Mysterious Brake Fluid Loss

[xdarkxfirex]

I have done quite a bit of work on the brakes on this car. Replaced several aftermarket wheel cylinders that went bad quick and get better ones. Also replaced a master cylinder with a dorman last year and put the old one on because it was fine, and dorman started leaking at where the circlip is at the booster.

Recently I notice a slight drop in fluid with no leaks. I took my master cylinder off, and found fluid, most likely from the old bad one, but none where the circlip and seal were. I mark the fluid level with a marker. Right after I filled it above the max line, probably a 1/8" from the very top. Drove around 25km, it dropped about an inch. Marked it again, drove home, then another 25km and its exactly where it is.

Could this fluid loss be from overfilling or settling where the catch basket was?

[tmontague]

It is more likely a loss from one of the lines. If you're filling the master cylinder from it already having fluid then it doesn't need to prime and shouldn't drop at all.

I had this issue a couple years ago and turns out I didn't tighten one of the rear nipples all the way down. It was snug but not really tight. Leaked brake fluid on my rear axle and stripped the paint off it. I tightened it down and it's been good since then.

Check all your lines and fittings for wet spot when it is dry outside. Recheck all calipers and cylinders for fluid as well

[xdarkxfirex]

No leaks on any lines at all or calipers or wheel cylinders. I would hate having the change out the MC again, I used my old original toyota, they seem to be better quality. Might try a scrap yard to get a spare in case I need it.

[tmontague]

That's weird? Has to be going somewhere. Does it continue to drop or once it drops the initial amount it stops losing fluid?

[Bluevitz-rs]

Make sure the clutch system isn't leaking. It uses the same fluid.

[xdarkxfirex]

Mine has the automatic transmission. Kept it like the way it was up till now few months. The basket inside makes the fluid level appear lower or higher sometimes. I took it out and realized that brake fluid also expands a little from the mark I put. Only thing I was really concerned about was minor fluid loss. Last time I pulled out the master cylinder completely, There was a little brake fluid on the back, but it couldve been from my aftermarket that went bad the year before. Didnt pull it out all the way this time, since one of my line nuts are stripped and I had to use pilars last time to get it off and bleed it.