arcticdoggie

I’m restoring my C3 and replaced the entire brake system, lines, calipers and all. I’m thinking of using DOT 5 brake fluid cause in isn’t doesn’t absorb water and I hear it’s good for collector and vintage cars. Not that I’m not going to drive my c3, but it will sit over the winter’s.

i spoke to someone who said make sure I confirm that all the parts within the brake system can support DOT 5, other wise use the 5.1. As it’s compatible wit DOT 3 and 4 brake systems. He said it could deteriorate the rubber parts.

How can I determine if my parts can handle 5.0? My parts are from typical auto parts stores like advanced auto, etc.

interpon

Well the calipers i bought from a 2 seperate vendors ( assume lone star) warranted 2 of them and said other than DOT3 , no warranty. Just an fyi, saved me a few hundred bucks.
one warranted 8 months and the other 11 months 1 year warranty.

Rescue Rogers

I never had a problem with dot 3....how can water get in if it's a sealed system...just make sure it's full when you put the lid on....no leaks, no air, so no water.
I hope your new brakes are o ring vs lip seal so you dont have the usual lip seal leak/ air suck problems

67:72

I've been a nearly 40-year proponent of DOT 5 and had zero problems (with lip-seals to boot!). It's the seals in newly rebuilt components that may not be compatible with DOT 5. The fluid hasn't changed, but the type of rubber seal chosen by rebuilders has (going with the cheapest option for them?). What you want is EPDM, it's an old-school rubber that is compatible with all modern brake fluids, 3 and up. If you were to rebuild your own sleeved calipers, Raybestos seal kits are EPDM.

From what I hear, Lone Star is having some independent testing done to see about switching to EPDM so they can stop the warning about DOT 5 on their products. It wasn't until the last 10 years that rebuilders went with other seals – maybe that coincides with the o-ring offerings. I believe the o-rings are silicone which is absorbing the fluid and making them swelled and soft. EPDM o-rings are readily available, so it's not an availability issue with the rebuilders.

If your auto parts store components don't have the warning label, I'd use DOT 5 if desired. Although it's an extra step, you can convert to DOT 5 later without much more than a system flush. If you decide to go with non-DOT 5, make sure you are bleeding the brakes every couple years to put new fluid in the system as it absorbs water. (Something not required for DOT 5.)

MelWff

Since you have no way of knowing what seals were used in your brake components your choice is 4.0 or 5.1.

BBCorv70

FWIW, I used Dot 5 for many years with no issues until about 10 years ago when I refreshed my calipers with new seals. I had constant problems afterward, finally gave up and had to have calipers with o rings installed. We switched to Dot 5.1 from then on. It feels like something changed, either seals or formulation of the Dot 5 fluid. It seems safer to avoid Dot 5 now.

redwingvette

If switching from dot5 to dot5.1 do I need to flysh the system with anything or just use the dot 5.1 and push the old stuff out?

MelWff

Remove all fluid from the master, refill with the new fluid, and start bleeding all 6 bleed screws. Either gravity bleed or pressure bleed, no pedal pumps to avoid master cylinder seal damage.

theandies

I've been running DOT5 for years without any issues whatsoever.

4-vettes

.how can water get in if it's a sealed system...just make sure it's full when you put the lid on....no leaks, no air, so no water.
[/QUOTE]
AHHH, THIS IS JUST FLAT OUT WRONG! No system is sealed as well as you think! Moisture in the air can go right through hoses, seals, etc. Just because you can't see at a molecular level, doesn't mean it doesn't happen. I do moisture tests on brake fluid daily. Everytime, it's a sealed system. Most of the time the fluid fails to high moisture content.

I asked Mr. Google, tons of hits. Just a sample. Believing that your system is sealed and it's impossible for moisture to enter the system is just burying your head in the sand.

67:72

Just consider the piston seals. The dust boot only "grips" the upper ring of the piston; it's in no way a sealed connection. Road spray and puddle water will seep in past the dust boot/piston connection. Once inside the bore area, braking action sweeps the seal (lip or o-ring) over the moisture-exposed bore. Each back and forth of the seal pulls in minuscule amounts of moisture. I think this is where DOT 5 has an advantage. The moisture is repelled by the fluid and all of the coated surfaces rather than being absorbed (& pulled) into it like the ethylene glycol fluids (3,4,5.1). In brake hoses, the silicone fluid should act similarly by repelling moisture entering the material.

