SRAM Road (Red) brake slowly losing pressure when squeezed
 

I just set up a bike with with some nice used SRAM Red brake levers with new Force calipers. On the front, when I squeeze the lever, it will slowly lose pressure and the lever will touch the bar. Braking is great in the short run but slowly gets worse the longer I squeeze. Any ideas what it might be? No fluid is leaking and I can pump them back up by flicking the lever. Fresh bleed.

looks like a case of air in the system?

Don't think so. The system is bled and pressurized. First thing I checked.
IMHO, air in the system would make it spongy. This is solid at first the peters out like its losing pressure.

This is exactly what hapenned to me. I bled the brakes, to my knowledge saw no more bubbles when bleeding, pressurized the system, then called it a day. The brake feel was great intitially. But as the ride progressed and the more the brake got used, the longer the lever travel became until the levers touched the handlebar without the piston engaging.

Took it to my LBS. They bled it again and now it worked. Turns out, I sucked at bleeding the brakes myself.

Which red shifters / brake levers? If sram red hrd with double tap ie cable shifting are they the recalled models or are they the functional ones?

Recalled models had the nasty habit of losing braking power due to seal failure.

Did you check if any fluid was leaking? Also when you say “started out great” are you testing this on the road?

Would help if video attached, or a better explanation of the exact lever pull procedure which leads to the lever going back all the way to the bars. But just an FYI, I’ve found on SRAM hrd brakes liquid pressurization is key to getting them feeling solid and not squishy.

No fluid leaking and the serial number is not etched where the manual says it should be. I may pull the lever apart and change the seals.
This is what happens: with the bike sitting in the stand, if I squeeze the brakes hard and steady, if I hold the squeeze long enough, the lever will slowly lose pressure like fluid is leaking past the seals, until the lever basically has no pressure and I have to "pump" it back up. Again: no fluid is leaking.

So this is normal behavior on the stand, as the bladder is made to expand/inflate without rupturing in the event of fluid heating up with constant brake load.

If you haven’t taken a quick ride on it and tested the brakes a little on a gentler stretch of road then I would suggest doing so. Try the bed in procedure, and of the brake blades are touching the bar when you do a quick hard stop then reveled with a slight overfill to try to get rid of the play.

Problem is, it doesn't happen on the other lever.

It sure does sound like fluid is moving past the seals on the master cylinder.

dave

I've found rebuild kits, but they're all for the left lever. Since the piston is round, I would assume it could fit either side. I think the piston will be all I need. What do you folks think?

I had a shimano MTB brake that did what you are describing. It was caused by a small leak at the master cylinder.

Are you sure the MC isn't leaking? Could also be where the brake line enters the lever or caliper.

This.

Found it. For the good of the community, I'll admit what an idiot I am: the leak wasn't in the lever, it was where the hose attaches to the caliper. I hadn't torqued the nut down tight enough to seat the olive. I didn't see it until i decided to keep squeezing and pumping until I saw something.
Done and dusted.
Gonna have to bleed it again...