| Author | Message | ||
| Jim (Jim_in_california)
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What I mean is, for somebody who plans on doing as much of their own maintenance as possible, a lot of the 4104s/4106s out there are a good deal and came originally with 671 straight blocks and Spicer 4sp manuals. More or less half today seem to be repowered with 8v71s, half of those seems to be autos, probably old transit drivelines. Three thoughts: * The original drivetrain would be lighter on the aluminum frame and mounts. (I realize the weight difference isn't THAT extreme, the engine swap is just a couple hundred pounds difference - but an auto tranny is at least 400lb more, right?) * Running the rack on the straight block would be easier, and God knows what else. * Power oughta be adequate esp. with a 4valve head, and a real score would be to find one somebody did a proper turbo conversion on. Does this sound about right? Put another way...what's it like to wrench on an 8v71 in a fairly small bay, esp. on the back rack? Am I missing anything else regarding the pros/cons of these drivelines? | ||
| RJ Long (Rjlong)
Rating: N/A |
Simple answer: The PD4104, with the inline 6-71, is virtually unbreakable, and very simple to work on - for a bus! More complex answer: But it's also slow - top speed is 65. (Remember the children's fable about the tortoise and the hare? This is the tortoise.) Turbocharging the 6-71 in an '04 will give you the same HP as the stock 8V71 in the '06, but your top speed remains the same - it's all in the bevel gearing setup on this model ('04). Figure 30 mph up the Grapevine. . . There is no real significant power difference between a two-valve 6-71 head and a four-valve, except you can find Jake brake components easier for the fours. A 4106 will climb the Grapevine at about 45 in third, if you're not loaded down to 32K. (BTDTWB) With 11R24.5 tires, an '06 will top out a little over 80 mph, faster than most folk really want to push these things. If you repower a 4104 with a 350 hp 6V92TA/V-730 out of a transit, along with a 4106, 4107 or 4108 rear axle, the powertrain will weigh about the same as the stock '06, but will really get up and scoot! Same for the identcal swap into an '06, w/o the axle problem. Fuel mileage suffers, tho, 'cause then they're really fun to drive!!  "Running the rack" only has to be done about every 100,000 miles, unless something breaks. So you're not in there very often. There's also an access hatch inside the coach under the rear seat that makes it a lot easier - unless someone's blocked it off permanently. Probably the worst maintenance item on the V-block in a coach is the starter motor, as it's on the bulkhead side. Not impossible like the rear plugs on a big-block Pontiac Trans-Am, but awkward enough for body gymnastics and colorful language.  Ask any long-time bus mechanic, and they'll all agree that it's a LOT easier to work on a GMC V-drive than ANY of the T-drive coaches. Get out away from a computer screen and go see what I mean. . . GMC designed them that way for quick turn-around time in the shop - a coach doesn't make any money when it's sitting!! So, there you have it: Get yourself a 4106 repowered w/ the 350 hp 6V92TA/V-730, install a hitch similar to Daris Boutillier's (http://www.freewebs.com/darisb/), find a 30-ft toy hauler, put a Tuff-Tow on the trailer's tongue to keep the hitch load reasonable, and away you go! Problem solved! | ||
| Jim (Jim_in_california)
Rating: N/A |
Huh. Right. Well I think I can cope with 65mph. And I really do NOT need a 30ft toy hauler! As little as 10ft of pure "garage and shop" would be enough; going 18 - 20ft complete with "guest cottage" would be absolute max and those can be hauled around by a friggin' Pinto never mind a bus. I also suspect milage would be better with a Spicer 4sp on the floor versus more or less any auto, unless of course the overdrive feature of the 730/731 series matters a whole lot? | ||
| FAST FRED Rating: N/A |
80mph is a delightfull speed as 75 is allowed in the more advanced states . Only disadvantage is the RPM at 80 is too high for great milage. Keep it down to 73 on a stock 06 and 10 mpg is avilable . Works for me! The BEST part of these monocoque light weight coaches is when the 1936 engine finally dies , modern transit scrap will produce a 4 stroke engine , 4 or 5 spd (unfortunatly) automatic tranny, new rear with cheap avilable gears and BIG brakes. The transIT front will provide a very high cut angle and intergal PS if you need that and matching BIG brakes . ALL for $2000-$3000 and some heavy work! A KEEPER for the Next 60 years! FAST FRED | ||
| Doug Wotring
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My 6-71 is good for 78 MPH or so and gets 8-9mpg at those speeds. will also tow a Full size extra cab pickup effortlessly. except for really long grades speed is not really an issue. On a coast to coast run towing the truck I lost only 2 hours on what I did the same run with the truck alone the year before note this motor only has around 50k from new.... | ||
| mclough Rating: N/A |
Doug, what tranny and gears do you have. I have a 1957 4104 with a 6-71. i top out at 70 mph at 2150 rpm. and get about 10 mpg. i would love to get alittle more mph but i love this ole bus. I also plan on towing a 20 foot trailer total weight of 5,ooo lbs. mclough www.outreachacrossamerica.com | ||
