Brake pedal barely working - goes to floor - master cylinder?

[MrChris]

At the end of my recent track day the brake pedal on my 2 started going all the way to the floor. However, it does still apply the brakes, you just have to push it in to the floor.

I noticed there are small bubbles in the brake master cylinder. All brake lines/calipers etc. look fine. Is this indicative of the master cylinder being broken? Will a kit like the one below be worth a shot? I've read that buying a new master cylinder can be fraught with issues e.g. they're refurbished used units so no better than refurbing yourself or that they're for left-hand not right-hand drive cars (see Autodoc).

https://www.ebay.co.uk/itm/333551431579

[mr2garageswindon]

It sounds like you have boiled the brake fluid.
Do you know when it was last flushed?
I would bleed out all the calipers with fresh fluid before looking into master cylinder fault.
Jon

[MrChris]

It sounds like you have boiled the brake fluid.
Do you know when it was last flushed?
I would bleed out all the calipers with fresh fluid before looking into master cylinder fault.
Jon

I bled all brakes with fresh RBF600 fluid a couple of weeks before the track day. I did wonder about boiling it but seemed unlikely to me? Maybe my bleed wasn't very good, will definitely try a re-bleed first though thank you.

Must also say we were utterly hammering the brakes to the point of locking up wheels at points...

[Joesson]

I bled all brakes with fresh RBF600 fluid a couple of weeks before the track day. I did wonder about boiling it but seemed unlikely to me? Maybe my bleed wasn't very good, will definitely try a re-bleed first though thank you.

Must also say we were utterly hammering the brakes to the point of locking up wheels at points...

As a reference I replaced / renovated all four calipers and used one litre of  brake fluid to refill/ bleed.

[Dev]

 When you use high performance fluid and if it takes in very little water or contaminants the boiling point drops dramatically. This is why high performance fluid has to be flushed out frequently especially before a race.
Dot 3 on the other hand can tolerate water and contaminants for a very long time without much fall off.
I had problems with RBF600 especially in the cold because it was more viscus. When I added it to the  clutch master it would work for a month or so and then it would fail.  I believe it is due to seal compatibility. 

[shnazzle]

When you use high performance fluid and if it takes in very little water or contaminants the boiling point drops dramatically. This is why high performance fluid has to be flushed out frequently especially before a race.
Dot 3 on the other hand can tolerate water and contaminants for a very long time without much fall off.
I had problems with RBF600 especially in the cold because it was more viscus. When I added it to the  clutch master it would work for a month or so and then it would fail.  I believe it is due to seal compatibility. 

Did I include the two bottles or RBF600 and are those the ones you used?
If so, it could be because they're old. I don't know how they age or what the use-by date is.

But, the reason I never used them is because of what Dev said. You're much better off with a good Dot3 or 4.

[MrChris]

When you use high performance fluid and if it takes in very little water or contaminants the boiling point drops dramatically. This is why high performance fluid has to be flushed out frequently especially before a race.
Dot 3 on the other hand can tolerate water and contaminants for a very long time without much fall off.
I had problems with RBF600 especially in the cold because it was more viscus. When I added it to the  clutch master it would work for a month or so and then it would fail.  I believe it is due to seal compatibility. 

Did I include the two bottles or RBF600 and are those the ones you used?
If so, it could be because they're old. I don't know how they age or what the use-by date is.

But, the reason I never used them is because of what Dev said. You're much better off with a good Dot3 or 4.

No you didn't, I used new RBF600.

Slightly confused as RBF600 is Dot4 which I thought was also a good quality brake fluid. RBF600 was my goto on my BMW 130i and never let me down. Any recommendations for the 2?

[Dev]

Did I include the two bottles or RBF600 and are those the ones you used?
If so, it could be because they're old. I don't know how they age or what the use-by date is.

But, the reason I never used them is because of what Dev said. You're much better off with a good Dot3 or 4.

The story goes that a friend and I split a case of RBF600. When I flushed out all my fluid it worked fine but as the temps dropped in the winter the pedal became wooden.  I flushed out the fluid and added fresh RBF and it was fine again until it started having the same issues and that is because DOT 4 is more viscus than DOT 3. As for the clutch the following spring it would not fully disengage causing grinding until it wouldn't disengage at all but once I let it cool it came back to normal. I have a very strong pressure plate so the demands are high and after another flush the same thing happened.
I suspected the fluid so I changed back to Toyota DOT 3 and never had a problem after that.

I come to find out from a leading authority on brakes the nuanced reason. On the internet they say DOT 4 is compatible and it might be for some other cars but not all cars especially where it says DOT 3 fluid only.

https://centricparts.com/getmedia/aaff9ed4-541c-45a4-abc2-a3b667385808/Centric_and_APC_Technical_Whitepaper_D1-Brake-Fluid-1A_8-2018.pdf

Also Toyota brake fluid has a special polymer lubricant in the formulation that is specific for the seals and it was a known cause of a brake master failure for a particular car that went bad because alternative fluid was used as sited by Toyota.
Although our cars was not part of the bulletin I believe the Toyota formulation has merit for the longevity and health of the seals.
 

