2008 Hino 268 mediocre brakes

Horacio

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2008 Hino 268 with 260k miles on the clock. Front and rear brake pads are 60-80%. Running the truck at 35 mph and I stick my foot all the way into the brake pedal, she doesnt want to stop nearly as well as the other 268's I've driven. I replaced both front brake lines bc I found one line chaffed and wearing. I bled the brakes, test drove and I still yield the same result. When the tires were being replaced, I stuck a big flatblade screw driver in the caliper to make sure they weren't seized. This is a new to me truck. It looks like its spent some time back east due to the surface rust I see and how difficult it was to break the lines free. Penske turned the truck loose and its been in CA for at least 5 years if I had to guess. So the million dollar question, where do I start to trouble shoot weak brakes? I had the dealer test drive it, the tech had no suggestions other than he could only guess that someone did a pad-slap along the way. I think there's more going on than just this.
 

greasytshirt

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Were the other Hinos you've driven air brake? In my opinion air brakes are more effective and take much less pedal effort than hydraulic disc. It sounds like you've already checked the caliper pistons for sticking. This has a hydrovac brake booster, does the steering effort feel normal?
 

Horacio

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I've driven an air brake 268 as well and know that would be comparing apples and oranges. The other 2005 268 I have stops so much better than the 2008. The '05 will darn near lock up and ABS would engage. The 2008 wont even come close to locking up or stopping nearly in the same distance and feels like brake fade all the time. Steering the 2008 feels normal and the same as the 2005.
 

Horacio

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Do you think if someone did a pad-slap and didnt turn or replace the rotors, that this would be the outcome? That would mean smooth rotors on new pads and the pads getting glazed up as well? This part I'm unsure of.
 

greasytshirt

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SOP is to pad slap them until the rotors are worn out, or until the tone rings rust off. Could that contribute to poor brake performance? Maybe. If the pads have already conformed to the rotor's surface irregularities, then I don't think that would be the issue. Also there's no way of knowing which brake pads have been used without taking it apart. I could see an extended life, rock hard brake pad having poorer performance than one designed for aggressive braking and severe use.
 

Horacio

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I see.
Where do I go from here? Remove the wheels and mic the rotors to see where they’re at? If under spec, replace the rotors and pads?

Is there a proportioning valve for the rears?
 

greasytshirt

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There is no proportioning valve. You can measure rotor thickness, but that's not going to affect normal braking performance.

You can put a pressure gauge on each corner and see if each caliper is receiving the same pressure. There could be a blockage in the ABS module or something like that.

Is the hydrovac system working? If it's not, that would greatly increase pedal effort.
 

coalminer

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Just thinking about this but was the power steering fluid and filter changed? Years ago when I got my Hino the steering would stick when trying to turn at idle and the fluid was pretty bad, never noticed if it affected the brakes but I didnt drive it long before I did the fluid change to fix the steering issue. There is a filter in the little reservoir where you check the level.

Worth a try if it has not been changed.
 
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