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Author Topic: what are the weight limits of towing 4905  (Read 2504 times)
Lonnie time to go
Lonnie
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« on: March 12, 2009, 07:19:59 PM »

I have a GM 4905  What I need to find out is what are the limits of towing.  I have a CDL so over 10.000 won't be a problem.  I have read old posts which state that there is a limit on the weight the bus itself can handle.  Hope I can get  some good info thanks
Lonnie
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1976 4905
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« Reply #1 on: March 12, 2009, 07:42:09 PM »

I don't know of any state that has manditory scales for RVs so I would let the towing equipment and trailer dictate the weight. A pintle hitch setup and some semi axels and rubber could be good for 20,000 lbs. How strong is the back of your bus?
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« Reply #2 on: March 12, 2009, 09:16:50 PM »

How strong is the back of your bus?


I think that is what Lonnie is trying to find out.

I know a lot of GM buses don't handle towing to well but I seem to recall a thread that mentioned that some hounds pulled some fairly heavy cargo trailers.  I think that may have included the 4905's.

One very important key would be to minimize tounge weight.  If it needs to be a heavy trailer, I would seriously consider one of these:  http://www.mrtrailer.com/stinger.htm
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Charles Seaton
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« Reply #3 on: March 13, 2009, 11:57:14 AM »

Greyhound never had 4905s but both Scenicruisers and MC 7s were used as cargo haulers.
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Jeremy
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« Reply #4 on: March 13, 2009, 12:23:08 PM »

If it needs to be a heavy trailer, I would seriously consider one of these:  http://http://www.mrtrailer.com/stinger.htm


'Tongue weight' is an issue for me too, and I have considered this type of device but cannot believe they can be a satisfactory solution on vehicles with large rear overhangs, and therefore the potential for lots of vertical movement at the tow hitch. It seems to me that a drawbar trailer is the obvious answer, but 'small' drawbar trailers seem very rare and I would be a bit concerned about getting one custom built without fully understanding the geometry of the drawbar mechanism first. They'd be difficult to reverse too, but other than that seem to be by far the best solution to the problem.

Jeremy
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Lonnie time to go
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« Reply #5 on: March 13, 2009, 12:31:27 PM »

Stinger Hitch is a great idea.  I do know that the tongue weight must be in proportion to the total weight of the trailer.  My main worry is what kind of tongue weight  can my bus handle without worry of damage.
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1976 4905
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« Reply #6 on: March 13, 2009, 01:26:17 PM »

Greyhound Canada still pulls trailers, with DL and G coaches. A lot of the DL's have Cat engines and 7 speeds.....Bill
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gus
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« Reply #7 on: March 13, 2009, 01:40:24 PM »

Older GM buses support the engine weight almost completely from the upper rear overhanging body structure. I assume the 4905 has the same monocoque body construction as the earlier ones.

If that is all true then the tongue weight is the deciding factor.The other important part is to make sure the horizontal part of the hitch is firmly attached to the lower body of the bus, not just to the engine cradle. If the horizontal bar is attached only to the engine cradle then all the trailer pulling force will be taken by the two huge bolts that hold the cradle to the firewall.

Unfortunately I have no idea where to find out what these limits are and have never seen them listed anywhere. If anyone knows this it is RJ.
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PD4107-152
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Lonnie time to go
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« Reply #8 on: March 13, 2009, 03:46:16 PM »

.
http://www.sherline.com/lmbook.htm#refrn9

Found this site, if correct the max percent of a trailers weight on the tongue
is 15%.  So if i guess the trailers weight at 10.000 lbs and the tongue weight
at 1500 lbs.  Then will ( if hitch is properly mounted ) support 1500 lbs of
tongue weight.
the bus is a 1976 p8m 4905A
Hope this info helps

.
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1976 4905
sdibaja
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« Reply #9 on: March 13, 2009, 06:36:37 PM »

Tongue Weight is a minor issue for the 4905...
mine pulled a VW Thing with No notice but that was only 2500 pounds, maybe less... BUT if I hit a bump just right the front wheels of the VW would shimmy and really shake my tail.
the 4905 has just about no structural "beef" in the tail... I think the dynamics of a heavy tow slamming around if you drop a wheel of the edge or into a ditch could rip the tail off the bus.
My hitch attached to the bumper and also had 2" square tube in a big triangle running up to the corners of the bulkhead.  Beefy but maybe not 10,000 pounds worth.

and, what about braking?  a long grade with a bunch of extra weight heating up the brakes... think you should consider active brakes on the tow if you are packing much.

safety fist but balls to the wall!
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« Reply #10 on: March 13, 2009, 06:59:57 PM »

I sure wouldn't expect to be able to hang an extra 1500 pounds on the engine cradle (tongue weight).

sdibaja, keep in mind that there are two very distinctly different forces involved.  Total trailer weight and tongue weight.  Both are important, but the killer for several bus designs is tongue weight.  That is the weight pushing down on the hitch and therefore directly adding to the effective weight of the engine cradle.

