Intermittent loss of speed/power

Having an intermittent but serious issue with my 2013 sport (DCLB, v6, 4x4, 150k miles) that's happened twice, and despite taking it to a trusted mechanic for a diagnostic, he didn't find anything and sent me on my way.

I'm mechanically inclined but have little experience working on my own vehicles.

Here's a timeline of symptoms—
Once or twice in the past winter/spring, after wet weather I noticed the brakes felt spongy. (concerning, but assumed it's the old brake fluid) Mentioned it to Mechanic when other front end work was being done and he didn't flag anything.

A few weeks ago someone mentioned hearing a grinding sounds from the front passenger side while I was making a low speed right-hand turn. I assumed a piece of pea gravel had been picked up by the caliper (this happens to my wife's car sometimes) kept an eye on it and the noise went away.

While driving a few weeks ago 45mph around a slight right-hand curve I tapped the brakes and the truck suddenly lost speed down to 10-20mph, engine revs still went up with throttle but the truck felt bogged down like it was in mud.

No lights or codes. took it to the independent mechanic for a test drive, we were unable to reproduce.

The next week, at about the same speed I tapped the brakes to enter a a highway onramp and when I got back on the throttle the same thing happened. This time I was paying closer attention, confirmed that the revs were responding to the pedal, shifted manually in and out of a all gears including reverse, got on and off the brakes a few times, engaged/disengaged the e-brake, and turned the truck on/off a couple of times.

Finally after reversing and braking hard (angry at this point) I put it back into drive and things were fine.

First up is a brake flush and fill, and 4 corner brake inspection to see if I can isolate: slide pins, clogged lines, pistons, proportioning valve. Will replace brakes if they're in bad shape.

A friend mentioned that hubs/bearings can bind and cause similar issues with grinding and loss of speed.

Grabbing a code reader and OBD Fusion for live monitoring and diagnostic codes, are there any ABS/Brake codes that might show up if a caliper was sticking?

Anything else I should do or be looking into?

 

Does the VSC light flash when the event happens?

 

Being that the onset of the issue is tapping the brakes, I'd wager that one of the calipers was seized, either on the slide pin(s) or the piston itself, holding the brake clamped shut. Seems the hard braking broke it loose, for now.

Also make sure the rear drum brakes are properly adjusted. If they're very loose, that'd explain the sponginess as well, and excessive play may(?) cause them to bind up? Not sure about that last part but worth checking out anyway

 

I would suspect brakes...something is sticking, either a caliper or drum is sticking...to slow you down THAT much, I would say caliper. Thats where I would start

 

Ultimately, I'm leaning towards a replacement of brake lines and front calipers anyway given age and northeast corrosion. Brake system doesn't feel like a place to let things be worn out.

in the short term, I'll get the wheels off and inspect the calipers/lines for issues.

 

they are pretty straight forward to replace. my truck has 133k and I live in WAYY northern Michigan so I have a set sitting in the box for this weekend! The only issue is bleeding the ABS/VSC. If you have a local garage, see if they have a scan tool to complete this. Yes, you can use the ol' gravel road method, but it may not get all the air out.

 

Autozone had rebuilt oem calipers (last year) for around $100 each. I believe there was a core charge.

and if you are going to open up your drums, I would recommend buying at a minimum, the spring/hardware kit for the drums before you open them.

when the springs in there get rusted up, the drums become unpredictable. I had several springs that were gone into dust...

 

update to this:

A few weeks after posting this thread, my alternator seized (smoked the serpentine belt on startup) and I'm wondering if the sudden loss of power could have been related to a drop in voltage.

Have inspected the brakes, had the brake fluid flushed and I'm keeping a close eye on it for now.