Master Cylinder - bubbling/gurgling in the reservoir
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Master Cylinder - bubbling/gurgling in the reservoir
I have a 96 C1500 Suburban with the 5.7 V8. The driver side rear wheel cylinder started leaking, so we replaced both rear wheel cylinders, shoes, springs, and drums. When we attempted to bleed each of the wheels there was no hydraulic pressure to the wheel cylinder and very little fluid came out of the bleed valve. When we checked the master cylinder and reservoir, we noticed a bubbling/gurgling of the fluid when the pedal is depressed. Video attached. I've never seen anything like this before. Has the master cylinder failed on us? What could be causing this? Recommendations for resolving this issue? Thanks!
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From: Central Iowa
That’s quite interesting indeed. It’s normal to see a few bubbles, but nothing that extreme.
A couple possibilities:
1) Air got into the master cylinder during repairs and you’ll have to bench bleed it before you can bleed the lines.
2) If there was a sudden loss of pressure (pedal abruptly sunk to floor when you tried to brake), one of the cup seals inside the MC got inverted and is just pushing fluid around the bore rather than building pressure.
Did you adjust the shoes correctly before attempting to bleed? That could also be affecting the lack of pressure build up. A hydraulic system is the equivalent of a steel rod when working correctly, but if there’s enough gap between the shoes and drum, any attempts to build pressure are lost in taking up that slack. It may help to adjust the shoes clear out for bleeding, then back them off when it’s done.
You can also try letting it gravity bleed until you see fluid dripping from the cylinders, then attempt a manual bleed. I’ve found that can help immensely with those square reserve MC’s (we don’t have an adapter for them for our pressure bleeder so we have to manually bleed them a lot).
There’s also a valve on the ABS module block that needs to remain depressed during bleeding. There’s a special tool for it but a large enough hose clamp and a penny would do the same thing. I can post a pic later if you’re not sure what I’m referring to.
A couple possibilities:
1) Air got into the master cylinder during repairs and you’ll have to bench bleed it before you can bleed the lines.
2) If there was a sudden loss of pressure (pedal abruptly sunk to floor when you tried to brake), one of the cup seals inside the MC got inverted and is just pushing fluid around the bore rather than building pressure.
Did you adjust the shoes correctly before attempting to bleed? That could also be affecting the lack of pressure build up. A hydraulic system is the equivalent of a steel rod when working correctly, but if there’s enough gap between the shoes and drum, any attempts to build pressure are lost in taking up that slack. It may help to adjust the shoes clear out for bleeding, then back them off when it’s done.
You can also try letting it gravity bleed until you see fluid dripping from the cylinders, then attempt a manual bleed. I’ve found that can help immensely with those square reserve MC’s (we don’t have an adapter for them for our pressure bleeder so we have to manually bleed them a lot).
There’s also a valve on the ABS module block that needs to remain depressed during bleeding. There’s a special tool for it but a large enough hose clamp and a penny would do the same thing. I can post a pic later if you’re not sure what I’m referring to.
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Joined: Nov 2019
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Thank you for taking the time to reply, Gumby22. You were correct, one of the cups seals failed in master cylinder. We replaced the MC and was successful in bleeding the system and getting the truck back on the road. Thank you!
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