How often to flush/change dot 4?

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70DusterBob

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My Duster is going through a major rebuild, engine, trans, exhaust system etc. It has been sitting around for 2 years now. I plan on swapping out all four wheel cylinders and the master. May as well flush and change out the fluid if it needs it. It had all new fluid 15 years ago, but I don't know how long the brake fluid (dot 4) lasts seeing how it can gather moisture.

Any input? Thanks.
 
The rule of thumb we use at our shop is every two years . There are test strips to test the quality of course if it passes I do not flush the system .
 
My wife's car is an 04 Escape. 162,*** miles bought new in December 03. Still has the original DOT3 in it.
 
The rule of thumb we use at our shop is every two years . There are test strips to test the quality of course if it passes I do not flush the system .

TWO years???? Holy crap!!! I am wayyyyyyyyyyyyyyyyyyyyy over due. We have high humidity here, but not much rain. Consider it changed!
 
TWO years???? Holy crap!!! I am wayyyyyyyyyyyyyyyyyyyyy over due. We have high humidity here, but not much rain. Consider it changed!
I would test it first , I only sell work that is needed , the escape is probably ok but ....
 
My Duster is going through a major rebuild, engine, trans, exhaust system etc. It has been sitting around for 2 years now. I plan on swapping out all four wheel cylinders and the master. May as well flush and change out the fluid if it needs it. It had all new fluid 15 years ago, but I don't know how long the brake fluid (dot 4) lasts seeing how it can gather moisture.

Any input? Thanks.
Drain the master almost completely....then fill it cap it and bleed it almost empty...then repeat 3 times.
 
Putting a new master on it too. I don't take chances with brakes. It doesn't matter how fast your car is if it can't stop... right??
 
Two years? Ridiculous. Bear in mind a properly done brake system is SEALED it is not vented
 
Flush with Dot5. We did with zero issues. 67 cuda factory disc.

I'd like to. I will look into it. Puttin a new master and all four wheel cylinders at the same time. Now would be the time to do it.
 
Two years? Ridiculous. Bear in mind a properly done brake system is SEALED it is not vented

If you have an original master cylinder with the bladders, to a point it might be sealed, at least until you lose a large amount of fluid. All newer vehicles have a "venting slit" in the cap which will open under pressure or vacuum. The 80s aluminum Mopar Master cylinders have this feature too.

Depending on the fluid it usually says on the can 2 or 3 years. My opinion is you put DOT4 in everything that started with DOT3 since they are compatible. Anything with ABS should get DOT4 LV ( ATE SL.6 or similar) and our old cars should get regular DOT4 ( ATE Typ.200 or similar). If you have really dark fluid or rust in the master cylinder, I would suggest not being too aggressive when pumping fluid through, because in some cases it will wreck the master cylinder due to all the junk that was in there getting caught in the seals.

Don't put DOT5 anywhere near that already filled system, asking for trouble, and it's also more compressible so it decreases your braking performance.
 
Yeah 15 is way over due. It is dot 3, my mistake.

Doesn't really matter. The only difference between DOT3 and 4 is the boiling point is higher with 4. They are totally interchangeable.
 
We flushed Dot 5 into a system that was holding dot 3. That was 7 years ago. Zero problems, brakes feel fine. That's our experience with it.
If you have an original master cylinder with the bladders, to a point it might be sealed, at least until you lose a large amount of fluid. All newer vehicles have a "venting slit" in the cap which will open under pressure or vacuum. The 80s aluminum Mopar Master cylinders have this feature too.

Depending on the fluid it usually says on the can 2 or 3 years. My opinion is you put DOT4 in everything that started with DOT3 since they are compatible. Anything with ABS should get DOT4 LV ( ATE SL.6 or similar) and our old cars should get regular DOT4 ( ATE Typ.200 or similar). If you have really dark fluid or rust in the master cylinder, I would suggest not being too aggressive when pumping fluid through, because in some cases it will wreck the master cylinder due to all the junk that was in there getting caught in the seals.

Don't put DOT5 anywhere near that already filled system, asking for trouble, and it's also more compressible so it decreases your braking performance.
 
The new DOT 5 fluid. As I said zero issues. That was spring of 2012. I replaced the front steel jumper lines on front calipers in 2017. When I bleed brakes I noticed nothing abnormal. Jumper lines were replaced as they had kinks.
What did you flush the old dot 3 out with?
 
Just don't change to DOT5 It's taking a big chance.

I've worked in Engineering at two different top 5 OEM automotive brake parts suppliers and I am not aware of one of them that will sell a part for a DOT5 silicone fluid system. A lot of the aftermarket companies will also not warranty parts with DOT5. The long term material compatibility is not always there, and also since dot 5 does not absorb water, it can have water pockets form and create corrosion for that reason. The old natural rubber isn't as tough as the EPDM so it's likely you get some swelling that you don't want. You want the water to be in suspension, not in pockets in your system.

If you kept DOT4 and even changed it every 5 years or when you change the pads, whichever comes first, you'll be good. I worked on an 07 Saturn Ion over the weekend that as far as I can tell has never had the original DOT3 flushed after 13 years and 135k miles and there isn't "an issue" either, pistons slide perfectly. Michigan is a terrible place for temperature changes (Yearly swing between -25F and 100F most years, and it's damp) That's no guarantee on the longevity of any of the parts, however, this is still reasonable given the manufacturing of the vehicle. No US car company has any service recommendation for brake fluid flushes in their owners manuals.

