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The 30k service calls for a brake fluid flush. I had my dealer do it while they were replacing the transmission. Anyone know why this needs to be done at 30k and 10 months? Anybody else have this done?
 

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Pretty routine for most vehicles. My Nissan Xterra is every 20K miles.
Over time, air contact ruins brake fluid. Apparently enough air can make its way into the system/reservoir etc that it needs to be flushed.
i have the setup to do this myself, but don’t really have the time anymore. I think it’s just over $100 to have done a la cart.
EDIT: Water, not air, gets into the fluid over time.
 

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Brake fluid is hygroscopic, i.e. it absorbs water. Over time, this water absorption can lower the boiling point of the fluid. As we all know, water boils at 212 degrees F, whereas pure brake fluid typically won't boil until it reaches over 400 degrees F.

If brake fluid should ever boil during heavy usage where the brakes become very hot, air bubbles can form in the lines. Unlike fluid, air is readily compressible which would considerably weaken the hydraulic force required by the braking system to operate properly. Your brakes could become spongy or fail completely. So you definitely don't want brake fluid contaminated with water. Water can also cause rust to form.

30,000 miles is a good interval to change the brake fluid to ensure water absorption does not cause issues. If you have the proper tools and knowledge, you can do it yourself for very little cost. If you don't, it's worth the cost to have someone else do it to properly maintain your braking system. Never go more than 45,000 miles or 2 years before changing the fluid and always use the brake fluid the manufacturer recommends because not all types are compatible.
 

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I am thinking a brake fluid flush on an Ascent should be pretty simple. Does anyone know the recommended sequence or where I can find it? Thanks!
 

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Brake fluid is hygroscopic, i.e. it absorbs water. Over time, this water absorption can lower the boiling point of the fluid. As we all know, water boils at 212 degrees F, whereas pure brake fluid typically won't boil until it reaches over 400 degrees F...
That's actually why hygroscopic fluid is used. If water got into the brakes system and didn't mix with the fluid, it would boil at 212F. As it is, it mixes with the brake fluid and only slightly depresses it's boiling point.

Years ago I had an experience with that very thing on a motorcycle running DOT5 (silicone, not miscible with water). Lost the front brake when it heated up and the lever just went to the bar. Fortunately I had enough space to run out and use the rear brake to not crash.
 

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I am thinking a brake fluid flush on an Ascent should be pretty simple. Does anyone know the recommended sequence or where I can find it? Thanks!
Unless you're over 30,000 miles already, I think it's too early for a change. But it won't hurt to change it early.

For full instructions, it depends upon which maintenance equipment you have. If you have a pressure type brake system bleeder use this video:


If you have a vacuum type brake system bleeder use this video:


If you don't care for either of these, there are many more available on YouTube.

The sequence is usually to start from the wheel farthest away from the master cylinder and then work your way to the closest. For typical US cars that's usually (but not always) RR, LR, RF, LF.
 

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That's actually why hygroscopic fluid is used. If water got into the brakes system and didn't mix with the fluid, it would boil at 212F. As it is, it mixes with the brake fluid and only slightly depresses it's boiling point.

Years ago I had an experience with that very thing on a motorcycle running DOT5 (silicone, not miscible with water). Lost the front brake when it heated up and the lever just went to the bar. Fortunately I had enough space to run out and use the rear brake to not crash.
Good info.
 

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Page 456 says never mix DOT 3 and DOT 4 brake fluids, then page 489 lists both types as compatible.
My question is which fluid comes from the factory so I can replace it with the same?
 

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Page 456 says never mix DOT 3 and DOT 4 brake fluids, then page 489 lists both types as compatible.
My question is which fluid comes from the factory so I can replace it with the same?
I am away so I can't verify myself, but I would first look on the power steering reservoir cap. I suspect that will tell you for sure.
 

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^^ I’ve always wondered what the shelf-life is after opening the can. It’s crazy dry here in CO was usual, butIve heard many people say you never want to put “old” DOT4 in. What’s old? How does one tell when to toss the can?
 

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@BroDoze with the number of brake flushes I do (very few), I plan on disposing of any extra fluid when the job is done. If its sealed and unless you contaminate the fluid it should last a while. The fluid in your reservoir is also vented so its not like the fluid immediately goes bad.
The fluid in the system is only as good as the worst fluid added. If you flush with 2-yr old leftover fluid then its almost pointless to do the flush. If you replace a caliper and need to top off the reservoir, adding more of the same batch probably wont hurt.
 

