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Old 12-07-2021, 12:04 PM   #1
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Air over hydraulic brakes with low air pressure.

We have just purchased our first serious motor home. 2019 Dutch Star 3736.
Has air over hydraulic braking system. I will need to drop my air pressure to about 30 psi to fit the unit in covered storage. Will I have enough braking control to stop it?
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Old 12-07-2021, 12:38 PM   #2
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It will more likely not move at all due to the parking brake coming on at 45 to 50 PSI.

You need a way to dump the suspension air but not the system air.

Air over hydraulic brakes ? Are you sure ?
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Old 12-07-2021, 12:43 PM   #3
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Seriously doubt you have air over hydraulic brakes.


Likely AIR. Much less likely is hydraulic over hydraulic.


Check with your chassis maker for how to dump suspension air without dumping air for the brake system, because if you do have air brakes, dropping air pressure to 30 PSI will automatically engage the parking/emergency brake.
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Old 12-07-2021, 01:04 PM   #4
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As others have said, doubt you have “air over hydraulic” brakes. Just plain old air.
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Old 12-07-2021, 03:19 PM   #5
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I read a brochure on that rig and it lists hydraulic disk front brakes and hydraulic drum rear brakes
Most likely a misprint .
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Old 12-08-2021, 01:20 AM   #6
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Not sure on a air over hyd. But on a traditional air brake system you should have three air compartments. Primary, secondary and aux. If you only have two tanks then one should have two compartments. Aux is the air source for the suspension air bags. There is a one way check valve on the output of the secondary tank that does not allow air into the aux compartment until the primary and secondary compartments are around 90 psi. On a traditional air brake system you may notice that the bags do not start to fill until you see 90 psi on the dash air gauge. If the check valve I mentioned is working correctly you should be able to dump air from the aux compartment without dropping air from the primary and secondary. You would need to determine which compartment is aux and put a drain valve and pull cable on it, like trucks use to drain moisture from the tanks.
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Old 12-08-2021, 06:36 AM   #7
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Specs on the Newmar site say hydraulic brakes.
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Old 12-08-2021, 06:49 AM   #8
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Raise the door. You may remember to drop your air ride every time you back(or forward drive) into your garage. But, there will be a time, you will forget(guaranteed) to leave the air suspension system ‘empty’ before you exit the garage.
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Old 12-08-2021, 07:41 AM   #9
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According to Freightliner, you are all pretty much correct. Service tech said that 55-60 psi is safe to move it into parking. I did measure it at both 60 and 75. It didn’t change the height and I’m good to go with that.
Thsnks
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Old 12-08-2021, 10:26 AM   #10
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According to the chassis specs from Freightliner, the 2019 Dutch Star 3736 has air brakes.
https://cdn.fccchq.com/specsheets/5b...Dutch-Star.pdf


To the best of my knowledge, neither Freightliner nor Spartan produce a diesel pusher chassis with air-over-hydraulic brakes. Nor does the actual Newmar brochure show hydraulic braking (that info seems to be from a non-Newmar website).
https://library.rvusa.com/brochure/2...tch%20Star.pdf
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Old 12-08-2021, 10:52 AM   #11
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Quote:
Originally Posted by Billy9iron View Post
According to Freightliner, you are all pretty much correct. Service tech said that 55-60 psi is safe to move it into parking. I did measure it at both 60 and 75. It didnít change the height and Iím good to go with that.
Thsnks
How are you stopping the air from building up with the engine running ?
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