DOT 5 leaking from lower plunger on disk brake distribution block

[headejm]

@MoparLeo Sorry, don't understand your comment and the pdf you attached does not open. Thanks!

[MoparLeo]

Sorry, try the link now.

[Katfish]

Don't spill brake fluid. How often do you even mess with fluid ? Usually only when you do a brake service.


As someone who has 2 firewalls damaged from DOT 3, I learned my lesson.
All it takes is a failed MC to leak out the back, and that's pretty common failure.

Switched to DOT 5, firm pedal and no worries when the next MC fails, because it will.

[toadstool]

I have the same problem, also purchased everything new from inline tubes (with Dot5). I got distracted on other projects and have not resolved this yet. If I could I would just try and find a used hold off valve.

[headejm]

@toadstool Be careful with using used parts (that previously used DOT 3/4) on DOT 5 systems. If you find a used part, completely take it apart and thoroughly clean it before installing it in a DOT 5 system. The different fluids don't play well together.

[toadstool]

Back here again with the same problem. I have purchased both the inline and fine lines versions of the metering/hold-off valve for a late 1970 disc/drum setup. It is leaking out from the plunger. I use DOT5 fluid. I think I have (2) options first is to rebuild the new units I have with the kit from Muscle Car Research. Not sure if the machining is the exact same diameters. or second to find a older unit and rebuild that one. I hope the rebuild parts on the MCR rebuild kit is happy with the DOT5. Also there is a mention of a second "O" ring, anyone encounter this?

Any other suggestions.

[moparroy]

Get rid of the Dot 5 fluid. It is attacking the rubber parts in the block. I would flush the system and go with Dot 3 or 4 if it was me...

Nothing is more compatible with rubber seals than silicon (base of the DOT 5). Check the chemical compatibility charts on line. Common reco to use silicon fluid / spray to condition rubber seals like weather stripping.
I've got DOT 5 in everything from my '82 GL1100 to my 2010 Challenger to the wire's 2013 Town and Country - and the '74 Cuda.
I am having a slow seeping issue with my combo valve but no way you convince me its the fluid - tried several new o-rings - figure the case has a score / scratch  in it that the o-ring cannot seal.
The aerosol silicone spray stuff you do need to be careful with cause it is full of propellent that may not be particularly kind to rubber - but the brake fluid, never seen it do anything but a good lube on rubber

[moparroy]

@toadstool Be careful with using used parts (that previously used DOT 3/4) on DOT 5 systems. If you find a used part, completely take it apart and thoroughly clean it before installing it in a DOT 5 system. The different fluids don't play well together.

While it is certainly not recommended to mix them, I don't think you have to be overly fussed with cleaning every part. The issue with mixing is you don't know what the perf spec (ie boiling point) of the fluid is in the system. I have converted numerous systems from DOT 3 to DOT 5 by simply flushing out the 3 with the 5. I have found small traces of 3 in the system (they separate) even years later - in my '85 when I decided to do the rear drum and rebuild the wheel cylinders but never had any issues after conversion.
Its not recommended for modern ABS systems - but I use it there too. No issues, panic stops, ABS engaged in the winter - all good. For me the paint friendliness and hydrofobic features are the winners. In my '85 I was replacing calipers every couple years when I started storing it with DOT 3 - never a single one after I switched to DOT 5. Its the car I've had this stuff in the longest.

[toadstool]

Everything is new. Lines, Cyl, calipers. System has never seen DOT 3.

[bc3j]

Here's the setup I'm running from Inline Tubing.

I used the same valving with DOT3. No issues.