DOT5 actually also has some compressibility so it will have at least a small decrease in performance.

If you can pour fluid without spilling and have a tight system DOT5 provides no benefit. If you do spill, just flush the paint with soapy water.

My ATE Typ 200 after 2 years in the car is amber just as brand new. It's not attacking the rubber whatsoever. The darkness is either contamination from dirt or the carbon leaching out of the rubber.
 
Every 2 years is a good idea for a car that sits outside. For a car that stays in a heated shop then maybe 3 or 4 years. For my daily drivers I change all of the fluids on a regular basis. Coolant, brake fluid, PS fluid, etc. Flush it all every 30,000 miles.
 
Every 2 years is a good idea for a car that sits outside. For a car that stays in a heated shop then maybe 3 or 4 years. For my daily drivers I change all of the fluids on a regular basis. Coolant, brake fluid, PS fluid, etc. Flush it all every 30,000 miles.

I can honestly say , I have never changed the brake fluid on anything , tractors , or car/trucks , hotrods , unless doing a complete brake job ,and had to ----------
 
Much wrong info, but I'm not going to point to specific posts and upset people. DOT 4 can absorb more moisture than DOT 3, so is better. DOT 5.1 is even better and is the first glycol fluid which meets the DOT 5 spec. It is named 5.1 to distinguish from silicone DOT 5. They are all compatible. Ignore auto-counter "experts" who tell you that mixing DOT 3 & 5 will cause spooky problems. Of course best to first blow out all glycol fluid w/ air, then flush a little ethanol thru, then blow to evaporate that out. But, in my 1996 Voyager, I just flushed DOT 5 thru until I saw blue dye at each wheel. That is an ABS minivan and ABS still works fine so ignore the "lawyer-added" disclaimers on DOT 5 bottles ("not for use in ABS systems"). If worried about getting water into silicone fluid, then you should worry about that in your power steering system too. With silicone, you never need to flush again or worry about internal corrosion or removing paint from your pretty engine bay. The compressibility is no concern, but be careful to pour it slowly down the side of a funnel since any air bubbles take a long time to settle out. Re seals, some British cars in the 1950's required silicone fluid since glycol attacked their rubber. Silicone is much more benign than glycol. If you use glycol fluid, flush thru new fluid every 10 years in CA/AZ or every 4 years in the east, maybe 2 years on the Gulf Coast.
 
Much wrong info, but I'm not going to point to specific posts and upset people. DOT 4 can absorb more moisture than DOT 3, so is better. DOT 5.1 is even better and is the first glycol fluid which meets the DOT 5 spec. It is named 5.1 to distinguish from silicone DOT 5. They are all compatible. Ignore auto-counter "experts" who tell you that mixing DOT 3 & 5 will cause spooky problems. Of course best to first blow out all glycol fluid w/ air, then flush a little ethanol thru, then blow to evaporate that out. But, in my 1996 Voyager, I just flushed DOT 5 thru until I saw blue dye at each wheel. That is an ABS minivan and ABS still works fine so ignore the "lawyer-added" disclaimers on DOT 5 bottles ("not for use in ABS systems"). If worried about getting water into silicone fluid, then you should worry about that in your power steering system too. With silicone, you never need to flush again or worry about internal corrosion or removing paint from your pretty engine bay. The compressibility is no concern, but be careful to pour it slowly down the side of a funnel since any air bubbles take a long time to settle out. Re seals, some British cars in the 1950's required silicone fluid since glycol attacked their rubber. Silicone is much more benign than glycol. If you use glycol fluid, flush thru new fluid every 10 years in CA/AZ or every 4 years in the east, maybe 2 years on the Gulf Coast.

If you are saying 3/4/5.1 are compatible, then yes that is true. The DOT 3/4/5.1 differences is mainly the boiling point requirements but whatever.

If 3/4/5.1 was compatible with 5 then you would have no need to flush it out with ethanol or blow through it. Clearly you were also worried about it. It's also more risky to your paint to blow through a line than just flushing with DOT 3/4/5.1 for most of us.

As I stated before I've worked on braking systems as an engineer at two companies that do the OEM systems and none allow DOT 5. I'm sure you know better than all the engineers and chemists at companies that designed the parts, the fluid manufacturers, and the OEM manufacturers though. The DOT5 will likely aerate during an ABS event and is therefore dangerous since the vehicle may not react as expected, the absorption properties of DOT3/4/5.1 is superior here. Those modules are rarely "Air Free" especially if the system has been opened since it was evacuated and filled when the car was new. Just because you got away with it so far, doesn't make it a good idea, and it's poor advice to have people change their systems after they were already filled.

Most OEMs don't even have a brake fluid service interval in their owners manuals so the corrosion from water in DOT3/4 isn't a huge problem for the design life of the car. If there's water in your system with the silicone fluid because it's not absorbed into the fluid it absolutely can and will cause corrosion in your system. Given that the car was not built with DOT5 when it was evacuated and filled at the plant there is absolutely some amount of water in the system, it would still be a good idea to flush it eventually.

Brake fluid's #1 job is to not be compressible. More compressible fluid makes the pedal longer, the stopping distance also gets longer.
 
I flush my 72 Demon every 2 years since 1986, when i bought it. And i will keep doing it. Every vehicle; cars , truck, sleds that i owned get that procedure and no problems with braking system. Also improve brake feel as a firmer pedal operation. Every 2 years.
 
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