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  #1  
Old 02-11-2019, 03:43 PM
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Easy way to deflate rear air springs?

I recently lowered my truck and installed M5 bumpstops. These are shorter than the originals and want to verify that if a rear air bag fails while driving that the rear tire won't contact anywhere in the wheel well. Bumpstops are critically important for cars with self-leveling suspension for this reason.

Hoping for a quick and easy test without having to disconnect airlines.
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Old 02-12-2019, 10:51 AM
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Just disconnect the air lines at the compressor. You won't need to jack the car up. It's like 4-6 screws to get the panel off.
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Old 02-12-2019, 01:08 PM
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Figured that would be the answer. I thought about disconnecting the level sensor arms and moving the sensor wiper position all the way down but not sure that will release all of the pressure.

I'll disconnect at the compressor but will roll the rear wheels onto ramps for some added working room.

Thanks!
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Old 02-12-2019, 05:07 PM
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Let us know if tire or suspension rubs anywhere at full compression!
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Last edited by SF2000x5; 02-14-2019 at 12:35 AM.
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Old 02-13-2019, 10:55 AM
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loosen the lines above the air-bag; you just lift off the trunk floor no nuts/screws involved. same as when replacing the air bags. UNPLUG the air compressor fuse or the car will try to inflate them; the system is live when the car is off.
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Old 02-13-2019, 12:06 PM
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I loosened the lines at the compressor. It was easier than I thought.

So, with 20" type 333 wheels wrapped in 315/35 tires, 14MM spacers and M5 bump stops the top of the sidewall comes within 1/2" of contacting the inner edge of the plastic fender trim. Without spacers the tire would clear to the inside of the trim piece and has about an inch to the wheel well liner.

This makes sense as the M5 bumpstops are about 1" shorter. If you had rear passengers or a heavy load you would likely have rubbing before you could get safely stopped (ie on the freeway). But, I don't think it would be catastrophic - the tire tearing apart the liner and trim.

Another note - I am surprised at how little travel the rear OEM shocks have with self-leveling. It's not much more than an inch before hitting the OEM bumpstops. I suppose this is sufficient with self-leveling but I have noticed in the past before lowering that with 3 rear passengers I would hear the squeaking of the bumpstops compressing going over dips.
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Old 02-13-2019, 12:42 PM
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I've replaced a few shocks lately and was also surprised at the limited range of compression before bump stops. Seems most of the range is expansion.
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Old 02-14-2019, 12:38 AM
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Thanks for the info Hit_Apex.

I'm now considering shorter rear bumpstops now since I lowered the rear a good 2-3 inches. I don't think it's bottomed out after a few thousand miles with the lowering links though.
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Old 02-14-2019, 11:42 AM
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Quote:
Originally Posted by SF2000x5 View Post
Thanks for the info Hit_Apex.

I'm now considering shorter rear bumpstops now since I lowered the rear a good 2-3 inches. I don't think it's bottomed out after a few thousand miles with the lowering links though.
Reminder that the M5 bumpstops need to be pressed into the top cup (retainer). They're squishy so it takes a little soap and a few rounds of squeezing in a vice.

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