Disaster Strikes
We have been doing the AL Can and Alaska since the end of May. We had were winding up a 4 day stay in Denali NP, and the area around it on 6-22. We left our RV Park and drove both the MH and toad ...
Forum Discussion
Rick Jay wrote:
Well maybe he is, but you're making some too. I beieve there are lots of people without RVs that use their personal vehicle for vacation travel. Not everyone is as fortunate as us to have an RV! LOL
Yes, good point, the SUV driver is guaranteed to have some level of inconvenience in any case. But it's not like the OP carelessly backed into his vehicle on purpose, have to admit it's kind of funny that the dog did it. Although it wouldn't have been so funny if the RV went careening off the cliff with the dogs inside. OP got a good wake up call, next time may not be funny at all.
Vehicles under 26,000 lbs GVWR typically use hydraulic brakes, where the brakes are normally "off" and pressing the pedal forces hydraulic pressure to apply the brakes. When you release the pedal, you release the hydraulic pressure, and the brakes release.
Air brakes are required for vehicles with a GVWR of 26,000 and up, and work the opposite of hydraulic brakes. The brakes are held in a fully applied position by strong springs, and air pressure is used to release the brakes. So air pressure keeps the brakes unapplied, and when you step on the brake pedal, you dump air from the system, allowing strong springs to return the brakes to their applied position.
In addition to a compressor, there is an onboard air storage tank. Pulling the parking brake knob dumps all the air from the wheel lines and applies the brakes at all wheels. Pushing the knob back in allows air to flow from the tank, re-pressurizes the lines, and releases the brakes. As one poster noted, if you pump the brake pedal repeatedly after applying the parking brake, you will drain air pressure in the tank to zero, so even if the knob is pushed in, there will no air pressure available to release the brakes.
The reason that these HD transmissions have no park 1) the vehicle is parked with the brakes locked at every wheel, and 2) a pawl in the transmission gears is not enough to hold a heavy vehicle like we are talking about.
DOT requires air brakes on these heavy vehicles so the brakes fail to "fully applied" instead of "unable to apply".
Next time you're on a shuttle bus with air brakes, look at the shift lever....it will only have "D", "N", and "R".
