1990 V1500 Suburban 4x4, vacuum brakes, RWAL, disc front, 14 bolt SF with drums rear. Daily driver last 6-7 years. I had a front brake pad separate and start squealing, so I changed the pads. Went to drive without bleeding and pedal went to the floor, so bled I them. Had some air come out in the rears. Used a whole bottle and bled them enough to replace all the fluid in the system. Now I have good pedal feel after bleeding. When I start to test drive, pedal is spongey and goes to the floor. When I pulled the booster check valve, it was very obviously holding air. Have ORD soft lines 5-6 years old, can't find any leaks, I can bleed all four wheels, autozone master cylinder/booster is maybe 2-3 years old. Replaced all rear drum parts last year, calipers are a few years older. I'm really stumped and starting to think the master cylinder/booster has already gone bad. The brake light does come on and off sometimes but I thought it was related to the speedo signal issues. It doesn't stay set. I haven't been able to get codes off of it. Any help is greatly appreciated.
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Daily Driver brake issue. Must fix quickly
- Thread starter Tattood08
- Start date
I bet the MC seals went out when the pedal travelled farther than it's normal wear area when the pedal went to the floor. Now it's most likely bypassing internally.
Will a bench bleed help or just replace it?
It will need to be replaced.
Thanks for the info guess I'll get that swapped out this afternoon.
I bought a new master cylinder in May from rock auto, installed it and it leaked out the back, sent it back got a new one, it leaked, finally got a good one at NAPA
Yes your master cylinder failed.
This can happen if you force the caliper piston back into place with out opening the bleeder screw. Not opening the bleeder screw pushes dirty nasty rusty brake fluid and debris back into the master cylinder, past the neoprene cups and spool valves.
They can be damaged.
So for future reference. Use a hose on the bleeder nipple into a container, open bleeder, then slowly compress the pistion back into the caliper. Close the bleed screw before removing pressure on piston.
Good luck report back on results
This can happen if you force the caliper piston back into place with out opening the bleeder screw. Not opening the bleeder screw pushes dirty nasty rusty brake fluid and debris back into the master cylinder, past the neoprene cups and spool valves.
They can be damaged.
So for future reference. Use a hose on the bleeder nipple into a container, open bleeder, then slowly compress the pistion back into the caliper. Close the bleed screw before removing pressure on piston.
Good luck report back on results
So I swapped out the master cylinder, bled the lines and still does the same thing. Feels ok with engine off. When you start the engine holding the brakes the pedal sinks almost to the floor.
If you feel confident the MC is good, I hope new and not rebuilt, have a helper step on the brakes with engine running. Hold each brake hose in turn as brake pedal is pressed, you are trying to feel for swelling brake hose. check all the soft lines. also look for leaks.
It still sound like MC is bypassing internal.
The Rwal system is very simple and doesn't have a huge fluid capacity. I still after doing a service would test drive and purposely do 1 to 3 anti lock brake events. This moves the old brake fluid, and any air in rwal module out into regular hydraulic system. Then redo the normal service bleed.
It still sound like MC is bypassing internal.
The Rwal system is very simple and doesn't have a huge fluid capacity. I still after doing a service would test drive and purposely do 1 to 3 anti lock brake events. This moves the old brake fluid, and any air in rwal module out into regular hydraulic system. Then redo the normal service bleed.
Honestly the rwal setup is garbage. I spent two days following GM procedures to bleed mine including having the right tool on the prop valve. The prop valve is different than all earlier squares without rwal. It is discontinued like all the other rwal parts.
I went to the boneyard and pulled a non rwal prop valve and the two lines from the master to the prop valve. Only issue is the rear line at the front frame where the non rwal prop valve goes had the wrong tube nut. Got the right one from the truck the prop came from, cut the old end off and reflared. Just like factory.
Once retrograded, system bled like it should have.
I went to the boneyard and pulled a non rwal prop valve and the two lines from the master to the prop valve. Only issue is the rear line at the front frame where the non rwal prop valve goes had the wrong tube nut. Got the right one from the truck the prop came from, cut the old end off and reflared. Just like factory.
Once retrograded, system bled like it should have.
Yes it wasn't a great system when new, I not sure if I have my Rwal technician training manual I might have tossed it. since they aren't repairable anymore
I'm not confident in parts store parts anymore so I guess it could be the MC still. I have ORD braided stainless lines. I don't think ballooning is happening but I can look again. I will look for leaks again but I haven't found any. It bleeds just fine, I've done it few times while I've owned it. The pedal is nice a firm until you start the engine. I guess I will try getting one from napa. They do have a pretty decent track record.
When my MC was bad (No RWAL) my brakes were spongey, but when it went to the floor, I was able to "pump" them up by repeatedly pressing and releasing the brake pedal while running.
Based on what you said, I would have guessed MC failure as well.
Bled my brakes years back with an old MC, ended with a spongey pedal, bled and bled and bled and could never get the sponginess out. Worked, just spongey. Eventually driving it one day the brake light came on and the pedal went to the floor at a stop. Before I made it home it did it again. Swapped new MC and problem was gone.
Based on what you said, I would have guessed MC failure as well.
Bled my brakes years back with an old MC, ended with a spongey pedal, bled and bled and bled and could never get the sponginess out. Worked, just spongey. Eventually driving it one day the brake light came on and the pedal went to the floor at a stop. Before I made it home it did it again. Swapped new MC and problem was gone.
You can surely blame air in the prop valve for a spongey pedal, but going to the floor does sound more like a leak/bypass. I guess it depends on how large that unit is - I've never had RWAL, but thought there was a bleeder on it.
I went through the same thing recently with one of my GMT800s. The ABS is impossible to bleed (without the scan tool) so the solution was to get the thing sort of drivable, then take it out and skid on gravel until the ABS cycles, then bleed some more. Could be hard if you live in an asphalt jungle. I did replace the master cylinder prior (had 310,000 miles, so MAW) because it kept going to the floor, new one is good and working fine still, but initially it was also going to the floor. (I had replaced all the brake lines.)
I went through the same thing recently with one of my GMT800s. The ABS is impossible to bleed (without the scan tool) so the solution was to get the thing sort of drivable, then take it out and skid on gravel until the ABS cycles, then bleed some more. Could be hard if you live in an asphalt jungle. I did replace the master cylinder prior (had 310,000 miles, so MAW) because it kept going to the floor, new one is good and working fine still, but initially it was also going to the floor. (I had replaced all the brake lines.)
Is not hard to get an abs event to happen, smooth concrete parking lot and 15 20 mph panic stop should do it.
I'm still waiting for a part, I'll put in in tonight and get back to you guys. Thanks for the advice so far. Anyone ever heard of bleeding brakes with the car running? Sounds off to me but someone suggested it to me.
Yes if you have braided brake lines you are probably ok, had to give options to my suspected bo new mc.
You could run engine, but it shouldn't be needed.
Do you bench bleed mc, install then bleed at mc with a helper pressing the pedal?
Last would be brakes at the wheels, starting with right rear left rear right front and last left front
Do you bench bleed mc, install then bleed at mc with a helper pressing the pedal?
Last would be brakes at the wheels, starting with right rear left rear right front and last left front
