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Info Needed on Changing the Rear SLS Shocks
Topic Started: Wed May 27, 2009 4:29 pm (1,306 Views)
stwat
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Im soon to be changing the rear shocks on the 16v and need a bit of info.

Whats the best way to release the pressure in the shocks before taking them off? Do they need bleeding once re fitted?

What is the correct fluid for the system? Is it ZHM? Is it a Dealer only fluid or can it be bought from GSF or ECP?


Is it OK to just replace the one that is knackered, just for the time being.

Thanks in advance,

Stu
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cossie connoisseur
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there can be only one ;-)
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zhm fluid is what you want and can be brought at gsf for less than half the price from MB and its exactly the same quality and product

after refitting you leave the unions slightly loose then with the engine running you will get a bit of fluid out and this is when you nip them tight.

also bleed the nipple on the valve which connects to the ARB.

its best to change the fluid as you will lose a fair bit anyway.

as for the struts i took mine to a garage to do but with the car jacked up they are easy to remove and with both pipes removed and covered in a rag you can change them without worrying.

will you do the accumulators too?

and yes you can just change the one as they are different to standard shocks and wear differently
Edited by cossie connoisseur, Wed May 27, 2009 4:37 pm.
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stwat
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Many thanks, Nick :)

So to release the pressure, do i simply have to open the olive nut on the strut and simply let it drain until all the pressure is released?


I'll be replacing the accumulators too yes.

I'm helping the mechanic to replace most of the stuff back there. We replaced the springs this afternoon and it feels a lot better. The ride is a lot less choppy and bouncy than it was before.
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cossie connoisseur
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there can be only one ;-)
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i would take the accumulators off first then there should be no fluid or pressure in the struts so can be removed then
Edited by cossie connoisseur, Wed May 27, 2009 7:13 pm.
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Will
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Hi Stu,

What's actually wrong with your hydraulic struts? They don't wear out like a shock absorber does. The damping is done by the accumulators.

The only time you would need to replace a strut would be due to physical damage (unlikely - bent etc?), or if it was leaking. Occasionally the bushes can become worn, I'm not sure whether they can be purchased seperately though?

It's probably worth overhauling the SLS pump with new seals etc - they're peanuts from MB. If your hydraulic fluid is black, it's probably sucked in engine oil through the exhaust camshaft. You will sometimes also see engine oil leaking out which runs down to the O/S of the engine camshaft cover and then runs down the block etc.

My order of works would be:

Replace all of the seals in the SLS pump (unless you're 100% certain it's perfect)
Inspect the SLS pipework under the car, replace as neccesary.
Inspect/replace the accumulators if needed (2 pipe fittings and 2 nuts each - simple :) )

As I say - it's very unusual to get a faulty strut - they don't wear like a shock absorber, and they don't do the 'damping' either - so it's normal practice to just replace one if it were to be deemed faulty.

I wouldn't worry too much about the pressure, just slacken the unions carefully, perhaps with a rag around it and have a drain pan nearby. Buy a couple of bottles (1L each) of ZHM. One should be sufficient for the system, but a second bottle if you're planning to flush it through or for topping up in the future (not that you should need to!) would be advisable - better safe than sorry ;)

Will
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stwat
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Hi, Will


The strut is knocking inside, badly. I replaced the bushes but that didn't cure it. We had it up on a ramp today to replace the rear springs and when moving the wheel and lower arm up and down, the knocking was clearly coming from inside the top of the strut. It does seem to have some oil on and around it too.

The fluid is nice and clean thankfully.
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Will
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Which side is it Stu?

If you need a spare I have a good one somewhere :)

Will
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stwat
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Its the drivers side one. I have ordered a new one from ECP which will be here Friday. But many thanks for the offer :) I'm also buying a strut and other assorted bits from mazza. Il use that strut for the other side as that has a bit of oil leaking also by the look of it.

I'm on a very tight time scale to get the car ready for Le Mans next month. I'm not looking forward to tackling the spheres as the bolts are rusted to hell :o :'( Thankfully most of the pipework looks sound and the nasty brake pipe that goes up and over the sub frame looks to have been replaced recently :)

I have had a good afternoon today, getting under the car on a ramp for the first time. We were both pretty impressed at how good it all looks under there :)
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Ukmerctechie
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Dir is Kool. WKKP Forever!
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DO NOT UNDO THE UNIONS ON THE STRUTS!!!
Put a bleed tube/bottle on the leveller valve bleed nipple with the engine off,open the bleed nipple and the car will sink on the struts relieving the pressure.
The SLS system runs at 133Bar+,hence the struts are pressurised to 133Bar.Releasing the strut/accumulator unions will spray fluid everywhere at high pressure.
The nipple is there to relieve pressure not bleed the system,the system is self bleeding.
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Will
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Ukmerctechie
Wed May 27, 2009 11:19 pm
DO NOT UNDO THE UNIONS ON THE STRUTS!!!
Put a bleed tube/bottle on the leveller valve bleed nipple with the engine off,open the bleed nipple and the car will sink on the struts relieving the pressure.
The SLS system runs at 133Bar+,hence the struts are pressurised to 133Bar.Releasing the strut/accumulator unions will spray fluid everywhere at high pressure.
The nipple is there to relieve pressure not bleed the system,the system is self bleeding.
Never had a problem when I replaced both rear accumulators on my old 2.5-16. As you know, both fittings on the accumulators are on the pressurised side feeding into the struts from the control valve.

