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MECHANICALS With a 30 year-old automobile, there will always be discussion here - maintenance, modifications and mechanicals.

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Old 30th December 2008, 01:35 PM
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Default Rear Suspension Problems

This morning I decided to swap wheels and tyres on the 690SEL to try and find out where a 'tap tap tap' noise came from (it had developed after the day at Oran Park in November).

I was almost sure it was tyre related as it almost disappeared at higher speed (or it was drowned in road noise).

I did the usual hydraulic lock (centre position) on the dash and proceeded to replace the rear wheels first as I thought they were the cause of the problems (see pics of 690SEL on three wheels available on other thread relating to track day)

However, upon bringing the car back to the ground the rear end refused to come down and no amount of coercing (lifting it up and down on many occasions and keeping the controls in all different positions for a total of three hours) would bring it down from its fully extended positions.

I even drove it around the block and it felt as if it needed new spheres at the back (replaced all spheres in August).

So... I am stumped....

Any suggestions?
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1978 W116 690SEL # 3312
1985 R107 500SL AMG
2000 W208 CLK430 Coupe
2003 W163 ML320
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Old 30th December 2008, 01:54 PM
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Default Re: Rear Suspension Problems

AFAIK, this can happen under certain conditions where the valve becomes hydraulically locked. It sounds like the system was still pressurised when you lifted it, filling the fully extended struts.
Did you set the main valve to the service position with the engine running prior to lifting the rear?
I would actually depressurise the central sphere and see what happens.

Tim
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Last edited by TJ 450; 30th December 2008 at 01:57 PM.
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Old 30th December 2008, 02:12 PM
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Default Re: Rear Suspension Problems

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Originally Posted by TJ 450 View Post
I would actually depressurise the central sphere and see what happens.
Tim
HOW?
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1978 W116 690SEL # 3312
1985 R107 500SL AMG
2000 W208 CLK430 Coupe
2003 W163 ML320
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Old 30th December 2008, 03:37 PM
B13 B13 is offline
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Default Re: Rear Suspension Problems

I think if you disconnect the cable at the distribution valve and swing the plate all the way back its supposed to de-pressurise the system (which is why its can't be moved to that position from the dash control... wouldn't be a good look the car sinking while travelling along the highway etc.)

Ian.
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Old 30th December 2008, 04:15 PM
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Default Re: Rear Suspension Problems

You have managed to get more pressure into the circuit between the rear levelling valve and the rear struts than there is in the circuit between the distribution valve and rear levelling valve. This causes the rear valve to lock up and refuse to discharge. I have had this on both the front and rear of my car at various times. I'm not sure what the proper procedure is, but I supported the car on stands, and drained off some of the pressure from the rear bleed screw to lower the rear circuit pressure below the system feed pressure again. You need to work with caution - the fluid comes out at ridiculous pressure.
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Old 30th December 2008, 05:48 PM
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Default Re: Rear Suspension Problems

S class is right and you will need to support the car and release the pressure in the rear circuit.

If you have a later car with a bleed valve at the rear all you will have to do is crack it open with the car lifted and supported and once the pressure is out tighten it up and all should work as expected.

If you don't have a bleed valve then crack one of the pressure lines and it will leak out a small amount of hydraulic fluid under pressure and then should behave itself again.

Just don't get sprayed by high pressure fluid or drop the car on yourself.

Alabassi had the same problem with a 6.9 he was repairing last year and he cracked open a line and the rear suddenly deflated and then worked normally.

Bill
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Old 30th December 2008, 06:53 PM
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Default Re: Rear Suspension Problems

Thanks for the answers...

Sorry for the late reply but I was out for the afternoon.

Would you do the depressurisation with the lever in the middle position (service)?
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1978 W116 690SEL # 3312
1985 R107 500SL AMG
2000 W208 CLK430 Coupe
2003 W163 ML320
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Old 30th December 2008, 11:18 PM
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Default Re: Rear Suspension Problems

Lifting the car with the lever in the middle position will keep pressure in the system which you do not want.

You can either lift all four wheels off the ground with the lever in the normal position which should depressurise the system sufficiently or if you want to be sure disconnect the cable and move to the "M" position (which removes the pressure from the central sphere but there won't be much in the systen anyway after a straight lift) - then depressurise the rear by loosening a line or the bleed valve.

When the pressure has been released and the coupling or bleed valve have been tightened again, lower the car so that the car is supported by the lifting device but the wheels are on the ground at or around normal ride height then start the engine and let the hydraulics pump up to normal ride height.

All should be well and so long as you have not been penetrated by flying high pressure oil all you will have lost is a bit of time and a few tablespoons of oil.

Bill

P.S. Checked in the Workshop manual and front and rear vent (bleed) nipples were fitted after chassis no 1985 so your car should have them.

Last edited by WGB; 30th December 2008 at 11:30 PM. Reason: Additional information
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Old 1st January 2009, 02:19 PM
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Default Re: Rear Suspension Problems

Thanks everyone

It's Saturday's project as tomorrow I am off to the SummerNats in Canberra
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1978 W116 690SEL # 3312
1985 R107 500SL AMG
2000 W208 CLK430 Coupe
2003 W163 ML320
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Old 1st January 2009, 06:57 PM
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Default Re: Rear Suspension Problems

Oh Michel........summernats.........grow up man!
Tattooed fu*kwits in bright coloured heaps on big mags doing burn-outs while shouting 'show us yer t*ts', surely you are over that by now.
C.M.
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Old 1st January 2009, 07:10 PM
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Default Re: Rear Suspension Problems

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Originally Posted by GreaseMonkey View Post
Oh Michel........summernats.........grow up man!
Tattooed fu*kwits in bright coloured heaps on big mags doing burn-outs while shouting 'show us yer t*ts', surely you are over that by now.
C.M.
You never get over that

However, I go there for two reasons.

I need to cover the event for my magazine and I keep an eye on the latest car creations...
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1978 W116 690SEL # 3312
1985 R107 500SL AMG
2000 W208 CLK430 Coupe
2003 W163 ML320
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Old 1st January 2009, 07:13 PM
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Default Re: Rear Suspension Problems

Ok.
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Old 1st January 2009, 07:18 PM
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Default Re: Rear Suspension Problems

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Originally Posted by GreaseMonkey View Post
Ok.
Does that mean I have your approval?
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1978 W116 690SEL # 3312
1985 R107 500SL AMG
2000 W208 CLK430 Coupe
2003 W163 ML320
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  #14  
Old 1st January 2009, 08:09 PM
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Default Re: Rear Suspension Problems

So you are visiting us in "Capitown" as Cam2 calls it? Just one day or a few? Didn't come down in the 690SEL per chance?
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Old 1st January 2009, 08:19 PM
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Default Re: Rear Suspension Problems

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Originally Posted by Michel View Post
Does that mean I have your approval?
Why would you need my approval?
I made it clear above what I think of such things, but you have your job to do.
Have a nice weekend, and I hope the t*ts make the trip worthwhile.
C.M.
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