Brakes, what have I overlooked?


#1

I’ve done brakes on my cars and other family members cars, and a few friends cars over the last 40 years and I’ve never had a problem that I couldn’t solve until now.



We have an 86 Toyota Tercel 4wd wagon. Its been in the family since new, and no we didn’t name it and the check engine light is not on. 330k miles.



Its brakes have been deteriorating over the last year or so. I have replaced brakes on it several times over the years, but in the last year, it seems like its been harder to stop. In the last 5 years, all the flexible brake lines have been replaced. The rear wheel cylinders have been replaced with new ones (made in China). In the last two years, the rear drums, shoes and hardware have been replaced. In February, I was doing another brake job on the front, new rotors and pads and caliper kits. One of the calipers had a lot of rust on the piston so I bought a reman caliper and used it instead. I put in new caliper bushings and pins, hardware and rubber seals for the pins.



During the bleeding, the master cylinder started leaking, so I got a reman for it. The pads I used were ceramic pads. The brakes were ok for awhile, but continued to deteriorate. I pulled the front calipers off and found the ceramic pads had cracked, so I went back to semi metallic (Autozone Duralast, which I’ve always had good luck with). No improvement. I could feel the pedal going to the floor so I figured the reman master cylinder had an internal problem so I took it back and got another one, the threads for the fittings were buggered up so I took it back and got another one, it was missing the seals so I took it back and got another one, it looked good so I tried it, no improvement, still felt like an internal problem.



So I bought a brand new one, it feels better but the brakes still require too much pedal effort and pedal travel and the stops are long. I cannot lock up the wheels no mater what. It feels like the rotors were greased. Even though the rotors were new, I had a little shaved off them to rough up the surface, still no better.



Even though the booster passes all the tests listed in the FSM, I put a reman on anyway. I matched the boosters push rod with the master cylinder so there is no play between them. Still no good, but I can lock the passenger side front wheel now. I pulled the metering valve and checked it, its good.



I have bleed the brakes by gravity, the old fashion two man way and with one of those Mityvac hand pump things (that doesn’t work very good, it sucks air in around the bleeder valve). Even though the pedal travel is excessive, the brakes do not “pump up” like brakes do when there is air in the system.



There are no leaks in the system, the fluid level in the master cylinder does not drop. When I hit the brakes, it requires more effort and there is more pedal travel than there should be for normal stops. Stand on the pedal and it will stop from 60 mph in just under 150 feet. The front end will nose dive on hard braking, but there are brand new shocks and struts all around (KYB’s). What have I missed?



I have replaced the stock 175/70-13 tires with 185/65-14 tires, Dunlop SP40, but the brakes were going down hill before I did this.




#2

off hand i think you may not be getting all the air out of the MC. even though you’re changing the MC, the rod needs to be adjusted each time to get full throw to have a full stroke, so it can ppush all the air out.

do you have the factory bleed sequence after you bleed the MC? usually it is rr, lr, fr, fl. although that may be different for your car. i dont own one, aso i can’t tell you what it actually is.


#3

Another thought. Did you change or check the check valve to the brake booster? The check valve makes sure there is plenty of vacuum available to the booster, but if it is not functioning properly, the booster will not hold vacuum.


#4

upon re reading your post,

did the mushy brakes start in feruary after you did the master cylinder replacement? it appears if your time line is correct, that before the master cylinder work, you only had poor braking, and failing pads, correct?

if im reading it correct, the mushy part didnt start till after the MC started leaking, and you replaced it right?


#5

Have you tried bleeding the master cylinder at the tubing connections at the master cylinder? It might help some. Make sure the master cylinder is level too. You might have to jack the car if it is not. Nobody else would recommend this, so let me know if it works, or don’t.


#6

I agree with the idea that there is still air in the system. Did you successfully bench-bleed the master cylinder when you replaced it?

Is there an external check-valve for the booster (sometimes they will put a check valve in-line rather than on the booster itself)?

