| Author | Message | ||
| Austin Davis (Zimtok)
Registered Member Username: Zimtok Post Number: 51 Registered: 9-2006 Posted From: 216.37.73.226 Rating: N/A |
Has anyone ever tried to fit a 2 speed differential into a 4104 or similar bus? I would think that it would give you the option of highway speed gearing without sacrificing local city street gearing. In fact it may even help with gearing on local streets. I often think that the perfect gear for city streets is something between 2nd and 3rd or between 3rd and 4th. . | ||
| Bob greenwood (Bob_greenwood)
Registered Member Username: Bob_greenwood Post Number: 511 Registered: 7-2006 Posted From: 64.136.49.228 Rating: N/A |
you have no options,with a left hand engine & a V drive trans & an unusual rear end,you are pretty much stuck with what you have ,hundreds of people love the 4104 just like it is,they drive them up to 70,when they were designed for 60 mph roads in their day | ||
| Austin Davis (Zimtok)
Registered Member Username: Zimtok Post Number: 53 Registered: 9-2006 Posted From: 216.37.73.226 Rating: N/A |
Don't get me wrong I do love the 4104 and find that driving it is getting easier and more fun all the time. It crossed my mind that adapting a 2 speed diff would be difficult if not impossible due to the configuration. But I thought I'd raise the question and see if others had given it any thought. My bus seems to only have a top speed of around 63mph, which is ok for most of the driving I'll be doing. I wish I could get up to 70mph on the longer trips. . | ||
| Jim Wilke (Pd41044039)
Registered Member Username: Pd41044039 Post Number: 102 Registered: 2-2001 Posted From: 69.77.151.82 Rating: N/A |
Hi Austin, It's nearly impossible to do a two speed diff on a GM V drive bus because the differential has an angle built into it to match with the V transmission angle. "T" drive buses such as MCI, Eagle, Prevost, etc can use other differentials because the components originally used are standard. Some 4104s came with an optional splitter clutch in the bell housing that gave them 8 speeds but they are rare & trouble prone. I find that if the bus is running well, 3rd is a perfect city gear. It can be used from 20 to 50 in town if your throttle foot is gentle at the lower speeds (don't "lug" the engine.) City driving is no problem with these buses once you get the hang of up & downshifting at the right speeds. (Took me 5000 road miles in a 4104 to get comfortable with downshifting while rolling!) Once my brain/hand/foot got the hang of it, I can shift up or down even outside of the proscribed shift points by varying the engine speed while VERY lightly pulling the shifter towards the gear I want to go into. (Lightly so you can JUST hear/feel the gears rubbing together. When the teeth slow/stop, pull it into the gear. DON'T FORCE IT!! Your throttle will need to be the original cable type and well adjusted & greased for this to work as GM designed it. Honestly, the only trouble a 4104 has is hauling it's butt up tall hills & mountains. In the rolling hills, you learn to drive the way the old truckers did until about 30 years ago. They used to go like h_ll down the hill to build up speed to get up the other side. (This does not work well today in heavy traffic as you run over the guy in front before you get to 75-80 mph!) I have climbed 9% grades with my 4104, (towing an Explorer) full throttle in 2nd gear at 20MPH for 30 minutes at a time. You get the feeling that something may let go at any time but these old 6-71s are governed and very tough if in good shape. Bottom line (my opinion): Don't be in a hurry to modify the bus. Make sure the drive train, throttle, clutch linkage, etc is in good shape, so often these are worn so badly they are ready to fall apart and are improperly repaired by several generations of bad mechanics. For instance, when I got my 4104, it would not shift up or down smoothly. The problem turned out to be that since the throttle cable hadn't been removed & lobed in dacades, it had gotten stiff & would stick (open!). The "mechanic's" solution was to add 2 more throttle return springs, giving it a very heavy throttle and causing the throttle to actually close too quickly which made the engine decelerate too quickly to shift properly. When I maintained & adjusted the cable properly and discarded the extra springs, the bus almost falls into the next gear upshifting, very sweet! | ||
| Jim Wilke (Pd41044039)
Registered Member Username: Pd41044039 Post Number: 103 Registered: 2-2001 Posted From: 69.77.151.82 Rating: N/A |
