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Suspension pump

Started by koan, 18 May 2009, 02:19 AM

koan

Uploaded a few pictures of a suspension pump in pieces. Intention is to add some text and possibly more pictures detailing its rebuilding.


W116.org Gallery  » Garage  » koan's bits  » Suspension pump repair

koan
Boogity, Boogity, Boogity, Amen!

oscar

Hey koan, how did you get this part out and do you reckon the band around it acts like a one way valve?
1973 350SE, my first & fave

koan

The steel block is a tight fit in the alloy case, boiling the lot in a saucepan should allow the block to be lifted out (with the oven mits), aluminium expands more than steel. It it doesn't lift out you might have to resort to what will be described in the last picture, a roll of tape  (lid off a peanut butter or Vegemite jar also works) stuck to the case and the lot wapped down hard on the bench to free the front o-ring, that's all what is holding it in.

I think you can see in the pictures that the cross-section of both o-rings is flattened, that's why they often don't seal again once the front cover is removed.

The strip is the reaction band, it is a valve, just moves away a fraction to allow the fluid to pass out of the cylinder and sits back down.

I'd expect some sort of valve to let fluid into the cylinders but there isn't, just holes in the piston, a bit like a two stroke port.

koan
Boogity, Boogity, Boogity, Amen!

s class

very impressive koan, thanks.  There has been a lot of talk here and at M100 about these pumps, and finally someone has gone ahead with the stripping.  I would love to know if there really is any difference between the early HPF and later W126 era pumps.

Is there any critical aspect about the relative angular positioning of the steel insert within the alloy housing?


[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

Excellent. It's good to see that they're not particularly complex, just very precisely machined parts.

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

koan

Quote from: s class on 18 May 2009, 05:42 AM
I would love to know if there really is any difference between the early HPF and later W126 era pumps.

All HP pumps are the same I think, LP pumps appear to be of slightly different
design with a bigger gap between pump body and cover. I think sometime during the 6.9 years production was rationalized to the HP pump only. By W126 all pumps have HP-? stamped on the front.

Quote
Is there any critical aspect about the relative angular positioning of the steel insert within the alloy housing?

Only critical thing is to place the pegs of the reaction strip away from the pump outlet. Directly opposite makes sense, that puts the pistons at 45 degrees to the outlet too.

koan
Boogity, Boogity, Boogity, Amen!

WGB

I have always thought that repairs to this pump with a permanent result were frought with failures and although they are expensive purchasing a new one was a reasonable long term alternative.

It would appear that long term sealing is the main issue with repairs and I wonder how you can get bearing clearances tight enough in an old pump to prevent new seals from being chopped out.

Anyway - fascinating stuff KOAN.

Bill

s class

Bill, I understand the primary reason for failure of 'repaired' pumps is that once the cover has been removed, the two o-rings between the steel insert and aluminium body may start leaking - and they are usually not replaced.  Leaking of these seals subjects the rear shaft radial seal to full hydraulic pressure with the result that it too leaks, and the usual diagnosis is that 'replacement of the rear radial seal was unsuccessful'. 

Koan's approach is, as I understand it, the method most likely to lead to success.

Having said that, I fitted a W126 SLS pump to trusty rusty.  Before I fitted it, I removed the cover to clean it, and replaced the rear radial seal.  I was quite concerned that it might be discharging fluid into the engine, and before my recent long trip to the Cape I had actually not done enough mileage to see if this was a problem.  Consequently I took a lot of hydro fluid with, plus a lot of engine oil in case a half-way engine oil change became necessary.  It seems I was fortunate and the hydro fluid level did not drop in the 3800km. 


[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

oscar

Quote from: s class on 19 May 2009, 03:32 AM
Bill, I understand the primary reason for failure of 'repaired' pumps is that once the cover has been removed, the two o-rings between the steel insert and aluminium body may start leaking - and they are usually not replaced.  Leaking of these seals subjects the rear shaft radial seal to full hydraulic pressure with the result that it too leaks, and the usual diagnosis is that 'replacement of the rear radial seal was unsuccessful'.   

