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02-05-2008, 08:47 AM #1
OT: Chains hanging from truck back axle
Being on the road for service work most days I have seen on occasion over the years seen chains hanging from the back axle of some larger trucks. Odd thing is that it seem to mostly been on fire engines or emergency vehicles. At first I thought perhaps it was a place of convenience to hang the chain in case of need. But not too long ago I noticed it on a large delivery truck. I sped up beside of the truck and to get a better look and the chains seem to be hanging off the brake assemblies or rather the small round cannisters mounted on the back axle. Does this have to do with what I now suspect is weight issues for the vehicle and brake system?
I'm stumped, I've googled, ask around and found nothing for 6 months. Does anyone here have a clue as to why the chains are there? And yes when you spend most of your day on the road you begin to wonder and at times even ask aloud stupid questions.
02-05-2008, 09:02 AM #2
It's always been my understanding these chains provided a method of grounding to a vehicle, breaking a static charge.(which I would think is quite welcome on a gas truck...)
02-05-2008, 09:04 AM #3
they sound like check chains to me
this is to only let the axle drop down so far ...when its jacked up or goes over rough terrain.
usually there, to prevent road spring or such falling out ...or the stretching brake pipes.
all the best.markj
02-05-2008, 09:29 AM #4
They Are Auto Tire Chains In Use up here in AK by the THOUSANDS...
Many rigs up here have auto tire chains, School Buses, Fire Apparatus, Ambulances, etc have them. The chains are on a angled wheel , that when lowered, lets chains hit ground,. When they hit ground they fling themselves under tire for no hassle traction, Not ideal for LONG trips, but work fine when needed. Perfect for me, it is -30 F right now and putting a tire chain on with a switch would be much easier on hands and back...
Here is a pic of one style in down position:
And a view from behind raised:
02-05-2008, 09:37 AM #5
See them an most emergency vehicles around here. I'm pretty sure bigstu has it right. Static eliminators. They merely hang from the undercariage. Only attached at one end.
02-05-2008, 09:42 AM #6
Not For Static See Above Post
NOT FOR STATIC SEE ABOVE POST
Static ground would be seen on Tanker Trucks mostly, ( Some of which are forbidden to use Chains due to spark and Tank puncture danger.)
02-05-2008, 10:09 AM #7
abarnsley, I missed your links. Very interesting. That is obviously what Rusty was refering to. I was thinking of the two or three individual chains I see hanging under fire/rescue vehicles around here. (not located near the rear tires) My bad.
02-05-2008, 10:22 AM #8
My best guess would be for static also. I would think that pulling hose off of or putting it back on a truck could in the right conditions create quite a charge.
Also the gear that firemen wear could also create static energy.
Then there is the water pumping, I know that heliocopter/water rescues have problems with static created from the rotor and water vapor stirred up. I've never figured that one out because I have only experienced static electric during lack of humidity.
Rescue vehicles- not good to shock someone while loading or unloading. The strecher padding material might be a factor here.
02-05-2008, 10:43 AM #9
We have them on school busses out here, and I don't think static is all that much of a problem with school busses :-)
Funny thing is, whenever there is the SLIGHTEST hint of even a rumor about the possibility of maybe there being a snowflake, they cancel school.
02-05-2008, 10:45 AM #10
Abarnsley is correct, they're powered snow chains.
02-05-2008, 10:46 AM #11
Some large trucks run a loop of chain around each side of the axles to keep the suspension from overextending and breaking the air bags or shocks, biggest problem seems to be with Internationals. If it's just a single chain and not a loop, then maybe it's for static discharge, although the static discharge devices I have seen on trucks consists of a flexible strap.
02-05-2008, 11:03 AM #12
they are snow/ice chains, they are not powered
the actuator simply posistions them so that as the tire rotates
it catch and the chain, and causes it to start rotating
as the vehicle is driven down the road the chains really start spinning giving the
illusion that they are rotating under power, when the reality is they are not.
my business partner just bought a set last week off ebay,
for the life of me i cannot remember the manufacture, other than
it is a German company.
02-05-2008, 11:19 AM #13
We have the automatic chains on all the school buses around here as well.
02-05-2008, 11:51 AM #14
02-05-2008, 03:48 PM #15
I was under the impression thaat lamp black (carbon) was added to the rubber mix for making tyres, purely to make them conductive for static discharge.
02-05-2008, 04:00 PM #16
You guys that have actual experience with them, do they work when backing up?
02-05-2008, 04:11 PM #17
the chains are for grounding any static charge that may build up. The local Kroger store had a static build up problem with the shoping carts, you could get a blue spark 3/8" long off them. 4" of chain screwed to the bottom tube and draging the ground fixed it, no more static charge
02-05-2008, 04:26 PM #18
They're snow chains. All the Gov. vehicles have them in MT. They'd have to hang down on the ground to have any grounding effect right? These don't... when not in use they hang in mid air.
Not to mention sparks flying from chains on the ground....
02-05-2008, 04:31 PM #19
02-05-2008, 04:34 PM #20
Not for grounding as dragging chains create sparks, drop links, send metal flying, etc. There are other more reliable methods for that. Shopping carts - well that's another matter. They work there and on the chairs we have here in the plant - all for ESD purposes.