I have never seen one of the small hand vacuum pumps that will bleed an entire system. If push comes to shove, you could just take it to a brake/alignment shop and ask them to bleed it. It won’t cost much and you’ll have peace of mind (and I know it sucks to have people tell you that you can’t bleed brakes, it seems like such a simple procedure. Some cars are just trickier than others.)


#7

" We have an 86 Toyota Tercel 4wd wagon. Its been in the family since new, and no we didn’t name it and the check engine light is not on. 330k miles"

333,000 miles…At this point, the tired engine may no longer have enough vacuum to properly operate the PB booster unit. Check the vacuum at the booster fitting. If THAT checks out, install a set of genuine Toyota pads and shoes.


#8

At 317k I replaced the old 3AC engine with a reman 4AC. Vacuum at idle is 20+ inches.


#9

The new master cylinder bench bled beautifully, some of the remans were difficult to get to bleed right.

There is an external check valve in the line to the booster, and it holds. I am going to look for a shop that has a pressure bleeder. I’m thinking that one of the lines loops upward from the MC and it might be very difficult to get air out of that loop.


#10

No I didn’t do it there. I did bench bleed it and installed it when it was full of fluid so fluid was flowing from the fittings as I hooked up the lines.


#11

The pedal isn’t mushy so much. The pedal travel is excessive and it takes more pedal pressure than it used to, but with the latest MC, the pedal isn’t mushy. Its kind of hard to describe the feeling but the closest thing would be that the pads and rotors are covered with grease.


#12

I adjusted the rod each time using a caliper. I don’t have that special gauge the show in the FSM and don’t know where to get one. The FSM lists it under common tools. The sequence isn’t quite so exact on modern systems as it was in the days of single master cylinders. Left front and right rear are connected to one cylinder and the right front and left rear to the other. So you just do the rears, then the fronts.


#13

Here’s a shot in the dark. At any time (and don’t take this personally)when you did the front brakes did you by any chance put the calipers on the wrong wheel. On many vehicles, calipers will fit both wheels but if they are on the incorrect wheel the bleeder valve will be towards the bottom rather than towards the top. This will prevent the system from ever being completely bled.


#14

Just a hunch, lift the rear wheels and while a helper presses the brake pedal attemt to turn the rear wheels. I suspect that the proportioning valve is not allowing the rear brakes to operate.


#15

Then you did better than what I said to.


#16

They’re not interchangeable. Also, I only do one side at a time, use the other as a reference, though by now, I think I have it burned in memory.


#17

There may well be a problem with the rears, but its not the metering valve. The parking brake sets normally but it doesn’t hold well either, never has. But they do hold well enough to torque the wheel nuts to spec. I put on new shoes and drums because the old ones didn’t hold well, even though they weren’t worn down but the new ones don’t work any better. I think they are a very poor design, as are all Japanese rear drum brakes.

On American cars with drum brakes, the star wheel is at the bottom, each time it adjusts, the wheel cylinder goes back to the same position. In Japanese drum brakes, the star wheel is just under the wheel cylinder, so as the shoe and drum wear, the wheel cylinder keeps going outward. I have seen the wheel cylinder seals pop out even though the shoe and drum were still within their wear limit. It’s a very unsafe design.


#18

The wheel cylinder seals keep moving outward.

The proportioning valve appears to be working. I did remove it and check it for obstructions. It also allows me to bleed the rear brakes and I have torqued the rear wheel lug nuts with someone stepping on the brake pedal.


#19

Check for strong vacuum at the booster unit. Sometimes the rubber hose can collapse or delaminate internally pinching off the line…Also, the booster has a check valve to hold vacuum at WOT. Make sure it’s working properly…You said you replaced all the flex lines. Check them again to be sure none are “ballooning” and stealing fluid volume and pressure…


#20

Did that. 25" of vacuum even when working the throttle. Goes even higher when working the throttle because on decel, the vacuum builds and the check valve holds it. I bought a new vacuum line tonight just because the ends are getting stiff and brittle, they won’t be long for the world.