Brakes Are Weak
06-17-20, 06:59 PM
#1
Brakes Are Weak
The car is a 98 SC300 that is pretty much stock. I restored most of it after hurricane Harvey flooded it. Search my other threads if you are curious about what I did.
Anyway I went for a test drive and the brakes are horrible. It is not corrosion on the rotors. The pedal is mushy and when simulating a panic stop I feel what I believe to be the ABS kicking in. The pedal is as far as it can go but there is poor braking taking place. I also hear an electric motor which I believe it the ABS pump trying to build pressure. My theory is that the solenoids in the ABS block are stuck partially open and an internal leak is diverting pedal pressure internally instead of taking it to the wheels.
Another odd behavior on the first drive was after the car came to a stop in the panic stop the idle speed surged to 1500 rpm if I applied very hard pressure to the brake. It did this even under normal braking conditions if the car stopped and I kept pushing hard on the brake.
The next day to test if the booster was leaking internally I removed and plugged the vac line and he pedal was rock solid plus no idle surge when slamming the brake. I reconnected the booster and the pedal was mushy but no idle surge now.
A few years ago I got into a minor crash when I lost all braking due to the ABS unit leaking internally. The part was unavailable new and no one rebuilt them at the time. The dealer mechanic told me the Bosch ABS systems are generally garbage and have caused bad collisions when they leak internally. I had to have a used one put on the car back then. They were very reluctant to do the job but did it anyway. The car flooded in 2017 and sat gutted in my garage for about 2 years. The first drive since 2017 was literally yesterday.
Toyota now sells the ABS unit at around $1,200 and I have no problem spending it for safety if it will fix the problem. I suspect some regulatory agency forced them to keep the part available. Anyway, what do you guys think?
I have a spare used ABS unit from a junked car I can test out but I am a little stumped here. Another option is to unplug the ABS unit completely and test it out on the isolated streets in my area. Right not it is now throwing any codes.
Anyway I went for a test drive and the brakes are horrible. It is not corrosion on the rotors. The pedal is mushy and when simulating a panic stop I feel what I believe to be the ABS kicking in. The pedal is as far as it can go but there is poor braking taking place. I also hear an electric motor which I believe it the ABS pump trying to build pressure. My theory is that the solenoids in the ABS block are stuck partially open and an internal leak is diverting pedal pressure internally instead of taking it to the wheels.
Another odd behavior on the first drive was after the car came to a stop in the panic stop the idle speed surged to 1500 rpm if I applied very hard pressure to the brake. It did this even under normal braking conditions if the car stopped and I kept pushing hard on the brake.
The next day to test if the booster was leaking internally I removed and plugged the vac line and he pedal was rock solid plus no idle surge when slamming the brake. I reconnected the booster and the pedal was mushy but no idle surge now.
A few years ago I got into a minor crash when I lost all braking due to the ABS unit leaking internally. The part was unavailable new and no one rebuilt them at the time. The dealer mechanic told me the Bosch ABS systems are generally garbage and have caused bad collisions when they leak internally. I had to have a used one put on the car back then. They were very reluctant to do the job but did it anyway. The car flooded in 2017 and sat gutted in my garage for about 2 years. The first drive since 2017 was literally yesterday.
Toyota now sells the ABS unit at around $1,200 and I have no problem spending it for safety if it will fix the problem. I suspect some regulatory agency forced them to keep the part available. Anyway, what do you guys think?
I have a spare used ABS unit from a junked car I can test out but I am a little stumped here. Another option is to unplug the ABS unit completely and test it out on the isolated streets in my area. Right not it is now throwing any codes.
Last edited by texan_176; 06-18-20 at 06:52 AM.
06-17-20, 09:24 PM
#2
did you flush the fluid? if it flooded and sat for 3 years then moisture and air could have gotten into the system. If you had an internal leak you would see the fluid in the reservoir go down over time. i wouild say start the car and sit there pumping the brakes for like 10 mins and then check the fluid. Same concept would apply to check the abs as well but you'd have to drive around slamming your brakes to engage the abs and then check the fluid level after some time of driving. If the leak is bad enough that the car barely stops then it shouldnt take too long for you to notice the difference in fluid level
Last edited by - V -; 06-17-20 at 09:44 PM.
06-17-20, 11:40 PM
#3
This does sound like it could be brake fluid and/or ABS unit related but also keep in mind that the factory SC front brakes, even on SC400's and 98-00 SC300's, are not really the sized the best for these heavy cars. Depending on how you drive the car you may want to upgrade to the 1995-2000 LS400 front calipers and rotors. They are a night and day difference from stock. With my factory stock front brakes in newly serviced condition any minor panic stop would immediately start the ABS unit pumping and the brakes barely hauled the car to a halt safely.
When you reference Bosch ABS systems are you referring to your SC300? I wasn't aware that Toyota used Bosch as one of their OEM suppliers. I thought their ABS unit was by Aisin. And your brake booster should be 100% ruled out for any leak suspicions before moving to the ABS accumulator. A failing booster plus the tiny stock front brake calipers and rotors can cause some of the symptoms you are describing if really pushing the bone stock SC braking system hard.
However even accounting for the generally poor performance of the stock SC front brakes and if ruling out a failing brake booster also then IF the problem can be definitely pinpointed to the ABS accumulator unit failing due to a leak or something else then I'd say the new $1200 part from Toyota/Lexus is probably worth it although I'd get it from one of the more discounted Lexus dealers online if you need it.
