SL55 ABC mind of its own!

[television]

I have just started mine up and looked and there is only a minimum of circulation, that is as far as the valve block in the front wing. From the valve block on and into the pipes that operate the struts, this fluid is static other than the extra fluid that is pumped into the struts on a very rough track road, or when the car is raised. There is no return line for the fluid from the valve block to the rest of the car, so the fluid in the wheel valve blocks, the struts is not circulating at all.

So Any dirt, debris in the pipe lines and wheel valve block might get pushed back in the circuit, if the car is raised and lowered especially from the front struts but little chance from the rear ones owing to the length of the pipes.

 

[Lexman8]

Interesting as that implies that the DIY way to change the ABC fluid might leave a lot of old fluid in the system even if you raise and lower the car several times during the procedure.

Malcolm, did you start your SL and is your diagram for an SL? It shows the reservoir pipe going to the ABC radiator and then to the valve block. This is different to the diagram I have for a 215 which shows the reservoir feeding the pump directly.

 

[television]

Interesting as that implies that the DIY way to change the ABC fluid might leave a lot of old fluid in the system even if you raise and lower the car several times during the procedure.

Malcolm, did you start your SL and is your diagram for an SL? It shows the reservoir pipe going to the ABC radiator and then to the valve block. This is different to the diagram I have for a 215 which shows the reservoir feeding the pump directly.

Yes I started it and then looked, and yes the 215 is nothing much like the 230 in the pipe runs, this is the 215

 

[SL63 Mark]

I asked my local MB dealership recently if it was worth changing the ABC fluid, and the service manager looked at me and said "why do you want to do that Sir ?". I said the car settles a bit after a few days parked, and he said - "they all do that, Sir".

It was nice to hear of a dealership actually trying to save a customer money. They are not all bad, contrary to what you hear on here sometimes.

 

[Malcolm Johnson]

talked to my preferred indie, he said it does cycle the fluid around the system
he said if you wished to cycle change the fluid do it every few hundred miles
to allow for circulation.
so i guess not great circulation

 

[television]

talked to my preferred indie, he said it does cycle the fluid around the system
he said if you wished to cycle change the fluid do it every few hundred miles
to allow for circulation.
so i guess not great circulation

Only in the front small loop, not the whole thing including wheel valve blocks, this is why we get quite a few post where the rear end does funny things, and cleaning the valve block returns things to normal.

One can see from the size of the header tank that there is not much fluid in it and its only ever half full at that, and this raises the car to max without using much fluid.

 

[Lexman8]

I've bought 6 litres of Pentosin to do a DIY fluid change in the spring so it'll be interesting to see how much I have to replace before the fluid from the return line starts to look 'clean'.

 

[Philedge]

The fluid definitely circulates through the reservoir. Having done the DIY flush I know that if you disconnect the return line from the top of the reservoir fluid flows continuously out of the line and the reservoir empties quite quickly. Takes 5-10 mins to fill a 10 litre bucket when cycling the suspension up and down on the level buttons

The pump delivers pressurised fluid to the valve blocks which is injected into the strut when preloading the coil spring to raise the car or react to roll/dive/bumps etc. When the springs need to be unloaded fluid is vented from the strut which then returns to the reservoir via the oil cooler.

The only fluid that doesnt continually circulate is the fluid trapped in each strut and the pipe to each strut furthest from the valve block. The rest of the fluid is continually being returned to the top of the reservoir via the top, through the filter and drawn from the bottom by the pump.

 

[lovemerc]

I have just started mine up and looked and there is only a minimum of circulation, that is as far as the valve block in the front wing. From the valve block on and into the pipes that operate the struts, this fluid is static other than the extra fluid that is pumped into the struts on a very rough track road, or when the car is raised. There is no return line for the fluid from the valve block to the rest of the car, so the fluid in the wheel valve blocks, the struts is not circulating at all.

So Any dirt, debris in the pipe lines and wheel valve block might get pushed back in the circuit, if the car is raised and lowered especially from the front struts but little chance from the rear ones owing to the length of the pipes.

So it sounds like it's safer not to raise the car to prevent debris problems... How disappointing. I prefer motorway driving with mine raised as you can see through the car in front a little easier and vehicles ahead...

 

[Philedge]

So it sounds like it's safer not to raise the car to prevent debris problems... How disappointing. I prefer motorway driving with mine raised as you can see through the car in front a little easier and vehicles ahead...

Thats not the case! When you raise the car a small amount of fluid is pushed down the pipe to each strut to pre load the coil spring and raise the strut. When you lower the car again virtually the same fluid is vented from the pipe and returned to the reservoir.

As the fluid is circulating through most of the system all the time any debris is going to get carried back to the reservoir and filtered out. Only exceptions to this are larger pieces that get trapped and all debris in the strut bodies where the fluid is stagnant.

