Leaking master cylinder seals

[phaetn]

My brake fluid bottles always go down over the winter as the seals on the top of the master cylinder (where the hoses are clamped) leak and fluid spills. It did it with my old master cylinder and I figured the seals were just old, but it happens with a brand new master cylinder, too, that I installed within the past couple of years when I replaced the brake booster. So I don't think that just new seals will help.

I think the seals must just shrink a lot on cold winter nights in my unheated garage. Any suggestions? Any way to make them seal more tightly? Is there a product I can use that will withstand brake fluid and not risk contaminating the fluid within the master cylinder?

As a preventative measure I siphon out brake fluid from the bottles when the car is stored so as least there isn't the gravity-fed pressure on the seals and they will only leak the contents in the hose.

With thanks,
phaetn

[18Fiatsandcounting]

Almost every master cylinder that I've had, whether original but varying model years or aftermarket replacement, seems to have a different method for connecting those two supply hoses from the reservoir(s) to the master cylinder. Some have straight plastic barbs, some come off at an angle, some barbs are permanently installed with a locking clip and some just slide into the rubber seal, etc. Most of mine have not leaked, but I've never cared for the design as it always looked like it might leak if you stared at it long enough.

But, are you sure your two supply hoses are not weeping fluid, and that fluid is drawn down by gravity and collecting near the barbed connection? If the original hoses, it's time for a replacement. If they have already been replaced, they must (repeat: must) be specifically brake fluid hose. Brake fluid will eventually start leaking through vacuum, fuel, or coolant hose. Different rubber formulations.

-Bryan

[phaetn]

Thanks for the reply. I replaced the hoses within the past few years and put on a pair a friend provided -- I forget the brand -- they were blue and German. They were definitely brake hoses but he may have had them lying around in a box for years. Maybe I should investigate getting new ones.

My thought was that it was the seals and fluid was leaking up from the M/C and not down from the hoses at the clamps, but I could be wrong. It's not an issue unless it gets really cold. This weekend, for instance, it's going down to -20°C (-4°F) and -29°C with the windchill (-20°F) and my garage is separate from the house and unheated.

I'm getting new brake fluid reservoirs in billet aluminum so I'll change out the hoses at the same time to see if that improves things.

Thanks and cheers,
phaetn

[18Fiatsandcounting]

Let us know if things improve with the new brake fluid supply hoses, or if you find another solution. As for temperature, I spent 10 years in cold climates where it could go below 0 oF and none of my Fiats had the issue you mentioned, but admittedly this was in the late 70s/early 80s and the cars weren't nearly as old. Getting them started and running was the main challenge!

-Bryan

[phaetn]

So my A/R order came in this week and I ordered new spouts (both sizes) and see if those will make a difference, but I doubt it. I also ordered new braided brake fluid cable (brown exterior) and we'll see if that's a better fit.

The master cylinder is off to get powder coated. There was some slight corrosion where the seals fit in so I suspect that might be the culprit for the leak, though it happened on both an older and this newer m/c. It doesn't leak at any other time but our cold winter so it could be the combination of seals contracting and the pitting.



You can see the damage from brake fluid spilling on paint on the frame rail. It was quite nasty to have it bubble and peel off as I tackled it with a plastic scraper. We've had some shockingly mild weather this past week which allowed me to address it but we're back to below freezing weather again. Hopefully things will get mild again soon -- when they do I think I'm going to have to take the brake booster off (not looking forward to getting under the dash again -- it was a tough job three or so years ago). I'll need to space to address some other areas and as part of repainting the bay. I might POR-15 the area where there's rust to really seal it and then paint over that.

Other goodies arrived, too. New 9.8:1 pistons and a 40/80 reground cam. The block should be off to the machinist next week, hopefully.


I'm also planning on putting in a billeted aluminum brake reservoir to effectively match the Allison's coolant reservoir I have on the other side. It will mount a little lower than where it is positioned now for this mock up (the hood will clear, but lower will still be better as long as the drain is above the m/c).



I know it's not as safe as it only has one chamber so the dual circuit brakes won't be in play but I think it will be fine. I check the fluids often and if I rip a brake line I've got bigger issues... It's kind of like how the red dash light informing you that your brakes are failing only ignites as you're already careening off the cliff.

Cheers,
phaetn


Cheers,
phaetn

[18Fiatsandcounting]

Appreciate the updates; keep 'em coming! And yes, if you need to remove the brake booster, this is about as easy as it will ever get in terms of access inside the engine bay. Just remove the 4 nuts inside and the center plunger from the brake pedal, and that bad boy will come right out.

-Bryan

[phaetn]

Yeah, I've pulled the brake booster before and it's the being upside down under the dash that is no fun. Luckily my car doesn't have a big circular air filter cover or a maze of anti-pollution devices so even when the engine was in situ it was pretty easy from the engine bay side. Same thing with installing a modern gear reduction starter -- access was pretty straight forward. I look at friends' '79 or '80 cars and there isn't nearly the space / arm room.

A modern engine: forget it! They're now even getting away from things running off serpentine belts from the main crank and moving towards modular electrical pumps connected by a wiring loom. You don't even have to line anything up -- you bury it under something else at whatever angle, plug it into piping and the loom, and Bob's your uncle. A consumer spends as much on the labour to get at it as the actual part or labour to fix it (it's modular and just replaced).

I'll pull the seat and everything should be good. It's all a bit more complicated in my case since I have custom welded brackets for my Corbeau Clubman seats and the roof is up to stop it contracting too much in the cold (plus the hood is on it), but I'll figure it out with some warmer weather.

Cheers,
phaetn

[phaetn]

Beautifully warm day here today (and will be for the next few days) so I spent some time in the garage. I pulled the brake booster and it was no bit deal -- just the spring will be tricky to get back on. There was a lot of paint damage at the firewall and under the M/C so it will all have to get cleaned up.

Block and pistons are at the machinist and he will lighten the flywheel, too.

Not sure that I'll get the car back together this week (waiting on some synchro sliders), but hopefully before the end of April.

Cheers,
phaetn

[phaetn]

Got the brake booster back from the powder coater. It sure looks pretty. I hope it can stay that way. Lots of bits done beyond the cam covers and brake booster (rad fan support, distributor plug for the head, heater pipe, various thottle link brackets, etc.)



It's rainy and cold so I won't reinstall the brake booster today but I've been degreasing all the wiring looms and getting ready to put things back in place so the engine can go back in hopefully about two weeks.

Cheers,
phaetn