Hydraulic Brake Seals: Lifetime?

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The hydraulic disc brakes on my MTB, SRAM Guide RSC, are 7 years old with several thousand miles. As I was bleeding them yesterday, when I applied vacuum to the caliper end, it drew air in through the lever, even while the lever was fully depressed/activated. The only way the air can get in, is past a bad seal along the hydraulic line, past a leaky piston in the caliper, or past the seals on the pistons in the master cylinder. When I applied the vacuum, I could hear air leaking through the master cylinder/piston inside the lever, so that narrowed it down. I hope that rebuilding the lever with fresh seals will fix it, in other words the problem isn't scoring on the inside of the master cylinder.

I've given these brakes regular maintenance, doing a fluid flush & bleed every year. They've been fine until now.

Is this a normal lifetime? How long do the seals in your hydraulic brakes last? Is it always the lever piston seals that fail, or have some of you seen the caliper pistons start to leak?
 
Had no issues with the wifes hydraulic brakes so far but do wonder what fluid they uses on bicycles.

EDIT: magura uses a very thin mineral fluid I just found.
 
AFAIK, it’s fair to treat hydraulic brakes on a pushbike the same as a car or motorbike. SRAM brakes, from what I’ve heard aren’t that great - I know a few who swapped out for Shimano.
 
Sram brakes use DOT brake fluid as mentioned above. After a few seasons, they get cruddy and begin to leak. Shimano brakes with the mineral oil seem to be much longer lasting. I did wreck the seals in a Shimano caliper once by letting the pads get too worn. Replaced the caliper, no more problem.
I have a few sets of Shimano SLX brakes that are ten years old. I never got more than three years out of Sram.
 
These SRAM brakes have worked well so far even under severe conditions. They did have the "stuck piston" problem a few years ago which I fixed. From responses here, it seems my experience with the lever seals wearing out and leaking isn't unusual. I'll rebuild the levers using the factory overhaul seal kits and see what happens.
 
The brake cyls aren't really meant to seal vacuum.
One part of the standard bleed procedure is to fix the brake lever in the fully depressed position (which seals off the lever reservoir) and apply vacuum with a syringe at the caliper bleed bolt to draw out any air bubbles.

If I skip this step, I can still bleed these brakes despite this lever seal leak, and the brakes do work. However, this step is part of the standard bleed procedure for good reason. The fact that the seal has just started leaking under vacuum, when they never leaked before, tells me they are near their end of life. I'd rather replace them now, than have them fail on me when riding.
 
These SRAM brakes have worked well so far even under severe conditions. They did have the "stuck piston" problem a few years ago which I fixed. From responses here, it seems my experience with the lever seals wearing out and leaking isn't unusual. I'll rebuild the levers using the factory overhaul seal kits and see what happens.
SRAM had to issue a recall on their first generation road hydraulic brakes - it happened at a major cyclocross event in Portland or near Chicago. Freezing temps allowed for brake fluid bypass in the MC part of the shift/brake lever assembly.

A redesign of the SRAM HRD(at the time, it was before eTap/AXS but it was a Red/Force-level part) system fixed that.

I also see bike shops bleeding these with DOT3 fluid. If I ever used SRAM brakes, I’m only running DOT4 LV(ATE SL6/Bosch ESI 6) or DOT5.1(Motul/Liqui Moly/Prestone Max) to prevent things like that from happening.
 
SRAM had to issue a recall on their first generation road hydraulic brakes - it happened at a major cyclocross event in Portland or near Chicago. Freezing temps allowed for brake fluid bypass in the MC part of the shift/brake lever assembly.

A redesign of the SRAM HRD(at the time, it was before eTap/AXS but it was a Red/Force-level part) system fixed that.

