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RRC Soft Dash ABS brakes lock on with ignition on.


wayne5666
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Good evening all ..

Please help with my frustrating brake problem

I have a 1994 300 soft dash thar is causing so much trouble it's untrue !! My brakes stick on once ABS pump has pressurised the system .The saga started when I bought the vehicle with a rok hard pedal ,the brakes worked only when stood on ,and pulled furiously to the left .After rebuilding callipers ,replacing all flexible hoses ,copper pipes and re bleed it still pulled to the left ,although the pedal felt slightly better ..took off the modulator and cleaned it through ..damaging the "ribbon"wiring in the process !!! Bought a replacement working modulator from the US after waiting 3 weeks ,and paying customs over £100 for the privilege! ! Fitted and bled ..All was good until activating the ignition and the pump ..It did all bleed out as per factory manual ..but as soon as pressure builds the brakes all stick on .Unplug the pump..the wheels run free ,but I can't drive it as brakes are quite useless ..Just been outside and bled it again ,and wheels are free until pressure (power) system is activated ..im.at my wits end (and my wallets) and feel like burning it ...please help

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Thank you for your input ...I will buy another pump today and get it in there ..stripped down my pump last night ..cleaned it through .A lot of pressure was needed to get pressure swith to go in ..I coukd just get the plunger in by pushing it against the bench ..when I did the microswitch clicked ..I then squeezed it gently in the vice and left it there for a while ..then reassembled it all and bled it ...exactly the same !!!

I shall get replacement pump and switch today and will keep you up to date ..

Thanks guys ..

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Have you seen this thread when I had trouble with a pressure switch on my last RRC? About half way down the page and post #332.

http://forums.lr4x4.com/index.php?showtopic=69483&page=17

The fact that your brakes are very hard suggests to me that the modulator is letting to much of the pressure stored in the accumulator through to the calipers via the modulator.

The pressure swicth just does 2 things. It turns the pump on and off depending on the pressure in the system, and also it turns off the ETC warning light before the full pressure is reached.

If your pump is running when you turn the ignition on, then cutting out as full pressure is reached, and the traction control light is going out I suspect your pressure switch is good.

So the question is what is your pump doing?

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Thank you duncmc...your train of thought is the same as mine on this ..I have replaced the switch ,with a known proven one from a P38 ..and no surprise, it is the same ..!!!

My thought is this ...the pump is controlled via the pressure switch to give the accumulator the specified pressure ..when that is reached ,the pump cuts off .. (which all seems to happen as it should) ..It is then up to the booster unit (modulator ) to draw from that pressure as necessary ..if that pressure is "allowed" through an outlet ,it will apply the brakes ..I feel that the pressure is bleeding past a valve/seal inside the modulator and is getting to the outlet ..I have 2 more modulators ,and will swap one over ..

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Hi,

I had this a couple of years back, when you refitted the modulator did you put the clevis pin in the correct hole in the brake pedal? On mine ('92 hard dash) there were two, with it in the wrong hole the brakes were partially applied even with the pedal fully up so as soon as system pressurised the brakes locked up.

Mike

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BRAKES ARE FIXED !!!

Thanks to Mike you are the man !!! ..Took out retaining clip and clevis pin ..brakes freed off .Found second hole in pedal ..fitted it ..re adjusted stop lamp switch .and away we go !!

Several morals to this story ..

1 .If you have a manual ..READ IT Even if you know what you are doing (or think so) .It clearly states in capital letters ..fit pin in UPPER hole

2 Do not regard changing brake fluid as a task never to do ..the black sludge that was in the original modulator and callipers killed them .Bearing in mind a new modulator shows in excess of £2800 plus vat ..some DOT 4 and a couple of hours is a good investment

3 Always throw the question out there ..someone else would have had the same problem .

Thank you to all who have helped ..It is very much appreciated .Now I can sort SRS light out ..Finish welding ..Repaint ...

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Thanks folks. .that was my thought too .I guess you guys know ,but for those that don't ..The pressure switch is the same as P38 to '02, Saab 900 and 9000 ..and so I was told yesterday ..Ford Granada.

I know have 2 spare modulators ,an accumulator and a P38 pump and pressure switch ..They cost a packet ,but not bad stock to have ..

Thanks again to all ..with new incentive ,I ve fitted a new steering damper,adjusted free play in the box ,and am going out for a drive !!

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