spongy brakes
August 5th, 2023, 9:20 PM
#1
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spongy brakes
I have replaced master cylinder and brake booster along with calipers and brake hose. I have also bled the lines 6 times and I still have spongy brakes. does anyone have an idea on what's wrong?
August 5th, 2023, 10:17 PM
#2
Please post your details.
You might need to bleed the ABS with a diagnostic tool.
MC needs to be bled too.
You might need to bleed the ABS with a diagnostic tool.
MC needs to be bled too.
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sk47 (August 7th, 2023)
August 7th, 2023, 4:25 PM
#4
CF Beginner
Hello; About a year ago I replaced both rear calipers on my 2004 Silverado. Lost a lot of brake fluid getting the banjo fitting free of a copper/brass washer. Think i allowed some air in the ABS module.
Thought i was going to have to take it to a shop to get the ABS bleed and cleared. Think I made a thread about it with details. Point being i did find a way to bleed out the system on my own. I will search and if i find the thread post a link.
Thought i was going to have to take it to a shop to get the ABS bleed and cleared. Think I made a thread about it with details. Point being i did find a way to bleed out the system on my own. I will search and if i find the thread post a link.
August 7th, 2023, 4:34 PM
#5
CF Beginner
Hello; First let me say this is a thing I learned about Chevy antilock brake systems. I needed to replace the rear calipers on a 2004 Silverado. When I loosened the bolt at the banjo fitting from one of the calipers I discovered the soft copper washer had been squeezed and deformed to the point of being tight in the threads of the thru bolt. Took me a while to get the washer freed from the bolt. I wound up pounding on the bolt enough to move the copper washer and get a grip with some pilers. After getting the washer off I could remove the thru bolt. All that time brake fluid was dripping out.
The rubber plug picked up at a local parts store did not actually plug the banjo fitting, so it still was leaking fluid. By the time I found a bolt and two washers to stop the leaking a lot had leaked out.
Replaced the two rear calipers, changed the front pads and bleed the brake lines all around. Had a good solid pedal and thought i was finished. Started the engine. The antilock brake light lit up and the pedal became soft. Turns out air had gotten into the system.
The system in a 2004 cannot be bled at the anti-lock pump. Though i was going to have to take it to a shop having the needed scan tool and pay $100. Had a few days before the appointment so tried some things. The shop owner suggested doing a gravity bleed for an hour. Just open the rear calipers bleed screws and let it drip while keeping the reservoir full. Did not work. ( note- maybe should have done the fronts also at the same time. likely will never find out as I hope to never let one leak out again.)
Saw on the internet about another way. Already had the truck up on jack stands with all wheels off. That method was to have the engine running in gear at 20 MPH and hit the brakes 10 or fifteen times. (note- had some lug nuts on to keep the rotors from flopping around.) Did not work. The idea is a sudden application of the brakes would activate the pumps in the antilock system and purge the trapped air.
I was about to give up but the next day decided to try the running in gear with the four wheel drive engaged. After 8 or so stabs at the brake pedal the ALC light went out. I guess the front axels needed to be turning for the antilock to kick in. Did another all around bleed to get out the air purged from the antilock system. All was good or so I thought.
Put the wheels back on. Took it off the jack stands and did a test drive back and forth in my driveway. Brakes seemed fine. Parked the truck and was about to go clean up. Looked under the truck and saw brake fluid on the inside of a rear wheel. One of the new calipers was leaking. Removed it and got a replacement. Got that changed and finally all is good. ( note- the new calipers that leaked had a 7/16 inch sized bleeder screw while the one which sealed has a 10mm bleeder screw. The second new caliper that does not leak also had a 10mm bleeder screw. Just something noted.)
The rubber plug picked up at a local parts store did not actually plug the banjo fitting, so it still was leaking fluid. By the time I found a bolt and two washers to stop the leaking a lot had leaked out.
