Leaking Front Caliper

[Timothy B.]

Re: Leaking Front Caliper

Joe,

Why do these calipers require new pistons, I rebuilt the vette brakes stainless calipers on my 67 with new seals only and now seven years later there is leakage again. I never noticed anything wrong with the pistons but would like to know what to look for when I fix-em..

Also used silicone fluid..

[Patrick H.]

Re: Leaking Front Caliper

Joe,

Why do these calipers require new pistons, I rebuilt the vette brakes stainless calipers on my 67 with new seals only and now seven years later there is leakage again. I never noticed anything wrong with the pistons but would like to know what to look for when I fix-em..

Also used silicone fluid..

If there is any corrosion of the aluminum piston at all - ANY - then they need to be replaced. You can't stop the corrosion once it starts.

FYI, according to a couple of the major Corvette brake rebuilders most Corvette brakes leak from lack of use. Using them actually helps the seals to work better.

Patrick

[Jim T.]

Re: Leaking Front Caliper

What causes the corrosion of the pistons in the calipers?
I would speculate that moisture in the system combined with DOT3/4 brake fluid. DOT3/4 is hydorscopic.
Would the same corrosion affect aluminum pistons if DOT5 silicone fluid is used? In a clean system to start with and silicone fluid not absorbing moisture like DOT3/4 would caliper pistons still corrode?

[Timothy B.]

Re: Leaking Front Caliper

Patrick,

I bet that's my problem, not enough use. I don't recall any problems with installing new seals and the stainless inserts were fine. I was suprised to find them wet.

I want to install new pads and power brakes for this car.

[Patrick H.]

Re: Leaking Front Caliper

What causes the corrosion of the pistons in the calipers?
I would speculate that moisture in the system combined with DOT3/4 brake fluid. DOT3/4 is hydorscopic.
Would the same corrosion affect aluminum pistons if DOT5 silicone fluid is used? In a clean system to start with and silicone fluid not absorbing moisture like DOT3/4 would caliper pistons still corrode?

Depends where / if there is any moisture in the system.
It's hard to "totally" clean it out, but I suspect that it's less likely with silicone.

[Michael W.]

Re: Leaking Front Caliper

What causes the corrosion of the pistons in the calipers?
I would speculate that moisture in the system combined with DOT3/4 brake fluid. DOT3/4 is hydorscopic.
Would the same corrosion affect aluminum pistons if DOT5 silicone fluid is used? In a clean system to start with and silicone fluid not absorbing moisture like DOT3/4 would caliper pistons still corrode?

If moisture is allowed to enter, it won't make much difference what type of brake fluid is used. Choose your poison.

[Joe C.]

Re: Leaking Front Caliper

Dot 3/4 brake fluid is hygroscopic..............Dot 5 is not.

[Michael W.]

Re: Leaking Front Caliper

That simply means that the water will sit in puddles rather than being mixed. End result is still the same. Keeping the system sealed is the key.

[Dennis D.]

Re: Leaking Front Caliper

My .02

Been around the block with this issue for many years. Finally installed a kit from ZTI, who developed the o-ring design. Nice guy, I want to say Mike. He told me if the bores could be honed not to SS sleeve. I listened, honed and still no issues with my original calipers. Believe he sold to an outfit in Florida years ago.

FWIT.... my original calpers had very small matching numbers stamped into each halve on the top flat area somewhere. very hard to see. Search the archives if you're interested. I believe Sal Carbone had an explanation, or someone will cime in.

[Joe C.]

Re: Leaking Front Caliper

That simply means that the water will sit in puddles rather than being mixed. End result is still the same. Keeping the system sealed is the key.

Not so. Hygroscopic materials have an attraction to moisture, and so will draw moisture from the atmosphere. Non silicone brake fluids are hygroscopic. Boiling points increase as DOT numbers increase, but any moisture in the system will flash before the working fluid will.

Neither Dot 3, 4, 4+, or 5 are miscible with water, so water will separate out from any of them. Any water in the system usually does the most damage and causes problems when it attacks the anodized aluminum caliper pistons, almost always within the seal groove. This is not salvageable and always requires replacement.

[Terry M.]

Re: Leaking Front Caliper

Not so. Hygroscopic materials have an attraction to moisture, and so will draw moisture from the atmosphere. Non silicone brake fluids are hygroscopic. Boiling points increase as DOT numbers increase, but any moisture in the system will flash before the working fluid will.

Neither Dot 3, 4, 4+, or 5 are miscible with water, so water will separate out from any of them. Any water in the system usually does the most damage and causes problems when it attacks the anodized aluminum caliper pistons, almost always within the seal groove. This is not salvageable and always requires replacement.

Joe,

I find it hard to believe glycol based brake fluids are not miscible with water based on my experience disposing of them. When diluted with water for disposal down a sanitary drain the resultant mixture appears as a whitish fluid with no discernible fluid separation. Also from Wikipedia:

"Any system that has used glycol based fluid will contain moisture, glycol fluid disperses the moisture throughout the system and contains corrosion inhibitors. Silicone fluid does not allow moisture to enter the system, but does not disperse any that is already there either. A system filled from dry with silicone fluid, does not require the fluid to be changed at intervals, only when the system has been disturbed for a component repair or renewal. The United States armed forces have standardised on silicone brake fluid since the 1990s." I added the bold to the quote and there is much more to the Wiki post..

http://en.wikipedia.org/wiki/Brake_fluid

Of course we all know you can't believe anything you read on the Internet.

[Joe C.]

Re: Leaking Front Caliper

Joe,

I find it hard to believe glycol based brake fluids are not miscible with water based on my experience disposing of them. When diluted with water for disposal down a sanitary drain the resultant mixture appears as a whitish fluid with no discernible fluid separation. Also from Wikipedia:

"Any system that has used glycol based fluid will contain moisture,glycol fluid disperses the moisture throughout the system and contains corrosion inhibitors. Silicone fluid does not allow moisture to enter the system, but does not disperse any that is already there either. A system filled from dry with silicone fluid, does not require the fluid to be changed at intervals, only when the system has been disturbed for a component repair or renewal. The United States armed forces have standardised on silicone brake fluid since the 1990s." I added the bold to the quote and there is much more to the Wiki post..

http://en.wikipedia.org/wiki/Brake_fluid

Of course we all know you can't believe anything you read on the Internet.

Terry,

You must still be using that benzene laced Perrier water from 1990.

Joe

[John H.]

Re: Leaking Front Caliper

Neither Dot 3, 4, 4+, or 5 are miscible with water

Nope. 3 & 4 are miscible with water. DOT5 is not, so moisture collects in "puddles" at the low points in the system with DOT5 rather than diluting the fluid like 3&4 do.

[Joe L.]

Re: Leaking Front Caliper

Joe,

Why do these calipers require new pistons, I rebuilt the vette brakes stainless calipers on my 67 with new seals only and now seven years later there is leakage again. I never noticed anything wrong with the pistons but would like to know what to look for when I fix-em..

Also used silicone fluid..

Timothy------

Sometimes corrosion does damage the pistons but it's not the major factor and rarely a factor if silicone fluid is used. However, most pistons are still not suitable for re-use. Here's why: if ANY of the hard anodize is worn away on the major diameter of the piston, then the piston is SCRAP. This means that if any of the "goldish" coloration on this surface is worn away and ANY portion of the surface is then "replaced" by a bare aluminum, "silver" color, the piston is SCRAP. If any piston has been in service for any significant period of time, you will almost always find that this wear exists. A serviceable piston is the rare exception rather than the rule.

The attached photo shows a NEW GM piston. The pen points to the surface for which ANY wear is critical.