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Old 10-06-2012, 05:12 PM   #15
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Per EM suggestion earlier in the year, I purchased the bottle jack he mentions, and I also have some 12T jack stands which I keep at home. I was going to put one in the coach, but don't know as I have anyplace to keep it aboard. I will give thought to having another bottle jack and keep it in the coach as well. Not sure I want to carry that weight and not use it much. Wood Blocks come to mind, to slip between the sections of the coach to keep it from dropping down on me, not sure that would work either.
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Old 10-06-2012, 06:15 PM   #16
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Algoma- Interesting thought.
I've shut off the engine while rolling just to see what happens and coasted to a stop. The air release/actuation for the park brake seems to act just like it does engine running, i.e. doesn't automatically actuate, at least within the 1st ~10 seconds which is about as long as I've run this experiment. There is air in the line & "roto chamber" brake release till I pull the Haldex brake knob out & release the air.
The DOT req'mt I was referring to (and I could have these fact wrong) is that if you have air actuated brakes, they require a back up system (tank) for operation beyond engine operation. If you have air service brakes, they require "redundancy," one variation of which is to have front & rear tank systems. The Avalanche & other air brake coaches I've seen have air gauges for front & rear systems so the operator can tell when she's got pressure sufficient to operate everything.
I haven't heard of a DOT req'mt to stop the coach/truck if the engine dies; I know SAE has such a requirement to shut off fuel pumping when the engine dies.
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Old 10-06-2012, 07:10 PM   #17
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The interesting thing about air brakes [atleast to me] is that you only need air pressure to release the brakes. Just like our parking brakes on the Alpine, std air brakes are actuated by springs and air pressure is used to pull against the springs and reduce the stopping friction of the pad on the drum. For example, if an air hose breaks or disconnects on a semi-trailer, the wheels lock-up. So on our Alpines, once the pressurized air in the reserve tank is depleted, you can no longer disengage the parking brake. So if you dont have air pressure, the brakes are locked on and you aint moving--strange but true!
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Old 10-06-2012, 07:44 PM   #18
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Quote:
Originally Posted by Old Scout View Post
The interesting thing about air brakes [atleast to me] is that you only need air pressure to release the brakes. Just like our parking brakes on the Alpine, std air brakes are actuated by springs and air pressure is used to pull against the springs and reduce the stopping friction of the pad on the drum. For example, if an air hose breaks or disconnects on a semi-trailer, the wheels lock-up. So on our Alpines, once the pressurized air in the reserve tank is depleted, you can no longer disengage the parking brake. So if you dont have air pressure, the brakes are locked on and you aint moving--strange but true!
Your post is not correct.
The service brakes are activated by straight air pressure, both front and rear. The parking brakes (only on the rear) are activated by springs when air is removed. That's why the brakes lock up when air is removed.
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Old 10-06-2012, 08:31 PM   #19
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Mike,
Because we have hydraulic service brakes and steering, if the engine dies you have lost control of the coach. As I said earlier, with the hydraulic release parking brake the brake immediately activates and you have a chance of surviving. With air brakes there is a reservoir of compressed air to operate the service brakes but you have still lost power steering if the engine stalls. With the air release parking brakes its seems, from your brief test, that you have neither service brakes, steering nor auto park brake activation. I think I am happy with what I have.
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Old 10-07-2012, 12:25 AM   #20
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Originally Posted by Old Rv'er View Post
Per EM suggestion earlier in the year, I purchased the bottle jack he mentions, and I also have some 12T jack stands which I keep at home. I was going to put one in the coach, but don't know as I have anyplace to keep it aboard. I will give thought to having another bottle jack and keep it in the coach as well. Not sure I want to carry that weight and not use it much. Wood Blocks come to mind, to slip between the sections of the coach to keep it from dropping down on me, not sure that would work either.
Re: wood blocking
Once upon a time (c. 1965), I worked at the San Francisco Bay Area Rapid Test Track and as the name indicates a lot of testing was done. In one case as we swapped out a test car's trucks [wheel/frame/electric-motor/brake assembly] to test another type of braking system.

The test car had to be lifted and set on some cribbing in order to: safely roll out the old trucks from under the car; fabricate the new equipment stanchions; roll in and connect the new trucks. The "cars" were about the size of a railroad box car and weighed about 40 tons.

Two four sided cribs made of railroad ties about 7' or 8' on a side was built under and toward the center of each end of the car [car end--truck--crib--middle of car--crib--truck--car end]. The car was lifted by a traveling crane (built into the building structure), the last layer of cribbing was slipped in, and car was set down upon the cribbing. This raised the cars up about another foot, but the total cribbing was about 5' high (ground to car floor). 40,000 pounds on each crib. Except for setting the last cribbing layer, nobody was allowed near the cars while they were hanging from the crane. But lots of work was done under the cars sitting on the cribbing.

Wood has really high crush resistance, the real issue is making the cribbing stable. For stability, the length dimension for each side of the crib base has to be greater than the dimension of the intended crib height.

In the end, packing this much wood along on on a road trip is not very practical. But if you have a flat surface at home it is possible to use wood cribbing of substantial size to hold up a coach. But, as hobbyists we aren't likely to have the proper sizes of wood just laying around.
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Old 10-07-2012, 05:49 PM   #21
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Check this forum occasionally even though we sold our coach in April. Had to respond on this one since I contributed to the crackpot air schematic after all the issues we had with low air pressure when cold. Forgot to add the tap for air horn to that schematic that E-Mike put together.

As Mike says, the tank is above the rear axle and slightly forward. I tapped the tee leading out of the tank at the bottom and put in a moisture release valve that can be accessed from the side of the coach. It allows moisture to blow out of the tank directly from the bottom, and I put an air gauge in at the combo air chuck/air release valve behind the battery compartment, next to the fuel filter/water drainer, where moisture is normally drained.

The parking brake is spring loaded into the on position in the roto-chamber via the quick release valve and it uses air pressure to compress the spring and pull/hold the brake off. So it needs air to release the spring and put the brake on, and air to pull the brake off.

Once we got our roto-chamber rebuilt, to solve the cold air problem, our pressure was 110-120 psi when the engine is running and air is built up. It would drop to 0 or at least near 0 when I leveled the coach since it let the air out for 45 seconds.

Short answer, Road Warrior, is I don't think there's anything wrong with air system on your coach.
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Old 10-14-2012, 01:30 PM   #22
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Originally Posted by Alpine Road Warrior View Post
I installed an air pressure gauge on the dash so I see where my pressures were running. When running down the road it runs 110 -120 psi. When I park and put jacks down it drops to 80-90 psi. Within 48 hours the psi will go to 0 psi. Is this normal or do I need to look for a leak?
Road Warrior. I am a retired cross country trucker and former owner of a small fleet of road trucks. You are in good shape with these readings. All air systems will leake off over a period of time. 48 hours is excellent. In the trucking business 4 hours would be acceptable. old trucker
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