Wilwood Disc Brakes On Going Bleeding Issue

[JOP33]

I have the Wilwood Drilled & Slotted brakes on my FFR '33 & it seems like a constant battle in keeping them bled & operating correctly. The brakes will work amazingly until the first drastic temperature drop & then they go to nothing. There are absolutely no leaks in the system, the reservoir stays static, no fluid in the floor of the shop or along any of the lines - & again, when the ambient temperature is warm to hot, they perform as expected. When the temperature changes, I have to rebleed them & then they will work fine again, so it has to be a bleed or air in the system issue. I have reached out to Wilwood directly on this & they assure me they have never heard of ambient temperature affecting the brakes, however I spoke to a mechanic & he compared it to those annoying tire pressure alarms when the temperature changes. If you have air in a pressurized system & the temperature drops, the pressure in the system will drop as well. Wilwood's specific advisement on their FFR Balance Bar system has been this...

"With a balance bar pedal and dual master cylinders you really need to do a three person bleed to get all the air out. If you don’t do one front and one rear caliper at the same time, you won’t be able to get both master cylinders to stroke fully. Theres a video showing how to do it here - https://youtu.be/jELllXdtjdc"

I have had the car on the road for 5 years & 32k miles & have tried bleeding the brakes everyway I know how & I might add, to a point that I feel they are successfully bled - that is until the temperature drops again. I have bled furthest to closest, manually & with a vacuum, I have bled front & back at one time, manually & with vacuum, etc..

Just wanted to see if anyone else had experienced this?

Thanks in advance!

J

[gbranham]

Have you tried pressure bleeding from the reservoir(s). I tried this method for the first time on my build, after using vacuum for decades. I'll never go back. It was very easy.

[RoadRacer]

Not the same but similar. My front left brake needs bleeding regularly, say once maybe twice a year. My brakes get spongy overnight, not gradually. Maybe it's the same as you, but I've never noticed the temperature changing at the same time.

It's always the same brake, and it's always fixed by reverse bleeding, i.e. pushing fluid into the caliper and watching bubbles come out of the reservoir. No obvious leaks or loss of fluid. But air sneaks in somehow! After that one wheel, the whole system is amazing again. I've always just blamed the MC seal, because I've had one completely fail.

FWIW, I've always had way more success with reverse bleeding than the normal direction.. pushing air down seems intuitively harder than pushing it up.