brake fluid

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I have done it without issue on my cars over the years, the main difference is boiling points. I am sure you will hear differing opinions on this, but it has not caused problems for me.
 
DOT 4 is synthetic, made to replace DOT 3 which is a semi-processed petroleum product.
Both DOT 3 & DOT 4 are mixable and compatible. DOT 5 is not mixable with any other brake fluid
 
A few corrections to above are required.

All brake fluids are synthetic (i.e. not from "minerals" occurring in nature), and always have been. Putting "synthetic" on the label was marketing genius, I think first by Valvoline. No "modern" brake fluids are petroleum based (perhaps in 1920, so don't flame me).

DOT 3, 4, and 5.1 fluids are glycol type. Downside is that glycols absorb moisture from the air which causes internal corrosion and lowers the boiling point (bad, pedal will go to floor). If you use them, flush in new fluid every 2 years or so, especially if you live in humid climates. All brake fluids are required to be able to mix (even silicone).

DOT 5 is a quality rating, not a fluid type. Until recently only silicone could meet this higher rating. When a glycol finally did, they required it be labelled "5.1" to avoid confusion, but it certainly confuses. Silicone has the advantage that it does not absorb moisture, so never requires flushing, unless you stupidly drip water into it. All kinds of misinformation spread about it, like that it could mystically cause more corrosion by not absorbing water. I recently removed a single pot MC I had used silicone for 20 years and it looked pristine inside (changed to dual MC). It causes no strange problems if mixed with glycol (test reports), though the jars warn not to (lawyers?). It won't degrade your seals, indeed some British cars in the 1950's required silicone since glycol attacked the brake seals. Most trailer queens use it because it won't ruin their $10K paint job. I use it because I like no maintenance.
 
However in a race car silicone is not ideal because it is more compressible, which translates to the pedal feeling less firm and possibly more 'mushy'.

The glycol brake fluids are actually intended to absorb moisture. The idea is the if regular maintenance is performed then the flushing of the fluid will remove the condensed moisture from the system. The typical problem crops up because that maintenance isn't so regular. I know better and I still don't do it as often as I should.
 
ntsqd said:
However in a race car silicone is not ideal because it is more compressible, which translates to the pedal feeling less firm and possibly more 'mushy'.

The glycol brake fluids are actually intended to absorb moisture. The idea is the if regular maintenance is performed then the flushing of the fluid will remove the condensed moisture from the system. The typical problem crops up because that maintenance isn't so regular. I know better and I still don't do it as often as I should.
Click to expand...
Correct, the silicone type will not absorb there for on low spots in the brake lines water may collect and corrode. Both have advantages and disadvantages one is not really better than the other.
 
I remember when silicone brake fluid was billed as the Second Coming. Today, not so much.

I wouldn't use it on anything except for trailer queen show cars, and maybe not even then.
 
I don't notice a spongy pedal in any of my cars. There is slight "lost motion", but that is normal (pads & shoes must move to contact). Racers use glycol because it has a slightly higher boiling point when new and pristine. They probably flush it before every race, plus rebuild the engine and tranny, etc. The main reason silicone is hard to find is because it is not recommended for ABS systems, which are everywhere today. I don't know if there are known problems or it was just never tested and qualified (i.e. accountants & lawyers input).
 
BillGrissom said:
I don't notice a spongy pedal in any of my cars. There is slight "lost motion", but that is normal (pads & shoes must move to contact). Racers use glycol because it has a slightly higher boiling point when new and pristine. They probably flush it before every race, plus rebuild the engine and tranny, etc. The main reason silicone is hard to find is because it is not recommended for ABS systems, which are everywhere today. I don't know if there are known problems or it was just never tested and qualified (i.e. accountants & lawyers input).
Click to expand...

You are correct. I'm a stability control hydraulic engineer. We only allow Dot 3/4/5.1. The silicone brake fluid is something we don't use due to the higher compressible and it is in some cases incompatible with the materials in the ABS/Stability control module.

The silicone fluid will not trap water molecules in it, however, that doesn't mean you cannot get water in your brake system that would cause corrosion. There is some minor leakage in all systems.

ATE SL.6 or TYP200 are good fluids. The most important thing is that you use fluid only from a new, sealed container.
 
... The most important thing is that you use fluid only from a new, sealed container.
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This part gives me the most trouble. I just can't seem to get guys to understand this. It's not rocket surgery, yet they insist on using up the dusty partly empty bottle that's been sitting on the shelf for who knows how long.
 
BillGrissom said:
I don't notice a spongy pedal in any of my cars. There is slight "lost motion", but that is normal (pads & shoes must move to contact). Racers use glycol because it has a slightly higher boiling point when new and pristine. They probably flush it before every race, plus rebuild the engine and tranny, etc. The main reason silicone is hard to find is because it is not recommended for ABS systems, which are everywhere today. I don't know if there are known problems or it was just never tested and qualified (i.e. accountants & lawyers input).
Click to expand...

Yes exactly. It road, circle track and that type of racing where some of silicone's slight compressibility becomes more of an issue. IIRC it has to due with the heat transfer and brake pressures involved. Agree that brakes should be bled before each race or weekend, and at minimum begining of every season.

Of course if the car is VERY Heavy and VERY Fast and uses front disks, then fluid temperature and condition could effect stopping at the end of the drag strip too. Drum brakes better isolate the fluid from the heat of friction so less likely to have issue with degraded fluid temperature.

That said, I've found it best to bleed the brakes of my vehicles every spring even for street use. Doing so really reduces the amount of fine rust which is hell on caliper pistons. For years I was using Castrol's LMA but after discovering Valvoline's "Synthetic" (now renamed something else) I've been sold on it because the fluid comes out much cleaner during the annual bleed.
 
Any place where brake modulation is important won't want silicone fluid. Drag racers and tractor/truck pullers pretty much just need an on/off switch (not talking about any steering brakes in the latter). Very little modulation needed in a system set-up correctly since braking happens 'after the fact' as it were.

I've played with the idea that a really fast, really heavy drag car might benefit from having an LBS in the front brake system. Classically drag car brakes are heavily rear-biased to avoid locking up those tiny front tires. An LBS might allow for more front brake w/o resulting in the loss of steering locked front tires.

I'm wondering, do you think the Valvoline product is doing a better job of keeping the system clean or a poorer job of cleaning the system?
 
That's a good question. My guess was (and still is) that Valvoline's product was simply more resistant to absorbing moisture.

The Girling Castrol LMA (Low Moisture Absorbing) had been around awhile by the early 1990s. Biggest change I knew of was that it was harder to purchase in metal cans, although Pegasus Racing and probably others could still provide it that way. I came across the Valvoline product in Pensacola around then and based on boiling points it seemed to be a leap ahead.

DRY:527F -- WET:347F --- VALVOLINE SYNPOWER DOT3 & DOT4 (corner carvers)
DRY:509F -- WET:311F --- CASTROL LMA (2007 Castrol pdf)

My understanding is that the LMA had been developed for competiton where moisture absorbtion was an issue. Probably things like Eurpean rallys where dry boiling point could be traded for less absorbtion. Some race type fluids really were/ are very suseptible to moisture and lose any advantage they had initially.

Castrol has newer product out now that's supposed to be better than the old LMA. Below from Pegasus Racing's website:
Castrol Advanced Performance Specifications:
Dry Boiling Point: 509° F minimum
Wet Boiling Point: 329° F minimum

Mentioned by Golduster318:
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DRY:536F -- WET:392F --- ATE SUPERBLUE/TYP200
(also from the old corner carvers thread)
This is getting into a more serious racing fluid.
 
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