Author Topic: Flushing 6.9 Suspension  (Read 224 times)

Rolo

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Flushing 6.9 Suspension
« on: 14 October 2020, 02:46 PM »
Noticed about a year ago, the dip stick was brown.  Drained tank (need to wash out the sludge in the bottom - where does it come from?), replaced filter, and now ready to flush the lines in the front and back from the bleed nipples.  Somewhere I found tips on flushing.  Raise the car first.

This seems counter intuitive.  If you want to flush clean fluid through the lines and controllers, seems like you'd want the wheels on the ground.  The system tries to suck oil away from the struts and reservoirs when the wheels are up.  Opinions?

daantjie

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Re: Flushing 6.9 Suspension
« Reply #1 on: 14 October 2020, 03:34 PM »
Here is my method, not sure if it is the "right" way but seemed to have worked for me.

I used the main leak line (hard line connection at the pressure regulator) to dump off the return fluid.  This is the "D" line in schematics.
Your "H" function must be working correctly to do this.  Disconnect the hard line (D) at the pressure regulator, then connect a catch tube here and run your tube into a catch bottle. 
Then run the engine and cycle your switch to "H".  Have the tank open with cap removed.  Use a strong light to shine into the tank to see what's going on.
You will see fluid drop rapidly in the tank as fluid is pumped into the struts.  Then cycle back to "N", then the return fluid comes back via the leak line into the catch bottle.
Then top up the reservoir with fresh fluid, and repeat.  Simple 8)
Daniel
1977 450 SEL 6.9 - Astralsilber

Rolo

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Re: Flushing 6.9 Suspension
« Reply #2 on: 14 October 2020, 04:20 PM »
I like the sound of your method.  The only thing that counts is getting brown oil out and clear oil in.

One question: wheels up or down?

daantjie

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Re: Flushing 6.9 Suspension
« Reply #3 on: 14 October 2020, 05:33 PM »
Car on wheels in "ready to drive" orientation.
Daniel
1977 450 SEL 6.9 - Astralsilber

Rolo

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Re: Flushing 6.9 Suspension
« Reply #4 on: 14 October 2020, 09:52 PM »
Got it, wheels on the ground.  But for position H, does it work on USA cars?

Thanks a ton

daantjie

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Re: Flushing 6.9 Suspension
« Reply #5 on: 14 October 2020, 10:27 PM »
The system is capable regardless. On US models there is a sleeve on the cable preventing the selection but you can easily remove it.  If present you will see it at the height control switch (aluminum cube bolted to the pressure regulator)
« Last Edit: 15 October 2020, 08:09 AM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

BCK1963

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Re: Flushing 6.9 Suspension
« Reply #6 on: 15 October 2020, 01:41 AM »
The entire system holds appr. 6 Liters and the reservoir appr. 3 Liters.
You may as well pump out the volume of the reservoir and add new fluid before bleeding line D, like you would do when manually bleeding brakes.
btw: I want to change my air volumes next year and have aready read myself into the matter. Looking at the in- and outlet positioning on the balls I wonder how new balls can be entirely filled with oil after installation if the in- and outlet piece is not located as the highest point , as is the case with all but the central Reservoir.
What am I missing?

Rolo

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Re: Flushing 6.9 Suspension
« Reply #7 on: 15 October 2020, 09:49 AM »
I replaced all of the reservoirs.  They get filled when you start the motor.  The entire system is under a lot of pressure and all the air gets pushed out.

I'm still wondering where all the sludge in my tank came from.

daantjie

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Re: Flushing 6.9 Suspension
« Reply #8 on: 15 October 2020, 10:10 AM »

I'm still wondering where all the sludge in my tank came from.

The sludge is from all the years of use really, mostly from the rubber hoses that degrade over time.  You will see that the pickup in the tank is above the floor of the tank, thus once the sludge settles it has nowhere to go but accumulate in the bottom of the tank.
Daniel
1977 450 SEL 6.9 - Astralsilber

Rolo

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Re: Flushing 6.9 Suspension
« Reply #9 on: 16 October 2020, 06:57 PM »
What a warming thought -- rubber, that will all need replacing.

I got a serious problem now.  The high pressure hose from the pump to the valve on top of the tank is weeping.  The fitting is the cone type, but it's not very tapered.  Torqued to spec, 30 nm.  I looked in my factory shop manual and it says the connection was superseded in May 1978 with a cone and the photo shows another fastener on the hose fitting, I think.

Is there a newer fitting that won't weep?

daantjie

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Re: Flushing 6.9 Suspension
« Reply #10 on: 16 October 2020, 08:00 PM »
I looked in the service manual and the tightening torque is 45nm so you may need to snug it up more.  That hose was still available a while ago.  They tend to leak inside out after a while but leaking at the connection would be unusual.
Daniel
1977 450 SEL 6.9 - Astralsilber

PosedgeClk

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Re: Flushing 6.9 Suspension
« Reply #11 on: 17 October 2020, 08:17 PM »
What a warming thought -- rubber, that will all need replacing.

I got a serious problem now.  The high pressure hose from the pump to the valve on top of the tank is weeping.  The fitting is the cone type, but it's not very tapered.  Torqued to spec, 30 nm.  I looked in my factory shop manual and it says the connection was superseded in May 1978 with a cone and the photo shows another fastener on the hose fitting, I think.

Is there a newer fitting that won't weep?
What is weeping is the rubber itself. The fittings are likely fine. I had a high pressure hose rebuilt locally and simultaneously purchased a new one from ECS or someone like that. I got a bunch of emails for months that the high pressure reservoir hose was NLA, and I was OK with that, and after I had installed the rebuilt one, a package mysteriously arrived with a bunch of NOS stuff. I was annoyed, and at the same time, I was kind of charmed. I was making so much money a year and a half ago and was so busy that I didn't have any time to complain to ECS and just laughed it off that they had wasted $500 of my money but had found probably the last X of what I was looking for by calling every dealer in North America. I'm probably way off, but that is how I rationalized it at the time.

Not too long ago, I had an issue with a hose on a Honda product, and it was a similar scenario. It was a high pressure power steering hose with a right-angle bend. The slight seep of hydraulic oil always looked like a problem either at the crimp or at the fitting going into the pump, but that was never the case. Something in the rubber had split, and it was causing oil to leak around the crimp in the fitting.

Do you see a spray, a drip, or just a loss of fluid? Don't run your hand near the exit of the hydraulic pump. I have heard some bad stories of people injecting themselves with fluid from a pinhole leak.
1979 450SEL 6.9

Rolo

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Re: Flushing 6.9 Suspension
« Reply #12 on: 18 October 2020, 02:42 PM »
It's the fitting.  I used talcum powder to leave a trail.  The shop manual says 30 nm, but I'm going to try a little more torque.  It's scary because there's no place for a counter hold and the top of the tank is flimsy.