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Brake fluid is contaminated by more than just moisture while in use. Maybe you notice older cars have what looks like dark fluid in the master cylinder. That's contaminatin from rubber seals breaking down. Personally, I think more harm us caused by home mechanics doing their own brake flush than is gained with having fresh fluid because they usually do the flush by pumping brakes and over using the stroke of the master cylinder. Moisture is probably near the cap since it's vented. Rust or corrosion is also concentrated at that area just beyond the working stroke of the cylinder's piston. Pumping the brakes to flush causes seals to wipe this portion of the master cylinder and either wear on it or tear it outright. When that happens, a rebuild of the master cylinder will be required. Either that or replacement outright. Either let a ship do it using a pressure feed of fluid to the master, where the calipers are opened and a lot of fluid is allowed to flow without pumping brakes, or leave well enough alone until signs of brake fade Indicate service is actually needed.
 

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I’ve always tossed the can once I flush the car - guess I lol keep doing doing that. I can never seem to get all the vehicles on a simultaneous flush cadence. Also I use the pump bottle to perform the flushes. Makes it super easy/fast/thorough.
If only the rest of the brakes were as easy. I really hate pad n caliper work.
I’d rather (and have) swap full suspensions/struts/springs over any brake work. Hate brakes.
 

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Brake fluid is contaminated by more than just moisture while in use. Maybe you notice older cars have what looks like dark fluid in the master cylinder. That's contaminatin from rubber seals breaking down. Personally, I think more harm us caused by home mechanics doing their own brake flush than is gained with having fresh fluid because they usually do the flush by pumping brakes and over using the stroke of the master cylinder. Moisture is probably near the cap since it's vented. Rust or corrosion is also concentrated at that area just beyond the working stroke of the cylinder's piston. Pumping the brakes to flush causes seals to wipe this portion of the master cylinder and either wear on it or tear it outright. When that happens, a rebuild of the master cylinder will be required. Either that or replacement outright. Either let a ship do it using a pressure feed of fluid to the master, where the calipers are opened and a lot of fluid is allowed to flow without pumping brakes, or leave well enough alone until signs of brake fade Indicate service is actually needed.
There's no need to pump the brakes, anyone can buy their own pressurized brake bleeder for under $60. This is the one I've used for many successful brake jobs over the past decades.
 

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I think most uses DOT 4 which is synthetic (not mineral/dino) fluid and it likes to absorb moisture. The fluid has potential to be acidic and cause pitting in valves and stuff...
 

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The 30k service calls for a brake fluid flush. I had my dealer do it while they were replacing the transmission. Anyone know why this needs to be done at 30k and 10 months? Anybody else have this done?
I just completed the replacing the brake fluid at 28,000. Nothing wrong with my brakes but 30,000 was coming up and my dealer had 25% off. "The primary reason brake fluid should be flushed periodically is because it is a hygroscopic fluid, meaning that it readily absorbs and retains moisture. Though this might seem a bit odd at first glance, that is exactly what we want the brake fluid to do. With the understanding that many of the brake system components are made from metal, we can quickly see that moisture is the enemy. Brake fluid, by absorbing any moisture that gets into the system and retaining it, helps to prevent moisture related corrosion and failure of internal brake system components. Even the highest quality brake fluid can only retain so much moisture, however, so it periodically must be flushed from the system and replaced with new fluid. "

"A good general rule of thumb on the frequency for having your modern vehicle’s brake fluid flushed is to have it done every two years, especially on those vehicles equipped with antilock braking systems. Years ago, prior to the advent of antilock brakes, flushing the brake fluid was not as much of a concern. The more intricate fluid circuitry of the hydraulic control units on today’s antilock brake and traction-control equipped vehicles are much more sensitive to moisture and small particulate debris. Additionally, the actuation of these systems during braking or traction controlled events generate heat which further contributes to the breakdown of the brake fluid. With the potential of vehicle safety concerns and brake system repairs that could cost hundreds of dollars, the money spent on a brake fluid flush every two years is well worth the peace of mind. "
 
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