Resolved: Intermittent soft brake pedal

2015, SR5, DCLB
A couple of days ago, I noticed that my brake pedal is intermittently soft. I checked for leaks (none), the proper fluid level in the reservoir (right in the middle of min/max), pads are decent and shoes are good (I'd expect consistently bad braking if these were the issue). I'm looking for things to check before I start down the path of random part replacement. What and how can I inspect to try and diagnose this?

 

Check your wheel bearings.

One of mine failed and was causing a soft pedal. Not saying it is but would be good to check.

 

Wheel bearings feel fine, checked them out while I was changing wheels yesterday. The brakes still have plenty of pad left as well. I ordered a set of speed bleeders and will install them and flush the lines this weekend hopefully. It feels like it could be a trapped bubble, soft on the first pedal press but firms back up if I pump it. Got a line out to grab some braided lines too, if I can get them before the weekend I'll swap out the soft lines while I'm in there.

 

Okay, eating crow here. I put it up in the air again this morning and it definitely was the wheel bearing, or rather the lack of tightening on the axle nut when we did the ECGS bushing. I hit that with an impact and snugged it right up, everything is cool again.

 

Check behind (end) of master cylinder, if you see any wet type oily dirt you may have a bypass of the seal. This causes the condition you described very rare but it happens and when it does, it can drive a tech to drink!

Hope that helps
Cheers!

 

Glad you figured it out but just curious - did you reuse the castle nut cover and cotter pin ? wondering how the hell it could have come loose enough to actually cause that if that castle cap and cotter pin were in place ?

 

We did reuse both. I think that when we put it back together, I put that nut on by hand, I just didn't tighten it up enough. The part that gets me, is that I've driven on it for a couple of weeks now and it only started acting up last Wednesday. There was definitely some lateral play when I pulled the wheel this morning and after tightening the nut it's gone. Probably took a few thousand miles off that wheel bearing's lifespan but at least it's an easy fix for now.

 

wow crazy, damn good thing you did have the castle cap and cotter pin on if it was only hand tightened

 

Well, I don't mean hand tight. It was tightened to "good-n-tight" with my carefully calibrated 1/2" drive ratchet and nothing seemed to move at the time. But, yeah, it was late, we were getting tired and ready to finish up, shortcuts were taken and mistakes made. All fixed now and I get a nice reminder to always check the torque when working on this stuff.

 

the torque spec on those is around 170 ft lbs...or two guys standing on the handle of a 1/2" ratchet

 

I had my pedal go soft in the middle of Johnson Valley this year at KOH. I didn't realize I had had a wheel bearing fail until I was back to the bay area (6+ hour drive.)

 

Yup, 173 lb/ft is what I read. My biggest torque wrench goes to 150. When I tightened it up this morning, I took it there and then gave it a blast with the impact, just enough to see it move a little further. Probably not exactly to spec, but much closer than it was previously.