Currently when I am stoped with my foot on the brake pedal slowly bleeds the pressure and the pedal falls to the floor board. When I release the pedal and step on it again the pedal is firm and then slowly starts to drop. There are no puddles of fluid under the truck. The resivor is still full. Anybody have an idea. I know that the brakes are electronic on this truck. If there is a way to reset the system. I will try anything otherwise it will have to go in on Tuesday. Please help.
brake pressure problems
- Thread starter asmtrd
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big04runner
Member
See attached; hope it helps.
With the engine off and I hit the pedal I hear the compressor run for 3 seconds and then I hear what sounds like air pressure leaking slowly as the pedal falls. Is there a common issue with the master cylinder and booster. The truck stops fine but the booster dosen't seem to hold the pressure after I stop.
Dawg4Runner
New member
Sounds like you have a faulty master cylinder. Blackworksinc had a similar problem and after all the testing he did (he's a tech at a local Toyota dealership), he ended up having to replace the master cylinder assembly.
Here's the thread: http://www.toyota-4runner.org/4th-gen-t4rs/107245-inconsistent-brake-pedal-travel.html
Here's the thread: http://www.toyota-4runner.org/4th-gen-t4rs/107245-inconsistent-brake-pedal-travel.html
Narrowing down the problem.
After looking through the diagrams of how this booster system works I am going to try to replace just the accumulator. The pump is doing it job because when I hit the brake pedal I get the effect of power brakes and the truck stops as it should. Its when I and sitting at a stop with just enough pressure on the pedal to hold it from rolling the pressure on the pedal starts to bleed out. You can hear the leaking pressure. When the pedal is released and you hit it again the brake is back to normal. Has anybody just replaced the accumulator? If so who did the work. Is it a DIY project or something for the dealer.
After looking through the diagrams of how this booster system works I am going to try to replace just the accumulator. The pump is doing it job because when I hit the brake pedal I get the effect of power brakes and the truck stops as it should. Its when I and sitting at a stop with just enough pressure on the pedal to hold it from rolling the pressure on the pedal starts to bleed out. You can hear the leaking pressure. When the pedal is released and you hit it again the brake is back to normal. Has anybody just replaced the accumulator? If so who did the work. Is it a DIY project or something for the dealer.
BlackWorksInc
New member
The only issue is, you need to find the source of your leak, you said the pump kicks on for 3 seconds? Or do you hear the air hissing 3 seconds after the pump turns on and it continues to run? How long does it run for?
There's a pump and accumulator tank, so depending where the leak is, one or both may need to be replaced.
I posted this in the other thread, but here's a teardown I did of my old unit.
http://www.toyota-4runner.org/4th-gen-t4rs/120125-hydraboost-brake-assembly.html
There's a pump and accumulator tank, so depending where the leak is, one or both may need to be replaced.
I posted this in the other thread, but here's a teardown I did of my old unit.
http://www.toyota-4runner.org/4th-gen-t4rs/120125-hydraboost-brake-assembly.html
earthrealm
Senior Member
OLD THREAD, DID YOU END UP CHANGING THE ACCUMULATOR or the MC?