I guess as the hydraulic fluid can't really compress in volume very much, the high-pressure translates to a fairly small amount of fluid escaping once the union is undone. I simply slackened the fittings slowly on the accumulators with a drain pan underneath - no real issues and no additional mess (you're still going to get ZHM fluid leaking out as you dismantle the system anyway)

Although I fully accept that your advice regarding the use of the bleed valve is obviously the textbook method and possibly neater should you not undo the fittings as carefully/slowly as I did ;)

Will
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Ukmerctechie
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Dir is Kool. WKKP Forever!
[ *  *  *  * ]
Will
Thu May 28, 2009 12:08 am
Ukmerctechie
Wed May 27, 2009 11:19 pm
DO NOT UNDO THE UNIONS ON THE STRUTS!!!
Put a bleed tube/bottle on the leveller valve bleed nipple with the engine off,open the bleed nipple and the car will sink on the struts relieving the pressure.
The SLS system runs at 133Bar+,hence the struts are pressurised to 133Bar.Releasing the strut/accumulator unions will spray fluid everywhere at high pressure.
The nipple is there to relieve pressure not bleed the system,the system is self bleeding.
Never had a problem when I replaced both rear accumulators on my old 2.5-16. As you know, both fittings on the accumulators are on the pressurised side feeding into the struts from the control valve.

I guess as the hydraulic fluid can't really compress in volume very much, the high-pressure translates to a fairly small amount of fluid escaping once the union is undone. I simply slackened the fittings slowly on the accumulators with a drain pan underneath - no real issues and no additional mess (you're still going to get ZHM fluid leaking out as you dismantle the system anyway)

Although I fully accept that your advice regarding the use of the bleed valve is obviously the textbook method and possibly neater should you not undo the fittings as carefully/slowly as I did ;)

Will
Yep and i have never had a problem when i relieved the pressure on the hundreds of shocks/accumulators/sls systems i have rebuilt over the years.Why take a chance of getting an eye full of Hydraulic oil at high pressure for the sake of loosening a bleed nipple? But that said it is not my car or job to do.
The OP asked for the best way to relieve the pressure from the struts and this is what i offered,if you want another way then just drill a hole thru the knackered strut...that will relieve the pressure just as well ;)
Edited by Ukmerctechie, Thu May 28, 2009 12:50 am.
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stwat
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Many thanks for the info :) That certainly sounds like the best way to do it if the car is on a ramp, which it will be :)

Why oh why can't i have a proper ramp at home in the front room?!??!!? :lol:
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Will
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Ukmerctechie
Thu May 28, 2009 12:48 am
Will
Thu May 28, 2009 12:08 am
Ukmerctechie
Wed May 27, 2009 11:19 pm
DO NOT UNDO THE UNIONS ON THE STRUTS!!!
Put a bleed tube/bottle on the leveller valve bleed nipple with the engine off,open the bleed nipple and the car will sink on the struts relieving the pressure.
The SLS system runs at 133Bar+,hence the struts are pressurised to 133Bar.Releasing the strut/accumulator unions will spray fluid everywhere at high pressure.
The nipple is there to relieve pressure not bleed the system,the system is self bleeding.
Never had a problem when I replaced both rear accumulators on my old 2.5-16. As you know, both fittings on the accumulators are on the pressurised side feeding into the struts from the control valve.

I guess as the hydraulic fluid can't really compress in volume very much, the high-pressure translates to a fairly small amount of fluid escaping once the union is undone. I simply slackened the fittings slowly on the accumulators with a drain pan underneath - no real issues and no additional mess (you're still going to get ZHM fluid leaking out as you dismantle the system anyway)

Although I fully accept that your advice regarding the use of the bleed valve is obviously the textbook method and possibly neater should you not undo the fittings as carefully/slowly as I did ;)

Will
Yep and i have never had a problem when i relieved the pressure on the hundreds of shocks/accumulators/sls systems i have rebuilt over the years.Why take a chance of getting an eye full of Hydraulic oil at high pressure for the sake of loosening a bleed nipple? But that said it is not my car or job to do.
The OP asked for the best way to relieve the pressure from the struts and this is what i offered,if you want another way then just drill a hole thru the knackered strut...that will relieve the pressure just as well ;)
UKmerctechie - please read my reply again.

I wasn't arguing with you or disagreeing - far from it.

I fully accepted and noted that you highlighted the correct, textbook method.

Thanks,

Will
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cosser
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I undid my Unions very Slowly and Very carefully and I got a Face full Of FLuid for my troubles..lol
Do it by the book...Undoing unions is for experts..!!

hey UK merc Techie..do you fancy talking me through draining and replacing the SLS fluid and testing the Leveller valve is working..or can you piont me to a sticky..!!

Cheers Guys..!!

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merc190uk
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The Godfather

just to add to an old thread

it has to be ZHM fluid yes ??

i cant use any other hydraulic fluid then ??

any ideas once filled with fuid how long it takes to bleed itself ??

so many questions lol

can you guess i have just replaced my broken ram :)
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stwat
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Yes it has to be ZHM, Steve. About a fiver from GSF or a tenner from the dealers.

Nice one for replacing it B) Did you bite the bullit and get one from ECP?
Edited by stwat, Thu Nov 19, 2009 11:54 pm.
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merc190uk
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The Godfather

thanks mate

nope, a very kind member came forward with a second hand unit

sent it out without taking any money untill i know for sure it works :driver:

thats what i love about this place :$

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merc190uk
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The Godfather

any idea how much the system needs ??
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cossie connoisseur
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there can be only one ;-)
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a good couple of litres, you dont loose that much when changing the struts
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