Replaced the two rear calipers, changed the front pads and bleed the brake lines all around. Had a good solid pedal and thought i was finished. Started the engine. The antilock brake light lit up and the pedal became soft. Turns out air had gotten into the system.
The system in a 2004 cannot be bled at the anti-lock pump. Though i was going to have to take it to a shop having the needed scan tool and pay $100. Had a few days before the appointment so tried some things. The shop owner suggested doing a gravity bleed for an hour. Just open the rear calipers bleed screws and let it drip while keeping the reservoir full. Did not work. ( note- maybe should have done the fronts also at the same time. likely will never find out as I hope to never let one leak out again.)
Saw on the internet about another way. Already had the truck up on jack stands with all wheels off. That method was to have the engine running in gear at 20 MPH and hit the brakes 10 or fifteen times. (note- had some lug nuts on to keep the rotors from flopping around.) Did not work. The idea is a sudden application of the brakes would activate the pumps in the antilock system and purge the trapped air.
I was about to give up but the next day decided to try the running in gear with the four wheel drive engaged. After 8 or so stabs at the brake pedal the ALC light went out. I guess the front axels needed to be turning for the antilock to kick in. Did another all around bleed to get out the air purged from the antilock system. All was good or so I thought.
Put the wheels back on. Took it off the jack stands and did a test drive back and forth in my driveway. Brakes seemed fine. Parked the truck and was about to go clean up. Looked under the truck and saw brake fluid on the inside of a rear wheel. One of the new calipers was leaking. Removed it and got a replacement. Got that changed and finally all is good. ( note- the new calipers that leaked had a 7/16 inch sized bleeder screw while the one which sealed has a 10mm bleeder screw. The second new caliper that does not leak also had a 10mm bleeder screw. Just something noted.)
August 8th, 2023, 8:28 PM
#6
when you start you car does your brake pedal drop (shouldn't pass inspection if it doesn't)
do you have a vacuum booooster air leak? did you check that angle?
August 9th, 2023, 8:52 AM
#7
CF Beginner
Hello; First let me say this is a thing I learned about Chevy antilock brake systems. I needed to replace the rear calipers on a 2004 Silverado. When I loosened the bolt at the banjo fitting from one of the calipers I discovered the soft copper washer had been squeezed and deformed to the point of being tight in the threads of the thru bolt. Took me a while to get the washer freed from the bolt. I wound up pounding on the bolt enough to move the copper washer and get a grip with some pilers. After getting the washer off I could remove the thru bolt. All that time brake fluid was dripping out.
The rubber plug picked up at a local parts store did not actually plug the banjo fitting, so it still was leaking fluid. By the time I found a bolt and two washers to stop the leaking a lot had leaked out.
Replaced the two rear calipers, changed the front pads and bleed the brake lines all around. Had a good solid pedal and thought i was finished. Started the engine. The antilock brake light lit up and the pedal became soft. Turns out air had gotten into the system.
The system in a 2004 cannot be bled at the anti-lock pump. Though i was going to have to take it to a shop having the needed scan tool and pay $100. Had a few days before the appointment so tried some things. The shop owner suggested doing a gravity bleed for an hour. Just open the rear calipers bleed screws and let it drip while keeping the reservoir full. Did not work. ( note- maybe should have done the fronts also at the same time. likely will never find out as I hope to never let one leak out again.)
Saw on the internet about another way. Already had the truck up on jack stands with all wheels off. That method was to have the engine running in gear at 20 MPH and hit the brakes 10 or fifteen times. (note- had some lug nuts on to keep the rotors from flopping around.) Did not work. The idea is a sudden application of the brakes would activate the pumps in the antilock system and purge the trapped air.
I was about to give up but the next day decided to try the running in gear with the four wheel drive engaged. After 8 or so stabs at the brake pedal the ALC light went out. I guess the front axels needed to be turning for the antilock to kick in. Did another all around bleed to get out the air purged from the antilock system. All was good or so I thought.
