ABC: Change the front and rear pressure reservoirs - Mercedes-Benz Forum

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post #1 of 37 (permalink) Old 04-29-2014, 02:37 AM Thread Starter
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ABC: Change the front and rear pressure reservoirs

After replacing the ABC pump on my 2003 SL55 (134,000km) a few months ago I kept getting intermittent white ABC warnings, particularly after going around a corner with a bump slowly or after hard acceleration. For a while now the ride has seemed a bit hard and not like the magic carpet it used to be.

I decided to replace the pressure reservoirs. The best local price was $584 each (I didn't bother asking the dealer) The cheapest price was on parts.com but they don't ship to Australia. I ended up buying two from pelicanparts.com for $580 shipped

The reservoirs are located in front of the front and rear wheel behind the plastic wheelarch shrouds.

The procedure is sort of similar for both ends, I started at the back.

Chock the wheels, handbrake on, jack up the car and use a secondary support

Remove numerous plastic clips and nuts that secure the wheel arch shroud and gently pry it out... it's tricky

While holding a tin under the bleed screw crack it and you will collect about 150ml of fluid

I was dismayed at just how black and opaque the fluid was after I had flushed it with 4 litres of fresh stuff about a year ago ( yes I know I should have used more; the manual says 10)

Remove the nut securing the assembly (indicated in the photo) and the pipe clamp (in another photo) and gently pull it out to the rear and down as far as the pipes and hoses will allow.

Loosen the pipe nut with a 17mm spanner then remove the three nuts securing the reservoir.

Undo and pull out the pipe being careful not to let any dirt enter and remove the reservoir

Assembly is just the reverse, getting the nut on the pipe clamp is tricky

The front starts out the same. Only remove the front wheel arch plastic shroud

Loosen the bleed screw and catch the fluid that comes out; about 100ml is all I got

The valve/ reservoir assembly does not appear to come out easily so you must undo the pipe nut first then remove the three nuts that hold the reservoir in place. The two outer ones are OK, the inner one will need an extension on your 1/4" drive socket and you will need to stick your head under to see the little devil

Assembly is just the reverse but the car will be very low when you lower the jack

I had only bought 4 litres of ABC oil, not intending to do a total flush.

I syphoned out all of the oil in the reservoir then filled it up with fresh stuff running a hose from the return line down into bottles so I could gauge how much was being used

When I started the car it took a while to lift and the fluid level dropped pretty smartly.

After it had run for a few minutes and I topped the fluid level up the returning fluid was transparent and looked clean.

Unfortunately I only had another litre of fluid left and one rodeo cycle went through that pretty smartly.

The oil in the reservoir is certainly much cleaner but I have ordered another 8 litres and a filter and will do the job properly

The ABC fluid in Australia is prohibitively expensive with the dealer charging $90 per litre and Silverstar spares wanting about $60

When I contacted MB spares in the ACT they quoted $30 something per litre and I questioned that they were supplying the right part. When it arrived it was SWAG brand Power Steering Fluid and their website lists it as the same specification as the original Pentosin

The removal and replacement of the reservoirs took about an hour each and you could probably do it in half that time if the trim wasn't so difficult to remove and replace

It was a straightforward job and the car rides beautifully again with no warnings
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post #2 of 37 (permalink) Old 04-29-2014, 03:58 AM
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Great post Peter - will add this to the stickies when i get it up


get the fluid from Phoenix lubricants in oz - it is $26 a litre for Pentosin CHF11s
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post #3 of 37 (permalink) Old 04-29-2014, 04:04 PM Thread Starter
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Pentosin ABC fluid

Thanks for that,

Sourcing stuff in Australia is a bit of a jungle.

It's there but not always easy to see

Peter
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post #4 of 37 (permalink) Old 05-29-2014, 12:50 AM Thread Starter
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What's inside the pressure reservoirs

I was curious to find out why the reservoirs fail

I followed the procedures in the WIS to evacuate the reservoir of pressure for disposal

Don't tamper with the reservoir unless you have done this. The gas inside is under very high pressure and will do yourself serious damage.

