Electric Brake Booster or Master Cylinder going bad?

[judogti]

Hey guys -

I have a 2009 Limited with about 130,000 miles. Ive noticed at that at stoplights the Electric Brake Booster, hearing a motor sound from under the dash, is on and making noise all the time when stopped and in gear.

I know this is sometimes a normal noise for our vehicles, buts getting louder and and very noticeable, sometimes I can hear it over the radio.

Is this a sign something is about to break? Master Cylinder on it's last legs? Brake booster has a pressure leak? The brake fluid level looked fine. I'd hate to lose my brakes while driving.

I notice it most when Im in driver or reverse, but at a standstill with the brake pedal applied.

Thanks!

 

[BlackWorksInc]

It's possible there might be a pressure leak and/or a pump issue, but it's hard to tell. Does it still kick on every other time you brake or every time the brake pedal is depressed and for how long?

 

[judogti]

It's possible there might be a pressure leak and/or a pump issue, but it's hard to tell. Does it still kick on every other time you brake or every time the brake pedal is depressed and for how long?

Thanks for the reply.

Its on everytime Im stopped and have my foot on the brake pedal. Sometimes it takes a a second or two, but its on every stop these days, and its getting louder as well. Almost a rattle, instead of the mechanical motor sound.

 

[dkyleb]

Thanks for the reply.

Its on everytime Im stopped and have my foot on the brake pedal. Sometimes it takes a a second or two, but its on every stop these days, and its getting louder as well. Almost a rattle, instead of the mechanical motor sound.

Time to replace it before it fails. Members on here have had them fail while driving and completely lose brakes.

How handy are you? The replacement procedure is very in-depth, and also requires a specialty dealer computer to perform the bleed procedure. Here is the part you will need:

https://www.wholesalepartsexpress.c...s-pump-master-cylinder-repair-electric-motor/

The Toyota dealership will NOT just replace this part. They will want to replace the entire brake booster assembly. You may be able to find a Toyota-specific shop that will do the repair for you.

edit: I was able to find the whole assembly for you. The link I posted above was just for the 03-04 electric motor. Here is the full assembly: https://www.wholesalepartsexpress.com/product/2005-2007-complete-toyota-4runner-abs-unit/

 

[JB.]

Its on everytime Im stopped and have my foot on the brake pedal. Sometimes it takes a a second or two, but its on every stop these days, and its getting louder as well. Almost a rattle, instead of the mechanical motor sound.

I'd start measuring the cycle times at idle in park with no pedal (see thread).

Based on a sample size of 1, they can apparently go quite a long time before failing. If you decide to let it go for a while (not recommending), you should understand what happens when it fails. You still have brakes but the pedal pressure required goes up by an order of magnitude or so and the pedal feels like it wants to go to the floor. Unless your leg strength is compromised for some reason, it's not a problem as long as you're prepared for it.

http://www.toyota-4runner.org/4th-g...-cycle-history-failure.html?highlight=failure

 

[judogti]

edit: I was able to find the whole assembly for you. The link I posted above was just for the 03-04 electric motor. Here is the full assembly: https://www.wholesalepartsexpress.com/product/2005-2007-complete-toyota-4runner-abs-unit/

I notice the full assembly is for years upto 2007, I have a 2009 is it still the same part? Do you see any issue with purchasing a refurb or should I go new?

I do have 2 good Toyota specific shops in town that have good reps so Id feel comfortable taking it to them, but it looks like it will still be a $1000+ repair.

 

[judogti]

I'd start measuring the cycle times at idle in park with no pedal (see thread).

Based on a sample size of 1, they can apparently go quite a long time before failing. If you decide to let it go for a while (not recommending), you should understand what happens when it fails. You still have brakes but the pedal pressure required goes up by an order of magnitude or so and the pedal feels like it wants to go to the floor. Unless your leg strength is compromised for some reason, it's not a problem as long as you're prepared for it.

http://www.toyota-4runner.org/4th-g...-cycle-history-failure.html?highlight=failure

That is very interesting information. I feel better I will still have brakes, I was anticipating pedal to the floor and zero decrease in forward motion,...

My sound is only noticeable when the car is in gear (drive or reverse) and the brake pedal is depressed. If the car is in park or neutral or park and I press the brakes I do not get the sound. The link you provided asks to measure duration in park which Im not sure I can do....?

Also my sound is almost a rattle, it sounds as if a mount mine be missing a bolt and the assembly is vibrating against something as the electric motor runs... I might just take in it and ask the shop what they think. I hate doing that, Id at least like to have an idea before I take it in.

 

[dkyleb]

I notice the full assembly is for years upto 2007, I have a 2009 is it still the same part? Do you see any issue with purchasing a refurb or should I go new?

I do have 2 good Toyota specific shops in town that have good reps so Id feel comfortable taking it to them, but it looks like it will still be a $1000+ repair.

I would call and find out. These accumulators are very year specific.

 

[JB.]

That is very interesting information. I feel better I will still have brakes, I was anticipating pedal to the floor and zero decrease in forward motion,...

My sound is only noticeable when the car is in gear (drive or reverse) and the brake pedal is depressed. If the car is in park or neutral or park and I press the brakes I do not get the sound. The link you provided asks to measure duration in park which Im not sure I can do....?

Also my sound is almost a rattle, it sounds as if a mount mine be missing a bolt and the assembly is vibrating against something as the electric motor runs... I might just take in it and ask the shop what they think. I hate doing that, Id at least like to have an idea before I take it in.

In Park and at idle, pop the hood and watch the silver canister for a while and see if it ever vibrates for a second or two. If it doesn't, you don't have the problem (presumably pressure leakage) I did. But if you look you'll know for sure. Based on what mine was like, you can't miss the visible vibration and sound from under the hood.