3rd & 4th Generation (1992–1996 & 1997–2001)Toyota Camry Discussion for years: 1992-1996 & 1997-2001
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Got a 95 wagon, 4 cyl ABS. The pedal started to get a little soft inbetween brake jobs so I figure maybe the master's getting tired. No noticeable loss of fluid. Stops on a dime. Pedal is just a little soft and the bottom getting a little further all the time. Brakes are midway worn and the rear calipers are a little hung up give that uneven wear but I'm maybe 20,000 into a brake job.
So I pulled the master, no slight leak out the back, pumps like a bastard both ports. So I stuck it back on and start getting on the pedal. Now, I'm not sure if this was the problem all along or if in pumping it hard I finally got something to leak, but the 90 deg. bend in the outlet from the rear proportioning valve to the passenger's side tire is letting a tiny stream go. My favorite job, odne those lines on every wagon I've ever had. So I replace the lines to both sides in the rear and pull the calipers, free and lube the pins and throw on some new pads and go to bleed it.
Bleeds fine with the car off, air out, nice solid peddle. But as soon as I turned the car on I'm right back to bottomless peddle. It stops perfectly at high point on pedal travel, but that is a false bottom. Then it very slowly continues to ride to the bottom of the pedal travel - without any noticeable loss of brakes.
So I figure maybe the master was bypassing after all, even though it looked clean and no hint of a leak, maybe it is tired and just slipping a little fluid from the brake side of the circuit back to the reservoir side although the brakes hold through the whole process and it seems to maintain enough pressure to keep them on even when fully bottomed.
So I bought a rebuilt master, change the reservoir and toss it on there and identical symptoms. Now, maybe I got a bad rebuild, but thought it was time to ask if anybody has experienced this before I drive myself crazy. No apparent leaks or fluid loss anywhere. The brakes are hard without the car on, but the pedal chases slowly to the floor when its running and the power assist is there. I know it is hard to get the rear proportioning valve to bleed sometimes, but I bled at the line exits on the proportioning valve as well as out the bleeder screw on the caliper. And I can't pump it up and get better results. Same thing. Hit the pedal three or four times and get precisely the same result. Since I'm hitting it quickly I go as far as the false bottom and that point barely rises but as soon as I try to hold the pedal down it just starts that slow descent to the very bottom.
So there's the novel on this one. Any thoughts appreciated.
do you get a rough idle when the pedal is applied? maybe the booster or a possible unseen leak is the only thing i can think of
Thanks for the ideas. No stumble, don't think that there is vaccuum problem or problem with the booster. Maybe another tiny, tiny leak is a possibility. Some kind of infinitesimal hole that is passing a little fluid but not enough to show up anywhere. Blows my mind that I can't see it. I must have puthalf a gallon of fluid through this thing bleeding, pumping trying to get something to show up.
And when I did find the tiny leak by the rear proportioning valve I congratulated myself on solving the problem, but no dice.
Any other likely out of the way rot spots that lines usually go that I should check?
Hard pedal when the engine is off; soft pedal when there is power assist. Sounds like you need to bleed the ABS unit. I know some manuals may say it's not necessary, but that applies only if no air gets into the secondary pressure relieving circuits. And no, exercising the pump alone won't help. You have to open the pressure reducing solenoids and activate the pump. Be careful the short time limit you can activate them or they'll burn out. It's like < 10 seconds for every 5 minutes!
That generation is probably a Bosch 2 or a licensed copy. 97 and later uses the Bosch 5.3 or a licensed copy. The advantage of these older systems is that they're easier to bleed than later ones with variable-current tri-state solenoids, like the Bosch 7 and 8 with acceleration slip control, brake force distribution, proportioning valving, stability control, etc etc.
I don't know if these 94 systems have high pressure reservoirs. They're dangerous. I'd say call up a dealer, describe what you did. And ask if they can use an actuator to bleed the ABS system. And insist that's to be done, or you'll drive out with an empty wallet and still a soft pedal. (Actually you shouldn't drive with a less than perfect brake system ) See what they say or how much it's going to cost.
