Came out this morning and my wife's 2012 QX56 looked like a low rider in the back! I traced the air lines and inspected everything to find a hole in the rubber membrane on the left rear shock absorber part number E6211-1LA7A. Now for the tricky part... I can buy the shock for $200 but the car has the Hydraulic Body Motion Control (HBMC) system and to replace the shock I would need to reduce the pressure on that system, replace the shock, then bleed the air out of the hydraulic system once reconnected. The service manual suggests a pressure gauge KV40108000 and an oil pump KV40107700 to perform the procedure.

Anyone ever tried bleeding the HBMC system at home or is this a deal only item?
What have people paid for the deal to do that?

Thanks for the advice
Greg

sir i think you will be the first to do such a thing. let us know how it goes. get the wife to make a video too!

Well - I chickened out, at least partially. I replaced both rear shocks given the complexity of bleeding the HBMC and never wanting to crack that system open again if I can avoid it. I did this part at home for $400 in parts. Fairly messy job because the HBMC system is under pressure so you have to drain that down then remove both hydralic hoses on each shock. Reassembly was pretty easy and the top lock nut needs to be replaced but it comes with the new shock assembly. Once it was all re-assembled I tested the air leveling system (nothing to do with HBMC) and all looked good there again - no low rider QX. However, now the HBMC suspension system had air in the lines so was not working of course. Since I could not find the pump or gauge to do it myself at home I decided to take it to the dealer to finish the job. The car rode like a 70's jalopy with bad shocks - verging on unsafe road manners... Arrived at the dealer and they completed the rest in a half day charging me $232 in labor and and $18 for 4 containers of DOT 3 brake fluid to bleed the system (yes, seems to use brake fluid). Car is super tight and mission accomplished for about $650 total vs the dealer quote for the entire job of $1400.

when i first saw the new design qx and the hbmc, i took a lot of time studying it, reading the service manual on it, and watching every video i could about the patrol. the hbmc is a complex system indeed. its not passive, which makes for a more complicated setup.

even though it is mostly mechanical in nature, there is some electronic wizardry going on.

you sir, are the man...

betzgb wrote: ↑

Wed Sep 20, 2017 5:52 pm

Well - I chickened out, at least partially. I replaced both rear shocks given the complexity of bleeding the HBMC and never wanting to crack that system open again if I can avoid it. I did this part at home for $400 in parts. Fairly messy job because the HBMC system is under pressure so you have to drain that down then remove both hydralic hoses on each shock. Reassembly was pretty easy and the top lock nut needs to be replaced but it comes with the new shock assembly. Once it was all re-assembled I tested the air leveling system (nothing to do with HBMC) and all looked good there again - no low rider QX. However, now the HBMC suspension system had air in the lines so was not working of course. Since I could not find the pump or gauge to do it myself at home I decided to take it to the dealer to finish the job. The car rode like a 70's jalopy with bad shocks - verging on unsafe road manners... Arrived at the dealer and they completed the rest in a half day charging me $232 in labor and and $18 for 4 containers of DOT 3 brake fluid to bleed the system (yes, seems to use brake fluid). Car is super tight and mission accomplished for about $650 total vs the dealer quote for the entire job of $1400.

Hello Betzgb,

You are the first I have heard of who tried doing this DIY. Have the same car with the same problem...Blown bag on the left rear shock. Have the replacements I bought online but at a loss on how to at least change out the shocks before taking to the dealer for 'bleeding'. Can you help out with how you 'Drained' the system ? I have the Service manual and not having the dealer tools, not sure of how to depressurize the system. If I could get to that point, I think I would be OK.

Thanks

There is no need to bleed any hydraulic fluid from your vehicle to swap out your rear air shocks. The hydraulic fluid is contained within the shock itself. The only line going into the shock is the air supply coming from the air compressor.
I know this because I just had to replace mine.

A few things about swapping out your shocks:

It's fairly simple. I'm new to DIY car maintenance and I was able to get this done in 2 hours with a friend for assistance.

- You basically have 2 bolts per side that need to be removed in order to get the old one out.
- Then you remove the air line.
Tip: press the red tab and the air line together then pull out the line while holding the red tab in. It took me a few tries to get it out but it will come out. Don't break it. It's breakable but not extremely fragile just be careful tugging on it too hard. It should just pull out if you do it right.

- then pry the old air shock out with pry bar or flathead.
Tip : if you have a second jack or jacket ands, you can
Jack up the brake assembly (don't know what it is really called) to get the old shock out easier.
- Then put in the new shock in. Leave the side jacked up while you do this.
- put the 2 bolts in and the air line.

Thats it folks. Its about an easy of a job as you could imagind.

The main difficulty will come when you are trying to get the old bolts out. Hit it with pb blaster to loosen them. I suggest doing this an hour beforehand just to make the job easier. I ended up doing it right before attempting to remove the bolt, I broke my new milwaukee wrench tryo to break the bolt, lol, and I had to have my friend hit it with a torch until it was hot enough to come lose.

I did switch out the air compressor and leveling sensor first because I didn't want to attempt this job. I got those parts from the pull n pay junkyard for less than $50.
I got the 2 air shocks online , they were the same kind I could have bought from the local Orielly's auto parts store. Orielly wanted $450 approx after tax. I got them for $350 on ebay.
In the end, I paid about $400 and spent 2 hours swapping out my rear air suspension.

Other than those few hiccups it was fairly easy and wow I have to say I can really tell the difference. Its a night and day difference. I used to be afraid to hit any bumps or potholes in the road while driving on the highway. It was really scary driving up and down the mountain. Now it's like floating on a cloud.

Anyways hope this helps someone in the future. Cheers.

Nathanniice1 wrote: ↑

Mon Apr 04, 2022 8:21 am

There is no need to bleed any hydraulic fluid from your vehicle to swap out your rear air shocks. The hydraulic fluid is contained within the shock itself. The only line going into the shock is the air supply coming from the air compressor.
I know this because I just had to replace mine.

To clarify this, the HBMC and the Air Levelizer system are completely separate entities, although both work via the shock absorbers. Your '05 only has the Levelizer. HBMC (Hydraulic Body Motion Control) was introduced on the '10 Nissan Patrol and can be found on '11+ QX's. It uses hydraulic accumulators connected to the shocks at all four corners to basically act as intelligent sway bars. It responds to centrifugal cornering force rather than differential compression of the suspension like a sway bar. You can find a description of the HBMC system here starting on page SCS-7.
https://www.nicoclub.com/service-manual ... %2FSCS.pdf

@marctronixx is quite correct, it's a very complicated setup with a ton of plumbing.