Sinking brake pedal *solved*

[Sidewinded_idi]

since I bought my truck I’ve had a sinking brake pedal, it works although a bit soft but at a stop it’ll slowly sink and roll forward. I feel like the biggest idiot over thinking things as I had planned to replace the master and bypass my rabs valve. I read many others with the same symptoms and no solution.

Well yesterday while repairing my fifth wheel equipment trailer I had an epiphany. What if the auto adjusters didn’t work anymore? I jacked up the back, took 10 minutes with a screw driver spinning adjusters until they just barely dragged and now I have a rock hard pedal and no sinking! KISS worked here. If you have a sinking pedal and your e brake engages very close to the floor adjust your brakes!

 

[chillman88]

It's always the simple crap that gets me. I always overthink everything.

 

[79jasper]

That's what I always say to do first.
But of course, someone had to argue with it and say that's not possible, it can only be the master. Yeah, okay amigo.

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[Thewespaul]

Our auto self adjusters are just manual adjusters placed in a more inconvenient place. They simply will not adjust on their own

 

[Sidewinded_idi]

Yep I tried backing up and hitting the brakes to see if they were functioning and about an 1/8 mile of back up, hit brakes did nothing. Once I spun out the slack I can’t believe the braking difference. Makes me feel stupid though for overthinking something so simple and not trying to adjust them months ago.

It’s but a royal pain as when I tow the pedal is so spongy it wouldn’t activate my brake lights until about half travel so when my trailer brakes energized they thought I was at about half power so it was no brakes to full brakes pretty violently. Now with them adjusted the brake lights and trailer controller are working 100%

 

[DaveBen]

Some times you have to JUMP on them to get them working, when backing up.

 

[chris142]

Mine work as designed. Rare indeed.

 

[KZF250]

That solved the soft peddle for me on my shuttle bus as well. Just did the shoes in the rear drums on the E150 the other day and adjusted the stars until I could spin the wheel about one revolution and man that thing stops on a dime now.

 

[Bart F-350]

is it by any means possible that those starwheels retract during operation?

since on my new break shoes the rivet to attach the little steel wire (the mechanism to adjust that starwheel) is missing, I decommissioned that adjusting system, and adjusted them by hand.

I did notice though, that during the 1500 miles since overhauling the brakes the pedal position changed further down, so I guess that that could be these adjusters contracting.
could that be possible?

 

[79jasper]

Yep.

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[DrCharles]

But of course, someone had to argue with it and say that's not possible, it can only be the master. Yeah, okay amigo.

Is it possible that with the shoes properly adjusted, the master piston is now staying in a higher, less-worn part of its travel that is not leaking internally?

I know that amateurs (and careless mechanics) have caused internal master failures during manual bleeding by pushing the pedal down so far that a rough unused area of the bore causes damage to the piston seals.

Just wondering if this is a hidden failure mode we're not considering when shoe adjustment makes the sinking pedal go away.

 

[Bart F-350]

I see your point, but since this is only a 10.000 mile truck, I don't think much about wear.

 

[79jasper]

Right, but 99% of the time, they aren't adjusted correctly.
I highly highly doubt it would be in the master. Not much to do with the piston. By adjusting, you're essentially taking up slack for the hydraulic system. Same as if you set the parking brake down a little ways.

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[Bart F-350]

yep, That's the thing I did after repairing my system, involving replacing brake cilinders, hoses, overhauling the front calipers etc.,and since we don't have a brake test bank, I did it the old fashioned way, rear axle on a jack, turning the wheel and turning the starwheel until it blocked, and then retrackt 2 or 3 turns.
I had my truck registered, and that's quite an ordeal, having to undergo quite a strict physical test (for the truck that is.) and when the truck was on the test bank for the brakes the inspector said that he was quite happy with the results. both brakes braking equally all over the scale.

but then, after about 1500 miles I noticed that the brakepedal was decending, until I had hardly any brakes left. and after checking everything, leaks, fluid level hoses, the only thing left was those expander things.

 

[79jasper]

Yeah, they're notorious for not auto adjusting.
Mine, the cables to the adjuster arms snapped on both sides. So I just removed those arms.
I would bet they are backing off. It was one of those where they broke almost right after instal. So left a bad taste in my mouth. Lol

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