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How do I figure out what kind of brake fluid?

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Luke_Healey

Luke_Healey

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How do I figure out what kind of brake fluid is currently sitting in my system? The newer Sprite I bought has the brake fluid in it that was installed in 1989. Still looks 'new' and I'm too worried about the effects of mixing DOT4 and DOT5 to add any of my DOT4 to the system.

I obviously want to refresh and bleed it entirely and am curious if there is a way to determine if it has DOT5 in it right now?
 
Since DOT5 is not as hydroscopic as DOT4 (silicone doesn't absorb water), there might be a way of telling by seeing how well your brake fluid mixes with water as compared to a 'control' test.

So,
Sample 1: 1 oz of DOT4 and 1 oz of water
Sample 2 1 oz of the brake fluid in your car and 1 oz of water.

Shake them both up for the same amount of time. See how well they mix. If it's the same, they're probably both DOT4 or one is DOT 4 and the other is DOT 3. If not then repeat test with a sample of DOT5.

Then again...someone may know of another method. That's what I'd do to start...but I ain't no expert.
 
Hello Luke,

all the silicone I have bought is purple, but after a long time in the car the colour seems to fade so it is not a sure way of identifying what you have.
One way is to find scrap bit of painted steel and see if the fluid affects the paint, silicone won't, glycol will.

Alec
 
Dot 5 and Dot 3, 4, 5.1 do not play well together. Siphon out a small portion of the mystery fluid and pour it into a glass jar containing Dot 3, 4, or 5.1, whatever you have on hand. If the unknown fluid mixes well with the known fluid it is NOT Dot 5.
 
The water mix test above is the method I've seen mentioned elsewhere. I wouldn't go by color. The DOT-5 fluid I've used is purple when new and became an off-color over time.

I'm not sure how you'll know if you have DOT-4 vs DOT-3.
 
Bleed your brakes using DOT4. If it turns to sludge, it was DOT 5 in there! :smile: J/K Best of luck with the brakes. I always throw in a plug for speedbleeders when it comes to brakes. Some don't like them, but when it's just me bleeding brakes, they are great!!!
 
Is there a good speedbleeder that I can buy, or do I have to cobble one up from a trip to Home Depot?
 
The silicon is heaver and 'oily' looking...

Never use it....Even in a car you store for a long time.

It doesn't suck up water and the water will form little puddles where it will rust your lines.

It sucks for other reasons though /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
 
Hello all,

the silicone brake fluid I have used for more than twenty years is supplied by a U.K. brake specialist but made by an American manufacturer (unspecified) and the blurb says amongst other things that it is compatible with glycol brake fluids and will mix safely. Not that you would want to mix it but it seems that some if not all silicone fluids will mix.

Alec
 
WhatsThatNoise said:
The silicon is heaver and 'oily' looking...

Never use it....Even in a car you store for a long time.

It doesn't suck up water and the water will form little puddles where it will rust your lines.
Click to expand...

Except that since it repels water and is not hygroscopic, the water won't get there in the first place, unless you plan on pouring water into it. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif DOT 3 fluid absorbs moisture from the air; DOT 5 doesn't have that problem.
 
C'mon... we don't need another holy war. He just asked how to tell the difference.
 
Aha I had misinterpreted. I was thinking the kind of tool you'd put together from a small pressure sprayer to attach to the master cylinder cap to refill while bleeding.

So I guess I can do both...

In Speedbleeder's MG section they only mention Midgets from 72 to 76 which seems a weird range. Since the part number in Moss for Bugeye original front and rear as well as for later model front discs (which I have) is the same (180-100) I am going to assume the correct Speedbleeder part number is SB3824 for front AND rear in my case.
 
Think I will get some of these when I get around to it.

I used the pressure methoid and found it unsatisfactory as the top of the master cylinder leaked and seemingly there was no way to really stop it.

Comment? Had a new gasket on it as well.
 
jlaird said:
Think I will get some of these when I get around to it.

I used the pressure methoid and found it unsatisfactory as the top of the master cylinder leaked and seemingly there was no way to really stop it.

Comment? Had a new gasket on it as well.
Click to expand...

Assuming you are talking about the EZI-Bleed system, they can be tricky to seal the cap to the reservoir. It has a design flaw. If you look at the bottom of the cap, the fluid hose fitting is too close to the outside edge. This can 'upset' the gasket, not allowing it to lay flat and create sealing problems when it is tightened (especially if over tightened). I cut a small mouse hole in the I.D. side of the gasket to allow it to lay flat and make sure to tighten the cap just enough to seal the air. I make sure the air pressure source (I use the spare tire)is only about 7 to 10 lbs. and check that it is sealing properly before filling the EZI-Bleed canister with brake fluid.

As to the original question, I would use the 'paint test' to see if it Dot 3-4 or Dot 5 but the paint needs to be a single stage paint such as a spray can of krylon, lacquer primer, etc. and not a fully cured 2 part paint. I tested Castrol LMA (Dot 4) on cured PPG Acrylic Urethane and there was no effect after 3 days. With Krylon Acrylic Enamel it wrinkled immediately.

Cheers,
John
 
Actually I used an inter tube from a bike and had it clamped well on the filler hole. It was where the top of the MC is screwed to the cast MC that it leaked. I had a proper gasket but it did not seal as good as it should. Not a place for sealer I thought. Guess I need to make a thicker gasket, prob have some warpage on the pot metal top.
 
Hi Jack,

How much pressure did you have in the bike inner tube? It might be hard to get low pressure and have enough air to go through the bleed process. I would try with the partially deflated spare tire (7lbs) and a thicker, more compliant gasket. Once you get it set up, the pressure bleeding is a great way to go.
 
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