Replacing just the brake accumulator

[Rick2000]

My 2000 Land Cruiser (~290k miles) has started doing something new within the last few months and I’m trying to get ahead of it before it turns into a full booster/master replacement.

Photo attached:

• Left: key ON
• Right: ~2 hours after shutdown

You can see the reservoir level rises noticeably after the truck sits.

This behavior is fairly new. No warning lights.
Only symptoms so far:

1. Brake pedal pauses briefly on release
2. Pedal moves up slightly when the vehicle starts
3. Pedal sags slightly if I’m sitting at a long stop

Otherwise braking feels normal and the pump isn’t running constantly.

From what I understand this is consistent with an accumulator losing its nitrogen charge and pushing fluid back into the reservoir as system pressure bleeds off. I’m hoping that catching it early means I can replace the accumulator and avoid a full cylinder/booster assembly replacement.

Question for those who’ve been here​

Who has replaced just the accumulator sphere once these early signs showed up?

• Did doing only the accumulator stop the progression?
• How long did it last afterward?
• Any issues or surprises during the swap?
• Did you bleed the system or just depressurize and replace?
• What tool did you use to torque the accumulator back on? I see there's an SST.

Goal here is to head this off early and keep from having to replace the entire hydraulic unit if possible. Curious how many have successfully stopped the cascade by jumping on the accumulator right when these symptoms first appear.

 

[excessive]

from what i've noticed, that behavior is actually normal. I will see the fluid level fall when the truck is on ( assuming fluid sucked up into the accumulator) and when the truck is off , say over the course of a few days sitting, the fluid returns back to the reservoir.

 

[Rick2000]

from what i've noticed, that behavior is actually normal. I will see the fluid level fall when the truck is on ( assuming fluid sucked up into the accumulator) and when the truck is off , say over the course of a few days sitting, the fluid returns back to the reservoir.

From what I've read it should hold the level for at least a day. This is leaking down after just a couple hours.

In terms of symptoms, this doesn't look like something that needs to be taken care of right away, not like an alarm and ABS light, but replacing just the accumulator looks to be so easy and so much cheaper than a whole brake booster I'm hoping by doing the former I can put off the latter for another 100,000 miles.

 

[hoser]

From what I understand this is consistent with an accumulator losing its nitrogen charge and pushing fluid back into the reservoir as system pressure bleeds off. I’m hoping that catching it early means I can replace the accumulator and avoid a full cylinder/booster assembly replacement.

I'm not understanding the logic. If the accumulator lost charge, wouldn't it provide less pressure to "push" fluid back into the reservoir (other than just gravity). There's no valve in the accumulator itself. If fluid is leaking back prematurely, then I'd guess it is worn inside the pump or elsewhere.

 

[Rick2000]

If fluid is leaking back prematurely, then I'd guess it is worn inside the pump or elsewhere.

Good question. Perhaps the accumulator isn't pushing back hard enough for the seals?

From what I understand it works pretty much the same as the AHC globes, there's a membrane and a nitrogen charge. It made sense to me that the accumulator on the brake system could be the first link in the chain toward failure.

 

[2001LC]

Even new booster w/master. Fluid/pressure bleeds off. Fluid slowly returns back into reservoir, when key off. Key on, booster motor will fire up periodically.

 

[Dirt J]

Mine died at around 320k. I think you'll see others around that range too, with exceptions both ways depending on various factors (brake fluid flushing, etc.).

Have you followed the FSM on timing how long it runs after key on? There is a spec it should meet (less than so many seconds).

@2001LC is the brake guru.

 

[Patron100LC]

Or... you can do something stupid... I did.

Every old man that taught me mechanical work always said the same: "Don't fix if it ain't broke".

I replaced a perfect condition booster assembly in my 05' for a brand new one.

But, here's my logic behind that:
During Toyota sales the brake booster assembly sells for $1100 or so, and ships for free.

My old one had 280k miles on it, and even though perfect, it bothered me that the fluid was going dark real quick after flushes. Could have lasted another few years and several thousand miles? Sure, maybe..

But if you're in the middle of nowhere on vacation with wife and kids, and the booster goes, it can be a vacation (and marriage) killer. And if you're lucky to be around a Toyota dealer, you'll have to pay full retail (not online retail, but retail with that dealer markup (50-100% probably).

