Brake Booster Upgrade...Dot 3/4 or Dot 5

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Joined: Thu Jan 11, 2018 9:13 pm

Brake Booster Upgrade...Dot 3/4 or Dot 5

Post by arussharris »

Hi everyone,

I’m about to do a brake booster upgrade for our 1957 driver that has always had manual brakes. Mama needs a bit more stopping power to get her out of the garage with more regularity and I wanted to keep drums.

I got a decent deal on a booster and master cylinder from someone doing their own upgrade. Both units are in good shape and don’t really need a rebuild. The shortfall in my research digging is that these two piece have only ran silicone dot 5 and my brake system and master cyclinder have always ran dot 3. I’m aware of the incompatibility issues and the need to flush which is why I’m reaching out to the pros here for guidance of the recommended approach:

A. Flush the booster and potentially rebuild it to be dot3 compatible with my car (probably sell the dot 5 master cylinder).
B. Flush my entire system which sounds like it can be a PITA and remove and install the new master cylinder.
C. Do neither, re-sell the booster/master combo and find something that was a dot 3 piece of hardware.

As always, I appreciate the sage pearls of wisdom this group continues to push to the weekend warriors.

Posts: 160
Joined: Mon Apr 24, 2017 7:46 pm

Re: Brake Booster Upgrade...Dot 3/4 or Dot 5

Post by fordrodsteven »

There have been numerous discussions on different web sites (and different kinds of cars) regarding DOT3 VS DOT5. My understanding is that DOT3 is petroleum based and will attract moisture (causing corrosion of the brake system from the inside out and will also damage paint). Conversely the DOT5 fluid is silicone based and does not attract moisture like the DOT3 fluid. That said my preference in the situation you have given is to flush the brake system in the car and run DOT5 fluid. I'm not really certain if flushing / cleaning the system out with something like alcohol is required (some people say it is required).
I been told that on my Buick Reatta with ABS the pump is not compatible with DOT5. So in order to keep the ABS system functioning properly I have to replace all the DOT3 fluid on a 2 year maintenance schedule.
Steve - 1955 Thunderbird

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