I cut the reservoir in half and the photos show the story

There was a full charge of gas inside the reservoir and no oil escaped the evacuation hole so the diaphragm was still patent... no holes

The diaphragm had a number of "bubbles" or "aneurysms" that were full of gas so I assume that the rubber had deteriorated and delaminated. You can see these in the photos

The diaphragm was fairly hard and I am assuming that this was why they fail to absorb the shocks anymore.

Since replacing them a few weeks ago the ride is back to magic carpet and no more ABC messages

Peter
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theintelligent1, SinSL and Deplore like this.
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post #5 of 37 (permalink) Old 05-29-2014, 11:06 AM
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Fantastic post and diagnosis! I appreciate this so much. Thank you for taking the time to both document the change, and then investigate the source of the failure.
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post #6 of 37 (permalink) Old 05-10-2016, 10:19 AM
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front accumulator job

Beautiful write up. I am about to tackle my front one on my R230. I need to know if I jack up the front 2 wheels only will that let the pressure off after 30 minutes? Does the front accumulator just sort of lay there as in the photo? I thought it was interconnected to the valve block? It looks easy to pull it out if it just lays in there that way.

Moretech
USA
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post #7 of 37 (permalink) Old 05-10-2016, 05:01 PM
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Originally Posted by moretech912 View Post
Beautiful write up. I am about to tackle my front one on my R230. I need to know if I jack up the front 2 wheels only will that let the pressure off after 30 minutes? Does the front accumulator just sort of lay there as in the photo? I thought it was interconnected to the valve block? It looks easy to pull it out if it just lays in there that way.

Moretech
USA
I just did mine and I only jacked up the left side and removed the lower cover on that side for access. The accumlator is mounted to the valve block assembly chassis with three nuts and one hydraulic fitting. The hardest part for me was getting the accumlator out with out bending or disturbing any other fittings and tubing. It does come out though. You must wiggle in the new accumulator. Be patient and persistant and it will go back in.

As to the pressure, it relieves itself by the time you jack the car up and remove the lower panel, 15-20 minutes or so. You will lose a little fluid but not much so watch your eyes and wear safely glasses.

See attached file.

Good luck,

Bob
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File Type: pdf install front pressure reservoir.pdf (61.0 KB, 172 views)
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post #8 of 37 (permalink) Old 05-19-2016, 05:38 AM
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For all USA owners, Pentosin ABC fluid can be bought on Amazon for 65 dollars per 5 liter jug. If you are a Prime member shipping is free.
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post #9 of 37 (permalink) Old 05-20-2016, 06:03 PM
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front accumulator/ refill fluid to proper level

I will have my accumulator in the car tomorrow afternoon. Got panels down, looks very straight forward. Just one question. Just how do you bring system fluid level back to normal? I can catch all the drained fluid for a volume check but do I then start a partial flush? I need to see into the reservoir to make sure no air gets in the pump and to do this I need to pull the filter, fill it up good, and start a flush . Maybe 3 liters might get the air bubbles out.

Moretech
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post #10 of 37 (permalink) Old 05-21-2016, 04:01 AM
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Quote:
Originally Posted by moretech912 View Post
I will have my accumulator in the car tomorrow afternoon. Got panels down, looks very straight forward. Just one question. Just how do you bring system fluid level back to normal? I can catch all the drained fluid for a volume check but do I then start a partial flush? I need to see into the reservoir to make sure no air gets in the pump and to do this I need to pull the filter, fill it up good, and start a flush . Maybe 3 liters might get the air bubbles out.

Moretech
You should have minimal fluid loss during the change over. I lost perhaps an ounce if that. I just put rags up to catch the drops. Let the car sit idle for least 30 minutes before change over and you should be fine.

As to the reservoir, the system is self bleeding and any air bubbles you may introduce will work out on their own so no need to flush for air bubbles. However, if the fluid is dark green or brown then a flush is welcomed. See my post here.

Good luck,

Bob
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