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Silicon DOT 5 Brake Fluid

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About 5 years ago I had leaking brake calipers and upon tear down I discovered the bores were pitted real bad because water had gotten into them. I sandblasted the bores then smeared J.B.Weld into them then honed them. They came out as good as new and I've had no more trouble with their seals leaking. But to prevent water from getting into them I made the switch to silicon DOT 5 fluid and began to have trouble 3 months later. All of my brake hoses had swelled up to the point where my brakes didn't work. I found out DOT 5 will severely swell the OEM hoses so I replaced them with the later J-1401 hoses and that took care of the problem.

How many of you have switched to DOT 5 fluid?
 

Tom Bryant

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My wife bought a gallon of NAPA United DOT 5 and converted her '81 just after she took delivery of it in October 1980. It's still in there with no problems so far after 35 years. Still clean in the master cylinder too. I have read that the DOT 5 available today isn't the same as the old stuff. Can't swear to that though. I used out of the same gallon when I converted my '69 C10 step side to disc brakes also.

Tom
 

Vettehead Mikey

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Leaking C2/C3 calipers have little or nothing to do with what type of brake fluid is used. Substituting DOT5 will not make the problem go away and may make it worse.

The water that causes corrosion has leaked past the outer dust seal and is trapped in the cavity between it and the piston seal. As the caliper is made of cast iron, pitting and corrosion is inevitable. As the brake pad wears, the piston and it's seal move to compensate, causing the seal to leak fluid as a result of travelling into the damaged area. Having shiny new fluid would not change any of this.

Although GM never re-engineered the basic caliper design 'flaw', the aftermarket stepped in about 35-40 years ago and started sleeving damaged calipers with stainless steel. Corrosion problem solved.

The basic issue of outer dust seals failing still remains. If the water migrates past the piston seal (not rare on cars with rotor runout) it will mix with the brake fluid. If this fluid is non-hygroscopic like DOT5, the water will remain in globules possibly accelerating corrosion in a non-SS lined caliper.
 

GTR1999

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I have heard the pros and cons of using DOT 5 for years. It seems to work great for some but I never used it and never recommend it.

As Mike said the cottage industry on sleeving corvette calipers exploded about 1978, some got very rich from it. However sandblasting and using JB Weld is not the proper procedure. The bores of the calipers should be bored oversize, a SS sleeve pressed in for an interference fit, then final honed to size to return the bore to stock dimension. Lip seals are fine to use, I know O Rings are one of the lastest band aids out there but if you have a good caliper, lips seals, RTV the outside seam on the dust boot to piston, use DOT3, get the bearing end play to 001-002" and the rotor run out to under 003" you will have a great brake system. Use a Motive bleeder for best results, although the old 2 man methods works too. I don't care for gravity or vacuum bleeders.

If you store your car for the winter and can get to it, pump the breaks a couple of times a month. For best results bleed them again when you pull it out of storage- Although I am not about 7 years behind on doing this to my own 72!

The rubber hoses will swell from the ID and close up over time, using DOT3 and I assume DOT5. This is not a new problem so if you do a brake job and the hoses are older then 7-10 years replace them and the copper washers on the fronts.

DON'T CHEAP OUT TO SAVE A BUCK WITH BRAKES. I personally would toss out those JB Welded calipers.
 

Antz81

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Although GM never re-engineered the basic caliper design 'flaw', the aftermarket stepped in about 35-40 years ago and started sleeving damaged calipers with stainless steel. Corrosion problem solved.

Even then they can still fail. I had to replace one due to it leaking out from between the sleave and the bore. It wasn't the first time the local corvette specialist had seen this.
 

kpic

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You scare me.

He really scares me.

The first problem would be getting all the brake fluid out of the bores. If all of the brake fluid's residue is not removed; there will be problems.

Every adhesive project requires good preparation to be successful. You can ensure J-B Weld will perform to its maximum when you prepare and use it according to the package instructions. You’ll also want to prep the area to be repaired. For best results, use a detergent or degreaser to first clean the surface. Then roughen it with a file or coarse sandpaper. This will help create a successful and long-lasting bond.
Know Your Bond


| J-B Weld


I'm afraid to ask how he removed all the brake fluid from the bores.

toobroke... never fails to astonish.

