Dot 5 Fluid and CSSB Warning

[Jeff B.]

I was ordering a new Master Cylinder today from CSSB and notice that they now have warning that you will void you warranty if you use DOT 5 fluid. There is also a link to a rubber seal test that shows a dramatically expanded seal after being immersed in in DOT 5 fluid the 70 hours at 248 Deg F, as compared to a seal immersed in DOT 3 fluid for the same time and temperature which has not expanded. I called them and they said the manufacturer did a private test and they claim new chemical regulations may create problems for DOT 5 fluid. An SAE standard is referenced in the test, which I looked up and the standard relates to the stability of rubber brake seals between the temperature of -40 and 248 deg, so they are conducting the test at the upper temp limit for a long period of time. I can't find any supporting information about this on the internet, in fact DOT 5 is said to have compatibility with all rubber seals that are compatible with DOT 3&4.

I have used DOT 5 fluid for years in several cars without problems of any type and love that it does not take on water or dissolve paint. Has anyone experienced rubber seal problems with DOT 5? I'm thinking of ignoring the warning it since I already have DOT 5 in this car.

[Keith B.]

Re: Dot 5 Fluid and CSSB Warning

Just how hot does the system get under normal driving

[Jeff B.]

Re: Dot 5 Fluid and CSSB Warning

Just how hot does the system get under normal driving

My car has drum brakes, so I would think the wheel cylinders would get warm on the backing plate but no where near 248 degrees. The M/C won't get any hotter than the air under the hood so maybe 150. Plus, not for 70 HOURS at once. The test seemed silly to me, but it did show a big difference in the seals with the two fluid types under extreme conditions. I would like to see the same test with normal operating temps. Maybe this test shows you should not use DOT 5 for endurance racing! But I think we already know that. Or maybe they are using cheaper seals?

[Keith B.]

Re: Dot 5 Fluid and CSSB Warning

On anther forum it was stated that the military has been using Dot 5 for decades on all there vehicles. Wonder if that is true and if so what specs there seals are.

[Jeff B.]

Re: Dot 5 Fluid and CSSB Warning

I saw something that said the military is trying to move away from it, but I don't know why. I just find it very strange that with all the required testing and standards this would suddenly happen. You would think there would be a recall or something. Check out the CSSB website and click on the test results on the upper left of the home page. Maybe I will put some seals in DOT 5 and leave it out in the direct sunlight for a few days.

[Jeff B.]

Re: Dot 5 Fluid and CSSB Warning

FYI, here is a link to the test results: http://www.cssbinc.com/dot5warrantynew.01.pdf

[Terry M.]

Re: Dot 5 Fluid and CSSB Warning

I was ordering a new Master Cylinder today from CSSB and notice that they now have warning that you will void you warranty if you use DOT 5 fluid. There is also a link to a rubber seal test that shows a dramatically expanded seal after being immersed in in DOT 5 fluid the 70 hours at 248 Deg F, as compared to a seal immersed in DOT 3 fluid for the same time and temperature which has not expanded. I called them and they said the manufacturer did a private test and they claim new chemical regulations may create problems for DOT 5 fluid. An SAE standard is referenced in the test, which I looked up and the standard relates to the stability of rubber brake seals between the temperature of -40 and 248 deg, so they are conducting the test at the upper temp limit for a long period of time. I can't find any supporting information about this on the internet, in fact DOT 5 is said to have compatibility with all rubber seals that are compatible with DOT 3&4.

I have used DOT 5 fluid for years in several cars without problems of any type and love that it does not take on water or dissolve paint. Has anyone experienced rubber seal problems with DOT 5? I'm thinking of ignoring the warning it since I already have DOT 5 in this car.

Jeff

Several decades ago I did some research on DOT 5 before converting my 1970 to that fluid. I got several SAE publications on that subject. One of those publications cited military experience with mobile equipment stored for years in the Canal Zone. The temperature and humidity conditions were extreme; but no where near 248*F. The short take was that DOT5 was superior to polyglycol fluids in all respects, and no swelling of rubber components was observed.

I was told that Harley Davidson uses (or did use) DOT5 in their motorcycles. That is old information, and I don't know if it is still true.

I have had DOT5 in my 1970 for going on 4 decades and have had absolutely no issues -- passed PV and Founders award back about 3 decades ago. I changed the DOT5 just for S&G after about 20 years. I installed the DOT5 when I rebuilt the brakes; so I thoroughly flushed the system of polyglycol fluid. The master was rebuilt with a GM rebuild kit as were all the calipers after stainless steel sleeves had been installed in the calipers. The DOT 5, which I still have a supply of (none for sale), came from the 1970s.