[MrChris]

What a great response, thank you @Dev

Seems like this is a case of 'RTFM' (it does indeed state DOT 3 only) and 'don't believe everything on the internet' 

I'm going to get some quality DOT 3 and see how I get on. I just hope I haven't buggered the seals.

[Dev]

No you didn't, I used new RBF600.

Slightly confused as RBF600 is Dot4 which I thought was also a good quality brake fluid. RBF600 was my goto on my BMW 130i and never let me down. Any recommendations for the 2?

BMW is compatible with DOT 4 because it is DOT 4 fluid only. The 2007 BMW that I owned was like that and I assume yours is also.

Toyota DOT 3 is specified as a heavy duty brake fluid and is not your typical DOT 3. It is suspected to have a very high boiling point considering it is used in their heavy vehicles including those that are used for towing. I would switch to the Toyota brake fluid and give your car another track day and see if you observe any fade issues.

[MrChris]

Just spoke with local Toyota garage. They said based on my reg, DOT 4 is recommended... completely at odds with the manual. They did quote me on DOT 3... over £230 for 1 litre    Turns out that this is for the Lexus LFA and is the only DOT 3 they can get at the moment. I've found some Comma DOT 3 so will be getting that instead!

[shnazzle]

I also used ATE200 (blue) as it was then.
Utter shite. It lasted about 6 months before it was next to useless. It was phenomenal for a few good hard uses.
To be fair, the RBF600 site (and bottle?) even says to swap it out every track session.

When you got it, it just had bogtstandard DOT3 in it. That lasted best and brakes always flew through MOT with a higher efficiency ratio than they would normally see

[MrChris]

I also used ATE200 (blue) as it was then.
Utter shite. It lasted about 6 months before it was next to useless. It was phenomenal for a few good hard uses.
To be fair, the RBF600 site (and bottle?) even says to swap it out every track session.

When you got it, it just had bogtstandard DOT3 in it. That lasted best and brakes always flew through MOT with a higher efficiency ratio than they would normally see

I almost went for ATE but it was way more than Comma. Also I've had good experience with Comma in the past. Interesting about replacing every session, thought it would stand up to more abuse. Bedford is known for hard braking zones, but even so... I shall report back after the weekend hopefully as the DOT 3 should be with me on Saturday.

[Dev]

Just spoke with local Toyota garage. They said based on my reg, DOT 4 is recommended... completely at odds with the manual. They did quote me on DOT 3... over £230 for 1 litre    Turns out that this is for the Lexus LFA and is the only DOT 3 they can get at the moment. I've found some Comma DOT 3 so will be getting that instead!

 The fluid  you need is the factory fill fluid for all Toyota cars and trucks. It is inexpensive and should be available. I would not trust the garage as they are not officially Toyota representatives. It was the Toyota dealers that was servicing the Toyota cars under warrenty that was the cause of the  master cylinder failure by substitution of generic fluid and after investigation they were given an official notice by Toyota to only use their fluid because it contains the special lubricant that does not dry out seals.

 I just did a search and it seems that Toyota now carries DOT 4 fluid but it is probably specified for new Toyota cars that require it based on new seal materials and components. I would not use it in older Toyotas that specify DOT 3 only.

 I had a long lengthy debate on another forum where some said that "DOT 3 only" means it can use DOT 4 even though I presented my resources. As I researched further I stumbled on a Toyota car of the same generation where the master cap said DOT 3 or DOT 4 which was specific for that car. DOT 3 only in my opinion means DOT 3 only.




 

[Joesson]

I almost went for ATE but it was way more than Comma. Also I've had good experience with Comma in the past. Interesting about replacing every session, thought it would stand up to more abuse. Bedford is known for hard braking zones, but even so... I shall report back after the weekend hopefully as the DOT 3 should be with me on Saturday.

For other than track days there was, what turned into a thread about brake fluid:
https://www.mr2roc.org/forum/index.php?msg=873276

In my ownership there has been Dot 3, followed by Dot 5.1 as recommended by my Main Dealer, and now Dot 4, following the discussion as link above.

Track day fluid is another kettle of aquatic creatures.

[Call the midlife!]

I'd imagine the much more sophisticated BM brake system is dissipating the heat better as well, if not generating less with the piston to weight ratio.

[Dev]

 There is a lot of variation between two different DOT 4 fluids. Some are high viscosity and some are low viscosity and they can have different formulations that can create issues. Even if you use a DOT 4 fluid with success it doesn't mean its ok to use as you might be damaging the rubber seals and after a prolonged amount of time your brake components might not last as long.

