dot 3 or dot 5 good and the bad

[joe 1950]

1950 ford cpe just need some input from you barners rebuilt my complete brake system @ 8 years ago cyls. lines hoses everything from front to back was new so the talk between my fellow car guys was to put in dot 5 and troubles are over well since then iv put in 4 stop light switches and one whl cyl better to leave it in or flush it out with dot 3

[Ol' Ron]

On my new system I was told not to use DOT 5. Not sure why?? Running DOT 3, sofar, so good.

[fortyfords]

Dot 5 doesn't appear to like your stop lite switches so it would be a ton of less work to install a mechanical switch on the pedal. I like the mechanical switches mainly because they put the brake lights on when doing light braking. I had to many people tell me that my brake lights weren't working but the system worked fine. I always noticed that people would come up on my rear real close sometimes and the hyd. switch was the cause. I love the dot 5, big thing to always remember, don't agitate it in any way to make bubbles as the bubbles are hard to bleed out. I hope this helps.

[sidevalve8ba]

I built a '31 Model A about thirty years ago with hydraulic brakes and I used DOT 5 fluid in it. I've put a lot of miles on that puppy over the years and (knock on wood) I've not had any brake problems. Never had to replace any brake related parts.

I would have to agree about the mechanical brake light switch. They can be adjusted to so the brake lights come on with very little pressure on the pedal. Good safety feature.

[RandyZ]

I have DOT 5 in the truck for 22 years now. Only problem was with the stop switch, but an external one solved all the problems. Other than that, still have the original master cylinder and all wheel cylinders. No leaks anywhere.

[Fordestes]

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I rebuilt the complete brake system in my one ton wrecker, and never had what I call good brakes, master cylinders always leaked, I dumped the D.O.T 5 flushed the system ,replaced the master cyl. and have good solid brakes.

[51 MERC-CT]

There seems to be a misconception that DOT 5 causes brake light switches to fail.
The contacts in the switch never see brake fluid unless faulty.
What is more likely to cause failure is the build up of carbon on the contact
points caused by arcing.

[V12Bill]

Over the past 35 years, I have had DOT 5 in 5 different cars. Other than brake lite switches, I have never had a problem. Always start with a clean system and get the double flares right and tight. I hear that Harley Davidson switches were made for DOT 5.

[tubman]

Fordestes : to be clear, are you saying you removed the Dot-5 and replaced it with Dot-3?

I am in the process of replacing the DOT-3 brake fluid in my '51. (It tested "marginal" on my electronic brake fluid tester after being in the system for 15 years.) I have a set of "Speed-Bleeders" coming and if they work as well as everyone says, I will be replacing it with Dot-4 (compatible with Dot-3, only better).

As a bit of addtional information, the DOT-4 brake fluid in my '67 Corvette tested as "OK" after being an the car for 9 years, and the 32 year old original brake fluid in our '84 Fiero tested as "unacceptible".

I did install Dot-5 in my '68 Corvette and while it seems to work well but was very hard to get bled properly, and I'd like to skip that experience if I can.

I'll post my findings on the "Speed-Bleeders" next week.

[redo32]

What is a good universal mechanical brake light switch to use? I was looking for one at the parts store and most of them were too model specific.

[sidevalve8ba]

This type of mechanical switch is what I used in the Model A and it works well.

http://www.speedwaymotors.com/Univer...itch,1972.html

[itslow]

Originally Posted by 51 MERC-CT

There seems to be a misconception that DOT 5 causes brake light switches to fail.
The contacts in the switch never see brake fluid unless faulty...

They may be using a diaphragm material that is not compatible with silicone in DOT 5 but would be otherwise compatible with the polyethylene glycol in the DOT 3/4/5.1 fluids.

