LN65 Hilux Brake Master Cylinder HELP!!!

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faiyaz
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Hi all, I'm in a bit of a pickle with my Hilux. A week back the master cylinder was leaking from the back. So I removed it and fitted a rebuilt unit, bled the brake system on all 4 wheels and tested the brake. When you initially press the pedal the brakes are hard like they supposed to be. However if your foot remains on the pedal, the pedal begins to sink down slowly. I changed the master cylinder and fitted a brand new unit. Had the same problem!! Decided to buy yet another master cylinder, same problem!! I've bleed the brakes and no more air comes out when I crack open the bleeders. On further inspection I noticed when the pedal sinks down, the back wheels are not holding. I've adjusted the back wheels but this did not make a difference. This problem is driving me crazy!! Any suggestions or experiences with such are welcome. Previously I changed all the flexible brake hoses with braided stainless steel ones and fitted a new load sensing valve (From China).
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Tim86
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I would start by doing some research on the load sensing system. If it runs a return then possibly all the pressure is being released by the new cheapie valve or something along those lines. Just a thought. Find the diagram for it in the manual on this site.
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A friend of mine had the same problem. At the end of the day the problem was that the brake system was not properly bleeded. Make quite sure that there is no air in the system. Start bleeding at the left rear wheel then the load sensor then right rear wheel,next front left wheel and final right front wheel. Keep brake master resorvoir full while bleeding system.
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faiyaz
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An Update! :

Finally got the brake pedal firm as it should be, after trying 3 master cylinders!! :crazy: :crazy: It was the cheap aftermarket Load Sensing Valve (LSPV) !! It has a return going to the front brakes. The valve was allowing all the brake fluid to the front instead of proportioning the fluid based on the load. The brake master cylinder has 2 outlets and 2 pistons within the bore. As you press the pedal the first piston gets pushed and sends fluid to the rear, once ample pressure is built up the second piston begins to move, sending fluid to the front brakes. Brake fluid being pushed out by the first piston was returning back into the master cylinder via outlet hole connected to the front brakes.

Decided to open the LSPV and was shocked to find there was no actual piston inside that would regulate fluid to the front brakes. Below is a pic comparing an original unit (left) to the one I had fitted off Aliexpress.
IMG_20210718_164139.jpg
For now I've fitted second hand valve. Not sure how long it will last, genuine unit seems to be costly around $200 :shock: I guess eventually I'll have to bite the bullet and buy one, sadly no kits are available from Toyota :think: . Decided to give a detailed explanation just incase anyone is facing the same problem. Brakes are great now!! :cooldude:
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faiyaz
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Tim86 wrote: Sun Jul 18, 2021 8:37 am I would start by doing some research on the load sensing system. If it runs a return then possibly all the pressure is being released by the new cheapie valve or something along those lines. Just a thought. Find the diagram for it in the manual on this site.
Thanks for the suggestion!! :thumbup:
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Bear
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Well it's great that Faiyaz is sorted out.
While on the subject of brakes, the equalizer on mine is leaking some fluid onto the shock. The wheel alignment guy brought it to my attention. I took in in to a brake centre, they kind of confirmed that it needs to be replaced but was surprised that there is no loss of pedal pressure. Any views on that?
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faiyaz
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The leak is probably very slow/little. So you don't notice the loss in pressure. Just a guess haha
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Bear
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Thinking about it, the brake fluid level did dropped very slow. Probably need to replace before I have a brake failure.
Travel is not really about leaving our homes, but leaving our habits.
Adventure tends to magnify all human emotions.
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faiyaz
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yh thats a good idea. try by all means to get a genuine unit
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