dot 3 or dot 5 good and the bad

[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.