1974 Spider. All new calipers, flexible lines, master cylinder all new fluid (DOT 4 - Pentosin).....

My question is - my reserviour for my rear brakes is overflowing at the expense of the reserviour for my front brakes. Fluid in rear res is dirty and keeps growing, fluid in front is clear, but level keeps dropping.

My question is - what would cause this? Do I have a compromised seal within the proportioning valve or something? My first thought was master cylinder, but since 1) it is new and 2) there is a distinct difference in fluid color between the two, I am thinking that it must be something else.

Brakes seem to work ok - as good as they ever did at least, and I don't have any pulling to one side or the other.

Help please?!? Is my problem a bad proportioning valve?

Happy

Happy, that is weird, but my guess is that there is an issue with the master cylinder. There is some sort of "pressure equalization" channel build into the MC, so maybe it's not working as it should? New MCs occasionally have issues, depending on the manufacturer.

Do you have two separate fluid reservoirs, one for the front and one for the rear? I can't remember the year, but at some point Fiat switched over to a single rectangular reservoir with two compartments internally, but they were connected in the air space at the top.

-Bryan

Yessir - mine has two seperate canisters. It is a new M/C, but I acknowledge that sometimes even new parts have issues.

I opted for DOT 4 to fill the entire system after putting on all new brake parts (mostly since I had a full unopened can on the shelf). Could my issue be compatability (or lack thereof) of the internal seals on the M/C with DOT 4?

The canister for the rear brakes is brown like weak coffee or really strong tea. I ocassionally use a sirenge to suck it down to manage the overflow and keep it from making a mess. The one for the front that is losing is clear as the day it came out of the can. Now I am thinking the coloration may be from the internals of the M/C slowly dissolving in the DOT 4????

Happy

DOT4 fluid is fine. I'd consider getting the later combined F/R tank.

Update on this topic....the problem seems to have resolved itself and both front/rear tanks are staying even now. Not sure what was going on. Could be the new M/C sealed itself internally over time somehow?

HappyHog wrote: ↑Mon Apr 22, 2024 11:30 pmCould be the new M/C sealed itself internally over time somehow?

I'm thinking it's something like there was an air bubble that was blocking an internal passage in the M/C, and that air bubble was dislodged or broke up over time. There's also a spring between the front and rear plungers of the M/C, and maybe that was sticking until it worked itself free. Whatever the reason, glad to hear it's better.

-Bryan