Hi Austin, It's nearly impossible to do a two speed diff on a GM V drive bus because the differential has an angle built into it to match with the V transmission angle. "T" drive buses such as MCI, Eagle, Prevost, etc can use other differentials because the components originally used are standard. Some 4104s came with an optional splitter clutch in the bell housing that gave them 8 speeds but they are rare & trouble prone. I find that if the bus is running well, 3rd is a perfect city gear. It can be used from 20 to 50 in town if your throttle foot is gentle at the lower speeds (don't "lug" the engine.) City driving is no problem with these buses once you get the hang of up & downshifting at the right speeds. (Took me 5000 road miles in a 4104 to get comfortable with downshifting while rolling!) Once my brain/hand/foot got the hang of it, I can shift up or down even outside of the proscribed shift points by varying the engine speed while VERY lightly pulling the shifter towards the gear I want to go into. (Lightly so you can JUST hear/feel the gears rubbing together. When the teeth slow/stop, pull it into the gear. DON'T FORCE IT!! Your throttle will need to be the original cable type and well adjusted & greased for this to work as GM designed it. Honestly, the only trouble a 4104 has is hauling it's butt up tall hills & mountains. In the rolling hills, you learn to drive the way the old truckers did until about 30 years ago. They used to go like h_ll down the hill to build up speed to get up the other side. (This does not work well today in heavy traffic as you run over the guy in front before you get to 75-80 mph!) I have climbed 9% grades with my 4104, (towing an Explorer) full throttle in 2nd gear at 20MPH for 30 minutes at a time. You get the feeling that something may let go at any time but these old 6-71s are governed and very tough if in good shape. Bottom line (my opinion): Don't be in a hurry to modify the bus. Make sure the drive train, throttle, clutch linkage, etc is in good shape, so often these are worn so badly they are ready to fall apart and are improperly repaired by several generations of bad mechanics. For instance, when I got my 4104, it would not shift up or down smoothly. The problem turned out to be that since the throttle cable hadn't been removed & lobed in dacades, it had gotten stiff & would stick (open!). The "mechanic's" solution was to add 2 more throttle return springs, giving it a very heavy throttle and causing the throttle to actually close too quickly which made the engine decelerate too quickly to shift properly. When I maintained & adjusted the cable properly and discarded the extra springs, the bus almost falls into the next gear upshifting, very sweet! | ||
| Bob greenwood (Bob_greenwood)
Registered Member Username: Bob_greenwood Post Number: 512 Registered: 7-2006 Posted From: 64.136.49.228 Rating: N/A |
My bus was supposed to go 60 mph down the hyways in 1978..it will go faster..but..I drive 60, if the people behind me don't like it,they can go around,plus ,I get better mileage at 60 | ||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 1793 Registered: 1-2001 Posted From: 75.108.79.87 Rating: N/A |
I raised the max rpm to 2300 rpm and it would 70. Drove it many thousand miles like that. When I got my Eagle I also raised it to 2300 rpm and drove well over 100,000 miles with absolutely no problem. Find a portable tach and determine what your max rpm is. An additional 500 rpm will get you up to 70 mph I think. Richard | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 81 Registered: 12-2000 Posted From: 71.30.250.2 Rating: N/A |
There was a guy in California building two speed rears for the 4104 many years ago. I have some info on them posted on gmc-busnuts http://autos.groups.yahoo.com/group/gmc-busnuts/files/GM%20Two%20Speed/ This would be way beyond my capabilities but maybe someone will try it. Len | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 371 Registered: 10-2003 Posted From: 71.58.126.56 Rating: |
Your other option would be to change to the 3:55 rear which will increase top speed about 10mph; if goverened to 2250rpm with 11:00X20 tires or 12:oox22.5 tires, would run about 78 to 80 mph. The main drawback with the 3:55 ratio is starting out on a grade, and backing up. You will need a metallic clutch disc which will tolerate some slipping. You will have to avoid getting stuck at a traffic light on a hill. If you don't live in hilly areas, it would probably be ok. It will get over the road fine with the higher gears otherwise. What you use to pull in third might require 2nd gear instead, even though the road speed will be the same. The drive shaft is a little over 4 feet long, so a 2 speed could be fit in there. Forget it on a 4905.If you could find a hydrashift2 speed wet clutch setup you could have everything. The main problem is that they are scarce and most parts or knowledge about them next to non-existant. | ||