I also see bike shops bleeding these with DOT3 fluid. If I ever used SRAM brakes, I’m only running DOT4 LV(ATE SL6/Bosch ESI 6) or DOT5.1(Motul/Liqui Moly/Prestone Max) to prevent things like that from happening.
SRAM also had a field action on Guide levers from 2016/17. With these is was the opposite problem--seals swelling in hot weather. That said, both of mine failed in 60 degree weather. SRAM sent out tons of rebuild kits for these--though given the age of the OP's brakes, I doubt they'll do much at this point. I'm honestly surprised they made it as long as they did.
 
SRAM also had a field action on Guide levers from 2016/17. With these is was the opposite problem--seals swelling in hot weather. That said, both of mine failed in 60 degree weather. SRAM sent out tons of rebuild kits for these--though given the age of the OP's brakes, I doubt they'll do much at this point. I'm honestly surprised they made it as long as they did.
I did have the "stuck lever" problem with my brakes a few years ago. The problem wasn't the seals, but the pistons! They gradually expand over time until they scuff the inside of the cylinder. I read of folks having a hard time getting warranty replacement, so I fixed it myself. Brakes worked great for another year, until the problem hit again (the pistons continued expanding). At that point I bought aftermarket pistons made of aluminum, which fixed the problem permanently. I posted about that here, as it might help others.
 
PS: from what I read, SRAM revised the rebuild kits for the Guide RSC levers:
old part #: 11.5018.005.005
new part #: 11.5018.005.010
The bike shop told me the new part # is compatible with the old, it replaces the old kit and has the revised pistons that don't expand & stick.
 
SRAM also had a field action on Guide levers from 2016/17. With these is was the opposite problem--seals swelling in hot weather. That said, both of mine failed in 60 degree weather. SRAM sent out tons of rebuild kits for these--though given the age of the OP's brakes, I doubt they'll do much at this point. I'm honestly surprised they made it as long as they did.
The mountain bikers I know all mix up SRAM with Shimano brakes. If I ever had SRAM brakes on a future road or gravel bike, I’ll treat it like a car with regular flushes to try to stave off non-engineering related issues.
 
... If I ever had SRAM brakes on a future road or gravel bike, I’ll treat it like a car with regular flushes to try to stave off non-engineering related issues.
Exactly what I do. I think that's why my brakes lasted as long as they did. The old fluid always came out clean. The brakes still do actually work, though the air leak under vacuum shows that the seals are end-of-life. Should be like new after I overhaul the levers and replace the seals.
 
Exactly what I do. I think that's why my brakes lasted as long as they did. The old fluid always came out clean. The brakes still do actually work, though the air leak under vacuum shows that the seals are end-of-life. Should be like new after I overhaul the levers and replace the seals.
Sounds strikingly like the master cylinder seal issues Honda and Toyota had with certain Aisin units. aftermarket brake fluids were missing a ingredient that CCI(the supplier of OEM brake fluid and coolants, primarily to the Japanese OEs) used. Drivers complained of a squeak when the brakes were applied or there was a leak needing a new MC and booster. The fix was OEM bottle fluid, if no repairs were needed.
 
The mountain bikers I know all mix up SRAM with Shimano brakes. If I ever had SRAM brakes on a future road or gravel bike, I’ll treat it like a car with regular flushes to try to stave off non-engineering related issues.
I had a "no SRAM brake" policy after my experience with the original Guides, but I've grown weary of the moving bite point on Shimano XT's, which I love otherwise. I have the new GS brakes on my mtb (basically updated Guides), and that's my plan--bleed them a couple of times a year to try and stave off any issues. I will say that in terms of performance, I like them a lot better than the XT 4-pots. Modulation feels better, and the bite point is consistent. Fingers crossed that they're more reliable than the old ones.
 
Job complete. Those lever rebuild kits are quite complete: new pistons, seals, springs, lever pushrods, bushings, bleed screws, even the tiny little ball & spring for the reach adjustment dial. The threaded lever pushrod guide sleeves, which were plastic, have metal replacements. No more leaks under vacuum, brakes are like new again.
 
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