 I suspect why the RBF fluid did not last long in my car was due to seal incompatibility which allowed water and contaminants to breach and lower the boiling point quickly compared to a car that is specified for DOT 4 that uses different seal materials. When I drained out my clutch fluid it was abnormally dirty and full of contaminants. This was not the case when I used DOT 3 even for an extended time.

 One of the most misunderstood aspects of brake fluid is DOT 3 is more hygroscopic which means it absorbs more water from the air compared to DOT 4 which makes it sound like DOT 4 and DOT 5.1 is better for longevity.
What they don't tell you is that DOT 3 has a much higher tolerance for water and therefore the drop in dry and wet boiling points is minimal. DOT 4 on the other hand absorbs less but it is far more sensitive and therefore its drop is dramatic.

[Ardent]

Have long had a nagging question in my head.

Could it be the brake fluid chemistry that causes rear brake caliper adjusters to seize.

Not all.dot 3 r 4 are created equal.
They will meet the stansard but not ness oem recipe.

The brake master cylinder cap on my 2 and on my 7 years younger ct200 both say DOT3.

Replaced the dot 4 in the 2 with comma dot 3.
So far no issues.

Caveat. I don't do track days.

[Dev]

Have long had a nagging question in my head.

Could it be the brake fluid chemistry that causes rear brake caliper adjusters to seize.

Not all.dot 3 r 4 are created equal.
They will meet the stansard but not ness oem recipe.

The brake master cylinder cap on my 2 and on my 7 years younger ct200 both say DOT3.

Replaced the dot 4 in the 2 with comma dot 3.
So far no issues.

Caveat. I don't do track days.

 Hard to say.

 There are a lot of unknowns in any of these fluids when you deviate from the manual or what is written on the cap. The smallest details in a formulation can be overlooked. I do not want to find out (but I did) or worse will never know if using an unspecified fluid created damage over time to where you cant pin the blame on any one thing and after that you replace the components and use it again out of ignorance.

Even if DOT 4 is acceptable why would anyone consider it over DOT 3 for a street application. Did anyone experience brake fade using DOT 3 on the road. At least with DOT 3 it is more forgiving to change intervals and keeping its dry and wet point stable.

[AJRFulton]

I used RBF600 for 2 seasons with absolutely no problems, before moving to RBF660 with no problems. Although, importantly, I'm not using OEM brakes. It is a top quality brake fluid very popular with the track day crowd.

I wouldn't use anything but a high performance brake fluid at a track day. Not to say some of the OEM stuff isn't quality, but I've bled RBF600 between sessions with no air bubbles - and I like that.

I've had the discs glowing red without the pedal getting soft. However, I will doing a complete flush before every event, and maybe every 3 track days.

[MrChris]

Seems to me that the OEM brakes require DOT 3 as per the manual and using DOT 4 may have helped to compromise the system. I agree with you @AJRFulton that RBF600 is great and has been for me in the past, but as above, the MR2 as standard needs DOT 3.

I am going to flush through some DOT 3 and at least try and get the brakes back to where they should be for the road and take it from there.

[Joesson]

While this thread is about brake fluid and the pros and cons of grades that differ from that mentioned in the handbook and on the filler cap I wonder what consideration is given to those other fluids that may or may not be of some importance, such as:
Engine oil, how many Members use non synthetic (Toyota) SAE 5W-30 oil?
Gear oil, how many use (Toyota) SAE 75W-90 oil?
SMT oil- how many use Toyota Genuine Sequential M/T Fluid?
Coolant- how many use Toyota Genuine Long Life Coolant.
Also of note- Tyres- how many use 185/55R 15 81V front, 205/50R 15 85V rear or whatever the FL model is recommended?

Unrelated to brake fluid you might think, but these items were, around 20 years ago, what was recommended.

[MrChris]

Bit of an update as I had to pop out in the 2 earlier briefly: The pedal goes solid when the car is off - it does not go to the floor at all. As soon as engine is on, the pedal goes to the floor (but still stops the car). Does this point to another issue other than the fluid?

[AJRFulton]

Bit of an update as I had to pop out in the 2 earlier briefly: The pedal goes solid when the car is off - it does not go to the floor at all. As soon as engine is on, the pedal goes to the floor (but still stops the car). Does this point to another issue other than the fluid?

I'd be confident that isn't fluid. Whilst these fluids are not as long life, they aren't this short of a life.

However try and bleed them, if your not getting excessive bubbles then I'd think it's unlikely to be fluid and it points to something else.

[Joesson]

@MrChris
Seldom, if ever mentioned on here is the tandem brake circuit and the vacuum assist.
My understanding and the implication of their malfunction is insufficient to say whether either of these could be your problem. But the vacuum assist only operates when the engine is on. The tandem system is designed to be fail safe but does alter the feel of the pedal.