I usually don't like to cite anecdotal information, but the following comes from people I respect and who have no dog in this race. I have been told by others in the hobby (for some of us it still is a hobby) that the brake system seals are not made from the same material now days as they were 40 years ago. I have also been told that the DOT5 of today is not the same as that of 40 years ago. I can not vouch for the veracity of either of those statements. The same people as told me the above also cited difficulties with DOT5 and more recent seals (I don't know the source of their seals), and they refuse to use DOT5.

I can believe the material of the brake system seals has changed over the years (what product hasn't), but I have a hard time believing DOT5 has changed, but who knows.

Thanks for listening to my nickle on this subject.

[Thomas S.]

Re: Dot 5 Fluid and CSSB Warning

DOT5 fluid (silicon based) is not compaitble with certain types of rubber compounds which include most rubber compounds used in the break systems of very old vehicles. So its the combination of the type of fluid AND what it comes in contact with. There are are also water-absorption differences between DOT5, which is silicon based, and DOT2, 3, 4 AND 5.1. DOT5 does not absorb water which is why it hase a much higher temperature rating. DOT 5.1 contains siicone (70%) but is formulated to be compatible accross a wider range of rubbers and has the same temperature rating as DOT5.



Below is an excerpt from an article which is very detailed and will put you to sleep. http://www.buckeyetriumphs.org/techn...luid/Fluid.htm

EXCERPT

Another one ......
Rubber swelling additives must be mixed with silicone fluid to make the seals work properly. These additives are compatible only with EPDM rubber. When silicone is used with SBR rubber, the rubber swells too much and becomes too soft to seal against the brake line pressure. Most drum brakes still use SBR seals.
Silicone fluids of the 1972 era were reported to be compactable with SBR seals and current sources indicate that current silicone fluids are still compatible with all rubber formulations used on brake system seals.
This one is from a Land Rover site
Be careful not to mix the 2 different kinds. When "upgrading" to DOT5 brake fluid you should pay attention to some important points. First off all make sure ALL rubber components you use in your brake system are DOT5 ready. Older rubber parts will be eaten away by DOT5. Secondly flush your brake system thoroughly. Better renew all parts.

[Jeff B.]

Re: Dot 5 Fluid and CSSB Warning

Well that makes a lot more sense. Its possible that what CSSB's supplier is trying to say is the rubber seals THEY NOW USE are not compatible with DOT5 fluids. It interesting they are attributing it to the change in fluids - and I see no evidence that has happened. I know some rebuilders will send you a DOT 5 ready M/C that has been assembled using DOT 5 as assembly lube.

[Jeff B.]

Re: Dot 5 Fluid and CSSB Warning

Thanks for the info Terry. Check out Thomas Sutcliff's response - I think he may be onto something with the different rubber compounds. Maybe this is a result of them testing the seals they are not getting from their supplier.

[Thomas S.]

Re: Dot 5 Fluid and CSSB Warning

One more important point is that rubber is used throughout the brake system so each component part would potentially be affected, hoses, cylnders, calipers, etc.

[Jeff B.]

Re: Dot 5 Fluid and CSSB Warning

Its is interesting that the SAE standard states that DOT 5 fluid is (and must be) chemically compatible with all brake system rubber parts that are compatible with DOT 3&4 fluids. What you are saying is that this is not the case. Typically meeting these SAE standards and millspecs takes a lot of testing by the manufacturers and you would think that DOT 5 fluid would have to have a warning stating "not compatible with some brake system rubber parts". I have not seen any legal action or even any indication on product literature that there is an incompatibility with any rubber parts in the brake system. That being said, it makes sense that silicone brake fluid may need a seal expanding agent to seal correctly and that may be a problem.

[Rick G.]

Re: Dot 5 Fluid and CSSB Warning

Hi Jeff,

I recently purchased a complete brake kit from a competitor of CSSB's. They also said they would not honor their warranty if Dot 5 was used citing the make up of Dot 5 has changed.

Rick

[Jeff B.]

Re: Dot 5 Fluid and CSSB Warning

HI Rick
The CSSB site has a document that says something similar with a link to a new EPA regulation. But when you go read the EPA ruling it concerns glycol based fluids not silicone fluids so it does not seem relevant. By virtue of having a DOT label, DOT 5 fluid MUST be compatible with any rubber seals that are also compatible with other DOT approved brake fluids. That's why the standard exists. In this case I'm starting to wonder if the problem - if one really exists - is the rubber being used by the manufactures of reproduction parts. I sent CSSB an email asking if their seals meet the SAE J-1603 test requirements for brake seals. They are a good company in my experience so it will be interesting to see their response. I have been using DOT 5 for years and it states on the container that it's compatible with SBR, neoprene, EP, and natural rubber seals. Funny, silicone is used as a rubber lubricant everywhere and I have never seen it react with anything.

[Thomas S.]

Re: Dot 5 Fluid and CSSB Warning

Agree. The answer to this question rest with CSSB's explanation as to why the product is not DOT5 compatible.