Put the wheels back on. Took it off the jack stands and did a test drive back and forth in my driveway. Brakes seemed fine. Parked the truck and was about to go clean up. Looked under the truck and saw brake fluid on the inside of a rear wheel. One of the new calipers was leaking. Removed it and got a replacement. Got that changed and finally all is good. ( note- the new calipers that leaked had a 7/16 inch sized bleeder screw while the one which sealed has a 10mm bleeder screw. The second new caliper that does not leak also had a 10mm bleeder screw. Just something noted.)
The rubber plug picked up at a local parts store did not actually plug the banjo fitting, so it still was leaking fluid. By the time I found a bolt and two washers to stop the leaking a lot had leaked out.
Replaced the two rear calipers, changed the front pads and bleed the brake lines all around. Had a good solid pedal and thought i was finished. Started the engine. The antilock brake light lit up and the pedal became soft. Turns out air had gotten into the system.
The system in a 2004 cannot be bled at the anti-lock pump. Though i was going to have to take it to a shop having the needed scan tool and pay $100. Had a few days before the appointment so tried some things. The shop owner suggested doing a gravity bleed for an hour. Just open the rear calipers bleed screws and let it drip while keeping the reservoir full. Did not work. ( note- maybe should have done the fronts also at the same time. likely will never find out as I hope to never let one leak out again.)
Saw on the internet about another way. Already had the truck up on jack stands with all wheels off. That method was to have the engine running in gear at 20 MPH and hit the brakes 10 or fifteen times. (note- had some lug nuts on to keep the rotors from flopping around.) Did not work. The idea is a sudden application of the brakes would activate the pumps in the antilock system and purge the trapped air.
I was about to give up but the next day decided to try the running in gear with the four wheel drive engaged. After 8 or so stabs at the brake pedal the ALC light went out. I guess the front axels needed to be turning for the antilock to kick in. Did another all around bleed to get out the air purged from the antilock system. All was good or so I thought.
Put the wheels back on. Took it off the jack stands and did a test drive back and forth in my driveway. Brakes seemed fine. Parked the truck and was about to go clean up. Looked under the truck and saw brake fluid on the inside of a rear wheel. One of the new calipers was leaking. Removed it and got a replacement. Got that changed and finally all is good. ( note- the new calipers that leaked had a 7/16 inch sized bleeder screw while the one which sealed has a 10mm bleeder screw. The second new caliper that does not leak also had a 10mm bleeder screw. Just something noted.)
Had a strange, to me, thing happen. This time i had left the wheel + tire on the truck. During the brake bleed story, the wheel+tires has been removed. When checking the operation of the 4x4 I naturally had to apply the brakes. When i did apply the brakes the ABS light came on. This spooked me for a while.
Satisfied that the 4x4 worked i took the truck off the stands. I started the truck and backed it up about 30 feet. When i applied the brakes the ABS light went out. I was relieved. Since that day about two weeks ago my brake pedal has been both a bit higher and more firm. Brake light comes on and the truck stops good.
I have puzzled about this and can only come up with that only one wheel was spinning on each axle when on the jack stands. ( my truck has open differentials on both axels). That seems to me a possible reason for why the light came on, but i do not quite know why the brake pedal feel has improved so much. I get that the antilock brake system must have cycled. Anyway I am pleased with the better pedal feel. Over the years I would sometimes get a higher and firmer feeling pedal for a bit, but it would revert to the lower and softer pedal. Always had good braking.
Guess this story is for those who have a 4x4 and want to try to bleed out the brakes after having lost a lot of fluid as i did. As mentioned in the other story I had been able to do a good brake bleed on all four corners with the engine off. Got a good firm pedal. Then when I started the engine the pedal got softer, and the ABS light came on. The various tricks I tried did not work. It was only when I ran the engine with the trans in gear and 4x4 engaged while pumping the brakes that the ABS light went off. I do not know what someone with 2x4 drive would have to do.
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