DOT 5 compatibility testing of actual Lone Star brake seals

[Patrick B.]

[Gary B.]

Re: DOT 5 compatibility testing of actual Lone Star brake seals

Patrick,

I also think that the NOS GM rebuild kit I installed will perform fine with DOT-5. Once you told me the Lone Star rubber parts performed well, I kind of thought I shot myself in the foot by swapping them out. But your testing those seals gave us some valuable data.

Gary

[Joe L.]

Re: DOT 5 compatibility testing of actual Lone Star brake seals

I am sure the GM rebuild kit is fine with DOT 5. If it from 70’s, it is probably natural rubber or SBR rubber. FMVSS 116 requires that all brake fluid including DOT 5 are compatible with those kinds of rubber. Sometime later auto manufacturers began using EPDM rubber instead of the older types of brake seal rubber. The SAE standard that FMVSS 116 was based on was amended to include EPDM rubber in the compatibility test, but for some reason the FMVSS was never updated for EPDM compatibility, rendering it obsolete regarding material compatibility. Our tests showed that both old and new DOT 5 fluid was compatible with EPDM rubber, which is not surprising since the voluntary SAE standard requires compatibility of DOT 5 fluid with EPDM rubber. The myth that DOT 5 fluid had changed must have come from some problems with the non-EPDM o-rings, and believing their own myth, the Corvette brake suppliers applied this DOT 5 warning to brake parks with EPDM seals. I do not think these suppliers even know what kind of rubber is used in the seals they sell. That failing on their part is the problem we face and must solve on our own. They must think voiding the warrantee solves their problem even though compatibility with DOT 3 fluid is doubtful for the o-rings.

Patrick------


I think the curing process for EPDM has a lot to do with it. Quite some time ago I read somewhere that the major brake parts manufacturers had ceased using the curing process for EPDM brake parts. That might not be a problem when using DOT 3 or 4 fluid but could be a problem when using DOT 5.

As far as I'm concerned, peroxide cured EPDM brake parts is the only way to go whether using standard lip seals or o-ring seals.

[Patrick B.]

Re: DOT 5 compatibility testing of actual Lone Star brake seals

Patrick------


I think the curing process for EPDM has a lot to do with it. Quite some time ago I read somewhere that the major brake parts manufacturers had ceased using the curing process for EPDM brake parts. That might not be a problem when using DOT 3 or 4 fluid but could be a problem when using DOT 5.

As far as I'm concerned, peroxide cured EPDM brake parts is the only way to go whether using standard lip seals or o-ring seals.

[Gary B.]

Re: DOT 5 compatibility testing of actual Lone Star brake seals

... I am going to get some Lone Star or CSSB o-rings and test them in DOT 3 fluid. Any bets on the outcome?

[Patrick B.]

[Gary B.]

Re: DOT 5 compatibility testing of actual Lone Star brake seals

Patrick,

My bet is the O-rings will do fine in a DOT-3 test. But more tests will tell.

Gary

[Jim D.]

Re: DOT 5 compatibility testing of actual Lone Star brake seals

Going on 6 years with CSSB regular black O-Rings and DOT3 and have Zero issues.

[John D.]

Re: DOT 5 compatibility testing of actual Lone Star brake seals

Here is a very interesting SAE paper from 1981 on this topic. It deals mostly with the mixing of DOT 3 and DOT 5 in conventional brake systems with the conclusion that they play well together even at high mix rates on the vehicles tested. There is also data on the impact on swelling and hardness of the seals for both fluid types.

[Gary B.]

[Patrick B.]

Re: DOT 5 compatibility testing of actual Lone Star brake seals

I think the down side of not getting all the DOT 3 out is that any pockets of conventional fluid would still be subject to corrosion. Probably blowing out the lines and caliper halves with dry air and a wipe down is sufficient. It also appeared from this study that the only brake component rubber less compatible with silicone fluid than with DOT 3 was silicone rubber.