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 6.9
 Suspenion rehab
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Clayton

USA
86 Posts

Posted - 01/12/2018 :  18:23:31  Show Profile  Reply with Quote
My front end use to drop intermittently after turning off the motor. Now, it seems to be down all the time and the red warning light is on.The pull handle on the dash seems to have an effect but not on a consistent basis.I have replaced all spheres, rear leveling valve and rear struts to get to this point.So, the only things left are front struts and leveling valve....right? Can the pump be failing? What are the tests to isolate the issue?

Clayton

USA
86 Posts

Posted - 01/12/2018 :  18:26:06  Show Profile  Reply with Quote
In addtion, the lock out has never worked properly.
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daantjie

Canada
1005 Posts

Posted - 01/12/2018 :  21:18:02  Show Profile  Reply with Quote
Locking of the suspension does not work on most 6.9's not the end of the world frankly. Just observe safety measures when jacking.
Does the light go off when driving and after idling after start? The system should pressurize after about 30sec to 1 min of idling and no revving. Dropping at one axle only points to leveling valve and/or struts kaput.

Daniel
1977 450 SEL 6.9
Vancouver, BC
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Clayton

USA
86 Posts

Posted - 01/13/2018 :  06:37:07  Show Profile  Reply with Quote
The stage I'm at now, the light is on constantly and the front end rides low unless the lock out lever is pulled out.
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daantjie

Canada
1005 Posts

Posted - 01/13/2018 :  11:27:25  Show Profile  Reply with Quote
I would start by doing a refurb on the pump. Usually they need a refurb anyway so start there and see what happens. I still think you need a refurb on the leveling valve and struts too but start with the pump. Also I would pull the regulator and give it a good clean along with the small filter in there. Don't lose it as they are NLA.

Daniel
1977 450 SEL 6.9
Vancouver, BC
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rumb

USA
87 Posts

Posted - 01/13/2018 :  17:49:01  Show Profile  Reply with Quote
daantjie,

Other than a reseal is there really anything that can be rebuilt? I thought once the little pistons/bores get worn then it's all over.

rumb
68 250S, 77 450SEL 6.9, 91 300SE, 98 SL500, 14 CLS550
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daantjie

Canada
1005 Posts

Posted - 01/13/2018 :  20:07:33  Show Profile  Reply with Quote
Robert from my experience you just need to reseal with new orings. I test them by pulling a strong vacuum into the pressure side with feed plugged. If you can pull and hold 30 inHg of vacuum it should be well sealed.

Daniel
1977 450 SEL 6.9
Vancouver, BC
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Clayton

USA
86 Posts

Posted - 01/13/2018 :  20:35:02  Show Profile  Reply with Quote
I watched the YouTube of Kent Bergsma on this subject. If the cam has severe wear damage, a new pump may be best. Otherwise, replace the seals, sand the cam with ultra-fine sandpaper and your back in business. I should have this done in the next 10 days. I will keep you updated with my findings.
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mpmorris

USA
1352 Posts

Posted - 01/17/2018 :  20:43:05  Show Profile  Visit mpmorris's Homepage  Reply with Quote
Clayton --I scratched my head on a car that had similar symptoms as yours --I found two faults --air in system and the master controller valve pistons were sticking in the housing -did not slide easily --suppose debris went through the system at some point. I polished the valve pistons until they slipped freely through the housing, gave it a thorough bleed and even the lock system worked properly thereafter.

mpm

addendum: This issue started when the lever was pulled out to the lock position for a tire replacement --light and car height never had fault prior.

Edited by - mpmorris on 01/17/2018 20:47:53
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Clayton

USA
86 Posts

Posted - 01/19/2018 :  23:44:37  Show Profile  Reply with Quote
Wow, just when I thought I had my head wrapped around the system, Mike throws out "Master control valves". It makes sense but,where are those valves? There is the pump, reservoir canister, front and rear leveling valves, 5 spheres, struts and a lock-out pull knob.....Right?