 

GTR1999

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Even then they can still fail. I had to replace one due to it leaking out from between the sleave and the bore. It wasn't the first time the local corvette specialist had seen this.

A lot of places are gone now, but some bad shops are still out there. There was one in FL a few years ago that had a bad rep for ripping off guys by selling the junk, like cores as rebuilt. The guys first name is Carl.

I have had SS calipers lock up from bad DOT 3 fluid that was like mud. The pistons were stuck in the bores.
 

kpic

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Even then they can still fail. I had to replace one due to it leaking out from between the sleave and the bore. It wasn't the first time the local corvette specialist had seen this.

Antz81
As Gary said poor quality machine work. A loose fit rather than a press fit.

One of my first design work orders was to sleeve a differential air cylinder in a porous aluminum casting. A press of .0015-.002 with an anaerobic sealer such as Loctite 518 worked quite well.
It sealed 120 PSI of air in both prototypes and early production units until the porosity was addressed by "doping" the aluminum pour at the foundry.

As it has been decades, I'd check on 518's heat range etc or see if there are more appropriate anaerobic sealers available.
 

Vettehead Mikey

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A lot of places are gone now, but some bad shops are still out there. There was one in FL a few years ago that had a bad rep for ripping off guys by selling the junk, like cores as rebuilt. The guys first name is Carl.

I remember one shop, might have been in FL also, that was using thin wall tubing barely suitable for decorative purposes never mind brake calipers. Scary stuff.
 

SVO

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In either the 1978 or 1979 Chevrolet Shop Manual, Chevrolet recommended, for the first time, sealing the piston to piston seal using RTV, a move I believe to help prevent moisture collecting in the caliper bores.

Back around 1980 -1981, I converted a 1978 to silicone brake fluid, and as far as I know, it still has silicone in it to this day. The car also received Vette Brakes sleeved calipers at the time of change over. When I sold the car, 2 quarts of silicone left over from the change over went with the car. The owner hasn't mentioned any brake problems, but I have recommended more than once that he should tear down the brakes and go thru them with new seals and hoses. Brakes shoes are not the only expendables in a brake system that need replacement from time to time. My only complaint with silicone brake fluid was that I never was able to get a rock hard pedal using the silicone fluid. Due to that experience with the '78, I have stayed with DOT 3 fluid on my other cars. As part of my brake maintenance, I bleed the brakes at least once every 1-1 1/2 years to flush out the calipers.

I also had heard back in the day that there was silicone fluid being sold as DOT 5 brake fluid that wasn't. The give away was it was being sold in unmarked quart bottles.

All my vettes (except for my '62) wear Vette Brakes sleeved calipers, and I have never had a problem with their calipers or other parts that they sell. I'm currently trying out their o-ring pistons in my '72 coupe but haven't enough seat time to form an opinion as which is better, the o-ring seal or lip seal.

Back in the '80's, there was a club member who repaired his calipers & master cylinder using JB Weld. His wife suffered brake failure at speed while autocrossing at Texas World Speedway. She & the car survived. His butt didn't after wife got thru chewing on it.

As far as rubber brake hoses go, I use the Russell DOT approved stainless steel brake hoses and have had good success with them.

Long post & Just my opinion, FWIW.
 
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The water doesn't enter because of bad seals but rather is readily absorbed into the older DOT 3 brake fluids IN THE RESERVOIR and then that water migrates to the lowest point; the calipers. But the DOT 5 fluid will only absorb about 1% of it's volume because it's non-hydroscopic. That's why the instructions always tell you to never leave a brake fluid container OPEN. And using J B Weld to repair pitted bores is not dangerous at all.

The use of RTV is recommended to prevent air from getting sucked in; not to prevent water from entering.
 
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Vettehead Mikey

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The water doesn't enter because of bad seals but rather is readily absorbed into the older DOT 3 brake fluids IN THE RESERVOIR and then that water migrates to the lowest point; the calipers. But the DOT 5 fluid will only absorb about 1% of it's volume because it's non-hydroscopic. That's why the instructions always tell you to never leave a brake fluid container OPEN. And using J B Weld to repair pitted bores is not dangerous at all.

The use of RTV is recommended to prevent air from getting sucked in; not to prevent water from entering.