| Jim (Jim_in_california)
Rating: N/A |
You know, if it's 35ft long and getting 10mpg, that is NOT shabby. If it can hit 70, all the better . The Wanderlodge crowd is pulling 6 or 7mpg with any of the Cat3208 series, doesn't seem to matter if it's a 210 non-turbo or the 225/250 turbo motors. Then again, they've got so much crapola on the roof it's not even funny...guard rail all round, and what the HECK is that bizarre square thingie top and center of those rigs? Radar array!? | ||
| RJ Long (Rjlong)
Rating: N/A |
Doug - Does your 4104 have the rare 3.55:1 rear axle in it? Or 11R24.5 tires? Jim - The mileage is better with the 4-spd Spicer in either coach. Let's see if I can thoroughly confuse you about the so-called overdrive V-730. But first, let's look at a stock GMC V-drive powertrain: PD4104: In the '04, the layout is engine, clutch, transmission, bevel gears, drive shaft, rear axle. The 4-spd Spicer, in 4th gear, has a 1:1 ratio. The bevel gear ratio is also 1:1. The stock rear axle ratio is 4.125:1 The OVERALL final drive ratio, then, in 4th gear, is 4.125:1. (Trans x bevel x rear axle) This is important, so keep it in mind for later in this post. PD4106, 4107 & 4108: In the '06, GM changed the powertrain layout slightly to accomodate the higher torque output of the 8V71 engine. Now you have engine, clutch, bevel gears, transmission, drive shaft, rear axle. The 4-spd Spicer still has a 1:1 4th gear. The bevel gearset ratio is 0.808:1. The stock rear axle ratio is still 4.125:1, altho the pumpkin off-set is different. The OVERALL final drive ratio is now 3.333:1 (Trans x bevel x rear axle) PD4903 & 4905: Same as the '06, except the stock rear axle ratio is 4.375, giving an OVERALL final drive ratio in 4th of 3.535:1. V-730 Basically, this is a three-speed version of the HT-740, but built into a V-drive configuration. Third gear lock-up has a 1:1 ratio - which is not considered an overdrive. (If it was, the ratio would be like 0.72:1.) The stock bevel gearset ratio is 0.87:1. Bolted up to a stock 4106 rear axle (4.125:1) gives an OVERALL final drive ratio of 3.589:1. Bolting it to a 4905 axle yeilds an OVERALL ratio of 3.806:1 It's because of the bevel gear ratio that folk think the V-730 is an overdrive gearbox. . . So. . . As you can see from the OVERALL ratios, in theory, the stock 4106 4-spd at 60 mph should get the best fuel mileage, as it has the tallest ratio. Conversely, the 4014 should be the slowest coach, as it has the highest ratio. In theory anyway, in reality, however, YMMV. Make sense?? OK, now to really screw things up: If you take the 4106 with a V-730 in it, and put 11R24.5 tires that turn 471 revs/mile on the drivers, you end up with a coach that's just about as fast as the 4-spd, but your fuel mileage is still lower, especially around town, due to losses thru the transmission when in un-locked mode. (Of course, a 4106 4-spd w/ these same tires REALLY flies!!!) Oh, one final note: A heavy trailer (6K+) behind a stock '06 is hard on the clutch in 1st gear - gotta be real gentle with a dead throttle start so you don't destroy it. Thoroughly confused now??? RJ | ||
| Jim (Jim_in_california)
Rating: N/A |
No, I actually followed that. One remaining question though: am I right in thinking that a lot of 4106s still came with the 671, even though the thing was designed to be able to take the 8v71? And if so, when you have a 671 in the 4106, you've still got the "even more overdrive" gears (rear axle, Spicer 4sp, etc)? NOTE: I'm assuming in all cases here we've got a manual tranny. | ||
| TWODOGS (Twodogs)
Rating: N/A |
4106=8v71 | ||
| Jim (Jim_in_california)
Rating: N/A |
Ah. Huh. Wait... You're right, I just checked a pile over at gmbusguy.com and our site here and 'cept for the one Cummins oddball transplant(!?) 4106s are 8v71s. OK. That's interesting. <scratchhead> Next question: anybody know the normal headroom on a 4104/4106? As in, at 6'4" in bare feet I can deal with dodging the AC units and whatnot but standing up straight some of the time would be kinda cool...? | ||
| RJ Long (Rjlong)
Rating: N/A |
Jim - The 4106 only came with the 8V71/4-spd manual powertrain. It was designed around this engine, not the inline 6-71. Matter of fact, when the first 4106 rolled off the assembly line in early 1961, it was the first production coach to utilize the then-new 8V71. At the same time, the 8V became an option on the New Look transit models, too. Lots of folk have repowered theirs with a 6V92TA. Maybe that's what you were thinkin'?? | ||
| RJ Long (Rjlong)
Rating: N/A |
Interior height in the 4104 & 4106 is 75-21/32" at the aisle. | ||
| Brian Brown (Fishbowlbrian)
Rating: N/A |
Not to hijack the thread or anything, but since we’re talking auto trannies… Should we thoroughly confuse the issue with the fuel-sipping, high OD slushbox: the estimable VS2-8? I'm seriously considering popping mine out of my FishBowl and into my new 4106. Don has raved about this combo (4106 + VS2-8) for years as the flatlanders, high-MPG solution. BTW, unless anyone's been under a rock, busnut-speaking, RJ is THE MAN on these GMC v-drive matters. Always great to read his posts... FBB / Brian 4106 | ||
| Jim (Jim_in_california)
Rating: N/A |