In my opinion, even highly balanced heavy trailers could over stress things when going through dips.  For example, a loaded tandem axle trailer with a gross weight of 10,000 pounds gross balanced to keep tongue weight down to 500 pounds.  I suspect the dynamic loads while going through those dips could go way past the design limits of the cradle mounts.

I have wondered about the vertical travel issues with Stingers.  I wonder if a person could build a better version themselves and incorporate a coil spring and shock absorber to allow for some vertical movement of the wheel while still carrying the tongue weight.
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TomC
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« Reply #11 on: March 13, 2009, 07:15:50 PM »

Most any bus with a V drive (including my AMGeneral transit) has the engine/transmission in a independent cradle supported by 4 big bolts-two at the bottom front and two at the top back at the rear of the bus overhang.   The big deal is tongue weight.  The pulling weight can be compensated for by adding square tubing to the hitch and run it up to the suspension subframe.  Personally-wouldn't put much more than a few hundred pounds of hitch weight-and certainly not over 1,000lbs on the back-or else you might get some sagging or cracking of the rear most bus structure.  This is one of the big reasons I am converting my old Kenworth-because I want to pull a big trailerable trawler or cabin cruiser and it has a full truck frame.
Another consideration is startability with another 10,000lbs behind your bus.  If you just have a 4 speed manual, your startability on a hill is just barely enough to get the bus going-let alone with another 10,000lbs.  If you have a V730 automatic, it probably won't be a problem.  There are dollies made that will take vertical weight off the hitch-might consider that.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Lonnie time to go
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« Reply #12 on: March 13, 2009, 08:15:05 PM »

Thanks I think my question was answered. My thought are anything more then a small car is to much.  I just wanted to make sure.  It would have been nice to be able to tow the extra weight.
Thanks again
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1976 4905
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« Reply #13 on: March 14, 2009, 06:21:13 AM »

while we are on this,....when towing a car (or van) four down, I have presumed that the tongue weight was negligible.  As a result I had thought that the toad could be pretty big behind a GM transverse engine bus.  Is this correct?
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luvrbus
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« Reply #14 on: March 14, 2009, 06:59:28 AM »

Guys, buy yourself a equalizer hitch and adjust to it any amount of tongue weight you choose it will put the weight on the trailer and they have been in use for years a simple solution to tongue weight problems.I have a friend that tows a 24 ft enclosed trailer behind his 4104 and has for 15 years with no trouble  good luck
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4905 doc
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« Reply #15 on: March 14, 2009, 07:10:24 AM »

My 4905 towed a 22' trailer with a 2000 camaro, a suzuki motorcycle, 2 electric scooters, a 20' ext ladder,(don't ask :-) my gas barbecue and a bunch of other stuff with no problems at all. I used a modified reciever hitch from a 1980 southwind motorhome. And may I say,Thank you Fred Hobe for the welding work. Smiley
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4905 doc
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« Reply #16 on: March 14, 2009, 07:11:44 AM »

I should mention, the trailer was enclosed.
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Lonnie time to go
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« Reply #17 on: March 14, 2009, 11:06:41 AM »

wow there is hope for me yet
thanks
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1976 4905
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« Reply #18 on: March 14, 2009, 02:12:29 PM »

no problem. my bus had 24 volt system, so I ran a wire from one of the start batts up to the dash mounted 12 volt electric brake controller. found some flat ground and dialed in the amount of brake drag while the bus was rolling. Now that trailer won't stop the bus Grin but every bit of drag helped in a panic situation.
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gus
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« Reply #19 on: March 14, 2009, 04:52:03 PM »

Zub,

Since nobody responded to your question I will.

The tongue weight of a four-down toad is very little. Since you can pick it up you can see that it is very little.

The horizontal pull is not much either once the speed is stabilized. However, if it jerks around a lot that will put some big horizontal loads on the bus if the toad is real heavy.

What we are talking about here is rolling load, nowhere near the actual toad weight.
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PD4107-152
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