It's funny how a topic that's widely known, proven and accepted in the Corvette community and has been for decades is apparently rocket surgery to some. Sorry to say, but your lack of knowledge has gone past been amusing or fun for debating, it's now at the point of being dangerous advice that some noob might just inadvertently follow.

Please look past your small empirical amount of data and do some real research as to how and why C2/C3 caliper bores corrode.

Contrary to your theory, moisture does not enter at the master cylinder. There's a collapsible diaphragm/bellows in the M/C cap that isolates the fluid from outside air. The only water that might enter would be during servicing when the cap is off. If moisture did enter, it would be absorbed uniformly by the fluid and not migrate and settle at the lowest point as you suggest. We would see corrosion in the master cylinder reservoirs possibly followed by M/C seal failure long before problems at the calipers were observed.

On the other hand, if the fluid was DOT5 and water was allowed to enter, it would not combine with the fluid and would settle at the lowest spot- as it would and does if it gets past the caliper seals.
 

Antz81

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Back in the '80's, there was a club member who repaired his calipers & master cylinder using JB Weld. His wife suffered brake failure at speed while autocrossing at Texas World Speedway. She & the car survived. His butt didn't after wife got thru chewing on it.

And using J B Weld to repair pitted bores is not dangerous at all.

Yes I can see how that wasn't dangerous. The brakes were only there to stop the car. Don't know why car manufacturers bother fitting them at all.:chuckle
 

GTR1999

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One thing to note, some of this thinking actually is carried over to some of the vendors out there. I could run down a list of things I find with arms, boxes, and diff's that others thought or just didn't care about doing that were outright dangerous. The fact someone thinks their particular repair is safe,when it's questionable at best, puts their own life in danger but also that of many others on or near a road the car is on.
One case in point is with a well known Texas rebuilder who purposely installs worn out worm gears in steering boxes - upside down and sells them to guys every freaking day.
 

SVO

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I know who in Texas you are talking about Gary & have never bought or used any thing that they sell.

I think the saying "Just because you can doesn't mean you should" applies here. If JB Weld was a safe & approved brake caliper repair method, there would have been an magazine article covering it published sometime over the past 40 years. As members of the hobby & this forum, we should only be passing on advice that is safe and sound for a less knowledgeable person to follow.

Sorry for going off topic here. Again, just my opinion, FWIW.
 

GTR1999

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Actually there are at least 2 places in TX I would be concerned about - maybe 3. All I can say is check the parts or rebuilds you get. This has nothing to do with TX either, my buddy was just up here from TX and thinks I should move there.
 
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And somebody please explain to me why using a high temperature/high strength epoxy to fill in rust pits is dangerous. I would love to hear what you have to say.
 

Vettehead Mikey

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And somebody please explain to me why using a high temperature/high strength epoxy to fill in rust pits is dangerous. I would love to hear what you have to say.

Since you have not addressed the root cause of the problem (water ingress past the seal) then the corrosion will continue, most likely causing the specks of epoxy to dislodge, potentiality leading to a sudden, massive leak from the caliper.

Your 'fix' would be acceptable as a short term band aid just to get a person home. Nothing more.
 
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Since you have not addressed the root cause of the problem (water ingress past the seal) then the corrosion will continue, most likely causing the specks of epoxy to dislodge, potentiality leading to a sudden, massive leak from the caliper.

Your 'fix' would be acceptable as a short term band aid just to get a person home. Nothing more.


The moisture enters the system at the master cylinder and always has. The moment you unsnap the lid moisture instantly gets absorbed by the DOT 3 and once absorbed it'll travel to the lowest spot; the calipers. That's why it's recommended brake fluid containers should never be left OPEN. Also all of the master cylinders now days have clear reservoirs so you can see the fluid level without having to remove the cap. The higher the humidity is the faster water gets absorbed by the DOT 3 and that's why the DOT 5 is more desirable for cars that don't have anti-lock brakes. But DOT 5 must be used with the later J-1401 hoses because it'll severely swell the earlier hoses. When I switched over in my '71 my rear brakes quit working within 3 months because the hoses had swelled shut. The use of RTV is to prevent rust from forming in the outside end of the bores; not the fluid side.
 

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