We know that standard fluids absorb moisture when breaking the container's seal – it's advised against using fluid from a container opened 12 or more months prior. The master cylinder cap has the same moisture exposing condition as an opened container.

4-vettes

Every service I do. It's mandatory to test brake fluid for moisture content. Ever since Harley went away from Dot 5 because of antilock brakes. The ABS servos are easily damaged by high moisture content in the brake fluid. Causing a VERY expensive repair.
So, on these HIGHLY sealed systems. We test for moisture at every service interval. And far more often than not. They fail with high moisture content in extremely well sealed systems.
I am a vehement proponent of DOT 5 brake fluid.
I will go to great lengths to continue to use it.
It does not draw in moisture. DOT 3 and 4 do.
No matter how "Sealed" you believe your system to be!
Get your head out of the sand. Wake up and smell the coffee.

Bikespace

If you want to use DOT 5, go ahead. I just hope you haven't missed one of these warnings, tucked into your new brake parts, and likely discarded with the invoice, parts catalog, and coupons. (From CSSB Inc.)

If you can't find someone to vouch for each component, o-ring, hose, and seal, you can test them all. It's the only way to be sure.

67:72

What that label fails to mention is the seal material. Why are brake rebuilders using non-compatible seals when EPDM is readily available? The label is misleading: The chemistry hasn't changed according to a recent test using modern DOT 5 fluids analyzed against 40 year old fluid. If you click on the .gov link it doesn't say a thing about this issue. It is merely a testing protocol with no results provided for anything.

I don't recall what the warranty period against leaking is... anyone?

Bikespace

I don't control the brake rebuilders, but at least CSSB Inc. tells you that the seals they use are NOT compatible with DOT 5. Unless you know for a fact that every seal IS compatible, there is a risk that new seals are not. If you've been using DOT 5 for 20 years with no problems, great! Keep doing that. If you just replaced all of your brake parts with new, offshore rebuilds that use unknown components, well, caveat emptor.

Here's the link from CSSB Inc. https://www.cssbinc.com/dot5warrantynew.01.pdf
I don't think the DOT 5 has changed, but for whatever reason, folks are not always using DOT 5 compatible O-rings. A lot of O-rings (for face-seal applications), place the mold seam at the equator. Our cars mostly need bore seal O-rings (except between the calipers). Perhaps it is easier, or cheaper, to make these from something other than EPDM.

I see lots of folks knowledgeable about O-rings point out how EPDM O-rings are readily available and work for our cars. I never see any part numbers, or places to buy them, nor do I want to spec them from McMaster Carr and hope for the best. Until proven otherwise, it's safer for me to assume all new brake parts are incompatible with DOT 5, and use DOT 4 instead. Or this BOSCH ESI6-32N fluid instead.

70vetteinpieces

I didn't see mentioned here is a fluid that doesn't absorb water - Where does the water go that gets in the system? Typically the lowest place in the line and that spot tends to rust from the inside out.
Takes longer but I have seen rusted out stainless steel lines

Eric P

As someone that works multiple different makes I always use what the Factory recommends which in this case would be DOT3 , if you are worried about moisture and drive everyday bleed them out every couple years , if you drive in flood waters then bleed them out much sooner

MelWff

what about DOT 4? Came out in 2006 so the Factory never knew about it when the C3 was designed.

67:72

I'm no fluid engineer or chemist, but my thinking is that since DOT 5 is hydrophobic it should behave as its own seal in the system. The bores are completely full of hydrophobic fluid that is coating everything within and helps block the moisture from entering further. When ethylene glycol fluids contact moisture, they essentially pull the moisture in to the system further.

Years ago, I believe someone here or on the NCRS forum challenged anyone to present a brake line, rusted from the inside out, in a DOT 5 system. As far as I know, nothing has ever been produced. Was the stainless line you referred to from a new or flushed DOT 5 system? If flushed, old ethylene glycol fluid might have remained in the low points from less than complete flushing, then that could be the cause of rust-through.

My goal here is not to convince anyone to use DOT 5 – it does have its drawbacks: high cost; not ABS compatible; not intended for racing.
I'm just trying to relay accurate information about it so that informed choices can be made.

Bikespace

Here's a related, similar thread from a year ago. Some of the same pictures, too!

https://www.corvetteforum.com/forums...id-please.html