Intermittent Brake Problems

[B084R]

I have an 08 4R 4WD with Xres. About 7 months ago after a short drive I parked the car for about 30 minutes. Driving out of the parking lot when I applied the brakes the car would stop but the pedal would slowly go to the floor and the car would creep forward at idle. Pumping the pedal brought the brakes back so the car would stop but the problem persisted. I drove about 3 miles home and called the dealer. Took the car over to the dealer (About 3 more miles) and had the service advisor go for a test drive with me. Brakes worked fine on the test drive so he said to bring it back if it happened again.
Yesterday the same thing happened again under very similar circumstances. This time when I got to the dealer I got lucky and the service advisor was able to see the problem in their driveway. It was closing time so I scheduled an appointment for Monday and brought the car home. As soon as I left the dealer the brakes were back to working fine. So, I'm a little worried the dealer will have a bit of difficulty diagnosing and fixing the problem on Monday.
It would seem that the probable causes might be the master cylinder or something in the control circuits. The car stops straight so I'm thinking it probably isn't one of the calipers. I was wondering if anyone has experienced this and if so has found a solution. I would like to be able to point the dealer in the right direction if possible.
Sorry for the long post, it's my first but I have been reading the fourm since I bought the car in December. Any help would be greatly appreciated. Thanks.

 

[dcrogers11]

You just described the problem I started having this week. I just got my 4runner out of the shop after an accident. I am taking it back to see if they can repair it as soon as I get back home. I'll be interested to see what post come back.

 

[leftyguns21]

It

 

[Methodical]

in my opinion our 4runners have excellent brakes.

The master cylinders however, are not cheap, due to the fact they use an electric motor to pressurize a nitrogen-filled cylinder for brake assist, as opposed to the normal vacuum assist.

 

[B084R]

Update

I stopped by the dealer today. They have been in contact with Toyota Corporate and have decided to replace the master cylinder. They are not 100% sure this the cause of the problem but it appears to be the most likely candidate. No codes were set so this is quite difficult to diagnose.

I got really lucky that the service advisor was able to see the problem before it went back to working properly. He has been great a great help getting this through the system and has kept me updated.

I should get the car back tomorrow and will post an update then.

 

[B084R]

Update

Got the car back from the dealer today. They replaced the master cylinder and, working with Toyota Corporate, tested the brake system extensively. Seems like the pedal is a bit harder than it was previously which I hope is a good sign. Hopefully the problem will not reappear.

I was quite pleased with both the dealer (Hooman Toyota of Long Beach, CA) and with the response from Toyota Corp.

 

[ALFORDThomas]

Before you swap the master brake cylinder, I would rather exchange or at least thoroughly clean the ABS sensors 2 in the front (on the hub) one for the rear brakes (in the differencial). If they have distorted readings ABS could switch off and the brakes work as in a car w/o ABS. Or before you take a risk just have them swapped, there are older and may have deserved retirement.

 

[dcrogers11]

Just got back from the dealer on my brake problem as well and they are replacing the Master Cylinder also. My T4R has only 8500 miles on it so it must be defective. We'll see what happens when it is done.

 

[B084R]

Before you swap the master brake cylinder, I would rather exchange or at least thoroughly clean the ABS sensors 2 in the front (on the hub) one for the rear brakes (in the differencial). If they have distorted readings ABS could switch off and the brakes work as in a car w/o ABS. Or before you take a risk just have them swapped, there are older and may have deserved retirement.

The dealer did check the ABS sensors before deciding with Toyota to replace the master cylinder. The car only has 7,200 miles on it so none of the parts shouldn't be bad yet. I'm guessing it is some sort of fluke maybe in manufacturing or something like that.

In all of the searching I have done I have only found a couple of references that indicate the same problem and only of 4th generation 4Rs. Since it occurs so infrequently it is very hard to diagnose. None of the references pinned down a definite cause.

The dealer indicated that they will be sending the old master cylinder back to Toyota and that Toyota will tear it apart and see if they can identify the cause of the failure.

 

[dcrogers11]

Did the Master Cylinder swap fix your problem? they've ordered mine and will be in this week.

 

[B084R]

Did the Master Cylinder swap fix your problem? they've ordered mine and will be in this week.

As I indicated in my original post, after briefly exhibiting the problem to the service advisor, the brakes were working fine again. So, when the master cylinder was replaced the old one was actually working.
Since the problem has been so intermittent it is difficult to tell if the new master cylinder will actually fix the problem. It was Toyota's best guess as to what was needed. The brakes are working well with the new master cylinder. The pedal feels a little harder so I'm hoping it is a good sign that the problem is permanently fixed.
Is the problem you are experiencing intermittent or is it a solid failure? Please let us know the results.