[hardtimes]

Originally Posted by joe 1950

1950 ford cpe just need some input from you barners rebuilt my complete brake system @ 8 years ago cyls. lines hoses everything from front to back was new so the talk between my fellow car guys was to put in dot 5 and troubles are over well since then iv put in 4 stop light switches and one whl cyl better to leave it in or flush it out with dot 3

Hey joe,
I've just installed a complete Lincoln brake kit on my '30 Ford roadster. Installed dot 5 (synthetic fluid). Other than rechecking/retightening of various connections, no problems and no regrets !
Dot 5 cannot be mixed with other brake fluid types, as you are aware, so I do not know how well 'flushing' will work with that idea. IMO, if all parts are new and uncontaminated with rust/dirt/other fluid/wear, the dot 5 will do the best job that can possibly be done, absent the water absorbing/rusting that occurs with the other grade brake fluids. Merc 51 has it right , as to brake switch...i.e., that NO FLUID touches contacts. Bad switches can be bought, just like any other bad repro junk parts.
I give thanks here to three Fordbarn guys for my successful brake system installation; you guys who gave advice, the Barner who sold me the 'kit' and especially a Fordbarn buddy who helped /guided me in my first such endeavor ...successfully

BTW:
The main reason that I used Dot 5, is that I've driven older cars with hydraulic brake systems forever. We all know what happens to those systems when left sit for very long periods of time. My roadster sits for very long periods of time, and I do not want to deal with the rust/leaks created and repairs needed, under such circumstances when fluids other than Dot 5 is used. Your choice, eh.

[51 MERC-CT]

Originally Posted by itslow

They may be using a diaphragm material that is not compatible with silicone in DOT 5 but would be otherwise compatible with the polyethylene glycol in the DOT 3/4/5.1 fluids.

The one that is cut apart in the photo operated for over 4 years with
DOT 5 and was bone dry.

[oldbugger]

My experience has been a leak at the brake light switch with DOT 5, 3 switches in 4 years. the mechanical switch makes the DOT 5 work good for me. Paul

[Ken/Alabama]

Been using Dot 5 in my 40 for 20 yrs. Replaced the brake switch last year for the first time. I'm using a relay and am convinced that's what saves the switch.

[FireEngineMike]

Ted and others with mechanical switches,

Could you post a picture or two of the mounting setup for your brake light switch? Thanks. I have a 1-1/2 ton panel and am buying a mechanical switch but have not figured out an easy way to install it.

Originally Posted by sidevalve8ba

This type of mechanical switch is what I used in the Model A and it works well.

http://www.speedwaymotors.com/Univer...itch,1972.html

[sidevalve8ba]

Originally Posted by FireEngineMike

Ted and others with mechanical switches,

Could you post a picture or two of the mounting setup for your brake light switch? Thanks. I have a 1-1/2 ton panel and am buying a mechanical switch but have not figured out an easy way to install it.

Mike,

I don't have a photo to post but what I did was mount the switch on the engine side of the floor board by the brake pedal. When I push down on the pedal it triggers the switch. The nice thing about those switches is that if adjusted properly the brake lights come on as soon as the pedal starts to move. I had to use a shim or two to get it just the way I wanted it.

[rotorwrench]

Hydraulic brake light switches were made with good quality contacts inside for many years until they started cutting corners. This led to reliability problems and auto manufacturers changed over to mechanical switches. This put the hydraulic switches into an even lower production environment which led to the switches being manufactured outside the US with even cheaper contact materials. Suffice it to mention that there are no good quality hydraulic brake light switches manufactured anywhere anymore.

A capacitor might make it work longer but that would be in a clean environment. Most of them are mounted in swampy areas of the car so a capacitor would likely fail pretty soon too.

[oldford2]

Originally Posted by rotorwrench

Hydraulic brake light switches were made with good quality contacts inside for many years until they started cutting corners. This led to reliability problems and auto manufacturers changed over to mechanical switches. This put the hydraulic switches into an even lower production environment which led to the switches being manufactured outside the US with even cheaper contact materials. Suffice it to mention that there are no good quality hydraulic brake light switches manufactured anywhere anymore.

A capacitor might make it work longer but that would be in a clean environment. Most of them are mounted in swampy areas of the car so a capacitor would likely fail pretty soon too.

Rotowrench
I always read your posts and respect your information (probably like many Barners). But you should back up some statements with where you get your statistics/info.
John