C2 Another DOT 5 question

[Richard E.]

After reading as many of the forum comments I could find regarding silicone brake fluid, I did not find a clear response regarding successful flushing of DOT 5 fluid.

Has anyone successfully flushed silicone (DOT 5) from their C2 brake system and changed to DOT 3? If so, please share the process that was used.

The question above assumes the existing calipers, master, and hoses remained, and were not replaced with new parts.
Appreciate your comments. Thank you in advance.

[Owen L.]

Re: C2 Another DOT 5 question

I think just flushing with the DOT 3 is adequate. In my own testing with mixing DOT 5 w/DOT 4, nothing happened and the two liquids stayed separate – no jelling, as has been rumored would happen. You could flush with denatured alcohol and then the DOT 3 if you were particularly worried.

The thing is that with DOT 3 or 4, you should be putting new fluid through the system every couple years anyway, so any residual DOT 5 would get pushed out in the course of that maintenance.

[Ron K.]

Re: C2 Another DOT 5 question

I posed the same question to LoneStar last week. Flush with denatured alcohol, AND they highly recommend replacing the four rubber brake hoses. Said the silicone fluid (somehow) impregnates the rubber hoses.

[Richard E.]

Re: C2 Another DOT 5 question

Ron, Owen, thanks much for your input, very helpful. There is so much point / counterpoint written about this subject I found it difficult to draw a conclusion, but your comments provide good guidance.

[Patrick B.]

[Duke W.]

Re: C2 Another DOT 5 question

Most conversions are from DOT 3 or 4 to 5 not the reverse. This is the first time I've run across someone who wants to go the opposite way.

One thing to understand is that the two are not miscible and even if you can find the perfect solvent for DOT 5 you'll never be able to completely flush out all the DOT 5. Denatured alcohol? It's the solvent for DOT 3 or 4, but I don't know if it will work with DOT 5. You should experiment before you proceed.

If going from DOT 3 or 4 to 5 I recommend starting with everything clean and completely dry and that would require disassembling commercially rebuilt master cylinders, calipers/wheel cylinders because they are assembled with DOT 3/4 and reassemble using DOT 5. Flush out pipes with denatured alcohol and dry with compressed air. Do the same with brake hoses, including new because the swagged ends are usually are installed with DOT 3 as a lubricant. The bottom line is do everything possible to remove every molecule to DOT3/4 from the system, and if going the other way do the same with the DOT 5.

I advise the above because too many I've talked to who used the "bleed to flush" method to convert to DOT 5 ended up with problems. Perhaps they didn't sufficiently flush... don't know for sure.

One question I have is that if you have DOT 5 now, why do you want to go back to DOT 3 or 4?

Duke

[Owen L.]

Re: C2 Another DOT 5 question

I posed the same question to LoneStar last week. Flush with denatured alcohol, AND they highly recommend replacing the four rubber brake hoses. Said the silicone fluid (somehow) impregnates the rubber hoses.

If we assume the silicone does impregnate the rubber hoses, given its hydrophobic qualities, seems to me it would behave as a moisture blocker and would better protect the system. Kinda seems specious that the rubber could be impregnated with any fluid because that would be likewise detrimental with DOT 3 & 4 absorbing water and continuously exposing the fluid in the hose to moisture contamination.

I don't know... I tend to believe a lot of the warnings going to or from DOT 5 are rumor and not based on controlled testing. (I am just as guilty as I didn't test compatibility to any great extent, just my own curiosity of the jelling rumor.) This mindset is in large part due to those yellow labels warning about changes in DOT 5 chemistry when the citation had nothing to do with the chemistry.

[David P.]

Re: C2 Another DOT 5 question

I've been dealing with several brake issues recently and thought I'd share. Recently rebuilt several brake calipers using the NAPA 452/453 lip seal kits. As noted previously, they are EPDM and say right on NAPA's website that they are compatible with DOT 5. However, the issue I ran into with these seals is that they shrank once exposed to the DOT 5. When assembling you have to carefully fit the piston into the caliper as to not catch, bend or tear the seal and initially it provides the proper interference. However, once assembled for a day or two the seals shrink, enough that you can remove piston and reinstall without any interference from the seal. Finally switched to peroxide cured o-rings and no more issues.

[Richard E.]

[David P.]

