Brake master cylinder
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,453
Likes: 2,168
From: Loveland
Brake master cylinder
2014 Stingray. I have started to notice, when I am at a stop, I can feel the brake pedal slowly push down from the initial position. Has there been issues with the master cylinders piston seals going bad? I'm not sure if the fluid has been changed.
I am going to flush the system with new fluid soon.
I am going to flush the system with new fluid soon.
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,453
Likes: 2,168
From: Loveland
Nobody has had this issue? Well, I flushed the brakes with new DOT 4 fluid. This hasn't changed the pedal feeling like it settles a bit at a stoplight, geeeez!
Last edited by kodpkd; Jun 10, 2025 at 04:41 PM.
Melting Slicks
Joined: Feb 2018
Posts: 2,157
Likes: 1,032
From: North Texas
When you bled the brakes did you use the brake pedal to pump the old fluid out?
If you did, you might have damaged the piston seals inside the cylinder.
This event usually happens when there is corrosion or pitting that develops at the far end of the cylinder and then the piston seals travel over this damaged area, when you pump the brake pedal, to the very end of its stroke and the seals run over this damaged area destroying the seals ability to function properly.
Sorry for the 'wording' of this explanation, way too early in the morning for me. But I'm sure you get the idea. Thats why it's best to use a pressurized or vacuum bleeding system.
If you did, you might have damaged the piston seals inside the cylinder.
This event usually happens when there is corrosion or pitting that develops at the far end of the cylinder and then the piston seals travel over this damaged area, when you pump the brake pedal, to the very end of its stroke and the seals run over this damaged area destroying the seals ability to function properly.
Sorry for the 'wording' of this explanation, way too early in the morning for me. But I'm sure you get the idea. Thats why it's best to use a pressurized or vacuum bleeding system.
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,453
Likes: 2,168
From: Loveland
Yes, I have the Motive pressure bleeder and no I didn't pump the pedal to the floor. It didn't get worse, I just think it didn't get any better.
On the topic of pushing the master cylinder rod in to far. If the bore of your master cylinder is rusted, don't bother bleeding the brakes, just replace the master. I've remover the master on a 68 Corvette and the bore wasn't rusted. Not pushing the piston in to far on a master is one of those "old wives tales".
On the topic of pushing the master cylinder rod in to far. If the bore of your master cylinder is rusted, don't bother bleeding the brakes, just replace the master. I've remover the master on a 68 Corvette and the bore wasn't rusted. Not pushing the piston in to far on a master is one of those "old wives tales".
Last edited by kodpkd; Jun 11, 2025 at 11:42 AM.
Melting Slicks
Joined: Feb 2018
Posts: 2,157
Likes: 1,032
From: North Texas
The MC is made of aluminum, newer ones, so it does not rust but it can corrode inside the bore especially in the area where the piston usually does not travel. The last 1/3 to 1/4 of the pistons travel. Dirt, debris and corrosion all end up here.
Mainly were talking about corrasion in this area due to moisture in the brake fluid. it just takes a little to cause pitting in this area and that rough area will cause excessive wear on the piston 'O' rings causing them to leak. That's why it's always best to use a pressure or vacuum bleeding system when you bleed your brakes.
They even make small hones to smooth out damaged MC bores just for this reason. I've used them many times over the years. The older cast iron MC's were especially bad in developing rust / corrasion damage in this area but the newer aluminum MC's not so much.
Mainly were talking about corrasion in this area due to moisture in the brake fluid. it just takes a little to cause pitting in this area and that rough area will cause excessive wear on the piston 'O' rings causing them to leak. That's why it's always best to use a pressure or vacuum bleeding system when you bleed your brakes.
They even make small hones to smooth out damaged MC bores just for this reason. I've used them many times over the years. The older cast iron MC's were especially bad in developing rust / corrasion damage in this area but the newer aluminum MC's not so much.
Thread Starter
Le Mans Master
Joined: Jun 2019
Posts: 5,453
Likes: 2,168
From: Loveland
I just received my new GM master cylinder. Bleeding and install tomorrow using the Motive bleeder. I have one of the bore kits.
Installed the MC, my pedal feels better now. I used the Motive bleeder to bench bleed the MC, very easy.
Installed the MC, my pedal feels better now. I used the Motive bleeder to bench bleed the MC, very easy.
Last edited by kodpkd; Apr 18, 2026 at 12:57 PM.
