[hong_huo]

I fixed sticky front brakes by replacing the master cylinder (MC). After tearing down the broken Aisin MC I felt this problem could happen to others. I am posting my experience below. Hope it helps someone.

My car
1997 Camry LE 4cyl w/ 220K miles. It has front disc brakes and rear drums

Symptoms
Starting 2 months ago, I noticed some intermittent "drag." On highway the steering wheel shakes, and humming noise could be heard from front brakes. Brake pedal was hard and touchy. Stopped the car and inspected front wheels, both got very hot, and both were found locked up when the car was jacked up.

Troubleshooting
Checked both calipers. They clamped hard on the discs, and it was impossible to push pistons back. Opened bleeder on one caliper, both calipers released. Loosening front brake hydraulic line on MC did the same. Suspected fluid return path was blocked in MC.
Removed MC, found front port was indeed blocked at full release position, as opposed keeping a small flow to the reservoir. This caused pressurized brake fluid to be stuck in the line, locking both front brakes

Fix
Replaced MC. Very easy job, just two 10mm hydraulic line heads and 2 14mm nuts holding MC on booster. Don't need to remove ANYTHING else. Filled new MC with dot 3 brake fluid and did a bench bleed before hooking back on. Didn't bleed fluid to wheel ports. The brake pedal started a bit soft, but firmed up after driving a few blocks. (I was taking chance here - please follow proper bleeding procedure)

Analysis
Opened broken MC. It's an Aisin model. Found outer piston's (for front brakes) rubber ring blocked the tinny relief hole to the reservoir. I can think of two possibilities: Either the rubber ring deformed, or the shaft was stretched longer.

Thoughts
Toyota parts are famously (or notoriously) consistent. What happened to me could happen to others. If you are experiencing similar issues, pay attention to the MC.

 

[speedy25]

Similar symptoms also happen when the rubber hoses swell and fluid cant return to the MC. They fluid only moves under pressure. Opening a bleeder is the only way the car can roll again.

Glad to see that someone else besides me knows about the compensation post and the importance of it NOT being blocked. Besides debris it can be closed off when the pushrod is misadjusted.

Work Smart!

-SP

 

[hong_huo]

Yeah I thought about collapsed lines first, but that was ruled out when MC port relieved both calipers. Also hoped push rod adjustment was an option. Sadly the MC had to go in the end. The Aisin is a pretty good unit, still a mystery how its front return path got blocked over time. If you have any idea I can research further - I kept the original MC (in parts)

 

[Toyota_JP]

Someone needs to calculate an estimate for how much time and $$ the Toyota Forum saves its members with posts like yours. I don't have that problem (yet) but the problem just might pop up. The symptoms to watch for and the fix are now lodged somewhere in my memory and it's right here if I forget. Thanks!

 

[hong_huo]

Thanks for the encouragement. I learned so much from this forum. Glad I could contribute.

 

[speedkar9]

I had the exact same problem with similar symptoms to the OP on my Solara:

-Drag, feeling slow a highway speeds, in the city it was fine
-Brakes would get really hot after a highway drive
-Steering wheel starts to vibrate after 10 min of highway driving
-Brake pedal violently pulsates when they heat up
-Occasionally the brakes would "unlock" while on the highway and the vibration would go away
-More persistent the hotter the weather
-Brake pads worn down pretty quickly

I did a similar diagnostics, after a full brake service. While I didn't find cracking opening the lines instantly releasing the pressure, changing the master cylinder has helped eliminate the drag at highway speeds, and the car doesn't vibrate as violently anymore or feel lazy.

I feel like I might have permanently warped the rotors (slightly) and took a good amount off my pads.Should have diagnosed and fixed this issue earlier.

Just for reference, here's how to change the master cylinder:

 

[insightbrewery]

Hm, I think I have similar problems on a '95 non-ABS. I bench bled the cylinder and bled all four corners, but the pedal really only engages very close to the end. When I come back after a drive and take off the wheels, driver's front is very hot (lugs will burn you).

Just got a replacement from the Pick-n-pull, so will put it in tomorrow and see if it goes away and brakes work OK.

Thanks for the post

 

[hong_huo]

Is the passenger side hot as well? If only the driver side gets locked the problem is likely on this side. Suggest checking:
-Caliper piston stuck?
-Caliper pin stuck?
-Brake line blocked internally between caliper and master cylinder?

Deep pedal engagement is likely a separate issue. Push rod might be too short, causing large free-play, or there's still air in the brake lines, or master cylinder has internal leak.

 

[insightbrewery]

Is the passenger side hot as well? If only the driver side gets locked the problem is likely on this side. Suggest checking:
-Caliper piston stuck?
-Caliper pin stuck?
-Brake line blocked internally between caliper and master cylinder?

Deep pedal engagement is likely a separate issue. Push rod might be too short, causing large free-play, or there's still air in the brake lines, or master cylinder has internal leak.

Passenger as well, sorry forgot to mention. I bled the system for many cycles after the bench bleed, no air coming out. I'm betting on internal leak.