W126 HPF Tips and trick please - Mercedes-Benz Forum
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post #1 of 11 (permalink) Old 06-19-2019, 08:12 PM Thread Starter
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W126 HPF Tips and trick please

Hello

First of all Im am new to Benzworld, but this really looks like a great place for a Benz lover!!

I am looking to buy an W126 560 SEL with HPF, this wil be my fourth W126 so I know them well exept from the HPF system.

What to look for when inspecting the car? how to test the system?

if anyone have any information regarding HPF, both in how it works and how to fix/inspect it, i would be very glad if you post it here.

Many thanks from my home in Norway :-)
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post #2 of 11 (permalink) Old 06-20-2019, 10:11 AM
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Welcome!
I am sure member "KRH" (Kim) will weigh in, he has a W126 with full Gen 2 Hydro, very nice. They take a lot of sorting if the system has not been maintained.
For starters, I would check the "H" setting, pull the dash knob out all the way, the car should rise effortlessly to the High setting with engine running. Also you need to check if you have Gen 1 or Gen 2 hydro. The Gen 2 has active damping and speed auto - leveling, way cool, but even more complex, the control units for these wear out, as Kim will speak to I'm sure. Do a quick search, there has been some very detailed post not too long ago on what to look out for.
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post #3 of 11 (permalink) Old 06-20-2019, 10:12 AM
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I'll hook you up, here is the post:

https://www.benzworld.org/forums/w12...problem-3.html
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post #4 of 11 (permalink) Old 06-20-2019, 11:46 AM
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Yes welcome to you. Lots of general info in the search archives, but the thread posted by Didkaan is an excellent start.

'86 420SE
'90 420SEC


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post #5 of 11 (permalink) Old 06-20-2019, 11:49 AM
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HPF?

Current Stable:
2012 CL550 C4 4MATIC Coupe


Past cars:
1991-560 SEC AMG - Coupe - 199/261 - 300 HP Custom Built Motor - Highly Modified Coupe.
1990-560 SEL - Sedan - 199/261 - Stock. Euro Headlamps & Wipers
1987 560 SEC Black/Tan
1988 420 SEL Champagne/Brown



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post #6 of 11 (permalink) Old 06-20-2019, 12:16 PM
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In German it stands for Hydropneumatische Federung, or Hydro Pneumatic Suspension
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post #7 of 11 (permalink) Old 06-20-2019, 05:25 PM Thread Starter
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Thanks for good information so far, the link was very informative!

The car I am going to look at is an 87`560 SEL (ECE), so i guess it is the gen 2 of the HPF suspension.

The car is very good metal wise, no rust as it is an import from Italy, but it have an issue with the "info center", the digital dial shoving mpg and so on in the right side of the instrument cluster, it dosent work at all, anyone got any idé what is going on there?
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post #8 of 11 (permalink) Old 06-20-2019, 10:41 PM
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The Gen 2 version is a lot more complex than the Gen1
Easy tell is the switch on the aircon panel top row that has a pic of a shockie (strut) - if you have that it is a Gen2 version. It is for manual override to firm up the struts.
Also if you open the hood you will see a control valve with solenoids & wires on the left side of the engine bay behind the headlight - which controls strut firmness and lowering of the car at 120kmh

So like the Gen1 you need to see the red warning light on the gauge cluster go out within 30seconds of start-up to confirm system is at required operating pressure.

Then whilst still idling by pulling the height raising knob all the way out should see the car immediately raise in height about 30mm both front and rear evenly.
Pushing the knob back in will see the car go back to normal level immediately.

Whilst idling hood up and engine still idling - you should be able to bounce the front end by pushing down with with your hands to feel the strut firmness
Engine still idling- Then activate the switch on the aircon panel so the little red light on the switch activates indicating it is on - this firms up the struts
Engine still idling - Go back and do the bounce test to see if the struts are now more firm in trying to push the front end down with your hands.
If yes - then firmness function working - if not firmness function not working

If you can find a highway where you can go over 120kmh you should be able to test if the car lowers itself above this speed by aprox 30mm to hunkering down mode for autobahn driving (it also auto firms the struts at this speed)

These are just the basic tests to see if the system is working.
Check fluid tank for correct fluid level and also the colour of the fluid - it should be almost clear and not a brownish indicating old fluid
Look in the engine bay and under for fluid leaks
inspect each strut and under each strut for fluid leaks
inspect the rear dust seals for condition of boots (no splits or missing rubber)
The base of each strut has a ball joint with a seal - inspect for seal being in tact and not perished (same as like a front ball joint seal in the steering stub axle hub)

These are just the basic tests/inspection
After this further tests are more complex testing system pressure etc
If you get past the basic tests and want to proceed further - then we can guide you with more complex analysis and provide workshop data/diagrams etc.


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, on Flickr" border="0" />
87 White Euro 500 "ECE" 265hp SEC
88 Black Euro 560 "RUF"300hp SEC
89 Blue Euro 560 "RUF" 300hp Hydro SEL

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post #9 of 11 (permalink) Old 06-22-2019, 03:34 AM Thread Starter
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Thanks so very much for the checkpoints!

This was exact what I was after ;-)

Question;
- if the spheres are broken, witch might be the case on this one, will there stil be a difference in firmness with the strut button off/on when doing the bounce test?
- "inspect the rear dust seals for condition of boots" where are those?

THX
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post #10 of 11 (permalink) Old 06-22-2019, 11:35 PM
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Rear dust boots and ball joint seal seal in pic below
Boots can be easily viewed from looking from under rear of car - seals are a bit more tricky as require the car to be raised on jacks or a hoist
Fronts have a metal shield that protects the dust boots but not the ball joint seal which is below the shield and is easily visible

As to shot spheres i would assume the car would ride like crap and bounce over bumps as no damping as sphere would be full of SLS fluid

Look for signs of leaking fluid below each strut and in the general area as wind tends the blow the fluid everywhere
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87 White Euro 500 "ECE" 265hp SEC
88 Black Euro 560 "RUF"300hp SEC
89 Blue Euro 560 "RUF" 300hp Hydro SEL

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