Thought I’d do a write up and document it for posterity’s sake.

The air suspension used in Bentley Continentals (GTs and FS) consists of air springs, an air compressor, reserve, distribution block, and of course, an air suspension module. The first, and most common failure is a bladder leak at one or more of the four corners, or a line leak.

If a slow leak occurs in the bladder or the lines, no air compressor faults might be recorded at first, but with a leak left unfixed, the air compressor begins to run more and more, eventually continuously until it breaks. This write up might help you if/when that happens. Before getting into this, it is obviously important that once a leak is detected, it is fixed FIRST; otherwise, just addressing the air compressor failure, it will fail again.

About the air compressor failures, typically only two failures occur (only two that I’ve ever seen).

1. Short, open circuit to the air compressor

2. Plausibility error

The first failure is almost always the relay. The relay is #53 in the trunk fusebox on the first series GTs. Probably the same for newer series, easily checked. The compressor is a high draw unit and when running it draws lots of current. Add to this, if a leak is present, the compressor now runs more and more. The lines become hot and the relay gets overworked.

The second failure gets into the body of this DIY. A plausibility error essentially is flagged when the air compressor wears out and, even though still runs, is incapable of delivering the “expected” volume of air in the “expected” time limit. In all of these systems by any car manufacturer, the system is programmed to expect the command for air to the four corners is accomplished within a period of so many seconds. If the expected psi is not seen in the time limit, the plausibility error fault is sent.

About the compressor. All of the Euro cars I’ve seen with air suspension use the same air compressor manufactured by Wabco. It is sold as a complete assembly and replacement parts are NOT made available for sale. So, if you have a plausibility error, essentially you (or a shop maybe) are removing the compressor and replacing with a new unit at several hundred dollars for the part.

This compressor design is peculiar. It consists of a motor and a pump. The motor is overdesigned and never fails. It is a huge unit and probably can run forever. The pump has an inherent weakness. It is a simple design with a sealed cylinder/head, a flapper type valve, and a piston. The WEAK point of the pump is the piston ring. It is made of a soft nylon like material, it eventually fatigues and loses some or most of its seal, thus the compressor runs and runs, but the air delivery becomes less and less until the unit is incapable of delivering the needed volume in the time limit.

Now to the fix. A brilliant machinist from the UK figured how to make (remake) this piston ring in his shop. He experimented with it in his Audi with a plausibility error. He came up with a replacement piston ring that returns the air compressor to like new. He sells this part on Ebay. He is easy to find by using the Ebay search. His handle is bagpipingandy. So, if you’ve reached this far and determined your air compressor has failed, then you’ll want to head over to ebay and purchase a new piston ring from Andy.

In this write up I am not covering how to remove/replace the air compressor from the car as it is intuitively easy. On a Bentley continental, compressor is located in the rear under the spare tire. Start there, then it will become obvious what needs to be removed. There are youtubes out there to R and R the air compressor on a Bentley. One comment I’ll make about R&R – The youtubes start by disconnecting the battery. I don’t do that as the car is in jack mode and I don’t want the rest of the car’s systems disturbed (like fuel trims). Instead I remove the relay to the air compressor. It is #53 in the trunk. Removing the relay will electrically disable the compressor. DO NOT remove the 5a fuse to the air suspension module as powering down this module will disrupt jack mode on power up.

Other model cars place the compressor in different places. Jaguar mounts the compressor behind the front bumper. I’ve done about a dozen of these repairs on Jaguar. The last one I did on jacks in a friend’s garage, took about two hours with minimal tools.

I’ll show some pics of the compressor once it is out of the car. After that, the disassembly is pretty straight forward. The piston ring R and R is not complicated. Reassembly of the pump is not complicated at all so I’ll save the post length. I will also answer any questions if you find yourself in the process and stuck.

This is what the Wabco unit looks like when removed from the car and stripped of its hardware. The distribution block and mounting brackets are removed. You'll do that in the R&R.


You will remove the screws that hold down the cylinder head. Remove the cylinder to expose the piston.

The old ring still on the piston, new ring lying next to it.