Can the new one go bad? Sure! Should it last longer than a 280k miles part? It should.

Now, here's the trick. I sold my used booster for $420 on ebay a month later. (Fully disclosed condition and several pictures, wasn't trying to get a 100series owner stuck with a POS).
So, the new booster and peace of mind cost me $6xx plus a couple hours work.. (and fluid.. of course). I think it's not bad.

 

[Rick2000]

Mine died at around 320k. I think you'll see others around that range too, with exceptions both ways depending on various factors (brake fluid flushing, etc.).

Have you followed the FSM on timing how long it runs after key on? There is a spec it should meet (less than so many seconds).

@2001LC is the brake guru.

It definitely runs longer than the 30s specified. Also, it takes fewer pumps to drain the accumulator in the morning than it should, only 7 vs. 30ish.

 

[Rick2000]

Or... you can do something stupid... I did.

Every old man that taught me mechanical work always said the same: "Don't fix if it ain't broke".

I replaced a perfect condition booster assembly in my 05' for a brand new one.

But, here's my logic behind that:
During Toyota sales the brake booster assembly sells for $1100 or so, and ships for free.

My old one had 280k miles on it, and even though perfect, it bothered me that the fluid was going dark real quick after flushes. Could have lasted another few years and several thousand miles? Sure, maybe..

But if you're in the middle of nowhere on vacation with wife and kids, and the booster goes, it can be a vacation (and marriage) killer. And if you're lucky to be around a Toyota dealer, you'll have to pay full retail (not online retail, but retail with that dealer markup (50-100% probably).

Can the new one go bad? Sure! Should it last longer than a 280k miles part? It should.

Now, here's the trick. I sold my used booster for $420 on ebay a month later. (Fully disclosed condition and several pictures, wasn't trying to get a 100series owner stuck with a POS).
So, the new booster and peace of mind cost me $6xx plus a couple hours work.. (and fluid.. of course). I think it's not bad.

You know, no matter what I do this truck is going to need a new booster before it dies. I think you've got the best idea.

 

[Aracobuilt]

I don't think that replacing the accumulator will prolong the life of the booster by much maybe none. The age of the seals in the booster is the problem as well as dirty/contaminated brake fluid. I am beginning to realize that frequent brake fluid flushes with genuine Toyota brake fluid is crucial for our systems. On cars with conventional brake systems you should change the fluid every 2 to 3 years. If you don't it's not the end of the world. On our more complex brake systems I feel that replacing the brake fluid every year greatly prolongs the life of the seals. How do I know, I had a failing brake booster with a slight leak. The pump would rattle on start up and got worse as time went by, eventually the alarm would go off and I would get a Christmas tree of lights on the dashboard. I was all ready planning for the worse, a replacement. I decided to replace the fluid not expecting to achieve much. The problem went away, the leak went away. After a few months the problem came back, not the leak. I decided to perform another brake fluid replacement and the problem has not come back in over 7 month of frequent driving. Just last week I decided to do another brake fluid replacement as a preventative measure. I will do another this summer. If I'm still good, I will do a brake fluid replacement every year. My brake pedal feel is as smooth as ever and my fluid level only moves up and down for the first few days after a fluid replacement. After that I top it off to the max line and it stays there with very little fluctuation.

 

[Rick2000]

I don't think that replacing the accumulator will prolong the life of the booster by much maybe none. The age of the seals in the booster is the problem as well as dirty/contaminated brake fluid. I am beginning to realize that frequent brake fluid flushes with genuine Toyota brake fluid is crucial for our systems. On cars with conventional brake systems you should change the fluid every 2 to 3 years. If you don't it's not the end of the world. On our more complex brake systems I feel that replacing the brake fluid every year greatly prolongs the life of the seals. How do I know, I had a failing brake booster with a slight leak. The pump would rattle on start up and got worse as time went by, eventually the alarm would go off and I would get a Christmas tree of lights on the dashboard. I was all ready planning for the worse, a replacement. I decided to replace the fluid not expecting to achieve much. The problem went away, the leak went away. After a few months the problem came back, not the leak. I decided to perform another brake fluid replacement and the problem has not come back in over 7 month of frequent driving. Just last week I decided to do another brake fluid replacement as a preventative measure. I will do another this summer. If I'm still good, I will do a brake fluid replacement every year. My brake pedal feel is as smooth as ever and my fluid level only moves up and down for the first few days after a fluid replacement. After that I top it off to the max line and it stays there with very little fluctuation.

