Brakes broke

[fstued]

I was just going to the shopping ctr yesterday morning everything worked fine on the freeway but as aI went to get off I put my foot to the floor on the brake I pumped and pumped and manged to bring it to a stop made my turn into the ctr which was empty and tried to stop and coast right thru managed to stop in the next spot Gklad the place was empty.
Called a tow truck who took it to my mechanic that I have used for years. He checked it out the next day and everything worked fine. He did find one brake was a little low and is fixing that and changing out the fluid but per him everything should be working and he found nothing wrong that would con tribute to the failed breaks.
Does any one have a clue on what might have gone wrong with the breaks the mechanic thought maybe a sleeve slipped in the master cylinder. I guess we'll see tomorrow when I pick it up

[Bruceper]

Sounds like you boiled your brake fluid. Flush with clean fluid that is a step up from what currently is in your vehicle. Alternatively just use DOT5.1 fluid which is the highest temperature rated brake fluid.

[booster]

Originally Posted by Bruceper

Sounds like you boiled your brake fluid. Flush with clean fluid that is a step up from what currently is in your vehicle. Alternatively just use DOT5.1 fluid which is the highest temperature rated brake fluid.

I would agree on the boiled fluid, those are the classic symptoms. Since you weren't using the brakes, something else got them hot enough to boil the fluid. It could have been exhaust shield that fell of by a brakeline or any heat source. The most likely is that a caliper was stuck and the brake dragging and getting hot enough to boil the brake fluid in the cylinder.

If the brake fluid hadn't been changed recently it could be full of water which will lower the boiling point a whole bunch, making boiling much more likely. Current recommendations are to flush and replace the brake fluid every 2-3 years.

I am not a fan of the Dot5 silicone fluids for numerous reasons, so usually use Dot 4, which is normal chemical brake fluid but has a higher boiling point. I notice a lot of new cars are starting to use it, also.

If you don't find a stuck caliper or other assignable cause, there is also a chance that it could be the master cylinder or booster if your van uses one (newer Chevies don't). Stuck check valves in either can cause what you saw, also.

[Bruceper]

Dot 5.1 is the same as 2, 3 and 4 but with higher boiling temperatures. Dot 5 is the synthetic stuff that causes issues.

[booster]

Hadn't run across the 5.1, looks Motul is the major, maybe only? supplier?

Interesting that Wildwood makes a Dot 4 with a higher wet boiling point than the 5.1 Motul.

[fstued]

I don't think it was the brake fluid boil because I didn't ride them or do anything to get them hot but if a caliph stuck or something other strange occurrence happened it could be the problem.
The mechanic hasn't found the cause yet but we are changing fluids and inspecting the master cylinder.

[BBQ]

Originally Posted by fstued

I don't think it was the brake fluid boil because I didn't ride them or ....

YOu missed the whole point everybody has been telling you -- you don't need to ride your brakes to boil the fluid.

[D&J Phillips]

I'm not a professional mechanic but I have maintained and raced my Austin Healey 100-6 for ~20 years and this does not sound like boiled fluid to me for a couple of reasons.

You don't say what vintage or make rig you have, but since the early '70s most all vehicles sold in the US have had dual circuit brakes, one circuit for the front and one for the rear. If you had a stuck caliper and boiled fluid, the other circuit would theoretically not be affected and you would still have brakes, possibly a little spongier and softer, but still be able to stop.

Second reason is that you say your mechanic checked it the next day and everything was fine.....Boiled fluid means there are small air bubbles in the fluid that will compress (fluid can't compress) and those bubbles won't go away by themselves, so, unless your mechanic changed the fluid (bled), it would not be 'fine' the next day.

One possibility is that you were low on fluid and sucked in some air when you applied the brakes leaving the highway. If so, there may be signs of seepage (wetness) somewhere in the system. Also, fluid levels can also go down as pads and shoes wear because the pistons have further to go to apply brakes.

Was the fluid level low when your mechanic checked it the next day?
If not, then I would suspect an internal failure in the master cylinder, since both circuits seem to have been affected. Most master cylinders have internal valves that allow fluid to enter the cylinder from the reservoir and then close when the brakes are applied to force the fluid out the lines to the wheels rather than back into the reservoir. I this valve is stuck or otherwise failed, it could cause the symptoms you describe. (may be what your mechanic was talking about when you said something about a 'sleeve' in the master?)

Brakes are not something to go cheap on. I would recommend a complete rebuild/condition check of master, wheel cylinders, calipers, flex lines, pads/shoes, drums/rotors - the whole enchilada. I don't know where you are located but here in the Northwest we have a chain of tire stores, Les Schwab, that can handle our vans and gives lifetime warranty so you only pay once (and free system checks anytime you are concerned). That was the first thing I did with our 1999 Xplorer when we bought it in 2014.

Hope this helps,
Dave

[Porsche911]

Originally Posted by fstued

I was just going to the shopping ctr yesterday morning everything worked fine on the freeway but as aI went to get off I put my foot to the floor on the brake I pumped and pumped and manged to bring it to a stop made my turn into the ctr which was empty and tried to stop and coast right thru managed to stop in the next spot Gklad the place was empty.
Called a tow truck who took it to my mechanic that I have used for years. He checked it out the next day and everything worked fine. He did find one brake was a little low and is fixing that and changing out the fluid but per him everything should be working and he found nothing wrong that would con tribute to the failed breaks.
Does any one have a clue on what might have gone wrong with the breaks the mechanic thought maybe a sleeve slipped in the master cylinder. I guess we'll see tomorrow when I pick it up

I recently had a similar experience after leaving the freeway and trying to stop at he stop sign at the bottom of the freeway off ramp, fortunately home was not far away and the brakes recovered, I did have the brakes inspected shortly after purchasing the van and was told the brakes were in good condition, I have not as yet taken it to a brake shop to investigate further but will note the result when the visit is complete.
Thanks for everyone's views on here.