Grunting in rear when raising ABC car; Blown Return Accumulator?
Thread Starter
Super Member
Joined: Dec 2007
Posts: 980
Likes: 224
2005 S500 Designo
Grunting in rear when raising ABC car; Blown Return Accumulator?
I just did some ABC work on the 220 (new rebuilt pump).
The vehicle now grunts slightly from the rear when raising or if raising is induced (via driving).
I'm thinking of doing a rear valveblock rebuild, as a number of things point towards it:
- The aforementioned grunting when raising
- Unusual behavior where the rear will move/settle even after being turned off
- An unusual pronounced noise when going over road turtles
What would the symptoms be of a blown return accumulator? This is seldom if ever discussed.
With the valve block removed, is there a way to test the return accumulator on the bench?
The vehicle now grunts slightly from the rear when raising or if raising is induced (via driving).
I'm thinking of doing a rear valveblock rebuild, as a number of things point towards it:
- The aforementioned grunting when raising
- Unusual behavior where the rear will move/settle even after being turned off
- An unusual pronounced noise when going over road turtles
What would the symptoms be of a blown return accumulator? This is seldom if ever discussed.
With the valve block removed, is there a way to test the return accumulator on the bench?
MBWorld Fanatic!
Joined: Sep 2018
Posts: 3,247
Likes: 933
From: New Orleans Area
2015 E400 Sedan
for accumulator do you have picture?
They fail by the air hydraulic and air side mixing due to internal leak
OR
if piston type - the piston gets stuck due to contamination or something.
So remove and check air pressure on air side.
But as long as air and oil do no mix and air side can hold pressure they should work all day everyday.
Mainteance after years of service is Piston seals and maybe a clean up of bore etc
Replacing bladders or diaphrams.
These things tend to be nitrogen filler to about 70-90% system pressure
They have to have some sort of pressure for bladder type to ensure the bladder does not fold up and damage itself and leak.
Nothing to them:
Home - Accumulators, Inc.
They fail by the air hydraulic and air side mixing due to internal leak
OR
if piston type - the piston gets stuck due to contamination or something.
So remove and check air pressure on air side.
But as long as air and oil do no mix and air side can hold pressure they should work all day everyday.
Mainteance after years of service is Piston seals and maybe a clean up of bore etc
Replacing bladders or diaphrams.
These things tend to be nitrogen filler to about 70-90% system pressure
They have to have some sort of pressure for bladder type to ensure the bladder does not fold up and damage itself and leak.
Nothing to them:
Home - Accumulators, Inc.
Thread Starter
Super Member
Joined: Dec 2007
Posts: 980
Likes: 224
2005 S500 Designo
I pulled the rear valve block and rebuilt it. There was some weirdness going on in the back. Some of the o-rings were noticeable damaged, and I saw bits and pieces at the bottom of the solenoid.
While in there I also replaced the fuel filter. I noticed that the rear left strut shroud was rubbing against the liner. I sprayed it with some ballistol/water, but I don't think that was making that noise.
Putting it all back together (along with other maintenance items), the car has never ridden this well in years of ownership. It's back to being an S-Class.
I tested the return accumulator while I had the valve block out by inserting a straw. Nothing indicating a problem.
Per Mercedes own documentation, the ABC system cannot be automagically diagnosed with a computer. Reading Mercedes' documentation on the ABC System (available in DAS) would tell you this.
While in there I also replaced the fuel filter. I noticed that the rear left strut shroud was rubbing against the liner. I sprayed it with some ballistol/water, but I don't think that was making that noise.
Putting it all back together (along with other maintenance items), the car has never ridden this well in years of ownership. It's back to being an S-Class.
I tested the return accumulator while I had the valve block out by inserting a straw. Nothing indicating a problem.
Per Mercedes own documentation, the ABC system cannot be automagically diagnosed with a computer. Reading Mercedes' documentation on the ABC System (available in DAS) would tell you this.