Sigh. Whereas I measure 76" in my bare feeties. Heck with it. I just hope I get enough moolah to do that Crown Postal . 87" tall inside. Heh. The wheelwells are only 6" tall, even if I have to put a showerstall on one I'll still avoid that "Neanderthal Hunch". | ||
| Doug Wotring
Rating: N/A |
Interior ht is not that much of a factor in my case and I am 6'6"....you really don't spend alot of time standing in your bus. I am not certain what rear end gearing I have off hand....have that info in the books in the bus. However I can tell you that I have a 4 speed from a Suburban fishbowl. this is a happy middlegound between the two 04 transmissions as theyy came from the factory. It has a 1st gear that is in the middle of the two 04 transmissions and also has a pretty fair lack of gearing overlap between 3rd and 4th. This was engineered this way due to the typical operations of the suburban coaches....either stop and go or highway speeds. We bought it as a new rebuild years ago with a second one as a spare...which I have since sold. oh yeah..running standard 22.5 wheels Goodyear on rears and Michelin on frt unfortunatley I cannot tell you the correct RPM off had either as I have an incorrect tach drive.....which reads to high. I have the correction sheet somehwere. | ||
| Doug Wotring
Rating: N/A |
back to the initial question: a transverse mounted 6-71 as in the 04 is the easiest thing in the world to work on...everything is right in front of you except exhaust. when you go to the V series some stuff has to be either accessed from inside the bus or underneith......and on an odd occasion you must pull the engine | ||
| NelsonThomas Rating: N/A |
My 4104 with the 671 motor will go just about as fast as any v-8 powered coach on at least half of every hill or mountain. See you at the bottom. Nelson, Knoxville ps. Please offer no contrary remarks about this post. I like speed as much as the rest of you but this bus fits my budget and I am working hard to convince myself that slow is ok. | ||
| Jim (Jim_in_california)
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Good food for thought. | ||
| Phil Dumpster Rating: N/A |
While I'm sure some will disagree, the VS2 is not a good choice for a parlour coach, conversion or otherwise. GM may have sold some parlour models with it, but I'd hate to have to drive one through a mountain pass. There are only two gear ranges useable on the highway, and there is no provision for the driver to select them manually. Downshifting on a hill is only possible by bringing the coach speed down to the point where it downshifts anyway, which kind of defeats the point of downshifting to begin with. Even then, you'll end up riding the brakes all the way down the hill to control speed. Parlour coaches don't have the same braking capacity as transit coaches. The risk of overheating the brakes and having them fade beyond usefullness is very real. Going up the hill, you either maintain 45-50mph to stay in overdrive, or fall below the magic speed and grind up the hill at 30 mph. Further, if you can't maintain enough speed to stay in direct (very steep hill or heavily loaded, towing, etc) you run the risk of burning up the transmission. VS2s are not designed to run in hydraulic mode for extended periods of time. They generate a lot of heat when in hydraulic mode. On the flat they are great. West of the Great Plains, there ain't a whole lot of flat terrain. Allison developed the VS2 primarily as a transmission that would allow a city transit bus to also be used in suburban service. Prior to this, suburban busses used a 2 speed hydraulic transmission like a city transit bus but with taller axle gears to permit higher speeds. A city transit bus wasn't suitable for suburban routes because it couldn't go fast enough, most being geared for 45 mph. A suburban bus wasn't suitable for city routes because of the taller gears giving poor stop-and-go performance. The VS2 was meant to bridge this gap and allow the same bus to be used for either service. Allison developed the V730 for a reason. | ||
| Brian Brown (Fishbowlbrian)
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Thanks for the well-written caveats about the VS2, Phil. Duly Noted. As to the other v-drive auto option, I probably wouldn't want to pay the penalty in fuel consumption and top speed to go with a V730. So, I guess I’ll stick with grinding them gears in my new '06 for the best all-around highway crusin'. Brian | ||
| RJ Long (Rjlong)
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Brian - Check your private email. . . and read my article about shiftin' here on this site! <shameless-plug!> | ||
| jerry breeden
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I have a 4104 with the spicer 4spd . I have to put a clutch in before my first ride. It is the stock drive train with 11R-22.5 tires. I want to know what cruising speed would be. thanks | ||
| Jim Bob Rating: N/A |
There are two possible rear end ratios in the 4104: 3.55 & 4.125. My 1959 '04 has the 3.55 axle, 12R22.5 tires & will go 75 on flat ground at 2150RPMs with N60 injectors. (Faster with the wind at my back!) It gets 9.75 MPG. (My nephew's 454 powered motorhome gets 6 mpg!) I know that the original RPM setting for the 6-71 was 2000, but they will turn 2350 for long periods in marine duty and 2150 for more miles than I could ever put on it. I also don't drive at 75 but more like 68 but it's nice to have the speed for passing. Jim-Bob |