As driving speed increases the ABC automatically lowers the car to aid stability and reduce fuel consumption. Raising the car defeats that!!

 

[ajlsl600]

abc

I am not as well informed as many on this forum ,but yes thats what i understood of the situation .also if its not circulating, how is the rtn line filter filtering anything ? could only see that happening if some kind of unload valve is circulating oil when the system reached design or required working pressure and then filtering the returning oil to the tank . i pressume ? this pump is , engine running ,pump running ? and think its prob maintaining a constant pressure to a manifold or valve block that distributes as required and or returns surplus to the tank via the filter, that would explain "no return line from the struts" , would not be required . ?

 

[television]

Thats not the case! When you raise the car a small amount of fluid is pushed down the pipe to each strut to pre load the coil spring and raise the strut. When you lower the car again virtually the same fluid is vented from the pipe and returned to the reservoir.

As the fluid is circulating through most of the system all the time any debris is going to get carried back to the reservoir and filtered out. Only exceptions to this are larger pieces that get trapped and all debris in the strut bodies where the fluid is stagnant.

As driving speed increases the ABC automatically lowers the car to aid stability and reduce fuel consumption. Raising the car defeats that!!

Actually the extra fluid that is used to raise the car does not get filtered at all, not for any wheel, so if any debris in the struts will just make it back to the valve block on that wheel.

You can work it out, the reservoir does not hold much more than ½ litre to the correct level point, and there is another 6½ litres in the system. And that little bit in the tank has to be able to supply all for wheels with extra fluid.

 

[ajlsl600]

malc

so , basically most of the time the debris buck stops at the valve block ( which explains a lot of forum posts reated to valve block and soilenoids ). as nothing is circulated thro the struts just a little added or allowed out, as commanded by electronics and sensors ,so debris in the strut is unlikely and if found , most likely came from the strut in the first place .

 

[television]

so , basically most of the time the debris buck stops at the valve block ( which explains a lot of forum posts reated to valve block and soilenoids ). as nothing is circulated thro the struts just a little added or allowed out, as commanded by electronics and sensors ,so debris in the strut is unlikely and if found , most likely came from the strut in the first place .

Absolutely, as I have said before, the problems that most often come up are one corner sinking, the rear end raising when in R. this is another reason why the wheels must be hanging down when bleeding to empty the struts as far as possible.

 

[television]

It is a shame that many dealers will not just change the fluid, the same as it used to be with the 722.6 gearbox. In both cases the full instructions are there in WIS for doing the job.

 

[Philedge]

All fluid in the reservoir is filtered as its being drawn from the reservoir and returned via the filter all the time. The only time fluid is in the reservoir that hasnt been filtered is when fluid has been topped up through the open lid. Its vitally important that when you open the lid absolutely no debris gets in the reservoir as it will be drawn straight into the pump!!

Malc. When you looked at the flow into your reservoir there would have only been a trickle if the car was stationary. In this situation the throttle valve on the pump suction would have gone to the throttled position so there is virtually no flow through the system only enough to keep the pump lubricated. If you start driving or raising and lowering the car you'll see a big increase in flow.

 

[television]

Yes sure and I accept that, and nothing much happening in P.

It reminds me of the days when I had leaks and drove home 15 miles with all the red warnings of car too low, keep stopping and adding some fluid and looking in that tank to save the pump. Always carry a spare litre, it fits in the boot down by the side of the spare wheel.

 

[ajlsl600]

philedge

would it be fair to say then, that under stable road and driving conditions the pump is basically throttled until sensors/circumstances "see" demand ,thus signalling un throttling the pump ?

 

[television]

would it be fair to say then, that under stable road and driving conditions the pump is basically throttled until sensors/circumstances "see" demand ,thus signalling un throttling the pump ?

Not really, on a smooth road there is virtually no movements from the struts, therefore the valve blocks and the travel sensors would not call out for more fluid from the main valve block right up front that's in the pump flow circuit.

 

[ajlsl600]

Not really, on a smooth road there is virtually no movements from the struts, therefore the valve blocks and the travel sensors would not call out for more fluid from the main valve block right up front that's in the pump flow circuit.

exactly what i thought i was trying to say smooth roads smooth driving , no demand ,oil reaching valve block returning thru filter back to tank. demand seen ,pump unrestricted ,more flow , more oil returning to tank thru filter now back to these pumps. if eccentric, when there is little or no demand (load) the vanes tend to chatter a bit around the eccentric ring creating uneven and more wear . than when they are loaded . thus perhaps providing some explaination to issues of wear on this system, high miles v low miles failures, as i believe a pump on a car driven reasonably hard on less than perfect roads will probrably last longer than the same pump on a car poodling about on great roads. just my belief .