the Buffalo river valley. I thought I had a pretty place. For those who havnt been through the Ozarks and the Buffalo river, its really worth the trip. Ive been through most of the US and just cant think of anywhere prettier.

  Rick showed me around his Bus, and not having been around any Bus in over 20 years, I had forgotten how nice 4104's could be. Then he took me for a ride up the road a ways and back, and boy am I hooked. He has a real nice rig anyone should be proud of.

  And now im all confused. I really had my heart set on a 4107, followed by a 4106, but tooling around in Rick's 59 '04 really made me seriously rethink things. Engine offers more access, uses less fuel, systems a bit simpler. And it sounds from researching them they have better pulling power down low while still being able to reach freeway speeds. Certainly not 85 like an '06, but plenty fast enough. And maybe someone can answer what a standard 4104 should have for speeds in gears? Rick says 3rd is good for 55 or so, which seems high to me? How would a 4104 be for finding parts to keep it going?

[zubzub]

Pretty sure a '04 has worse pulling down low  than a '06.  Actually I'm hard pressed to think of any bus I've read about that has worse "startabilty".  I had to rock mine out of it's wheel ruts when I picked it up, it had traction put not enough guts to climb out.  Mine may be worse than most  though...it's the only '04 I've driven.  But I really like my bus, and the engine access is awesome.  Pulled my starter, "rebuilt" it and reinstalled in aprox 2 hrs and that was the first time I had done it and I was in a shopping center parking lot using road tools.  Problem with the starter, open the engine bay and engage it by hand (also works well when the batts are low as you don't waste current on the solenoide/bendix thing).  Parts availabilty seems good enough 'xcept they get turned in for scrap so much.  I think I remember that GM made more '04s than any other bus so that's good.  Problem area for me is all the vdrive stuff is on a different angle than for the rest of the GM highway coaches and the tranny is very specific....good thing is the tranny seems pretty tough.  Brakes are cool too as you can fit springs brakes from any truck stop on it (unlike '06 and possibly others).  The flat floor front to back is nice and there is the fact that an all original 4104 is a good looking bus. 

[RJ]

Art -

Pulled up my spec sheet on the 4104.

Bevel gear ratio = 1:1, located AFTER the transmission

First = 3.86:1
2nd = 2.50:1
3rd = 1.50:1
4th = 1:1

Two final drive ratios were available: 4.125:1 (stock) & 3:55:1 (optional, and VERY rare)

Forgot to look at the torque spec, but the 4-valve 6-71 puts out 238 hp @ 2100 rpm.  Can be boosted to 275 hp w/ a turbocharger.  Not uncommon to also set engine up for 2300 or 2400 rpm, they will survive.

No automatic available, unless you repower with a transit donor, must change rear axle, too (pumpkin's on the wrong side of the coach centerline for repowers).

TomC should have the torque specs for both NA and Turbo 6-71s, and can supply the gradeability.

5065 was the total number of 4104s built from 1953 thru 1960.  Early models had a generator, late production have alternators.  Originally 12V POSITIVE ground, most survivors have been converted to negative ground.

Good, solid, dependable workhorse.  Better built, too, than a 4107 or 4106.  More rivets, more aluminum, thicker skin.

Rear window glass is now made from unobtainium.

Front windshields, door, and driver's window glass is the same as all later production GM highway coaches.  (Scenic is different.)

One has to consider the time frame within which this coach was designed and built.  The Interstate system didn't exist till near the end of production.  Most highways were two-lane rural roads, on which 60 mph was considered "fast."  Simpler time, simpler machine, designed and built accordingly.

Understanding that time frame, and the related performance, equals enjoyable ownership.

Definitely The Tortoise from Aesop's Fable.

FWIW & HTH. . .

[artvonne]

  Has anyone around here looked at the 4107 in Cocoa Beach Florida? His fuzzy pictures have been on and off of craigslist for over a year now, andwhen I spoke to him a year ago he wasnt willing to send any more or better pics. I dont know if it would be worth looking at if he went down to $2500., its a long was for me to go to look at a dog.

  http://ocala.craigslist.org/rvs/1912449845.html

  Rick gave me a heads up, and I went to look at a 4106 conversion that popped up on craigslist yesterday over in Fayetteville. I am probably not the best person to rate it, but hes a bit high IMHO. Its a bit rougher than it looks in the pictures. Bags settle within a few minutes, add on electrical needs sorting, plumbing not real well engineered, but "works". Seems to start run and go down the road okay, but he wouldnt let me drive it so I cant comment on feel of controls. It has power assisted steering. OTR AC condensor and compressor are gone, gas tank for portable type 5500 watt gen in compressor bay. Gen cant power AC,s without tripping 20A breaker on gen.

http://fayar.craigslist.org/rvs/1925654535.html

[smokedetector]

I have talked to the guy in Cocoa. The first time he seemed like the bus was in ok condition and only needed cleaned up. We were planning to drive down and look at it and called him back, but something didnt seem right. The ad has changed many times and new pictures keep popping up. I knew he had the ability to take pictures and wouldn't so I didn't waste 2 days driving to look at. I have the feeling he is hiding something.

[TomC]

When figuring startability with a manual transmission, the engine does not produce full torque with clutch engagement.  Most all engine manufacturers will list clutch engagement torque rating on their engine.  For instance, the Series 60 produces 1650lb/ft torque, but makes 1000lb/ft torque at 900rpm for clutch engagement.  This is what startability is based on.
Figuring that a 6-71N with N65 injectors puts out 228hp (real horsepower) and 600lb/ft torque, this means that the engine probably puts out maybe as much as 400lb/ft torque for clutch engagement.  The 6-71T with N80 injectors could put out 300hp and 900lb/ft torque, and probably puts 550lb/ft torque for startability.
If we use the bus weighing in at 28,000lbs and the 3.86 low with 4.125 rear axle ratio and 485rpm 12R-22.5 tires, that works out to be-10.3% startability with the 6-71 natural and 14% startability with the turbocharged 6-71.  Not good-I've seen 4104's just about burn up the clutch trying to bump over a curb.  Just for emergency use, lets say that you are slipping the clutch to get it into its' torque range near 1500rpm.  The maximum startability on the natural engine (with full 600lb/ft torque) will be 15.4% and the turbocharged engine will be 23.2%.
Now lets intall a V730 into these buses and see how this changes with the same 4.125 rear end.  With the Allison automatic, the full torque of the engine can be used plus the 2.5 torque multiplication (on the V730, 2.0 on other Allisons).  1.77 first gear.  The 6-71 natural will have a startability of 17.7% and the turbocharged will have 26.6% startability.

For those that would like to fool around with startability-here's the formula.  First take the total weight of your rig and multiply it by 10.7 and put that figure into memory.  Then take the starting torque of the engine for a manual-or the full torque of the engine for Allison X Torque converter ratio if you have an Allison (2.5 for V730, 2.0 for all others) X first gear ratio X rear end ratio X tire revs per mile (actual).  Divide that by the figure in memory and that is your startability percent grade.  Good Luck, TomC

[artvonne]

I knew he had the ability to take pictures and wouldn't so I didn't waste 2 days driving to look at. I have the feeling he is hiding something.

  Thinking the same .