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Thread: Mercedes 814d t2 ln1 Load Sensing Valve, How can I check if it's working?

  1. #1

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    Mercedes 814d t2 ln1 Load Sensing Valve, How can I check if it's working?



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    I'd be grateful for advice on the braking system of my camper. It's a pre Vario Mercedes 814D.

    My van failed the MOT on the brake load sensing valve, I was advised to clean and use wd40 on it to free it up. I've done some cleaning, spraying with WD40 and levering repeatedly and it seems free and unstuck but I still don't know if it works.

    Before I take it back for a retest I'd like to be sure.

    Is there something I should be able to see if it's working etc?
    Should I expect to see something when the brakes are applied happening at the valve?

  2. #2

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    Mine started to leak on my iveco after mot men stamping on brakes,so i removed all the guts and sealed it just leaving the leaver doing nout,flued just now passes through,and it passed,see they have no way of testing it unless they load van with bricks,daft feckers.
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  3. #3

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    Most motor homes are almost fully loaded so you'll not see any movement in valve I'd have expected a MOT tester to have realised that
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  4. #4

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    Quote Originally Posted by trevskoda View Post
    Mine started to leak on my iveco after mot men stamping on brakes,so i removed all the guts and sealed it just leaving the leaver doing nout,flued just now passes through,and it passed,see they have no way of testing it unless they load van with bricks,daft feckers.
    Does that not effect the braking performance of your van eg lock the back brakes by sending too much pressure to the back, or the opposite and not send enough pressure to the back?
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  5. #5

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    Quote Originally Posted by witzend View Post
    Most motor homes are almost fully loaded so you'll not see any movement in valve I'd have expected a MOT tester to have realised that
    I'm grateful for your response but unforunatley it was far from it's max during the test (payloads about 3.5 ton).

    I was earlier under the van, with my wife applying the brake. I was hoping to see some movement at the sensing valve but it did nothing.

    Theres a levering bit on that was on the valve I managed to remove, I could then see what appears to a piston within a dislodged dust cover (packed in crud).

    I think the piston should move slightly out of the valve body when the brakes are applied until it is stopped by the lever part that is possitioned acording to the loading of the vehicle(the sensing action). I sprayed the crud around the piston away with a cleaning spray and then wd40. I hope to put it back together again tommorow will ask the wife to again apply the brakes and check for movement.

    I'm hoping after the cleaning and spraying with penetrating fluid there's some movement of piston thats in the valve body that nudges the lever part of the valve that I can observe when the brakes are applied. However still not sure what amount of movement to expect.

    Infact I'm not sure I've got the logic right either hence the help needed.
    Last edited by Gypsy; 16-04-2019 at 13:40. Reason: corrections

  6. #6

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    Quote Originally Posted by Gypsy View Post
    I'm grateful for your response but unforunatley it was far from it's max during the test (payloads about 3.5 ton).

    I was earlier under the van, with my wife applying the brake. I was hoping to see some movement at the sensing valve but it did nothing.

    Theres a levering bit on that was on the valve I managed to remove, I could then see what appears to a piston within a dislodged dust cover (packed in crud).

    I think the piston should move slightly out of the valve boy when the brakes are applied until it is stopped by the lever part that is possitioned acording to the loading of the vehicle(the sening action). I sprayed the crud around the piston away with a cleaning spray and then wd40. I hope to put it back together again tommorow will ask the wife to again apply the brakes and check for movement.

    I'm hoping after the cleaning and spraying there's some movement of piston thats in the valve body that nudges the lever part of the valve that I can observe when the brakes are applied. However still not sure what amount of movement to expect.

    Infact I'm not sure I've got the logic right either hence the help needed.
    The height of the vehicle on its suspension adjusts the operating lever and so adjusts the valve, raising and lowering the vehicle body adjusts the valve.

    (On a side issue hydraulic Citroen's have ride height valves, if you knock the plastic link off those the car will collapse on you, nothing to do with your brakes.)

  7. #7

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    Fixed Mercedes 814d T2 LN1 (Reg year 1994) Load sensing valve

    I'm posting this solution as it may help someone else with a similar issue one day.