| Douglas Wotring (Tekebird)
Registered Member Username: Tekebird Post Number: 44 Registered: 10-2004 Posted From: 69.136.90.146 Rating: N/A |
another option, find yourself a transmission from a Suburban fishbowl, they have yet another gear ration setup.....with very little overlap between 3rd and 4th..... provides low gearing for city and high gear for highway. Thats what I have and it works great everywhere | ||
| Michael Malloy (Busnut06)
Registered Member Username: Busnut06 Post Number: 34 Registered: 6-2005 Posted From: 63.27.61.71 Rating: N/A |
Austin, give Wayne Crawford, Mifflintown PA a call. His dad, Sam and Wayne did it many years ago in thier 04 before Sam made his final bus trip. They are bus nuts from way back. If you are interested in talking to Wayne, email me for the number. Michael | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 372 Registered: 10-2003 Posted From: 71.58.126.56 Rating: N/A |
The one Crawford's put in theirs came out of my 04.Worked great when it worked. What would be nice is if the components could be studied and matched to some of the parts that are rumored to be from the VS series Allisons. Then some entrepneur could maybe make the units available again. A Bob Thomas near me had one in his 04 for 30 years and claimed he neved had any problems with it. He told me that he did add an external oil cooler to it. | ||
| Frank Allen (Frank66)
Registered Member Username: Frank66 Post Number: 42 Registered: 10-2005 Posted From: 205.188.116.13 Rating: N/A |
dont know much about it but did see a 4104 with a 2 speed rear end yrs ago at a dealer, wish i knew more, i am sure its not the only one Frank Allen | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 272 Registered: 11-2005 Posted From: 63.97.117.36 Rating: N/A |
Frank, What you saw was probably the optional 2-speed clutch. Using it is described in the driver's Operating Handbook. I get the impression that they were pretty rare and have never seen one. | ||
| Frank Allen (Frank66)
Registered Member Username: Frank66 Post Number: 43 Registered: 10-2005 Posted From: 207.200.116.13 Rating: N/A |
Gus , you are probly right, i just seen the button on the gear shift and assumed it was a two speed, sorry, guess i need to stick with what i know which wont take up too much space, thanks Frank Allen 4106 | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 274 Registered: 11-2005 Posted From: 63.97.117.13 Rating: N/A |
Frank, The only reason I know about it is I read it in my 4104 Operating Manual. I don't think it is even mentioned in the Maintenance Manual?? Sure would like to have one but I've read on the forums that they had a lot of problems. It would be nice if it worked! | ||
| Frank Allen (Frank66)
Registered Member Username: Frank66 Post Number: 45 Registered: 10-2005 Posted From: 205.188.116.13 Rating: N/A |
Gus i never had any experience with a two sp clutch, but you are right, thats exactly what a 04 needs, too bad tey didnt have a better transmission , thats the biggest reason i bought the06 instead of the 04, even that had trouble starting out on a slight upgrade Frank Allen 4106 | ||
| Gardner Kent (Gardnerkent)
Registered Member Username: Gardnerkent Post Number: 2 Registered: 2-2007 Posted From: 76.21.19.9 Rating: N/A |
That guy in California who built the two speed diffs did in fact exist. I talked to him . I'll check the reference above. But maybe someone can pick up the phone and answer all real quick? I'm asking for a guy who has been dragged into my closed Lowell Oregon shop with a toasted 2 speed rear end in his PD 3751. I remember a retired aircraft engineer? He lived on the Southern California coast I talked to him once 15 to 20 years ago. As I recall this guy had cast an entire case and splitter sort of thing that bolted on a stock rear end. I'm afraid my friend is going to need some parts or at least some set up info. Anybody out there know anything about these rear ends or where a guy might find some parts. I was told these rear ends worked pretty good and I know this poor broke down guy wants to save his rear end.No Pun intended!!! Please give me a call or Dave the guy with the 3751 with the blown after market 2 speed diff. Gardner Kent 415 850 9910 Dave PD 3751 250 951 1920 |
