My understanding is that 5.1 has a higher boiling point and a better additive package than DOT 4 or 3. Does anyone know if it is less compressible? Word on some streets is that it helps improve the less than great brakes on the Gen7 Celica
Performance of DOT 5.1 compared to older glycols
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Originally Posted By: Rand
thats a silicone based brake fluid and shouldnt be used.
unless factory fill.
also all hydraulic fluids have very low compressibility if your brakes are mediocre I'd start with different pads and rotors and go from there.
Dot 5.1 is.compatible with dot 3 & 4 fluids. It is NOT silicone based.
Dot 5 however is silicone based and should never be used in dot 3 or 4 systems.
thats a silicone based brake fluid and shouldnt be used.
unless factory fill.
also all hydraulic fluids have very low compressibility if your brakes are mediocre I'd start with different pads and rotors and go from there.
Dot 5.1 is.compatible with dot 3 & 4 fluids. It is NOT silicone based.
Dot 5 however is silicone based and should never be used in dot 3 or 4 systems.
Dot 5 fluids are silicone....Dot 5.1 is ether based like Dot 3/4. It typically has a higher boiling point then the others, but it won't make a [censored] bit of difference if you are having brake issues with Dot 3/4 on a street car. If you are getting your brakes that hot, its time for a brake upgrade.
My best advice is to use a high quality Dot 3 or 4 fluid, and keep it fresh by flushing the system every year or so. Ether based fluids are hydroscopic, and will absorb water over time. This lowers their boiling point significantly, and can lead to various issues. If you keep it fresh, these issues can be avoided.
That said, with regards to "compressibility", a Dot 3, 4, or 5.1 will all be the same. If your pedal is mushy, try fresh fluid of any type, then look at the brake lines. Rubber brakes lines can expand as they age causing pedal issues. A nice pair of new rubber or even stainless steel lines can make for a very firm brake pedal. But note, stainless steel lines on a street car can run into issues with wear as grit gets trapped under the stainless braiding and wears the rubber/teflon tube below....but that's something that is often debated.
My best advice is to use a high quality Dot 3 or 4 fluid, and keep it fresh by flushing the system every year or so. Ether based fluids are hydroscopic, and will absorb water over time. This lowers their boiling point significantly, and can lead to various issues. If you keep it fresh, these issues can be avoided.
That said, with regards to "compressibility", a Dot 3, 4, or 5.1 will all be the same. If your pedal is mushy, try fresh fluid of any type, then look at the brake lines. Rubber brakes lines can expand as they age causing pedal issues. A nice pair of new rubber or even stainless steel lines can make for a very firm brake pedal. But note, stainless steel lines on a street car can run into issues with wear as grit gets trapped under the stainless braiding and wears the rubber/teflon tube below....but that's something that is often debated.
Originally Posted By: Rand
thats a silicone based brake fluid and shouldnt be used.
unless factory fill.
also all hydraulic fluids have very low compressibility if your brakes are mediocre I'd start with different pads and rotors and go from there.
Most owners regard the Gen7 Celica brakes as spongy and guys have spent small fortunes trying to improve things (hoses, discs, pads)without getting those brakes up to a really good standard. Hence the interest in the fluid, but my view is that DOT4 is in most cars and works fine, so it is hardly likely to be an issue in this one particular car.
thats a silicone based brake fluid and shouldnt be used.
unless factory fill.
also all hydraulic fluids have very low compressibility if your brakes are mediocre I'd start with different pads and rotors and go from there.
Most owners regard the Gen7 Celica brakes as spongy and guys have spent small fortunes trying to improve things (hoses, discs, pads)without getting those brakes up to a really good standard. Hence the interest in the fluid, but my view is that DOT4 is in most cars and works fine, so it is hardly likely to be an issue in this one particular car.
There are slight chemical differences in the various grades of glycol brake fluid which gives them their performance differences. In a very few cases the elastomers in the brake system won't tolerate these chemicals.
The difference brake fluid grades are about heat performance. If DOT4 isn't failing due to high heat, you don't need DOT5.1, although it probably won't hurt.
DOT5 silicone brake fluid is more compressible. The difference at the pedal can often be felt, and ABS systems might not work. Plus the other reasons for not using DOT5 in systems not designed for it.
The difference brake fluid grades are about heat performance. If DOT4 isn't failing due to high heat, you don't need DOT5.1, although it probably won't hurt.
DOT5 silicone brake fluid is more compressible. The difference at the pedal can often be felt, and ABS systems might not work. Plus the other reasons for not using DOT5 in systems not designed for it.
5.1 usually has the highest DRY boiling points, but not necessarily the highest WET boiling points. I believe they also typically absorb the most water and do it the quickest. That's a sweeping generalization, but this is what formulation/price tradeoffs result in.
Fluid is not compressible, period. It's air, rubber or other parts of the braking system that are compressing to result in spongy feel. Switching to 5.1 won't make a bit of difference in "compressibility" but you may need to change it far more often (and it might cost a lot more than DOT4 too).
Fluid is not compressible, period. It's air, rubber or other parts of the braking system that are compressing to result in spongy feel. Switching to 5.1 won't make a bit of difference in "compressibility" but you may need to change it far more often (and it might cost a lot more than DOT4 too).
Actually, fluid IS compressible. So is a steel block!
And big surprise for me, DOT5 silicone is more compressible than fresh DOT4 or 5.1
Quote:
stainless steel lines on a street car can run into issues with wear as grit gets trapped under the stainless braiding and wears the rubber/teflon tube below
I expect to have this problem with the Goodridge lines on my car, now looking for some that have a plastic covering heat shrinked over the braid before they let go.
stainless steel lines on a street car can run into issues with wear as grit gets trapped under the stainless braiding and wears the rubber/teflon tube below
I expect to have this problem with the Goodridge lines on my car, now looking for some that have a plastic covering heat shrinked over the braid before they let go.
Bazz
Is there any chance the lay out of that car's brake system results in an air bubble in a high point that is extremely difficult to bleed out? You might look at that and consider ways to either bleed every high point or find a way to allow the air bubble to migrate to a point that can be bled...park overnight on a very steep ramp with the pedal depressed, or whatever you can invent.
Is there any chance the lay out of that car's brake system results in an air bubble in a high point that is extremely difficult to bleed out? You might look at that and consider ways to either bleed every high point or find a way to allow the air bubble to migrate to a point that can be bled...park overnight on a very steep ramp with the pedal depressed, or whatever you can invent.
Originally Posted By: Craig in Canada
Fluid is not compressible,
The compressibility of diesel fuel is one consideration in the timing and layout of diesel engine injector systems. Many older diesels had a central injection pump and injection valves at each cylinder with equal length high pressure steel injection tubing in interesting curves to take up the unneeded lengths of tubing. The equal length tubes allowed for equal compression of the fuel as well as equal expansion of the steel lines. Unequal compression would result in uneven injection timing.
Fluid is not compressible,
The compressibility of diesel fuel is one consideration in the timing and layout of diesel engine injector systems. Many older diesels had a central injection pump and injection valves at each cylinder with equal length high pressure steel injection tubing in interesting curves to take up the unneeded lengths of tubing. The equal length tubes allowed for equal compression of the fuel as well as equal expansion of the steel lines. Unequal compression would result in uneven injection timing.
MolaKule
Staff member
Compressibility is based on the Bulk Modulus of the material, in this case, fluid:
http://www.engineeringtoolbox.com/bulk-modulus-elasticity-d_585.html
http://www.engineeringtoolbox.com/bulk-modulus-elasticity-d_585.html
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