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Old 02-09-2015, 02:19 PM   #1
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Stemco Wig Wag - What does it do? And Why?



It would appear to be related to compressed air and the STOP sign, but how does this STEMCO WIG WAG work and why do you even need it? Does it matter which way you push the lever? Why is in such a prominent position? I'm sort of guessing it is some sort of failsafe so the STOP sign works even when compressed air fails....
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Old 02-09-2015, 03:58 PM   #2
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http://www.stemco.com/product/wig-wags/

http://en.wikipedia.org/wiki/Wig_wag...raking_systems)
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Old 02-09-2015, 05:19 PM   #3
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I think they're cool, first truck I drove with air brakes had one. It was a manual reset, won't stay up if air pressure is too low. There certainly isn't any doubt if the pressure goes down. I wish I had one just for the heck of it.
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Old 02-09-2015, 06:13 PM   #4
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Wig Wags came in several different versions, one of which is still required under state spe'c for NY.

If your air pressure for your brakes ever goes below a certain PSI it will drop. Which is why some of them have stop lettered on them.

Without air pressure you won't stop which is why it will drop before you can't stop.

Some, like the one pictured, have to be reset by hand. Others will go up as the air pressure goes back up.
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Old 02-09-2015, 07:55 PM   #5
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Quote:
Without air pressure you won't stop which is why it will drop before you can't stop.
Actually, without air pressure you WILL stop. Modern air brake systems use air to release the brakes. No air the brakes are on.
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Old 02-11-2015, 10:05 PM   #6
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Quote:
Originally Posted by cowlitzcoach View Post
Without air pressure you won't stop which is why it will drop before you can't stop.
Quote:
Originally Posted by somewhereinusa View Post
Actually, without air pressure you WILL stop. Modern air brake systems use air to release the brakes. No air the brakes are on.
Both are correct. The parking brake, or "spring brake," is set by a strong spring and held back during travel by air pressure. If you lose your air, the parking brake valve pops out releasing the "emergency" air. The springs are no longer held back and the parking brakes apply themselves.

On the handful of trucks I've driven, the front wheels have one air canister for service brakes only. The double canisters for service brakes plus spring brakes were only on the rear axle.

The foot pedal or treadle activates the service brakes by applying pressure to the system. If you lose air, the service brakes go away.

Dick is the professional driver, so I won't say there are not any systems with an air solenoid that inverts the air pressure and allows springs to set the service brake shoes, but I don't believe that is the way they commonly work.
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Old 02-12-2015, 08:12 PM   #7
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Both are correct. The parking brake, or "spring brake," is set by a strong spring and held back during travel by air pressure. If you lose your air, the parking brake valve pops out releasing the "emergency" air. The springs are no longer held back and the parking brakes apply themselves. ...
I don't know when these systems first appeared, but interestingly, I discovered that Dodge trucks and school buses with air brakes are so equipped back in 1976.

After going thru. training and becoming a prof. school bus driver, I found out why so many folks here prefer air brakes. These emergency systems are a great idea!
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Old 03-11-2015, 07:02 AM   #8
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A follow-up question...Having fixed the severed airline and run the engine, the Wig Wag stays "up". However the next day the air pressure has dropped (you can see from the air pressure gauge on the dashboard)

Is this normal? Do I need to try and find the leak or is this to be expected? I.e. when the bus is running the compressor produces lot of pressure so a little loss is not important. One side effect is that in order to run the radio and get rid of the low air pressure warning noise I have to run the engine - and running a big diesel for short periods is not a good idea.
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Old 03-11-2015, 08:21 AM   #9
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Originally Posted by timbrass View Post
Is this normal? Do I need to try and find the leak or is this to be expected? I.e. when the bus is running the compressor produces lot of pressure so a little loss is not important. One side effect is that in order to run the radio and get rid of the low air pressure warning noise I have to run the engine - and running a big diesel for short periods is not a good idea.
I'll probably get jumped on here, but it is pretty normal. If the vehicle doesn't have an ACC position with the ignition key, I usually rewire the radio so it will play with out having the key on. You just have to remember to turn it off when you leave.
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Old 03-11-2015, 01:02 PM   #10
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Air systems leak down over time, even when new, there are standards on how fast they can leak out but overnight is fine. The spring brake is piggybacked on the rear service brake, uses same brake shoes. Your low air pressure alarm should come on when the pressure goes below 90 psi, the air brake valve should pop out and set the spring brakes at about 60 psi. You can hold it in and drive until the pressure goes below 40 psi at which point the pressure is too low to overcome the springs
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