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435 N14 more power

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Old 12-02-2012, 10:33 PM
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the good old pressure reducing steer axle valve, that is no longer driver selectable. yay.

Yeah, Like I say, too much broken junk, not enough time to look into the problem behind the symptom. Just find a solution RIGHT NOW and get it back on the road.

Have to dig a little further next time I see one of those trucks
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Old 12-03-2012, 07:07 AM
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How much foot pressure do you have to apply to duplicate the problem when bob tailing? Do the same symptoms exist at all when hooked to a trailer? Freightliner had some tredle valve issues that showed with some age.
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Old 12-04-2012, 06:37 PM
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It takes at least 25 PSI to to feel any braking at all, and at least 50 PSI to feel like you're trying to actually stop.

I'd look at the pin on the brake pedal, but it comes right back up when you let off. (I ran a 9400 for a couple years, that the windshield leaked, and froze up the pin, and after a couple days it stuck down.) Sometimes, it seems as if it stops better, braking with the left foot, or twisting my right foot so my toes move toward the throttle.

The pedal feels a little stiff but not that bad, think it's mainly because of how much air needs applied.

Pulling the trailer, empty weight is about 28,000 with the hopper, it takes almost as much air to stop it.

During corn harvest, I had to adjust trailer brakes a couple times a week, tractor brakes were always in spec.

Truck and hopper run the same type of automatic slacks.

I want to get drum temps with an infrared thermometer after a hard stop. I have a feeling there is very little drive axle braking, both while bobtailed, and while pulling a trailer.

Our other guy seems to be coming around to it needing some attention after some time with no trailer brakes and 63,000 pound gross weights. I should have him move the century and film it when he has to peel his face off the windshield after being used to the FLD.
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Old 12-04-2012, 07:07 PM
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Pull the treadle valve off the firewall from the engine compartment. Once you pull it push the foot pedal all the way till it stops. There is a pin in between the foot pedal rod and the treadle valve that goes through the fire wall and depresses the air valve when you apply the brakes. It is extremely common for this pin to corrode and cause the problems you describe. I have done dozens of these, just wire wheel it up nice and clean, grease the heck out of it and put it back in. If it is pitted get a new one.
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Old 12-04-2012, 10:11 PM
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Sounds easy, but I am thinking this pedal hinges off the floor. Could be wrong about that, I'll look.

How would it cause the need for such high service air pressure?
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Old 12-05-2012, 07:32 AM
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Im not sure when they made the switch from a floor pedal to a hanging pedal. If its floor mounted the valve could be corroded and full of dirt. You could also have a bad valve at one of the axles. If the dash apply gauges shows 25-50 psi before your feeling the truck slow down then i misunderstood what you were saying. I was asking how much leg pressure you had to apply to the actual pedal to get it to stop. As noted if your seeing 25-50 psi on the apply gauge with little braking I would be leaning on a tredle valve replacement. The only way to rule that out is to measure the apply air pressure at each chamber then back track your way to the foot valve.
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Old 12-05-2012, 09:23 PM
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I took the trailer back to its home today and kept a closer eye on the apply pressure. Pulling the trailer, even though it has no brakes it needs air for the suspension, it stopped fairly well, up to about 25 PSI tops. When I unhooked I stuck the trailer lines together and hit the trailer supply, and had air blowing back out under the dash. Stuck a quarter between the glad hands and did a stop mid-RPM in low gear. Did it again after hitting the trailer supply, and wow, what a difference!

When I had the trailer supply line pressurized, it stopped almost like a dream. Pop the valve, and it suuuuuccckkkked.

You were right, the pedal hinges off the firewall.

Do you know if that prop valve can be adjusted? I think the air to the axles it regulates is about where it needs to be when bobtailing, when it thinks you are hooked to a trailer.

Also, what might be causing the apply pressure to be bled off under the dash when the brakes are set? This is the only truck I have ever run that did that.

Glad to finally be figuring something out on this truck.
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Old 12-05-2012, 11:00 PM
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Do what I said in my previous post and report back. I think you'll be surprised. If not well go to step 2.
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Old 12-06-2012, 07:14 PM
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Will do, might be a couple weeks though our mechanic is on vacation.
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