And yes, I think brake systems should be bled at least every 2 years.
Quote:
Originally Posted by archibald tuttle
Bleeds fine with the car off, air out, nice solid peddle. But as soon as I turned the car on I'm right back to bottomless peddle. It stops perfectly at high point on pedal travel, but that is a false bottom. Then it very slowly continues to ride to the bottom of the pedal travel - without any noticeable loss of brakes.
So I figure maybe the master was bypassing after all, even though it looked clean and no hint of a leak, maybe it is tired and just slipping a little fluid from the brake side of the circuit back to the reservoir side although the brakes hold through the whole process and it seems to maintain enough pressure to keep them on even when fully bottomed.
So I bought a rebuilt master, change the reservoir and toss it on there and identical symptoms. Now, maybe I got a bad rebuild, but thought it was time to ask if anybody has experienced this before I drive myself crazy. No apparent leaks or fluid loss anywhere. The brakes are hard without the car on, but the pedal chases slowly to the floor when its running and the power assist is there. I know it is hard to get the rear proportioning valve to bleed sometimes, but I bled at the line exits on the proportioning valve as well as out the bleeder screw on the caliper. And I can't pump it up and get better results. Same thing. Hit the pedal three or four times and get precisely the same result. Since I'm hitting it quickly I go as far as the false bottom and that point barely rises but as soon as I try to hold the pedal down it just starts that slow descent to the very bottom.
So there's the novel on this one. Any thoughts appreciated.
Since this is mentioned. It seems like this happens to me but the other way. it becames hard to press but it still brakes. Almost like there is too much fluid
Hard pedal when the engine is off; soft pedal when there is power assist. Sounds like you need to bleed the ABS unit. I know some manuals may say it's not necessary, but that applies only if no air gets into the secondary pressure relieving circuits. And no, exercising the pump alone won't help. You have to open the pressure reducing solenoids and activate the pump. Be careful the short time limit you can activate them or they'll burn out. It's like < 10 seconds for every 5 minutes!
That generation is probably a Bosch 2 or a licensed copy. 97 and later uses the Bosch 5.3 or a licensed copy. The advantage of these older systems is that they're easier to bleed than later ones with variable-current tri-state solenoids, like the Bosch 7 and 8 with acceleration slip control, brake force distribution, proportioning valving, stability control, etc etc.
I don't know if these 94 systems have high pressure reservoirs. They're dangerous. I'd say call up a dealer, describe what you did. And ask if they can use an actuator to bleed the ABS system. And insist that's to be done, or you'll drive out with an empty wallet and still a soft pedal. (Actually you shouldn't drive with a less than perfect brake system ) See what they say or how much it's going to cost.
And yes, I think brake systems should be bled at least every 2 years.
Learn something new every day. I've often had trouble with the LSPV (Load Sensing Proportioning Valve) bleeding. The ones on the pick up trucks actually have a bleed screw right on the LSPV. So I wondered if the ABS could serve as a high point air trap as well.
before chasing how to deal with the ABS bleeding if that is the problem, let me carefully articulate the symptom again and the reason I'm doubtful it is air and then please feel free to tell me why I'm wrong. It is not precisely a situation of hard pedal without boost, soft pedal with boost.
The car has a primary bottom even with the boost. It stops on a dime. To the unskeptical not looking for a problem it feels fine. But if you stay on the brakes with good foot pressure you can slowly push them to the bottom although the brakes never let up. When I have air problems, I don't get that hard bottom and then it slowly pisses away. Rather you don't get brakes until well down in the pedal or after a couple pumps. And I can't 'pump it up' apply the brakes several times swiftly as a i would to pump up an aired system makes no difference whatsoever.