    1. Cleaned the linkages and outer of the valve.
    2. Removed dust cover to reveal plunger, cleaned and sprayed with penetrating oil.
    3. Piston part was seized.
    4. Used hair dryer to heat (in the hope that the cylinder will expand and release the seized piston, did not use blow lamp to heat as was worried of risk of fire and damage to seals within valve).
    5. When the piston got hot I sprayed more penetrating oil on the plunger part, in the hope that some oil will seep into the gap between the piston and cylinder part.
    6. My wife repeated apply brakes hard, whilst I continued heating the valve with hair dryer and spraying it with penetrating oil when it got hot.
    6. Tapped the piston carefully with hammer on a big screwdriver attempting to un-sieze.
    7. Noticed slight (less than a millimeter) movement when brakes applied.
    8. Repeated several times heating, spraying and tapping.

    9. Then after about an hour of the above, valve un-siezed. Moves a few millimetres (maybe 5mm) when brakes applied hard.

    Now load sensing valve works.

    I've saved 200 on a new load sensing valve and all the hassle replacing the old valve, then bleeding the brakes.
    Attached Images Attached Images
    Thanks witzend thanked for this post

  8. #8

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    Quote Originally Posted by Gypsy View Post
    Does that not effect the braking performance of your van eg lock the back brakes by sending too much pressure to the back, or the opposite and not send enough pressure to the back?
    No because when it came from factory the arm was at full pitch and bent up and down as axle moved hitting the floor,hence i first shortened the link arm from diff case which let the piston back,after failing 5 mot resits it started to leak,so i did the internal bypass mod
    and adjusted brakes to balance left and right,problem was the right wheel was to strong but left was just past,did the feckers tell me nop,i had to have a word with the boss whom i know,wink wink.
    The thing is i pulled them up a year or two before on a legal point and they have never forgot.
    Only dirty people wash

  9. #9

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    Quote Originally Posted by Gypsy View Post
    I'm grateful for your response but unforunatley it was far from it's max during the test (payloads about 3.5 ton).

    I was earlier under the van, with my wife applying the brake. I was hoping to see some movement at the sensing valve but it did nothing.

    Theres a levering bit on that was on the valve I managed to remove, I could then see what appears to a piston within a dislodged dust cover (packed in crud).

    I think the piston should move slightly out of the valve body when the brakes are applied until it is stopped by the lever part that is possitioned acording to the loading of the vehicle(the sensing action). I sprayed the crud around the piston away with a cleaning spray and then wd40. I hope to put it back together again tommorow will ask the wife to again apply the brakes and check for movement.

    I'm hoping after the cleaning and spraying with penetrating fluid there's some movement of piston thats in the valve body that nudges the lever part of the valve that I can observe when the brakes are applied. However still not sure what amount of movement to expect.

    Infact I'm not sure I've got the logic right either hence the help needed.
    In correct there is a set of internal valves or like iveco a double penny afare with pressure springs,the arm pushes the piston in decreasing the pressure on valve which in turn increases the flued pressure to back cylinders .
    Only dirty people wash

  10. #10

    Member Number
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    Quote Originally Posted by Gypsy View Post
    I'm posting this solution as it may help someone else with a similar issue one day.


    1. Cleaned the linkages and outer of the valve.
    2. Removed dust cover to reveal plunger, cleaned and sprayed with penetrating oil.
    3. Piston part was seized.
    4. Used hair dryer to heat (in the hope that the cylinder will expand and release the seized piston, did not use blow lamp to heat as was worried of risk of fire and damage to seals within valve).
    5. When the piston got hot I sprayed more penetrating oil on the plunger part, in the hope that some oil will seep into the gap between the piston and cylinder part.
    6. My wife repeated apply brakes hard, whilst I continued heating the valve with hair dryer and spraying it with penetrating oil when it got hot.
    6. Tapped the piston carefully with hammer on a big screwdriver attempting to un-sieze.
    7. Noticed slight (less than a millimeter) movement when brakes applied.
    8. Repeated several times heating, spraying and tapping.

    9. Then after about an hour of the above, valve un-siezed. Moves a few millimetres (maybe 5mm) when brakes applied hard.

    Now load sensing valve works.

    I've saved 200 on a new load sensing valve and all the hassle replacing the old valve, then bleeding the brakes.
    Like mine it may start to leak in a few weeks,do carry some flued to get you home ,if it does use the hand brake to get home as you will lose the back brakes and only have some front with a low soft pedal.
    Only dirty people wash

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