When you reference Bosch ABS systems are you referring to your SC300? I wasn't aware that Toyota used Bosch as one of their OEM suppliers. I thought their ABS unit was by Aisin. And your brake booster should be 100% ruled out for any leak suspicions before moving to the ABS accumulator. A failing booster plus the tiny stock front brake calipers and rotors can cause some of the symptoms you are describing if really pushing the bone stock SC braking system hard.
However even accounting for the generally poor performance of the stock SC front brakes and if ruling out a failing brake booster also then IF the problem can be definitely pinpointed to the ABS accumulator unit failing due to a leak or something else then I'd say the new $1200 part from Toyota/Lexus is probably worth it although I'd get it from one of the more discounted Lexus dealers online if you need it.
Last edited by KahnBB6; 06-17-20 at 11:50 PM.
06-24-20, 09:44 PM
#4
Thanks Guys.
I made little progress on the car; too busy with other things. However, I have an Autel mid grade scanner I hooked up after reading this:
https://www.clublexus.com/forums/rx-...s-problem.html
Well, the scanner says the SC does not support reading live data from the ABS system so that was a dead end. The service manual is very low tech when it comes to the ABS sensors and tone rings. It just says to check for a level of resistance between the pins on the sensors and to ground. The tone rings are just to be checked for corrosion or dirt. It seems as if even a Lexus dealer would be unable to read live ABS data.
Anywho, I did the booster tests detailed in the service manual and it passed. With the booster not assisting the pedal is rock solid with minimal play. I am not a body builder but even with my full force on the pedal it will not budge. So I went for another test drive around the neighborhood but could not replicate the ABS kicking in under hard braking. The brake is still weak but not as weak. Before it was a 3 of 10 and now it feels like a 5 of 10. My plan is to wait until a rainstorm and do the hard brake stop in a safe area to see if the ABS system works when it actually should be working.
About a month ago there was a junked 98 in a yard in my area so if it is still there I can buy all of the sensors and swap them out. The OEM sensors are over $250 each new so that's a little insane. Used, it would be a $50 experiment and if I do not need them I can have spares for my 99. All of my existing sensors were submerged for 8-10 hours during the flood.
There is an ABS delete kit I have seen where you bypass the module entirely and run lines directly from the master cylinder. I really do not want to do that but I might be forced to if I do not feel confident the car will come to a stop when I want it to.
More to come soon.
I made little progress on the car; too busy with other things. However, I have an Autel mid grade scanner I hooked up after reading this:
https://www.clublexus.com/forums/rx-...s-problem.html
Well, the scanner says the SC does not support reading live data from the ABS system so that was a dead end. The service manual is very low tech when it comes to the ABS sensors and tone rings. It just says to check for a level of resistance between the pins on the sensors and to ground. The tone rings are just to be checked for corrosion or dirt. It seems as if even a Lexus dealer would be unable to read live ABS data.
Anywho, I did the booster tests detailed in the service manual and it passed. With the booster not assisting the pedal is rock solid with minimal play. I am not a body builder but even with my full force on the pedal it will not budge. So I went for another test drive around the neighborhood but could not replicate the ABS kicking in under hard braking. The brake is still weak but not as weak. Before it was a 3 of 10 and now it feels like a 5 of 10. My plan is to wait until a rainstorm and do the hard brake stop in a safe area to see if the ABS system works when it actually should be working.
About a month ago there was a junked 98 in a yard in my area so if it is still there I can buy all of the sensors and swap them out. The OEM sensors are over $250 each new so that's a little insane. Used, it would be a $50 experiment and if I do not need them I can have spares for my 99. All of my existing sensors were submerged for 8-10 hours during the flood.
There is an ABS delete kit I have seen where you bypass the module entirely and run lines directly from the master cylinder. I really do not want to do that but I might be forced to if I do not feel confident the car will come to a stop when I want it to.
More to come soon.
06-10-21, 10:49 AM
#5
Solved my brake problems and thought I would post what fixed it if anyone read this thread down the line.
The slider pins in all of the calipers were sized so I essentially lost 50% of the brake force since only the brake piston side of the caliper was pushing the pad on that side against the rotor. I cleaned the pins and the ports on the brackets then greased it up before reassembly. The brakes bite hard now. They are still sort of less than what I think a coupe should have in terms of braking power but they work as well as a stock brake system should.
Oh, and another thing I noticed now that I am regularly driving the car is that the ABS pump will run and build pressure for 3-5 seconds once I start the car in the morning and get moving at 5 mph. If I restart during the day the pump does not come on since internal pressure is still present. My wife's Honda does the same thing. If you have a 97+ SC does your ABS pump fire up like what I described?
The slider pins in all of the calipers were sized so I essentially lost 50% of the brake force since only the brake piston side of the caliper was pushing the pad on that side against the rotor. I cleaned the pins and the ports on the brackets then greased it up before reassembly. The brakes bite hard now. They are still sort of less than what I think a coupe should have in terms of braking power but they work as well as a stock brake system should.
Oh, and another thing I noticed now that I am regularly driving the car is that the ABS pump will run and build pressure for 3-5 seconds once I start the car in the morning and get moving at 5 mph. If I restart during the day the pump does not come on since internal pressure is still present. My wife's Honda does the same thing. If you have a 97+ SC does your ABS pump fire up like what I described?
06-10-21, 11:35 AM
#6
According to the New Car Features for the 98 SC3/400 and LS400 booklet, the ABS self checks after engine start up and reaching 4 mph for the LS400. I'm assuming it's the same with the SCs because I too experience the ABS creating a low but strong buzzing noise every so often when I start driving my 99 SC400. It lasts around 3-5 seconds like you said and everything is normal after that. My car does have TT brakes installed w/ new brake lines so that could be one of the reasons it frequently is checking itself.
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