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Hydro suspension.

Started by koan, 10 April 2009, 06:10 PM

koan

From the "SLS pump for sale" thread

"s-class" and "PB" you both mention needing to bleed the suspension pump after a period of no use.

What are the symptoms when you start the car after sitting for a long period?

I'm again intrigued by the mysteries of the suspension pump after what I wrote about mine in the for sale thread, this adds another oddity.

koan
Boogity, Boogity, Boogity, Amen!

Big_Richard

#1
because the pumps arent actually good enough to pump air at the obscene pressure required to overcome the one way valve in the main valve, if there is ANY air in the pump when the car is started, it will sit there doing nothing untill you bleed it out. Oil isnt compressable obviously and as soon as it gets into the pump your in business.

The symptoms are obvious, the suspension will not raise when the knobs pulled apon, or if like mine the car is lifted countless times off the ground without locking the system it starts to go down, and it never pumps back up again till you bleed the pump. My car happily sits 6 months at a time without running and the suspension never drops (after repeatidly rinsing out and manually pumping the struts with petrol - plenty of crap came out, I only stopped when the liquid came out clear)

Since replacing the pump cover, bleeding the pump has been something that has to be done every time the car is started, the longest it lasts between primings is 3 days. This constant introduction of air into the system is also airating the oil - I'm going to need to replace this peice of crap pump pretty soon, but its not high on the priority list since i never even drive the car.


WGB

A part from the original startup after cleaning out the oil reservoir I have never had to bleed the pump.

I would think if the oil level is nearer the full mark when the level is checked that it would be above the level of the pump anyway - must check.

I think you have a small air leak somewhere PB.

I lnow the suspension gets better after a week or two of driving after being opened for repair  and I have assumed this is caused by air trapped in the system but I have never had any isues with primimg other than that one startup.

Bill

s class

Bill I think the pump is above the level of the oil in the tank, and that's why there is a problem.  In my case I'm fairly sure I have problems because the threaded inlet into the low pressure side of the pump isn't sealing completely. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan

Uploaded a cross section of the pump to the gallery.


(click for full size image)

The text says the pump is "similar" to the SLS pump whatever that means.

"PB", the pump leaking after a new front o-ring (12) is fitted could be due to the front and rear high pressure o-rings (10) not sealing after they have been unloaded.

I recently acquired (yes it was me) an SLS pump and have reduced it to its component parts for some photography. The high pressure o-rings are deformed and quite hard, I doubt the rear o-ring would seal if reused as it is very flat.

I recall seeing somewhere years ago (m100.org?) that the high pressure o-rings are something special but that could be just imagination. I'll investigate this, see what's available.

koan
Boogity, Boogity, Boogity, Amen!

Big_Richard

excellent work as always koan.

I suspect my pump is plain and simple rooted - I will be replacing it eventually, and air certainly is leaking into it when its been parked for a while, the outside of it is also damp with hydraulic oil so its certainly between the top and the body.

s class

I don't think (and koan's diagram supports this) that there are any valves in the pump assembly.  Its a plain and simple rotary pump. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan

Quote from: s class on 11 April 2009, 06:39 AM
I don't think (and koan's diagram supports this) that there are any valves in the pump assembly.  Its a plain and simple rotary pump. 

There is an output valve, "Reaction sealing strip" (9), it's a thin metal band about 6 mm wide around the "Center piece" (2) and held in place by two loose fitting pegs. The band has elongated holes for the pegs and gap between where the pegs secure it so it can move slightly. It sits over the holes in the tops of the cylinder bores. It lifts slightly to allow fluid out of the cylinders and snaps back to prevent fluid being drawn back.

Pictures later will explain better than I can.

koan
Boogity, Boogity, Boogity, Amen!

koan

#8
Quote from: Patrick Bateman on 11 April 2009, 05:20 AM
I suspect my pump is plain and simple rooted - I will be replacing it eventually, and air certainly is leaking into it when its been parked for a while, the outside of it is also damp with hydraulic oil so its certainly between the top and the body.

Well if you do replace it don't bin the old one like I stupidly did, lets have a go at fixing it.

SLS pumps are different to hydro suspension pumps, SLS pumps can't deliver the pressure and volume required by full hydro suspension. Original 6.9 pumps have "HPF" on the front, SLS pumps don't.  Current (new) pumps from M-B don't have the "HPF" on them but are suitable for both suspensions.

This info is from Walter Hanel out your way. I have a couple of emails from him close to 10 years ago on rebuilding the pumps. When I do the pictures and write something up I'll be including most of what he wrote back then.

koan

Boogity, Boogity, Boogity, Amen!

s class

THis is interesting, koan.  All info I've seen here and on other forums in the past in this regard has suggested that the SLS and 6.9 pumps are the same.  It would however not surprise me if this is not the case. 

the pump that was fitted to the blue car when I got it was stamped '76', which is consistent with the build date of the car, and therefore I presume it was the original pump.  I will go and check later in the garage if it's stamped HPF or anything else. 

The red car has a pump with a date in the 80's and therefore I presume its not the origina pump. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

TJ 450

The pump on my 6.9 has HPF and 76 markings... it's the original unit.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

s class

OK, the original '76 pump that came off the blue 6.9 is marked HPF.....  I originally removed it because someone had enlarged the bore for the rear seal and fitted a generic seal that only loosely closed aroud the shaft.  It was loosing fluid into the engine like crazy.  Now I think I will have to have a bush made up to restore the bore on that pump so that I can fit a proper seal and use the correct pump.  Interesting. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

Big_Richard

This is all very interesting.

I recall the previous owner of my vehicle saying that he'd replaced the suspension pump with one off a w126 380 SEL.

I'll never know now as my top cover has been thrown out due to a cross threaded inlet connection. I have installed a good second hand cover from S Class which is date stamped later than my car was made.

A new pump is now the only option.

s class

I wonder what, if anything, is different between the HPF and non-HPF pumps.  Maybe it relates to that 'reaction sealing strip'. 

I will say this, when I recommissioned trusty rusty after the suspension refurbishment, I had the W126 SLS pump in place.  I had a pressure guage onthe high pressure side after the regulator, and the pressure cycled between the upper and lower limits as specified without any problems.  In fact, there was no indication that anything was other than perfect. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

Big_Richard

I have performed backyard surgery on my crappy suspension pump.

I pumped the tank dry, into a container, removed the pump and pulled it apart.

The front cover was definitely not sealing correctly onto the pump body.

There was Dog hair on the new front O ring seal. I suspect my she'll be right attitude was in effect on the day that i assembled the pump last time.

I suspect absolute cleanliness, such as when working on an automatic transmission would be good to get into when working on these pumps ;)

Since I'm 100% going to ditch this pump anyway, i have reinforced the front O-ring seal by coating the whole thing in loctite gasket maker - If it leaks, it will never leak from the front cover again. Theres no evidence to suggest its leaking through the rear shaft seal, its in excellent condition and no suspension oil has ever gone missing. Engine oil level doesn't change either - then again it gets changed every 6 months, which equates to about 150km's of driving.  ::)