Strange Motorhome Movement

[ColoradoBnd]

I put my motorhome in storage several months ago when it was warmer. I put the motorhome in the unit really close to the rollup door on one end to maximize the space at the back of the coach to store things. When I went today when the ambient temperatures were in the upper 20's; I flung open the door and it hit my newly replaced mirror. I stopped, slowed down, and look things over and it certainly appears that the coach has moved forward some since I put it away for winter. The coach sits on a nice flat concrete slab, so I surprised it moved at all. It is sitting on the tires, so no issue from leveler lurch. I am puzzled because it just had a safety inspection and the air brake has always been very reliable.

So here is my question - when the air brake system dramatically cools (ambient temperature); can the pressure in the brake system reduce and release the air brake? Something else I am not thinking about?

[Spk64]

When the air bags bleed down the coach in many cases will move forward some. Ours moves about 3-4”.
This is from the suspension relaxing and the rear axle rolling forward.

[Skip426]

The air brake system " park brake " is air released and spring activated .

No air in the system the brake is ON.

That being said , you may have issues with the rear brake " auto slack adjusters" not doing their job 100% and with the cold ,the park brake not holding as well as it should , but on a level floor , I'm having trouble thinking that's the case .

A full inspection should have noticed any issues with the auto slack adjusters.

EDIT: I see Steve posted while I was typing and I have noticed a similar situation ; to what he has described . If I set my wheel chocks before dumping the air suspension , the tires will load onto the chocks in front of the wheels and the coach must be aired up and sometimes put into reverse to get the chocks out . I'd never though to measure the movement.

[Lt Dan]

I've also noticed a little backward movement as the system airs up. Never paid any attention to it as the air is dumped 'cause I'm usually in it.

[Skip426]

Originally Posted by Lt Dan

I've also noticed a little backward movement as the system airs up. Never paid any attention to it as the air is dumped 'cause I'm usually in it.

The more I think about it , I believe the situation is called " Kneeling " as the body of the coach moves forward , on the arc of the rear suspension .
Rear tires don't move because the brake has them locked in place , but front tires can roll some . Leaf spring suspension on the rear wouldn't do this , but trailing arm rear suspension will.

[Spk64]

Yep, this is why it is also important to check rear diff fluid at full ride height as the differential is tipped when air bags are deflated.

I keep our coach parked on ramps to level it out . So the movement is obvious and I have to account for it so it stays on the ramps when air bleeds down.
When I changed fluid this summer I neglected to bring it to ride height and could not get proper amount of fluid back in.

[twinboat]

Test your parking brake.

Start it up, put it in drive, and give it some throttle, 1200 to 1400 RPMs.
Shouldn't move unless you floor it and wait for the turbo to spin up.

Very unlikely your that the parking brake is your problem. If that far out if adjustment, it wouldn't stop well in normal braking.

[ColoradoBnd]

Originally Posted by Spk64

When the air bags bleed down the coach in many cases will move forward some. Ours moves about 3-4”.
This is from the suspension relaxing and the rear axle rolling forward.

Yes, I have seen that many times and I know the airbags loose fill over time. I guess that is the logical conclusion. I just thought the brake would compensate for a slow leak down. But to be honest, it is no different then when I am at a park and watching the forward movement when I level. The park brake is set then as well.

I was thinking about chocking, but I don't want that much stress on the tires with a chock. Sounds like I need to backup as quick as I can and then shutoff the engine. I hate to do that and not come up to operating temps, but I don't think I have any other choice.

[USMCRET]

All you need to do is ensure your air bags are fully deflated when you park the coach.

If space is that tight, turn the engine off, deflate your bags, then turn the engine back on only long enough to back up the 3-4” you need before the bags air up again. Then shut it down and deflate again.

[ColoradoBnd]

I’m not sure how to deflate other than leveling?

[alank]

Originally Posted by USMCRET

All you need to do is ensure your air bags are fully deflated when you park the coach.

If space is that tight, turn the engine off, deflate your bags, then turn the engine back on only long enough to back up the 3-4” you need before the bags air up again. Then shut it down and deflate again.

Only consider doing this if there absolutely no possibility that you won't forget to instantly move it forward before it airs up, other wise it will likely rotate back into the building while airing up. Then you'll have a ding in the back end to match the one you have in the mirror.

[Dutch Star Don]

You've got to stop drinking when putting the coach up for the season. I know it's a sad time!

[bentjm]

Originally Posted by ColoradoBnd

I’m not sure how to deflate other than leveling?

There should be a dump button on your leveler control panel.

I always dump the airbags "manually" before I level because my coach rolls forward several inches when the airbags deflate which affects where I place my jack pads.

[Dutchstar411]

Originally Posted by Spk64

When the air bags bleed down the coach in many cases will move forward some. Ours moves about 3-4”.
This is from the suspension relaxing and the rear axle rolling forward.

X2 on my previous 2002 DSDP, always took into account a 4" movement when airing down.