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

[51 MERC-CT]

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.

Just an idea on how I did mine.
Keep in mind that there is a mirror image switch that is available so that the electrical connections can be placed on the up side like mine is.
Also it is most likely the arm of the switch will have to be bent to work as intended.

[wbedwards]

what size/type capacitor are you using with the switch? across the leads?

[bill3337]

I've used Dot 5 ever since getting my '33 five window on the road. Been 18 years and 87,000, never had a minutes trouble with any braking component including the brake light switch, although I do run a relay in the circuit. One of the nice things with Dot 5 is that it won't eat the paint off your car if you spill it. I also use it in my hydraulic clutch, never an issue.

[Drbrown]

Car manufactures have been using DOT 5 for many years but I note that they prescribe that owners flush the brake systems variously at about every 50,000 miles .... not a cheap procedure. Our three family cars have hydraulic brake switches and clutches and never had a problem. It appears that the hydraulic brake switch problems are related to aftermarket units.

I use DOT 4 in my vintage but flush every 5 or so years.

[deucemac]

I put Dot 5 fluid in my roadster when I built it. Three brake light switches and 9k miles later, I installed a Harley switch and no problems since. Napa sells a replacement Harley switch P/N MC14011 For around $23, Harley sells theirs for $43. Dot 5 is hard to contain and the connections must be very clean and tight. It will leak in areas that seemed tight enough for Dot 3. That is the only problem i had other than eating Ford switches. Once the switch was replaced and the lines tight enough there has been good results, plus it will never absorb water and corrode the components like dot 3 does. I'm sold on it.

[FlatheadTed]

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Used Dot 5 / silicone in a Auburn and after two sets of cups cannot stop it leaking at the w/c ,the cylinders have been sleeved in stainless ,so maybe the Finnish is not polished enough ? .Ted

[fortyfords]

I used a GM brake switche, on my 40 sedan, I took a lug nut with the same threads as the GM switch and tack welded the nut to the frame, just in front of the pedal pivot. The lug nut threads are just perfect to add a little friction so the switch doesn't move one way or another. One guy told me that the switch would go bad from being in a hostile environment but it never has and I use the same set up on all my cars. The switch mounting has to be something that will work with your car pedals. The switches can be bought at an auto parts store or any 80's, 90's GM cars in a junk yard will have them. Just get the simple two terminal switch for brakes alone or multi contacts for lock-ups and cruise control. Bowler sells a nice looking black GM style switch which is the one that I use the most. Hope this ride helps.

[Huff]

What is used to flush out braking system before changing fluids. I am changing to dot 5.

[sidevalve8ba]

Denatured alcohol is the best I've found.

[phoneman]

last time I got dot3 fluid at Oriely's it said synthetic on the bottle. Any word on the formulation of synthetic dot3 does it attract water (I think hydroscopic is the word) like conventional dot3?

[RandyZ]

I had switched to a HD big buck switch and it lasted only a little longer than the standard ones. When I took all the switches apart, the contact compartment is full of brake fluid. This contaminates the contacts and they will not always make connection even though they are bright and shiny like the day they were made.

[rotorwrench]

For those that doubt the quality of hydraulic brake switches, here is a study of what was thought to be a quality switch from Germany. http://www.sw-em.com/hydraulic%20bra...es%20notes.htm

I have owned Harleys for many years my 1977 FLH which came from the factory with Dot 3 fluid, still has it's original switch. My 1981 FLH came with Dot 5 and has had several switches since it was new. OEM HD switches worked the longest but they have been manufactured in Mexico for a number of years now so you tell me how good they are.

These items plus ignition condensers , breaker points, and various other small run replacement items are getting hard to source in a quality part replacement. With Echlin being bought out by Standard, it's hard to say whether Echlin products will remain to be quality or if the name will die out like so many other old brand names. I certainly hope they do survive and continue to make good stuff but who knows?

[john in illinois]

I am trying to decide on fluid. What I know about dot 5: no new cars use it because ABS causes bubbles. Same for the military.

I had dot 5 in a Harley and it was fine.

If no new cars are using can we get rubber parts for old Ford brakes that are compatible. Dot 3 fluid swells the seals and I have been told Dot 5 does not.

My MT brake cylinders say no warenty with dot 5.

Hard decision for me.

John

[rotorwrench]

If the rubber is at least a good quality nitrile rubber or neoprene then polyethylene glycol based Dot 3 should not have any detrimental effect. Dot 3 absorbs water so it gets contaminated after a time and should be purged & renewed periodically. Dot 5 or silicon based fluid doesn't absorb much water but it has a tendency to hold suspended air in small quantities that make it slightly more compressible than Dot 3. Both types deteriorate and at about the same rate but Dot 5 has less effect on cast iron or aluminum cylinder bores than Dot 3 in the form of corrosion pitting in low lying spots.

If I had stainless sleeved components, I would just use Dot 3. Both types will damage painted surfaces if not cleaned right away. Dot 5 should really have fluorocarbon or fluorosilicone rubber seals since it is a bit harder to contain than Dot 3 but both generally are used with the same seals. For the most part only one type of rubber is used for most brake seals and it is difficult to find out what they are compatible with. Foreign made seals are an even bigger mystery.

[itslow]

Originally Posted by 51 MERC-CT

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

Manufacturer A may not be using the same materials as Manufacturer B. This is especially the case now that parts are being sourced from low-cost countries.

Originally Posted by Drbrown

Car manufactures have been using DOT 5 for many years but I note that they prescribe that owners flush the brake systems variously at about every 50,000 miles .... not a cheap procedure...

I use DOT 4 in my vintage but flush every 5 or so years.

No car manufacturers use DOT 5. They all use DOT 3/4/5.1 family of fluids.

It costs about $8 to flush brake fluid and replace with new if you do the labor yourself. All you need is a short length of hose, an empty peanut butter container, a flare wrench, and a patient helper.

The ONLY advantage of the silicone DOT 5 is that it doesn't eat paint. It still needs to be flushed periodically to prevent corrosion in the lines.

Originally Posted by phoneman

last time I got dot3 fluid at Oriely's it said synthetic on the bottle. Any word on the formulation of synthetic dot3 does it attract water (I think hydroscopic is the word) like conventional dot3?

Yes. It is still hygroscopic.