That makes sense sclass.  It's something I've never considered and I've never replaced the rear O ring simply because I didn't know the steel insert could be taken out and that there was a seal behind it.  In a couple of pumps I've pulled apart the shaft has also been worn where the double lip seal contacts it.  I was given a handy link ages ago showing that sleeves can be put on the shaft to build up the surface again.  Maybe some machining on a lathe might be beneficial first and I haven't tried it myself and the link is now a 404 but anyone intersted, google "speedi sleeves".  They seem like a good fix.

Re HP and LP pumps and 126 pumps.  Is there three types?
What is the one you're pulling apart koan, LP? 

There's an old comparison pic below showing the difference in gaps between covers and bodies.  I was told the pump on the left is from a 6.9 and you can see how the cover is thicker with a bit added on to close the gap between cover and body compared to the original one on the 350 on the right which I presume would be an early LP pump.  Neither of them show HP or LP markings that I can see.  I'm not sure how to tell the difference from the outside.  But from the inside, have you got one of each type of pump to compare side by side?  I'll send you down the one on the left and another off a 74 280 and you can strip them and get busy with a micrometer if you like?  Answer that age old question of what's the difference. 8)

1973 350SE, my first & fave

koan

Quote from: WGB on 19 May 2009, 03:26 AM

I wonder how you can get bearing clearances tight enough in an old pump to prevent new seals from being chopped out.


I don't follow your logic, is there any reason to believe replacing the pump rear seal is any different to replacing any other shaft seal, power steering or front main seal for instance?

The pump seal is at atmospheric pressure not output pressure and is a double spring seal to boot.

koan
Boogity, Boogity, Boogity, Amen!

koan

Quote from: s class on 19 May 2009, 03:32 AM
Bill, I understand the primary reason for failure of 'repaired' pumps is that once the cover has been removed, the two o-rings between the steel insert and aluminium body may start leaking - and they are usually not replaced.  Leaking of these seals subjects the rear shaft radial seal to full hydraulic pressure with the result that it too leaks, and the usual diagnosis is that 'replacement of the rear radial seal was unsuccessful'. 

You are clearly quoting from my PM to M100 gent who was being fed an enormous amount of rubbish about the pump, mostly from one particular source. It was not my intention to have my PM posted - especially in CAPS.

Looking at the pictures I posted the HP o-rings are in a bad way, they are deformed and have lost a lot of their flexibility, once disturbed they are not going to seal again.

Unless the shaft is damaged in the seat area, the shaft in the pictures has polish marks but no discernable groove, a new seal should be fine.

koan
Boogity, Boogity, Boogity, Amen!

WGB

Hi Koan,

My comments were not intended to be critical.

I have no experience with this pump at all except that I have heard several stories of doom and gloom whenever repairs have been attempted.

Very happy to hear that repairs are possible and your provision of the means to illustrate it is brilliant.

Bill

koan

Quote from: oscar on 19 May 2009, 12:14 PM
Re HP and LP pumps and 126 pumps.  Is there three types?
What is the one you're pulling apart koan, LP? 

I had the idea all HP pumps had HP-R or HP-K or similar stamped on the front. Maybe the differences in the pumps are just because they are from different OEMs.

Is it possible HP pumps are built to finer tolerances with selected parts and all look the same?

I'm always happy to accept old parts for to gain a deeper understanding of the universe oscar, I'll PM you about postage and etc.

koan

Boogity, Boogity, Boogity, Amen!

koan

Quote from: WGB on 19 May 2009, 06:28 PM

My comments were not intended to be critical.


Didn't take them as critical WGB, I was wondering why you see that seal differently to others, so I asked.

Maybe I was a bit short, sorry.

koan
Boogity, Boogity, Boogity, Amen!

s class

Quote from: koan on 19 May 2009, 06:08 PM
You are clearly quoting from my PM to M100 gent who was being fed an enormous amount of rubbish about the pump, mostly from one particular source. It was not my intention to have my PM posted - especially in CAPS.

koan


koan, I sense I have inadvertedly offended you?  I recall the posting on M100, and at the time I read it, it made sense to me, so I paraphrased it here because it seemed relevant to this thread.  At the time of my posting above, I didn't recall who had posted it over at M100, and certainly not where it originated from.  Anyhow, it is now there on the M100 site for public consumption. 

So sorry, no offence to anyone was intended. 


[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