I ordered a seal kit for the pump and plan to do that and a flush on Monday. Please advise.
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daantjie

Canada
1005 Posts

Posted - 01/20/2018 :  01:02:42  Show Profile  Reply with Quote
quote:
Originally posted by Clayton

Wow, just when I thought I had my head wrapped around the system, Mike throws out "Master control valves". It makes sense but,where are those valves? There is the pump, reservoir canister, front and rear leveling valves, 5 spheres, struts and a lock-out pull knob.....Right?

I ordered a seal kit for the pump and plan to do that and a flush on Monday. Please advise.



I think what is being refered to is the pressure regulator atop the fluid reservoir. You will see the high pressure feed line from the pump bolt into this unit.

Daniel
1977 450 SEL 6.9
Vancouver, BC
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rumb

USA
87 Posts

Posted - 01/20/2018 :  07:54:00  Show Profile  Reply with Quote
There are 2 methods to get the inner pump removed from the body.

One is heat the shell and then pull the pump out using a dowel insert into the pump cylinders using pliers. if you purchased the M-source kit, they will tell you to do it this way. It doesnt really take much heat to expand the shell, but it is awkward to pull the body out perpendicular.

The other is simply rap the edge of the shell on a block of wood - fairly hard rap, and the pump body will come out. I find this way much easier and less likely to damage the inside of the shell.

if you have any nicks on the inside diameter especially at the top of the unit it will never reseal again. liberally lube the new orings before inserting and push in slow and steady so you dont tear the top one.

Also there is a torque spec for the bolts, but will have to look that up later for you.



rumb
68 250S, 77 450SEL 6.9, 91 300SE, 98 SL500, 14 CLS550
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mpmorris

USA
1352 Posts

Posted - 01/20/2018 :  18:22:11  Show Profile  Visit mpmorris's Homepage  Reply with Quote
Yes Clayton, Daniel -the cast aluminum square block atop the reservoir -the unit the master control cable is affixed to. The rotating plate the cable is connected to distributes the pressure by pushing/relieving the pistons/via small steel balls; -ie 'regulating valve?' often indicating the pump has given out though a stuck piston in the valve housing can 'dump' the pressure. I honestly don't recall the correct name but it is a master control valve.

For accuracy, The cast aluminum block with the 'control disc' is called a "Level Selector Valve". The LSV is bolted to the "Pressure Regulator". As an assembly, it is the "Valve Unit"

(MB Service Book, Model Year 1977,Passenger Cars, USA Version, pg 369, fig 827)

mpm

Edited by - mpmorris on 01/20/2018 20:48:53
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Clayton

USA
86 Posts

Posted - 01/22/2018 :  20:44:19  Show Profile  Reply with Quote
Today was one of my top 3 most successful wrench days at Onager Mercedes. Everything Dan, Mike and Robert said led me to the end zone. Dan had it right to start with the SLS pump. I replaced the old and flat O-rings, verified the cam was in good health and cleaned all passages. The most interesting part was the mystery pistons in the "LSV". Mike had it spot on! There are 3 passages with a piston sandwiched in between 2 ball bearings. I had 2 that were not moving freely. End result....my lock-out that never worked, now works perfectly. No leaks, warning lights or red flags. My test drive and drive home confirmed my joy of the best my suspension has ever worked.

Edited by - Clayton on 01/22/2018 20:53:50
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daantjie

Canada
1005 Posts

Posted - 01/23/2018 :  00:08:48  Show Profile  Reply with Quote
quote:
Originally posted by Clayton

Today was one of my top 3 most successful wrench days at Onager Mercedes. Everything Dan, Mike and Robert said led me to the end zone. Dan had it right to start with the SLS pump. I replaced the old and flat O-rings, verified the cam was in good health and cleaned all passages. The most interesting part was the mystery pistons in the "LSV". Mike had it spot on! There are 3 passages with a piston sandwiched in between 2 ball bearings. I had 2 that were not moving freely. End result....my lock-out that never worked, now works perfectly. No leaks, warning lights or red flags. My test drive and drive home confirmed my joy of the best my suspension has ever worked.



Nice one!!!

Daniel
1977 450 SEL 6.9
Vancouver, BC
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