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Weird brake issue

ak diesel driver

ak diesel driver

6.5 driver
Messages
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Location
alaska
So I was driving my dually into town this afternoon and came up to the first stop light and stepped on the brakes. Pedal was really mushy and hardly any braking action stepped on it again and pedal went way down, stepped on it again and on the 3rd or 4th try suddenly I had brakes again. So I drove pretty cautiously into town wondering if I had broken a hose or something. Couldn't find anything and the brakes worked normally. Picked up about 500 lbs worth of stuff and headed home and when I got to that same stoplight the brake pedal went way down again when I stepped on it again the pedal jumped kinda like a port had opened suddenly and the brakes were fine again. Any ideas?
 
When I have that, I start with a flush and bleed, of corse inspecting all 4 brake points while there. Pads, rotors, tightness, lubed pins. If drums then make sure shoes swing freely, springs all good. No sign of wetness around cylinders- all 5 need looked at.

Possible:
Moisture or other contamination in fluid
Air in fluid
Seals worn (especially master cylinder)
Small leak somewhere
Pads or shoes coming free of backing plate.
Rotor or drum face scaling
 
Reminds me of when a pad came off the backing plate on my 1995. Pumped it back to life and considering stomping the e-brake pedal.

At home engine running stand on the pedal as hard as you can - this can finally trip the brake pressure warning light say if one system is blown out.

Engine off and discharge the accumulator by stepping on the pedal several times. Then stand on the pedal for a couple min. Does it go down at all indicating a leak?

Complete system inspection looking for leaks. Hidden leaks are a blown seal under dust covers. Nothing found? Start with master cylinder.
 
So I checked the fluid level it is fine, the only thing I noticed weird was the rubber boots were fully extended and I don't know why. When I did the front end work a couple of weeks ago I didn't break open the system, but I did retract the caliper a little to aid in getting them off. Put the truck up on the hoist and didn't find any external leaks
 
Does the ABS work? Maybe intentionally set it off a few times to re-test it. Air in the ABS and you are a careful driver so far and now the ice patch set it off and turned air loose in the system? NVH is out of hand and some sick reason the goal is to set them off without notifying the driver they have gone past the traction limits. Ever have ABS fail and release the brakes on you? Experienced a few from a broken tone ring, but, one van had a wiring issue that set them "off". Literally decided not to stop on dry pavement for a long distance.
 
Brake fluid-
With brand new rotors/ drums & pads/shoes- the system is as tight as it can be, in this condition you bleed and fill to the 100% full mark with rubber boots on the master cylinder collapsed.

From this point on, NEVER add brake fluid unless you have a leak.
When the rubber extends it is because the pads/ shoes are worn. Or there is a leak.
When you replace the pads/shoes, and collapse the boots, the fluid will be back up at 100% reading.

So with your boots expanded- you have pushed fluid down into the calipers or wheel cylinders OR you have a leak. You might have scratched a piston (caliper) or something..

Pain in the tailgate, but you need to fine tooth comb it. Thats why I suggested examine ALL the pads/shows carefully. Then flush the fluid and bleed.

Be sure, guessing and trying to figure things out via test drives is not the answer here.
 
It must have been full to the brim with the boots extended. If anything it is slightly overfull. Gotta remember Will I live in BFE not in a town. So while brakes are important to me it's not as critical as in town.
When I was in HS we drove to Anchorage and when we went to stop at the first red light the brakes locked up. Had no brakes after that. Finished up what we needed to do in town and drove 70+ miles home all with no brakes. Would I do that now? No but times are different now.
 
Reminds me of one certain creek bottom west of town, on the interstate, be driving east bound, get to the bottom of this creek and just as the 08 Malibu starts up the other side, it trips a code. Dont remember the code number, refers to air/fuel imbalance. No known causes and no known remedies. LOL
Might be a weird signal coming off that traffic light is interfering with the ABS system. LOLOLOL
 
No leaks and fluid down... The dust boots on the calipers will hold a lot of brake fluid. You get a surprise attempting to let the air out after pushing them back sometimes because it's not air inflating the dust boots.

Ice possible in brake lines?

Pull codes on ABS and have you set it off just to see if it may "jam up" releasing the brakes and "done" for a moment?

Brakes are the only thing I wouldn't think twice about throwing parts at.
 
There is a weep hole on the bottom of the booster/MC bore. Check its not plugged/wet. Think it had anything to do with the variable assist power steering? That might present in brakes going straight????? Might drive in figure 8's to see if the hydro boost and steering act up?

My truck hiccup's all kinds of stuff and has several intermittent issues. I wait til something presents problems fully now. Sometimes I can park it by the tool box and it fixes itself. Unfortunately, brakes are an area you can't be as patient with it fully presenting itself.
 
I did cycle the ABS but I usually do that without trying a few times every winter. The steering assist that you speak of has been disconnected for a year or 2 already. Hasn't hiccuped lately
 
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