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Good afternoon everyone,
I recently rebuilt the piston in my 2015 Porsche GT3 with a rebuild kit from racingbrake.com. I originally was just changing out the pads & noticed that the ceramic insulators were cracked. I rebuilt all 4 corners with the piston kit, rings & dust boots. When I was done, I did a complete flush of the brakes with Castrol SRF brake fluid. During the rebuild/flush, I made sure to keep the fluid level up in the master cylinder. Once I was done, I pumped the brakes to make sure they were firm, however they almost immediately fade, and my foot goes to the floor again. I've repeated this procedure several times with the same result. I even repeated the bleed twice all the way around thinking there might be some additional bubbles in the line but still the same.
I was hoping you guys might have some ideas on what else I might try.
Do you have any brake fluid leaks? If not, almost certainly you introduced air into the system somehow. May need to do a bleed with the PWIIS to cycle the ABS pump. This is usually not necessary if you successfully prevent the introduction of air into the system. When you removed the calipers, did you make sure the brake pedal was partially depressed to prevent fluid flow from the reservoir (this is a good idea)?
I capped the the lines once I disconnected the calipers which resulted in very little leakage. I did use my Motive Power Bleeder to flush the system once complete. I thought I was being so methodical. Just frustrated that I can’t find the culprit.
I have no direct experience with this issue, but I do follow some of the car builds by "home built by Jeff" and he was preparing his older 911 for a road trip and experienced the same problem as you, air trapped in the system and after multiple attempts at bleeding the brakes he realized he was not using both caliper nipples to bleed the system - when he used both the problem disappeared.
First make sure there are no fluid leaks at the calipers or lines feeding the calipers. Fill your reservoir to the fill line and start at the right rear caliper. Start your car and try bleeding the brakes the old fashion way. Pump the brakes and hold the pedal while you open the bleed valve, hold the pedal down until the bleed valve is closed. Look for bubbles in the line, do this a couple of times and move to the rear left, right front and then left front. You will obviously will need help unless you are faster than light. I think this should clear your lines of air. Repot back. BTW do not allow the fluid level to drop in the reservoir to less than half.
Repot back. BTW do not allow the fluid level to drop in the reservoir to less than half.
What happens if the reservoir drops to less than half? I actually had this happen to me as I wasn't paying close enough attention and then started to see bubbles come out . I ended up pushing through another 500mL, and the bubbles stopped and the brake pedal feels fine now. Do I need to worry or do anything else?
What happens if the reservoir drops to less than half? I actually had this happen to me as I wasn't paying close enough attention and then started to see bubbles come out . I ended up pushing through another 500mL, and the bubbles stopped and the brake pedal feels fine now. Do I need to worry or do anything else?
Nothing to worry about. It can introduce air into the lines. You kept bleeding through the air bubbles, pedal feels fine, so you should be good to go.
Additionally, take a rubber mallet and tap the caliper a few times. This will dislodged stuck air bubbles. And, as someone posted above, drain both nipples on each caliper.
And, keep filing the reservoir after working on each caliper.
When you start at the right rear, you would do the outside valve first, then the inside valve. The inside valve is just pulling air from the caliper, as the line should be good from the outside bleed you just completed.
Move to the left rear and do the outside valve and then the inside.
Repeat on the fronts.
As others have shared, top off the master cylinder after each corner is complete.
Additionally, take a rubber mallet and tap the caliper a few times. This will dislodged stuck air bubbles. And, as someone posted above, drain both nipples on each caliper.
And, keep filing the reservoir after working on each caliper.
I have one of those Capri vacuum bleeders. If you're using a Motive, you hopefully wouldn't need the vacuum bleeder. And I use the Capri solo. It works great, except the vacuum pulls air from around the bleeder valve threads. It does the trick and I've never had an issue with it, you just can't ever get straight fluid through the line. Always air bubbles. But I've done multiple vehicles and bikes and it works very well. And you don't need adapters.
I did maintain the level at all times in the reservoir during the rebuild process. I did also bleed/flush all 8 nipples. I will rebleed the calipers again & hopefully get any air bubbles out.
What is a PWIIS.
Thanks guys for the input. Appreciate the help!
02-23-2022, 04:17 PM
Rebuilt GT3 Calipers/Won't hold pressure
. I think this should clear your lines of air. Repot back. BTW do not allow the fluid level to drop in the reservoir to less than half.
. I ended up pushing through another 500mL, and the bubbles stopped and the brake pedal feels fine now. Do I need to worry or do anything else?
