Brake Booster failure....well almost, scary!

[uHu]

Just had a similar experience with our Benz ML430. BAS/ETC/ABS lights all set. Braking normal, because in this case it was the ABS pump motor that failed. Its a common problem, and MB replacement ABS module is over $2K.
Turns out that the most common failure is the ABS pump motor, and its a really simple fix:
- pull the motor
- replace the worn out brushes [$12]
- replace the bearings [$18] although the bearings in my 198K mile motor were in nice shape and really didn't need to be replaced.
- Replace the motor - done and done!

Only mentioning this because in cases where the LC brake accumulator motor has failed it would be well worth while to pull the motor, open it and have a look at a simple rebuild. Not sure if this has been done before but it could be a low-cost solution to an expensive problem.

Someone in here did that on an LC, yes.
Suppose it depends on how thorough you want to be. The booster pump will also be worn when the motor is worn, but maybe it can last twice as long? Don't know, but it might be worth a try if the pump sounds good. My 2004 pump has a bad sound, as compared to my older 2000 MY pump, so I will change the whole caboodle when it stops, or before.

 

[APKhaos]

Someone in here did that on an LC, yes.
Suppose it depends on how thorough you want to be. The booster pump will also be worn when the motor is worn, but maybe it can last twice as long? Don't know, but it might be worth a try if the pump sounds good. My 2004 pump has a bad sound, as compared to my older 2000 MY pump, so I will change the whole caboodle when it stops, or before.

Electric motors like this often sound bad because bearings are done. Its cheap and easy to rebuild one, and it should be good as new with new bearings, brushes, and a cleaned up commutator. Maybe the pump is worn too, but if the motor fails its probably worth doing that first and gaining some time on the pump. Just an idea given the recent good result with the ML430 abs pump.

 

[ffl3883]

When the booster is fully charged, you have enough pressure accumulated for 20 full stops, even if the booster pump stops working, and that's when the warning light and buzzer comes on.
So, as long as you stop immediately, you should be OK.

Loosing the booster really feels like a complete loss of brakes. There is only a small braking force at the front wheels with a lot of heavy pedal work. The rear brakes are completely booster driven.

The booster pump is run by an electric motor, with brushes, and it will fail sooner or later.

I have a 1999 LX470, I can hear the electric motor working in the booster whenever I press brake pedal 4-5 times. Is the frequency normal ? What are some symptoms of a failing brake booster ? Thanks

 

[OG 91 LC]

I have also been concerned with this issue; even more so when I first bought my LX and found out about the component. In the years that I have owned my LX the fear has subsided. Why? Every thread and story I have read here on MUD where the driver has lost all braking the common denominator has been that the truck has always given the driver ample notice that the braking was going; the chime or alarm.

I don't worry as much and I just drive my truck and enjoy the ride. If the chime or the alarm alerts me, then okay. I have to go find a used part from another truck or 4Runner ( there is a list here on MUD on what other vehicles uses the same braking system) and move on. If I have to pay $2-3k to fix well, then that sucks, but it won't stop me from enjoying my 100 series.

What are some of the symptoms of a failing brake system? On our 100 the chime or alarm will let you know.

 

[uHu]

I have a 1999 LX470, I can hear the electric motor working in the booster whenever I press brake pedal 4-5 times. Is the frequency normal ? What are some symptoms of a failing brake booster ? Thanks

That's about normal. Could be after only 1 or 2 "brakings" as well, depending on how hard you press. When it fails, you have a continous alarm (not very loud) and a warning light (same as hand (E) brake). When this comes on, you have to get down to pedestrian speed right away, with only one (or 10) pedal press. After that, you have to press like an elefant, to get stopping power like a tennis shoe on the tire.

 

[flintknapper]

That's about normal. Could be after only 1 or 2 "brakings" as well, depending on how hard you press. When it fail, you have a continous alarm (not very loud) and a warning light (same as hand (E) brake). When this comes on, you have to get down to pedestrian speed right away, with only one (or 10) pedal press. After that, you have to press like an elefant, to get stopping power like a tennis shoe on the tire.

Yep, but a properly working parking brake can be of 'aid' in such a situation, by holding the release button down and pulling up hard on the lever as you also apply the brake pedal. It WON'T stop you from highway speeds but should help stop the vehicle from slow speed if on fairly level ground. Good to remember.

 

[bdruff]

Subscribed and bumped.

Trying to narrow down my problem. Seems to be fairly common. Pulsating, almost a grinding sound coming from the master cylinder/abs area. Higher than max brake fluid at times. High pitch alarm with lights on the dash (Only happened once)

Then, everything back to normal.

I have had zero actual braking problems. Pedal feels good, stops great.

Forum is leading me to:
Master cylinder rebuild
Brake booster ?
Accumulator ?

I have tools but no FSM

No CEL

 

[jeetS]

Just experienced the same thing in our 2000lc...
Terrible grinding noise from the pump area, shortly afterwards lights on, then almost total brake failure....
Gotta be a cheaper fix that replacing the whole thing!

 

[WiscoLC100]

Just experienced the same thing in our 2000lc...
Terrible grinding noise from the pump area, shortly afterwards lights on, then almost total brake failure....
Gotta be a cheaper fix that replacing the whole thing!

I've also got a 2000 (LX470) My master is leaking in a few places now and I keep having to add fluid. I read a comment a while back about someone replacing the expensive LX/100 master with a much cheaper FJ80 booster and just ditching the ABS. Can this be done? Too many things to pay for right now. I thought I needed a new rear driveshaft for this strong vibration I get about 55-60 mph, but my mechanic thinks it's the CVs (204k miles on the LX so I'm sure they're due...). So...I'm trying to figure out how to afford CVs and a master or booster. I don't really care for ABS anyway tho...?? Especially in the winter.
Suggestions?