PSA: Stop using modern brake fluid in 60s muscle cars

I watched a guy at a car show last month pour DOT 5.1 into a '67 Mustang master cylinder... cringed so hard. Old systems with natural rubber seals will swell up and leak within 6 months if you use anything but DOT 3 or silicone DOT 5. Found this out the hard way back in 2019 when my '65 LeMans pedal went to the floor on a test drive. That rebuild kit cost me 80 bucks and a whole Sunday. Why do people ignore the little warnings on the reservoir caps?

2 comments

2 Comments

eric_johnson9d ago

You said "Why do people ignore the little warnings on the reservoir caps?" and that's exactly what happened to my buddy Dave with his '68 Charger. He thought he knew better and put some synthetic DOT 4 in there because the parts store guy said it was "better modern stuff." Within about two months the seals gave out and brake fluid was dripping down onto his exhaust manifold. He almost lost the whole car to a fire pulling into his driveway, smelled it first and shut it down quick. Had to replace the master cylinder, both front calipers, and flush the whole system. Cost him over 400 bucks and a full weekend. I told him that cap literally says "DOT 3 only" in raised letters you can feel with your finger.

the_amy9d ago

My dad did the same thing with his old F-150 once... @eric_johnson knows exactly how that story ends.