Now the old piston ring removed, the new one installed. Some tips on this rebuild - the inside of the pump should be pretty clean. You can use a little spray of a carb cleaner on the inside of the cylinder head and flapper valve, or I like to use a CRC product called brake clean. It doesn't leave a residue and dries almost immediately. Andy's kit comes with new O-Rings and new cylinder head bolts. Install the O-ring and use a small amount of dielectric grease on it. Re-assemble the cylinder head and now the unit is ready to go back in service. Andy might include instructions with his kit, I can't recall.

Here is the CRC product I use.







I should include the DISCLAIMER - I have no business relationship with Bagpipingandy from Ebay other than a customer for over a dozen years and over a dozen purchases.

NOTES:
1. If you are going to attempt this repair, take the p/n from the Wabco label; send Andy an ebay PM and ask him which kit you need.
2. Some of the fault codes you'll see in a VAG scan that this repair can solve.
01400 - Suspension Level Control: Control Limit Not Reached
01772 - Signal from Level Control Pressure Sensor (G291): Implausible Signal
01577 - Turn-Off due to Over-Temp: Upper Limit Exceeded
3. It is ADVISED you should replace the air compressor relay at the same time that you rebuild. This is a 40A relay and it takes a lot of punishment over time. As much as the air compressor does. The relay is position #53 in the trunk fusebox. The relay is p/n 141 951 253B. It is available everywhere. Just google this P/N and it should come right up.

 

Excellent write up! Putting this in my bookmarks.

Also +1 on CRC products. I've had good experiences with their electronics contact cleaner and lubrication sprays.

 

Excellent wright up Steve, your the man who's in the know ... nice work ...

 

@BWings what happen if the Electric motor fail.. can we order a spare part for it?
then we can Completely rebuild the compressor

 

NG,

In 14 years rebuilding these compressors, I have never seen a bad motor, so I have not done any research on it. No reason. The motor seems bulletproof.

 

BWings

do you recommend doing this rather than replace the entire air compressor assembly in my situation you advised about ?

 

I personally would not purchase a used air compressor from Ebay. I actually have, but to rebuild and keep for spares or resell as rebuilt. There is a good chance you will go from what you have to the same or worse with a used compressor. At $250 from your previous post, you have a 50/50 chance of getting one that is worthless.

How about first contacting the Ebay vendor, tell him what you have, make sure he has the part. If he does, and you're comfortable removing the compressor, (which you'll do anyway with a used one) I'll help you through the rebuild. Here is his link for the A8 compressor:

https://www.ebay.com/itm/Audi-A8-S8-...0AAOxyF0pThP5Y

 

@BWings do u think mine & me is the same.. I look at the part no and it the same.. and I don't want to take it a part yet until I have the Piston Ring...
Does the link u sent is the correct one? I will buy it..
Thank you and best regard

 

Greeting NG,

Hope you are well.

The best thing to do is send a message to the seller of the piston ring on Ebay. Ask him which one to order. Frankly, they might all be the same, maybe he just advertises for different models cars. If there is a difference I think I saw the Phaeton uses the exact same compressor.

Also, Jay has already rebuilt his. He has a post titled Notorious Suspension.... You can ask him which Ebay item he purchased.

Best,

Steve

 

Hi guys. Hope you can help.

Ive replaced the compressor with new piston ring repair kit from the guy in the U.K. my car is slow building up and front left hand suspension is down. It pumps up and some times you can raise the suspension to the higher stage then the warning light comes on “stop vehicle to low”.

Cant find any leaks and how can I test the output of the compressor to eliminate this part. Also could it be a blocked or broken suspension valve on the strut. ?

Hope you can through some some ideas before I cash out money for new struts!!!!!!

 

Hi, when did you have the piston rings replaced, have you driven the car since. you say that sometimes the car can be raised, does this mean its not always possible.
In the morning is the car at the same level you left it the night before ...

 

The piston ring was replaced last week and the suspension stays up in the morning after rest over night for about 5miles then drops. It’s difficult then to raise the fron to level ride hight

 

what your saying when leaving the car at the hight over night its still the same in the morning at the same hight, when driving the car for 5 miles or so the front end of the car drops.
Have you checked the AGM battery, is the battery fully charged & keeping its charge ...

 

One of the most common failure are the bladders, have you checked these for leaks, but then you say the car is at the same hight over night. I would check your AGM battery first ... Im sure you know its the battery on the left side of the boot ...

 

Will check Thank you.