Topklasse Discussion Board  
Home Forum Legal/Privacy Media/Picture Gallery Websites and Links Technical

Go Back   Topklasse Discussion Board > THE CRAFTSMAN - TECHNICAL DEPARTMENT > TECHNICAL INFORMATION

TECHNICAL INFORMATION How-to and detailed information on specific technical subjects

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 4th October 2020, 06:37 PM
Styria's Avatar
Styria Styria is offline
The Godfather
 
Join Date: Feb 2008
Location: Sydney
Posts: 8,678
Default The "Screw Driver" test

6.9 owners would be familiar with the full hydraulic system that , apart from struts and valves, plus some other components, incorporate five Pressure Cells - four for front and back, plus a Master unit that replenishes the system if there is a drop in the suspension level.

I recently required five units to be fitted to a car I had in my care. Endeavouring to purchase locally, I was unable to locate any units - neither front nor back. I did have three front units on hand which I purchased some two years ago, but I wanted to save those for Gleaming Beauty. Having drawn blanks from local suppliers, I located five front units in Great Britain, but no rears. I just have to back trek a little regarding local availability. Naturally, I let my fingers do the walking and located some front units at a quoted price of $300.00 each for three units. I told the vendor that I would buy four if he was prepared to negotiate on $250.00 each. Much to my pleasure, he agreed and I made arrangements to pick up four pressure cells the next day - I had a grand in my pocket to clinch the deal. Incidentally, the vendor had quoted the owner of the car $220.00 each, but I put this favourable price down to the fact that the owner of the car had done prior business with the vendor.

On arriving next day with the grand in my pocket, the vendor directed me to a work bench with about half a dozen pressure cells on display. Hmmm...."I take it these are new, are they" ? Ah no, they're second hand . Wow, $250.00 for second hand units I said to myself. "So tell me, how do you know that these are fully operational - have you tested them" ? Yes, I insert a screw driver and if the resistance is solid, the unit is okay. So, what happens if a unit is no good that I would have purchased from you - what guarantee do I have - bring it back and I'll supply you with another one. There was no mention however of any compensation for the work involved. In the next post, I shall explain some of the finer points about Pressure Cells. Regards Styria
Reply With Quote
  #2  
Old 4th October 2020, 07:05 PM
Styria's Avatar
Styria Styria is offline
The Godfather
 
Join Date: Feb 2008
Location: Sydney
Posts: 8,678
Default Re: The "Screw Driver" test

Front Pressure Cells and the Central Cell are pressure rated at 70 atms - in rough calculations, that translates to say 990 lbs/square inch, whilst the rear units are rated at 60 atms each. For the sake of correctness, each atm correlates to 14.9 sq/in. From memory at the moment, and to realize how critical the pressures should be, Mercedes Benz recommend that front cells should be a minimum of 60 atms, and rears at 40 atms. I could stand to be corrected, but those figures are pretty close. Mercedes also recommends a maximum of 8 atms variation between front and rear pairs. Anything at all that does not meet those specifications, the Company recommends replacement with new units at authorized repair stations.

So, let's get back to this screw driver test that's supposed to be accurate. It's unfortunately, nothing but a furphy. If one can insert a screw driver successfully to push back the membrane, the car would be undrivable as the cell would be full of oil and completely devoid of any damping. The car would be riding like a bogo stick and you wouldn't need to bother finding that screw driver. The units I removed from that 6.9 provided a reading of between 10 to 20 atms for each cell removed. Now, try and push a screwdriver against the membrane in the cell at 10 atms - you're pushing 149 lbs/sq.in. and you will not be able to move that membrane, with an even worse outcome at 20 atms. Forget testing at the recommended maximum or, more appropriately, at the quoted minimums ! No chance.

As a matter of interest, we have the measuring instruments and the capacity to check the pressure of Air Cells on the car, or alternatively if removed from the car charged out at $45.00 per unit - only when removed from car. It saves all the guesswork. Regards Styria

N.B. Needless to say, I couldn't walk away from that deal quickly enough, and in due course purchased five new Front Cells from Great Britain and I managed to find two genuine Mercedes (I believe Lemfoerder) rear units from a wrecker in Melbourne. They were NEW, not second hand.

