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Brake fluid question

M

mjbrown

Member
I'm replacing the clutch slave cylinder on my JD 2350. The operators manual says use dot 4 fluid. New slave cylinder is labeled for dot 3. Which to use? Does it matter?
 
Primarily DOT 4 has a higher boiling point than DOT 3. It is recommended to avoid mixing them.
cvphoto129232.jpg
 


Use Dot 5. It doesn't absorb water, it doesn't dissolve your paint, and best of all it comes in a pretty purple color.
 
Since dot 3,4,and 5.1 all show the same ingredients why is it not good to mix them? Just asking with the listing of the make up all three have the same.
 
My understanding is that the ratio of the constituents is different. The different ratios allow the bokling points to be different. DOT 4 apparently is less prone to absorb moisture. The caution about mixing 3 and 4 is primarily to avoid degrading and lowering the boiling point of straight DOT 4.
 
Dot 4 will be ok if not I have not had any issues with it. I speck I use 10/15 gal of it a year. It would get dot 4 if it was in my shop...
 
DOT 5 can only be used when everything is new and/or thoroughly flushed of all
other fluid.

It can not be mixed with other fluids.

The advantage is it does not absorb water. It is a favorite for motorcycles,
show cars, vehicles that spend time in storage.

The disadvantage, forgetting it has DOT 5 in it and topping it off with the
wrong stuff!
 
Guess I will continue to use dot4. I didn't want damage seals but it looks like that won't be a problem.
Thanks fo the input.
 
DOT 5.1 can be considered universal, compatible and superior to DOT 3 or 4. DOT 4 is also superior and compatible with DOT 3. If ever in doubt or want to carry only one type then find DOT 5.1, that is unless you need DOT 5.

DOT 5 is really the only unique brake fluid and is not compatible with any of the others.
 
DOT 4 meets and exceeds DOT 3. DOT 5.1 meets and exceeds DOT 4 and DOT 3, but is harder to find and more expensive; typically it's used in newer high performance cars.

I would not use DOT 5 silicone brake fluid. You should flush out all the old fluid if you do, and the next person to add fluid may not know the switch has been made. Hardley motorcycles use DOT 5, mainly because it won't hurt paint.

DOT 3 will probably work just fine, but I suspect JD was concerned about heat under severe conditions. DOT 4 has a higher boiling point than DOT 3.
 
Good Morning mj, FWIW based on what Ive read and my own experience, I pretty much agree with the other fine gents, I would use DOT 4

John T
 
Do NOT USE Dot 5! It is pure silicone, a heavier (more viscous) fluid difficult to bleed and not compatible with other brake fluids. The system must be disassembled, totally rebuilt to work. Flushing with alcohol as recommended by some does not work. Silicone, because it does not absorb moisture as traditional fluids do is a specialty fluid used in the antique automotive world (vehicles not driven regularly) and the commercial aviation (extreme high temps). It is a study in itself and too extensive a discussion for here. Traditional fluids should be flushed yearly with fresh as it absorbs moisture and that leads to internal corrosion and failure of traditional systems. Lots of info and it's pretty black and white, not speculative. This comes from 35 years in the road/racing competitive world and years of teaching. There's a reason it's recommended by new vehicle dealerships to flush brake fluid yearly. Larry
 
(quoted from post at 06:36:58 06/29/22) Do NOT USE Dot 5! It is pure silicone, a heavier (more viscous) fluid difficult to bleed and not compatible with other brake fluids. The system must be disassembled, totally rebuilt to work. Flushing with alcohol as recommended by some does not work. Silicone, because it does not absorb moisture as traditional fluids do is a specialty fluid used in the antique automotive world (vehicles not driven regularly) and the commercial aviation (extreme high temps). It is a study in itself and too extensive a discussion for here. Traditional fluids should be flushed yearly with fresh as it absorbs moisture and that leads to internal corrosion and failure of traditional systems. Lots of info and it's pretty black and white, not speculative. This comes from 35 years in the road/racing competitive world and years of teaching. There's a reason it's recommended by new vehicle dealerships to flush brake fluid yearly. Larry
Click to expand...

Larry, DO USE DOT 5! We all know the benefits, and when I switched mine over flushing was no problem at all. I simply put the DOT5 in and started bleeding. The DOT 5 fluid is the same light viscosity as the DOT 4. I had a vinyl tube on the fitting while bleeding making it easy to see exactly what was coming out. There was obvious mixed fluids for maybe three cycles until it cleared out. I went five more cycles after there was no more residual. Simple, No big deal. It costs a little more but it is cheap insurance against water damage of your baby. A no brainer.
 
(quoted from post at 22:31:12 06/29/22)
(quoted from post at 06:36:58 06/29/22) Do NOT USE Dot 5! It is pure silicone, a heavier (more viscous) fluid difficult to bleed and not compatible with other brake fluids. The system must be disassembled, totally rebuilt to work. Flushing with alcohol as recommended by some does not work. Silicone, because it does not absorb moisture as traditional fluids do is a specialty fluid used in the antique automotive world (vehicles not driven regularly) and the commercial aviation (extreme high temps). It is a study in itself and too extensive a discussion for here. Traditional fluids should be flushed yearly with fresh as it absorbs moisture and that leads to internal corrosion and failure of traditional systems. Lots of info and it's pretty black and white, not speculative. This comes from 35 years in the road/racing competitive world and years of teaching. There's a reason it's recommended by new vehicle dealerships to flush brake fluid yearly. Larry
Click to expand...

Larry, DO USE DOT 5! We all know the benefits, and when I switched mine over flushing was no problem at all. I simply put the DOT5 in and started bleeding. The DOT 5 fluid is the same light viscosity as the DOT 4. I had a vinyl tube on the fitting while bleeding making it easy to see exactly what was coming out. There was obvious mixed fluids for maybe three cycles until it cleared out. I went five more cycles after there was no more residual. Simple, No big deal. It costs a little more but it is cheap insurance against water damage of your baby. A no brainer.
Click to expand...

Water damage is not eliminated with dot 5 water will get into the system. Wherever the water settles it will start corroding the part. If I used dot 5 I would religiously flush the system once a year wither I drove it are not.

I never push dot 5 for those reasons.
 
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