Help with sporadic brake issue.

[NIevo]

I agree with OR VIETVET. I suspect the length and steepness of the grade had them overheated. Just "covering" the pedal slightly still builds up INTENSE heat when slowing down 6500 lbs@ 8%. Try manual mode with tow hall activated and find a gear that holds you close to the speed desired. From there use your brakes in a PLUGGING type motion - hold to slow 5 mph below the speed in a short distance, then release and let engine braking take back over. This will give the rotors time to cool again. Repeat as speed gets too high again.

Brakes work on the principal of friction and heat exchange. Cooler brakes can absorb more heat, therefor being more effective. Once hot or overheated, there is no more difference in heat exchange/rejection and that's where your pedal was on the floor and not slowing you down well. Your engine and Trans will do wonders for engine braking, the rpm will probably be at 4k on a grade like that, but just let her work.

As for the ABS. If you didn't drain the system completely at any corner (ie: line clamped off) while replacing components, then the likelihood of air in the ABS is slim. If you did evacuate any part of the system, then yes cycling the ABS is beneficial. If you don't have a tool or want to pay for one, go to a gravel road and do some ABS stops. Then get home and Crack the bleeder and see what comes out with gravity and the cap on the master cylinder loose or off. You'll probably see some bubbles at first. Then have an assistant pump the pedal 3 times and hold while you open the bleeder, close the bleeder, and then have them release the pedal. Repeat as needed until only fluid comes out.

And, your truck is vacuum operated. There is a belt driven vacuum pump where the power steering pump used to be on the older yukons.

Nope, wasn't overheating due to overuse. I've driven and towed plenty with this vehicle and others on much steeper and longer grades all over the NW and never had a problem. Towed and driven much worse grades with this vehicle and never had a problem till recently. Mile long 6%+ grades are nothing around here.

Grades are geared down, tow mode is always used and I don't ride them. It's something either mechanical, or messed up during install that just starting to cause issues. Lines were clamped and a brake bleeder was used to bleed all 4 corners as I went.

I'm almost wondering if the fluid might not have been old. It was Dot 4 from when I did a Brembo swap with my G8 and even though it was new, it was a few years old.

 

[NIevo]

Not saying that riding his brakes was the problem but was a guess because I have heard/seen where so many times people say they know how to use brakes going down a hill, towing or not, and then when you ask them to explain their process of that, they don't know how. What slows you down with brakes is friction and friction builds heat and when enough heat transfers to the fluid you got problems and the pad surface itself crests that temp threshold and stops wanting to grip that rotor and that rotor is fighting back the whole time. Having ran shops, I have seen the aftermath of that problem. He may have a whole other problem and what I was asking about may not be the problem but I draw the line at trying to help and then a response assumes I did not pay attention to what was said in the post. I do pay attention and ask questions accordingly to clear up the foggy areas of the story. I hope he gets the problem solved.

Sorry, might not have been 100% clear in the OP on the stoppage. As in the other post I just replied to I've towed plenty all over the NW with this and other vehicles and try to use brakes sparingly at all. I've never had braked overheat and that includes coming down some pretty bad grades like Snoqualmie and Lewiston Hill with a 7k+ trailer, 6 people in the car in a Durango.

 

[OR VietVet]

Sorry, might not have been 100% clear in the OP on the stoppage. As in the other post I just replied to I've towed plenty all over the NW with this and other vehicles and try to use brakes sparingly at all. I've never had braked overheat and that includes coming down some pretty bad grades like Snoqualmie and Lewiston Hill with a 7k+ trailer, 6 people in the car in a Durango.

Ok, just remember in the future, I ask questions to get to a place in my mind where I understand all of it and not just enough to assume the rest. I ran shops for 25+ years and asked bunches of questions from customers to try and help my techs with a complete story. Lots of times, because of my background in the industry, I knew exactly what the problem was from my questions and then when I handed the tech the ticket I asked him to check my guess first to try and save time and therefore diagnostic money. I had lots of customers tell me I asked more questions than any writer/manager/advisor they ever dealt with. That comment did not bother me a bit.

 

[B-train]

Ah, clearer picture now. There was a post earlier this week I read about a brake conversion and that guy having some weird caliper issues. If I can find it, I'll post it. You might want to grab an infra-red temp gun just for comparison sakes. I use that quite often in brake diagnosis. Just make sure to check the hat area that has a dull or flat finish. If you go to the shiny braking surface it will reas incorrectly due ro reflection.

If it's more recent after 1000 mi of driving, I'm going to lean towards a caliper hanging up then. It could also be a brake hose check-valving, but that doesn't seem to be as common as it once was.

 

[OR VietVet]

Ah, clearer picture now. There was a post earlier this week I read about a brake conversion and that guy having some weird caliper issues. If I can find it, I'll post it. You might want to grab an infra-red temp gun just for comparison sakes. I use that quite often in brake diagnosis. Just make sure to check the hat area that has a dull or flat finish. If you go to the shiny braking surface it will reas incorrectly due ro reflection.

If it's more recent after 1000 mi of driving, I'm going to lean towards a caliper hanging up then. It could also be a brake hose check-valving, but that doesn't seem to be as common as it once was.

Yea, haven't ran in to brake hose internal flap problems lately but hear about caliper hang ups every now and then. Especially in salt roads areas, proper caliper mount and caliper housing cleaning is important and always always always replace the hardware. IMO, brakes are the most important system on any vehicle.