Now, I suppose if the pathway to the aired up portions of the ABS unit is very small, maybe it very slow in a way I've never experienced to allow the fluid to displace into the air filled portion so I don't get a traditional soft pedal. I'm going to try pumping the pedeal again and following down several times to see if it is possible to get a completely hard pedal by this slightly slower method, inother words to fill some aired up area that is filling slowly, because presumably it would be just as slow for the air pressure built up during braking to force the fluid back to the master, so even though this pumping would be slower than what it normally take ssto catch up with air in a traditional system, I need a different approach.
I did take the car by my goto mechanics, some guys I knew as the local hotrod motorheads when I was in high school who graduated from the points and condensor era and have been my best diagnostic companions for the past 15 years. He confirmed my suspicion that the pedal feels just like a bypassing master cylinder. It offers a good stop and early resistance and then drops very slowly without releasing the brakes. We put the car on the lift and canvased for leaks again. (I have to do it lying under the car so this was another confirmation that I didn't seem to be missing any small leaks -- although I thank JJJJJJ (is that enough J's?) and abew330 for reiterating that this symptom definitely could also be a very small leak.
Could I have gotten a bum rebuild?. I don't know, for $69 for a new one I might just triple confirm that the problem is not the master before I go to the next level of inquiry into the ABS.
And muminiasty, I think if you have the opposite feel my first intuition would be a problem with the booster unit.
JohnGD -- As to actually bleeding the ABS, I confess this is an area of service I haven't spent a lot of time on because this is my only rig with ABS. Have two other 4 wheel Disc wagons (gen 3 96s) without. One of the ABS sensors has been bum on this one since I bought it with 120,000 on it and a blown engine. We took the codes back when I put it on the road and I knew which sensor and tried to take the thing off while doing an all around brake jobe and new rotors and it broke off and the remeant part wouldn't come out of the little pocket , so I've never operated the ABS and to my knowledge its has never been triggered or operated in the 6 years we've had this car on the road. I don't know if having one bad sensor would shut the thing down or not but brakes were perfect after that brake job and I just let sleeping dogs lie.
Of course the factory manual (for a 1994 Gen 3 posted at Automotive forum.com) offers no procedure for bleeding either the Nippondenso or Bosch Unit. After any work, they specify bleeding but refer you to a section of the manual which describes traditional bleeding from the master to the wheel and makes no reference whatsoever to addressing the ABS unit specially or independently.
I've definitely got a Bosch (their name is on it and it matches the appearance of the unit shown in the Bosch component location diagram in the repair manual). I'm not familiar with the internal geometry of the unit or what would constitute "opening the pressure reducing solenoids" or what constitutes "high pressure reservoirs". But 2 weeks ago I wasn't familiar with lifting or transporting 1000 lb slabs of granite and now I am thanks to thoughtful but cautious responses on stone working websites and my adaptation of my experience moving heavy machinery. Sounds like dealing with the ABS is another technical skill that requires study, understanding the equipment and is not recommended for amateurs. So, I'm ready to learn.
Color me empirical, but for my opening idea for bleeding something like this that keeps me out of high pressure areas or actuating it at all would be to crack the outlet brakelines one at a time as if they were bleed screws. Since, to my knowledge, the thing hasn't actuated during the 7 years we've had it and the brakes have been 100% until last couple months, is it really necessary, if the thing is a tiny boat anchor, to actuate it or if you bleed it through at its steady state might that help? Alternatively, I could just grab some metric double flare "t"s and eliminate the ABS from the hydraulic circuit.
So another novel, trying to be very specific and don't hesitate to let me know where I might be specifically wrong.
Checked with another mechanic I use and he supported the theory of bleeding the ABS.
Checked with a toyota dealer where I know the service manager and he gave me his goto guy, and his guy said that symptom which you most often associate with a master cylinder bypassing can also be duplicated by one of the calipers hanging up. Now I just lubed all the pins and replaced the pads lubing the ends of the pads in the clips.
Current plan is to put the thing on a lift on Thursday and make sure every brake is grabbing hard and doesn't appear to be hanging up.