Never would have thought a fluid change would work.

 

[Aracobuilt]

Never would have thought a fluid change would work.

I did not have my hopes that it would work at all, but glad I did it anyways. So far I've had 8 months of trouble free problems with the braking system. No noises, leaks, lights or alarms. If it fail then I'll deal with it.

 

[1998landcruiser]

Toyota Genuine #47950-60010
The accumulator uses a gland nut spanner wrench for the top 2 dimples. You use a 1/2 breaker bar, and it'll come loose instantly. It didn't take much pressure. I left everything mounted in the engine bay. Twist by hand counterclockwise. One screw for the bracket that holds the accumulator in place. It's a 5-minute job. Turn the key on, engine off, let the motor pump into the accumulator. Step on the brake and keep pressing until you hear the motor run. Do that process 3-5 times. The goal is motor activation after 8-15 brake pedal pushes. Bleed lines afterwards.

Before I would have abs yellow light pop up on the dash but no alarms or sound. Every 2-3 brake pedal push I get the motor running. Driving feels normal. Took about 39 brake pedal pushes to depressurize. I did a lot of research and I believe my seals are still good. I am replacing the accumulator tomorrow when the parts come in. I will give an update. If accumulator doesn't solve the issue, then it'll cost $1450 at the dealer parts pickup.

 

[Rick2000]

Toyota Genuine #47950-60010
The accumulator uses a gland nut spanner wrench for the top 2 dimples. You use a 1/2 breaker bar, and it'll come loose instantly. It didn't take much pressure. I left everything mounted in the engine bay. Twist by hand counterclockwise. One screw for the bracket that holds the accumulator in place. It's a 5-minute job. Turn the key on, engine off, let the motor pump into the accumulator. Step on the brake and keep pressing until you hear the motor run. Do that process 3-5 times. The goal is motor activation after 8-15 brake pedal pushes. Bleed lines afterwards.

Before I would have abs yellow light pop up on the dash but no alarms or sound. Every 2-3 brake pedal push I get the motor running. Driving feels normal. Took about 39 brake pedal pushes to depressurize. I did a lot of research and I believe my seals are still good. I am replacing the accumulator tomorrow when the parts come in. I will give an update. If accumulator doesn't solve the issue, then it'll cost $1450 at the dealer parts pickup.

Awesome that you’re giving it a go. I chickened out and replaced the whole module. I figured if I pulled it a little early at 300k, maybe this one will only last another 300k but I won’t regret it before then.

 

[1998landcruiser]

Awesome that you’re giving it a go. I chickened out and replaced the whole module. I figured if I pulled it a little early at 300k, maybe this one will only last another 300k but I won’t regret it before then.

I forgot to put that I have a 1998 Toyota Land Cruiser with 232k miles. I had this vehicle since it was around 60k miles. Not sure If I would keep it till 300k but it is an awesome SUV. Best of luck man.

 

[Rick2000]

I did not have my hopes that it would work at all, but glad I did it anyways. So far I've had 8 months of trouble free problems with the braking system. No noises, leaks, lights or alarms. If it fail then I'll deal with it.

Just to close the loop on this I did just replace the entire master cylinder even though it was working just fine. I decided I’m going to have to replace it sometime anyway it’s just not going to be anytime soon. The last one lasted to 300,000+ and 25 years. If this one lasts another 25 years it won’t be me replacing it.

The system was last flushed 3 years ago and when I dumped out the old brake booster it had some definite black particles floating around in it. I could see those particles interfering with seals and pistons, so it’s plausible that simply doing a flush could restore performance in some cases.

I used Toyota brake fluid. I’m not sure it makes much of a difference, but my old unit only ever had Toyota brake fluid and it made it to 300,000 miles and beyond. (It really wasn’t failing when I pulled it off.) So if the Toyota fluid has custom seal conditioners, they must work.