I like pressure bleeders. Try the early Corvette fixed calipers... The worst!
Corolla brake pedal sinking to the floor - master cylinder?
- Thread starter jsean
- Start date
Are the rear shoes properly adjusted?
Are the front calipers sliding? Pads worn straight (and not tapered)?
Are the front calipers sliding? Pads worn straight (and not tapered)?
Those instructions for MC bench bleed are NOT complete for every single time I’ve had to do it.
Whenever I’ve bench bled (on bench or in car), I installed small hose from the (or both) outlet ports back into the reservoir and pumped it repeatedly until clear of bubbles. No caps blocking flow - but full flow again and again until clear.
I would pull both lines off the MC, route hose back into the resi, and pump it 30 times, then reconnect the lines, then do a bleed.
Whenever I’ve bench bled (on bench or in car), I installed small hose from the (or both) outlet ports back into the reservoir and pumped it repeatedly until clear of bubbles. No caps blocking flow - but full flow again and again until clear.
I would pull both lines off the MC, route hose back into the resi, and pump it 30 times, then reconnect the lines, then do a bleed.
So I took the m/c off after work today. Purchased the Dorman bleeder kit from the local parts store. Verified no bubbles in the lines during bench bleed and put the m/c back on the car. Installed the m/c in the car, took of the hose/nipple adapater - installed hard line. Then repeat on the 2nd port. M/C level has not been dropped below the mid point of min and max today during the install and brake bleeding.
Proceeded to do the bleeding as usual - wife stepping on the pedal, open close the bleeder, foot off. I’ve gone through another 32oz of DOT3. Same results - super long travel on the pedal. RR, LF and RF all have strong consistent flow.
LR continues to be odd. Bubbles every single time - tried different tricks too (even speed for pedal down and up, press the pedal down fast and release slow, press the pedal down slow and release fast, pump the pedal 3x and then open bleeder) all same results. Bubbles every time. There were also some times when I’d crack open the bleeder and nothing would happen. Pedal wouldn’t sink either. But the very next time, I’ll open the bleeder and it’ll be a bunch of bubbles along with the usual pedal sink.
I’m just baffled by this thing. I had replaced the rear wheel cylinders in 2020 - brake flush at the time was straight forward. Did a simple brake flush /refresh in 2022 - same deal, no problem at all.
Proceeded to do the bleeding as usual - wife stepping on the pedal, open close the bleeder, foot off. I’ve gone through another 32oz of DOT3. Same results - super long travel on the pedal. RR, LF and RF all have strong consistent flow.
LR continues to be odd. Bubbles every single time - tried different tricks too (even speed for pedal down and up, press the pedal down fast and release slow, press the pedal down slow and release fast, pump the pedal 3x and then open bleeder) all same results. Bubbles every time. There were also some times when I’d crack open the bleeder and nothing would happen. Pedal wouldn’t sink either. But the very next time, I’ll open the bleeder and it’ll be a bunch of bubbles along with the usual pedal sink.
I’m just baffled by this thing. I had replaced the rear wheel cylinders in 2020 - brake flush at the time was straight forward. Did a simple brake flush /refresh in 2022 - same deal, no problem at all.
Yep properly adjusted. I follow the procedure on the Toyota Nation DIY - do it every 10k miles/2 oil changes. Tires spin about 1.5-2 turns on both sides after each adjustment and that’s where they are currently too.
Front rotors and pads look fine - no abnormal wear that I can tell. Pins are cleaned and lubed every fall and spring during winter tires going on and coming off.
Could the wheel cylinder on LR be toast? It’s not leaking but could it have failed somehow causing the air bubbles/poor flow?
Given how this one is going, I couldn’t imagine bleeding fixed calipers!
I have a pressure bleeder I use on vehicles with the normal (at least in my mind) threads reservoir caps. This Corolla has the push on cap and I’m not able to find a pressure bleeder that’ll work without reviews saying they leak. Perhaps I’m missing something in my search criteria - a pressure bleeder seems like exactly what I need…
Valid points. I did take the m/c off and bench bleed it the correct way with the tubes to visually verify no air bubbles. And this time during the install I verified that the fluid level didn’t drop more than half way between min and max.