Meanwhile, I'm also trying to chase down T's just to cut the ABS right out of the hydraulic system. It looks to me like each line coming to the ABS from the Master supplies two wheels split left front with right rear / and right front with left rear. So, if I use a straight T, and that is always the if because metric double flare brake t's are harder to come by than american thread, I can just jump around the ABS altogether and if the symptom goes away I know that was the problem.
Just got in from replacing the front rotors. I had the backs off and they didn't look that bad all around and I could see the outside of the fronts didn't look bad, so I didn't replace the rotors. But when we had the car on the lift my friend noticed that the inside of the front rotors were gruesome. so I pulled the front calipers and mounts again to change the rotors. And while I had them off I noticed that the inside pad on both sides was hanging hard. So I pulled the inside pad out of the mounts and ground the top and bottom maybe a 32nd or so and the pads moved much better, maybe even like they are supposed to.
I had a friend putting the front pads on and I didn't realize that the insides were so tight. So this is just the kind of symptom that the toyota dealer told me to look for. I've only driven it around the yard since I put it together, but I think that was the problem.
I still haven't figured quite how that symptom arises. So blue sky here. If you apply a certain amount of pressure and the caliper pushes against the inside pad, and it doesn't move easily, so the result is to pull the outside shoe against the rotor and you stop, but very slowly the inside pad travels in which makes the peddle drop slowly after you have already stopped. The only thing I can't figure out is why the pad is forced out far enough for the symptom to continually repeat.
Did you ever resolve this? I am having a similar problem, though it is non-ABS, and would be curious how you fixed it. I've started a thread on my problem at: Brake Pedal Sinks - http://www.toyotanation.com/forum/sh...36#post2986236
Thanks,
Kep
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Often, it's the loose screw between the steering wheel and the driver's seat that needs to be fixed first!
Id be more leaning to the booster, if it was air then the pedal would be soft with power assist and soft without, as u can compress air but not a liquid. The booster having a vacuum leak seems to be the only possiblity i can see. Is the reservoir staying topped up or losing fluid?
Did you ever resolve this? I am having a similar problem, though it is non-ABS, and would be curious how you fixed it. I've started a thread on my problem at: Brake Pedal Sinks - http://www.toyotanation.com/forum/sh...36#post2986236
Thanks,
Kep
Mentioned a couple comments back that the dealer's service manager (Bristol Toyota - thank you Chuck) suggested I check for brake pad hang up because that can cause what is universally thought of as the 'master cylinder bypass' symptom.
I thought he was puttin me on and we had just put new pads on. But I was doing the back while a friend was doing the front, and it turned out that the inside front pads were too tight when loaded in the caliper.
I pulled them off and ground the tabs slightly. A little more lube and off to the races. I still haven't worked out the physics of how it could keep repeating that symptom. I get how it could start that way if the pads didn't move with the first burst of hydraulic and then slowly succombed, but I can't figure that they would back off far enough from the rotor, unless you had that distinctive warped rotor feel or something, to repeat the symptom every time you brake.
But I suggest checking that the pads are moving freely in the calipers before moving on to exoctic solutions, cause that is the cheapest easiest thing to check.
Mentioned a couple comments back that the dealer's service manager (Bristol Toyota - thank you Chuck) suggested I check for brake pad hang up because that can cause what is universally thought of as the 'master cylinder bypass' symptom.
I thought he was puttin me on and we had just put new pads on. But I was doing the back while a friend was doing the front, and it turned out that the inside front pads were too tight when loaded in the caliper.
I pulled them off and ground the tabs slightly. A little more lube and off to the races. I still haven't worked out the physics of how it could keep repeating that symptom. I get how it could start that way if the pads didn't move with the first burst of hydraulic and then slowly succombed, but I can't figure that they would back off far enough from the rotor, unless you had that distinctive warped rotor feel or something, to repeat the symptom every time you brake.
But I suggest checking that the pads are moving freely in the calipers before moving on to exoctic solutions, cause that is the cheapest easiest thing to check.
Brian
I know you're still trying to figure out how it affected your brake feel... but could you discuss why when the engine is off, the brake pedal is hard?
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) See what they say or how much it's going to cost.
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