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color of spring
On Fri, 20 May 2016 12:12:06 -0700, Savageduck
wrote: On 2016-05-20 18:44:44 +0000, nospam said: In article 2016052011225163926-savageduck1@REMOVESPAMmecom, Savageduck wrote: When you start talking about brakes on 18-wheelers then you are dealing with vaccum and/or air-brake systems which will typically lockup if there is a vaccum pump or compressor failure. The most common brake failure on heavy trucks is overheating due to over use on serious downhill grades. One typical grade of that type is on the Northbound I-5 over the Tejon Pass, better known as 'The Grapevine'. There you will find two runaway ramps below the summit. The second one is a failsafe to be used if the first one is missed. best of luck if the brakes fail after the second ramp. The ramps are 9.5 and 9.8 miles below the summit, quite near the bottom. Miss either one of those and you have to negotiate the final wide curve to the left to where the I-5 in the Central Valley is billiard table flat, so you can roll to a stop. brakes don't pick a convenient place to fail. The biggest problem these truckers have is overheating brakes, or a missed shift which leaves them out of gear on the steep grade, and dependant on brakes, which are doomed. There is no way that a loaded 18 wheeler could safely descend such a hill on friction brakes alone. The driver will have changed down several gears and using an engine brake (if he has one) and a retarder also (if he has one). God help him if he misses a shift and ends up trapped in a neutral gear. There is also a CHP brake check station on Northbound I-5 before they reach the summit. The most use made of the runaway ramps is by large bus type RVs which don't equate themselves with other heavy vehicles. .... and are driven by less experienced drivers. -- Regards, Eric Stevens |
#2
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color of spring
On 2016-05-21 01:06:31 +0000, Eric Stevens said:
On Fri, 20 May 2016 12:12:06 -0700, Savageduck wrote: On 2016-05-20 18:44:44 +0000, nospam said: In article 2016052011225163926-savageduck1@REMOVESPAMmecom, Savageduck wrote: When you start talking about brakes on 18-wheelers then you are dealing with vaccum and/or air-brake systems which will typically lockup if there is a vaccum pump or compressor failure. The most common brake failure on heavy trucks is overheating due to over use on serious downhill grades. One typical grade of that type is on the Northbound I-5 over the Tejon Pass, better known as 'The Grapevine'. There you will find two runaway ramps below the summit. The second one is a failsafe to be used if the first one is missed. best of luck if the brakes fail after the second ramp. The ramps are 9.5 and 9.8 miles below the summit, quite near the bottom. Miss either one of those and you have to negotiate the final wide curve to the left to where the I-5 in the Central Valley is billiard table flat, so you can roll to a stop. brakes don't pick a convenient place to fail. The biggest problem these truckers have is overheating brakes, or a missed shift which leaves them out of gear on the steep grade, and dependant on brakes, which are doomed. There is no way that a loaded 18 wheeler could safely descend such a hill on friction brakes alone. The driver will have changed down several gears and using an engine brake (if he has one) and a retarder also (if he has one). God help him if he misses a shift and ends up trapped in a neutral gear. The posted speed limit for trucks on the decent is 35MPH. Most of those 18 wheelers are equipped with compression release engine brakes, better known as a 'Jake Brake'. Before they start the decent there are frequent signs advising of the grade, the speed limit for trucks, and that a lower gear should be selected before starting down the grade. The last thing those drivers want to do is depend on their friction brake systems, they will fry their brakes before they are half way down. http://www.crashforensics.com/tejonpass.cfm https://en.wikipedia.org/wiki/Jacobs_Vehicle_Systems There is also a CHP brake check station on Northbound I-5 before they reach the summit. The most use made of the runaway ramps is by large bus type RVs which don't equate themselves with other heavy vehicles. ... and are driven by less experienced drivers. Sometimes. -- Regards, Savageduck |
#3
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color of spring
On Fri, 20 May 2016 18:46:55 -0700, Savageduck
wrote: On 2016-05-21 01:06:31 +0000, Eric Stevens said: On Fri, 20 May 2016 12:12:06 -0700, Savageduck wrote: On 2016-05-20 18:44:44 +0000, nospam said: In article 2016052011225163926-savageduck1@REMOVESPAMmecom, Savageduck wrote: When you start talking about brakes on 18-wheelers then you are dealing with vaccum and/or air-brake systems which will typically lockup if there is a vaccum pump or compressor failure. The most common brake failure on heavy trucks is overheating due to over use on serious downhill grades. One typical grade of that type is on the Northbound I-5 over the Tejon Pass, better known as 'The Grapevine'. There you will find two runaway ramps below the summit. The second one is a failsafe to be used if the first one is missed. best of luck if the brakes fail after the second ramp. The ramps are 9.5 and 9.8 miles below the summit, quite near the bottom. Miss either one of those and you have to negotiate the final wide curve to the left to where the I-5 in the Central Valley is billiard table flat, so you can roll to a stop. brakes don't pick a convenient place to fail. The biggest problem these truckers have is overheating brakes, or a missed shift which leaves them out of gear on the steep grade, and dependant on brakes, which are doomed. There is no way that a loaded 18 wheeler could safely descend such a hill on friction brakes alone. The driver will have changed down several gears and using an engine brake (if he has one) and a retarder also (if he has one). God help him if he misses a shift and ends up trapped in a neutral gear. The posted speed limit for trucks on the decent is 35MPH. Most of those 18 wheelers are equipped with compression release engine brakes, better known as a 'Jake Brake'. Before they start the decent there are frequent signs advising of the grade, the speed limit for trucks, and that a lower gear should be selected before starting down the grade. The last thing those drivers want to do is depend on their friction brake systems, they will fry their brakes before they are half way down. http://www.crashforensics.com/tejonpass.cfm One of the worst thing about that hill is that as drivers descend the hill they will encounter an easier stretch at the 6 mile mark. This will tempt those who don't know the road to change back up a gear or two. Then they will hit the really steep part with hot brakes and in too high a gear. It's at this point that a belated attempt to change back down again may result in a missed gear change. If he is lucky the driver may be able to get back into too-high a gear but that won't help him much over the next several miles. No wonder they have run off roads. https://en.wikipedia.org/wiki/Jacobs_Vehicle_Systems Yep, and variations thereof. Some Allison automatic transmissions have hydraulic retarders built into them. Separate retarders are not uncommon in Europe (and hilly New Zealand). These may be hydraulic or electric. https://en.wikipedia.org/wiki/Retard...engineering%29 For an electric retarder see http://i00.i.aliimg.com/img/pb/980/5...web10_8277.jpg or http://tinyurl.com/zpb7uzm There is also a CHP brake check station on Northbound I-5 before they reach the summit. The most use made of the runaway ramps is by large bus type RVs which don't equate themselves with other heavy vehicles. ... and are driven by less experienced drivers. Sometimes. -- Regards, Eric Stevens |
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