I'm working on a Doosan D30S-7 forklift. About a month ago it was having issues with the brakes applying while in use. Everytime I would show up it wouldn't happen. Finally I saw it. It started doing it all the time. Leave it set for awhile and go again. It has hydraulic assisted brakes. The brakes are wet type. When the issue would happen I could crack the blades and release the brakes. I finally came to the conclusion that hydraulic pressure on the assist side of the master cylinder was bypassing applying pressure to the brakes. I installed a new master cylinder and it worked perfect. I got a call yesterday saying the condition was back. I drove out and tested the unit for about 30 minutes with no symptoms. I'm sure they will get more frequent like before. I cant imagine the new master cylinder is bad, but it's possible. Is there something I'm missing. My contact at Doosan has never heard of this issue. Thanks for any help.
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Wild guess; they filled the brake fluid reservoir with brake oil, dot 4 or similar, should be a mineral based iso VG 32.
Seals in this system don't handle the dot 4 well.
Specs according to manual;
iso6743/4 HM
AFNOR NFE48-603 HM
HAGGLUNDS DENISON HFO-HF2
CINCINNATI P68.69.70
ISO VG 32
We've had similar issues with the doosan brake systems, in the previous series.
Also we expierenced issues with drive axle oil, glazing of friction discs with the wrong oil resulting is a harsh pedal, reducec braking power and sqeeking of brakes..
I have plenty of end play. The oil is 30w. It was recently changed. There is pressure when the leaders are cracked. I havent check the pressure yet.
Enough free play in the pedal/brake-master?
What's the pressure from control valve to brake master?
What oil is used in the final drive?
When the situation occurs that the brakes are seized up, with motor not running does a fair amount of brake oil under pressure come from the brake-master bleeder screw?
Finally, what brake oil is used?
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