Re: C2 Another DOT 5 question

Components do exist that work with DOT 5. Silicone based fluids are used in a lot of industries. Why is no one marketing it to us, because it’s a very small niche market. Modern cars can’t use it, ABS,etc. You’re only left with classic cars and race cars. If you walk into Autozone, O’Reilly’s, etc., you can’t even find DOT 5 on the shelf. Not to mention, DOT 5 is about 3x the price of DOT 3/4. As far as our industry, I think there are just too many instances of user error and the few companies that are left can’t afford to replace or return items or field constant questions/complaints about the nuances of DOT 5. Much easier to blame the brake fluid and just sell stuff that people can’t mess up.

I did have the recent issue, as noted above, with the NAPA EPDM lip seals shrinking, which I’m not sure exactly why that happened, was it DOT 5 or just old seals, who knows how frequently they turn over that part at NAPA. How many applications are there for those specific lip seals?

Convert to EPDM peroxide cured o-rings and you’ll be just fine with DOT 5. Just my 2 cents.

[Owen L.]

Re: C2 Another DOT 5 question

I have a ’66 roadster (with DOT 5 fluid) that recently developed a left front caliper leak. (The car has a dual master cylinder with power brake booster) Unfortunately, I do not know what type of caliper parts are on the car; original, stainless sleeved, O-ring, etc. or possibly a combination as I have never worked on the brakes.

I'm sure this is not a fail safe method to determine O-ring calipers, but...
It appears to me that the o-ring pistons are either blue or black anodized while lip seal pistons seem to be either silver or gold anodized. You can see the pad end of the piston without taking anything apart.

[Patrick B.]

Re: C2 Another DOT 5 question

In our previous discussion and tests in this forum, we proved that the Corvette suppliers claim that DOT 5 fluid has changed and will now affect "brake rubber" is false. We also read the EPA rule that they blame for this situation and that the EPA rule did not involve DOT 5 fluid. The mention of the EPA rule was simply for deception. But here is the bottom line:

WHAT CAN A CORVETTE OWNER WHO WANTS TO KEEP A DOT 5 SYSTEM DO?

First of all, he should not change to DOT 3 brake fluid and lose the advantages of silicone brake fluid. It is only the Corvette vendors that who maintain the disinformation that DOT 5 changed. If you want to buy lip seal rebuild kits for calipers or master cylinders, do not buy them from Corvette vendors. They are available from NAPA, Summit, Rock Auto and local auto parts stores without any warnings about DOT 5. Lip seals are made by large companies who know the brake business and use EPDM rubber which is compatible with DOT 5.

The rebuilt master cylinders and calipers with lip seals from the Corvette venders probably use lip seals from the same big companies. Despite the DOT 5 warnings, the seals are most likely EPDM and will work fine with DOT 5. The only master cylinder lip seal from Lonestar that we tested was in fact EPDM. If the DOT 5 warning on the box causes you anxiety, buy rebuild kits without the DOT 5 warning from an auto parts store and replace the seals in the Corvette venders product.

I believe the only products from the Corvette venders with an actual incompatibility with DOT 5 fluid are the o-ring type calipers and the o-ring piston rebuild kits. The supplier is a machine shop that makes very nice aluminum pistons but does not understand that the brake parts industry uses EPDM rubber as the standard material for seals.

Fortunately, we Corvette owners can have the benefits of o-ring calipers with DOT 5 brake fluid by simply replacing the inferior o-rings supplied by Corvette parts sellers with high quality peroxide-cured EPDM o-rings.

The o-ring sizes we need are standardized in a series called AS568 Standard Inch O-Rings. The front o-rings are size AS568-325 (nominal 1-1/2 ID x 1-7/8 OD x 3/16 CS) and the rear o-rings are size AS568-318 (nominal 1" ID x 1-3/8 OD x 3/16 CS). Use the AS568 sizes because the actual sizes differ from the nominal. For example, the section size is about 0.210" actual but 3/16" nominal. They cost of the largest o-ring is only $1.67 online at theoringstore.com

[Richard E.]

[Patrick B.]

Re: C2 Another DOT 5 question

Richard -- The brake pistons for the o-rings are different from the stock type pistons for the lip seals. The stock pistons have a groove for the lip seal that is conical (the bottom of the groove is slanted). The pistons for the o-rings have cylindrical grooves (a constant depth). If you want to use o-rings make sure you have the right pistons. I am afraid that David (comment #10) may have put o-rings on pistons for lip seals.

[Ed D.]

Re: C2 Another DOT 5 question

This has been mentioned before, but I think it is important to say it again, to avoid confusion. Don't confuse DOT 5 with DOT 5.1. DOT 5 is Silicone based and is completely different from the glycol based DOT 5.1. DOT 5.1 has very similar properties to DOT 3 & 4.
Ed