Last edited by Styria; 4th October 2020 at 07:11 PM.
Reply With Quote
  #3  
Old 4th October 2020, 08:57 PM
sean sherry sean sherry is offline
Aristocrat
 
Join Date: Jan 2012
Location: sydney
Posts: 1,647
Cool Re: The "Screw Driver" test

If there was a truer word spoken it has to be ....." Caveat Emperor"
Reply With Quote
  #4  
Old 5th October 2020, 06:46 AM
Michel's Avatar
Michel Michel is offline
The Prince of Arabia
 
Join Date: Feb 2008
Location: Sydney, Australia
Posts: 9,293
Default Re: The "Screw Driver" test

Quote:
Originally Posted by sean sherry View Post
If there was a truer word spoken it has to be ....." Caveat Emperor"
"caveat emptor"
the principle that the buyer alone is responsible for checking the quality and suitability of goods before a purchase is made.
__________________
Michel

1978 W116 690SEL # 3312
1985 R107 500SL AMG
2000 C208 CLK430
Reply With Quote
  #5  
Old 5th October 2020, 08:08 AM
sean sherry sean sherry is offline
Aristocrat
 
Join Date: Jan 2012
Location: sydney
Posts: 1,647
Thumbs up Re: The "Screw Driver" test

Thank you Michael . Our Irish Spelling differs some what !!!
Reply With Quote
  #6  
Old 5th October 2020, 08:18 AM
Oversize's Avatar
Oversize Oversize is offline
Noble
 
Join Date: Apr 2010
Location: Melbourne
Posts: 5,023
Default Re: The "Screw Driver" test

If they come out of the car they go straight back in if ok or straight in the bin. Although I have kept some for just me on the unlikely chance they could ever be recharged. The screwdriver test is only good to check if the diaphragm is intact. If not, then bin it.

Only ever buy new ones. Correct pressure is critical so itís not worth using old ones from an unknown source.

Itís not easy to find new cells, so you have to ring around. Then try to find ones with a recent stamp date. Then you need to deal with the transport issue. Forget Aust Post as theyíre deemed dangerous pressurised goods. Air freight can only be handled by a few companies.
__________________
Mark

01 Ford AU 5L (Deep Blue)
88 420L Euro#-P
88 420L#-P
88 420L#2477-P
87 560L#2020 (Dora 2)
87 560L #9987
87 420L#4309-P
87 420L#-P
86 560L#5896-P
79 6.9#5541 (Red Bull)
78 6.9#4248 (Skye)
79 6.9#3686 (Moby Dick)
78 6.9#1776 (Dora 1)
77 450L#7010-P
75 450L#8414 (Gold Nugget)-P
57 Buick 73A (Titanic)
Reply With Quote
  #7  
Old 5th October 2020, 09:51 AM
Styria's Avatar
Styria Styria is offline
The Godfather
 
Join Date: Feb 2008
Location: Sydney
Posts: 8,678
Default Re: The "Screw Driver" test

Mark, to some degree if you're not superfussy, a car will still ride REASONABLY well on units that will only yield about 20 atms for each pressure cell. The car in question that I removed the cells from only exhibited a slightly wallowing experience on the right rear unit. It was down to 10 atms, with the others, once we tested them, giving a reading of 20atms.

The correct reading is particularly important on the Master Cell. If there is insufficient pressure, an excess amount of hydraulic oil will fill the unit and result in much slower response to the rest of the system. Some of you may also be interested in knowing that the rear Pressure Cells on cars fitted with springs at the rear and employing lower spec struts as on W116 and W126s operate on a pressure reading of about 11 atms. Regards Styria
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
FS: rial N7016523 "wiremesh" alloy wheels + bolts, brand new Afro107 TRADING POST/EBAY LISTINGS 15 17th April 2014 08:15 PM
Ebay~1961 MERCEDES BENZ 300d "ADENAUER" HARD TOP SEDAN 300SDude TRADING POST/EBAY LISTINGS 7 29th November 2011 04:59 AM
"Living the dream" 300D Adenauer 260ebenz ARTICLES 0 26th November 2011 05:34 PM


All times are GMT +10. The time now is 04:47 AM.


Powered by vBulletin® Version 3.8.10
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright Topklasse 2020