Same issues though - can’t tell what’s happening with that one corner. Here’s where I stand with failure modes:
1. Could the new m/c be defective? Maybe but I’d think not?
2. Can the proportioning valve be bad? Possibly - but shouldn’t that cause the rear wheels to lock up instead of a consistent poor pedal feel/long travel? And if it were bad - would it cause an entire circuit to go - meaning RF also should have the poor flow / excess bubbles? RF bleeds normally.
3. Wheel cylinder on LR decided to go on vacation permanently - I’ll jack up the back of the car tomorrow before work and verify that the wheel locks up when pedal is pressed.
4. Is air trapped at the proportioning valve? I think this is possible and I don’t know how to verify this one. Any suggestions on this would be helpful
Go get another one… I went through two Oreilly MC before I gave up and went to Autozone. Wasted alot of times messing with it.
Could the left rear brake cylinder be faulty
SammyChevelleTypeS3
$50 site donor 2023
Could be. Plus that brake fluid line should be traced front to back to check for kinks or leak spots. Replacement of the proportional valve may be the quickest thing.
I can't imagine these wheel cylinders are expensive or difficult? And you've gotta bleed that corner anyway.
If OP is truly experiencing weird results with only that corner, I'd probably throw a wheel cylinder at it just 'cause
Looks like about $25 B&M and $8 on RA (plus shipping)
If OP is truly experiencing weird results with only that corner, I'd probably throw a wheel cylinder at it just 'cause
Looks like about $25 B&M and $8 on RA (plus shipping)
That’s what my plan was this morning. The wheel cylinders are about 4 years old and have ~60k miles on them.
But I decided to bleed the back at a steep angle - basically have it jacked up as high as possible and lower the front as much as possible without tires. Then repeat with the front up and the back down below.
Getting steady flow out of LR also now. Pictures from the latest bleed. Brakes consistently, except maybe the first half-1” of the pedal travel. Fine otherwise now. I stood on the brakes at 30mph - stopped without drama, no dragging or locking up of wheels. I think I might be good?
What are these tiny bubbles though in each of the lines? I can’t seem to get rid of them
RR
LR
RF
LF
SammyChevelleTypeS3
$50 site donor 2023
It is harder to get a good seal on the bleeder valves that are not threaded where u connect bleed hoses. Air could be leaking in from any connection. Appears you are getting it. Close. All others were good ? I have seen some need to be driven and pumped a few times and then bled a last time to get remainder out. Too bad u do not have a pump and a helper to pump fluid back to the M/C to see if that changes anything.
Those tiny air bubbles are a result of air infiltration through the threads of the nipple. As the fluid passes through the loosened nipple, a slight negative pressure venturi effect causes some air to be sucked into the fluid path through the interface of the threaded surfaces. Some mechanics apply grease at the base of the nipple to block air infiltration.
Yes, all other bleeders and the LR as of this morning all have consistent brake fluid coming through them. No problem.
I did purchase the reverse bleeder kit that @Nukeman7 suggested. Should I try using it to do a reverse bleed as well? Will that improve things or let the brakes be as is?
Thank you for the explanation.
Are these bubbles just in the bleeder pipe or is it inside the wheel cylinder/piston/brake hard lines as well? Meaning these bubbles would cause an actual impact to brake pedal feel?
Just apply silicone grease on the threads of the bleeder and then bleed as usual?
Wheel bearing grease typicallyDidn’t even know that was a thing.
Do I just apply syl glide on the bleeder before opening it up? Or is there anything else I have to do?
The tiny bubbles are created when air migrates past the nipple threads and goes immediately into the bleeder screw's conical seating orifice. If you close the bleeder screw while the brake fluid flow is still exiting, there should be no (or insignificant) air trapped in the wheel cylinder, piston or brake line. It should not affect the brake pedal feel at all.
Notice that in your top 3 photos, there are no bubbles in the 1-inch section of tubing closest to the bleeder screw. That is because the air infiltration path was eliminated as you tightened the threaded bleeder screw. I'm also guessing the bleeder screw was not fully shut in the bottom photo.
You want to minimize the potential for grease to enter the wheel cylinder, so just dab some wheel bearing grease or silicone paste around the base of the bleeder screws to block the entry path for the air.
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