[TJay74]

Originally Posted by Norm Peterson

The concern isn't about the possibility of air getting into the system, it's the possibility that over time (and ABS activity) that the original DOT3 fluid that was trapped in the ABS hydraulic control unit could migrate into the normally active brake lines and lower the boiling point of the fluid that is being used.

Since you should be bleeding your brakes prior to each event, you should be able to chase the DOT3 concentration down to a negligible level fairly quickly (in terms of the number of track days).


I've never had any trouble with that approach, and I have the cracked XP8 and XP10 pads and the heat-checked rotors to show that I do get my brakes HOT.


Norm

part of what I am trying to say and explain is if the ABS module does not have air in it then when you bleed the calipers you will pull the DOT4 from the master to the calipers. The only time it becomes an issue is when the ABS module has air in it.

Fluid runs from the master cylinder to the ABS module, then out of the ABS module to the wheel calipers. The DOT 4 will flush out of the ABS module just fine. The ABS module just bleeds off pressure to release a locked up wheel by opening up the solenoids inside of it when the wheel speed sensor shows the wheel has stopped moving in relation to the other wheels.

[Norm Peterson]

ABS units include an accumulator - a hydraulic reservoir of sorts - which with any passages to/from can still hold 'old' fluid. A straight flush won't purge this. If you stay out of ABS, it won't matter what the accumulator was holding. The question then becomes whether or not you can stay out of ABS.

http://www.brakeandfrontend.com/abs-...r-diagnostics/


Norm

[Alpha1BC]

Awesome, thanks for the responses! All seems reasonable and logical to me.

[Nate...]

Originally Posted by Norm Peterson

ABS units include an accumulator - a hydraulic reservoir of sorts - which with any passages to/from can still hold 'old' fluid. A straight flush won't purge this. If you stay out of ABS, it won't matter what the accumulator was holding. The question then becomes whether or not you can stay out of ABS.

http://www.brakeandfrontend.com/abs-...r-diagnostics/


Norm

Nice diagram!

[Corbu]

Quick question : can we leave the DOT4 stuff in for regular road use after we are done with the track or do we have to switch back to DOT3?

[Norm Peterson]

I've never heard of anybody switching back and forth - or even seen that question before.

The only issue I can think of would involve low temperature viscosity. Too 'thick' and there might be ABS response time consequences if your car specifically calls for "Low Viscosity" fluid. Which still might not matter if you don't get into situations where the ABS gets interested.


Norm

[Corbu]

If the DOT4 is required for the track and it is also good for road driving, I wonder why GM doesn't fill it up with DOT 4 from the factory. Why they put in DOT3 to begin with? There must be a reason for this..

[Norm Peterson]

It can absorb moisture more rapidly. Like other engineered products, brake fluids represent a compromise among several qualities, and the optimum balance among those qualities is not going to be the same between street and track intended fluids.

The average street-driving-only owner isn't going to be as diligent as a track day enthusiast about periodically having the brakes bled just to keep the fluid fresh - the track day driver either knows from his own research going in about keeping his car's fluid fresh or gets told early in his interest in that activity. Average drivers generally do not have those avenue of information, even though it's something they should be aware of for DOT3 fluid as well.


Norm

[Timbo-1LE]

Question, believe I read the clutch used same reservoir, any thoughts here??

Did first track day with factory, was going to switch to dot4.

[Lafourche1]

I am old and lazy. I paid to have my brakes flushed the first time and I have them bled as part of the Tech Inspection that comes before each NASA track event. If you are running NASA, you are required to have your tech inspection signed off on by an ASE certified mechanic. Most shops will do the certification for free or a small amount. Since the car is put in the air for the inspection, bleeding the brakes is a small premium on top of the base charge.

Don't forget to change your differential fluid. I changed mine before and after my first track weekend. Now I change it every third track event.

[Centerforce_Clutches]

Originally Posted by Timbo-1LE

Question, believe I read the clutch used same reservoir, any thoughts here??

Did first track day with factory, was going to switch to dot4.

There's no problem at all with using DOT4 for the clutch. Bleed away!

[Gasoline_Farts]

Originally Posted by Norm Peterson

It can absorb moisture more rapidly. Like other engineered products, brake fluids represent a compromise among several qualities, and the optimum balance among those qualities is not going to be the same between street and track intended fluids.

The average street-driving-only owner isn't going to be as diligent as a track day enthusiast about periodically having the brakes bled just to keep the fluid fresh - the track day driver either knows from his own research going in about keeping his car's fluid fresh or gets told early in his interest in that activity. Average drivers generally do not have those avenue of information, even though it's something they should be aware of for DOT3 fluid as well.


Norm

I worked in service at Porsche, even there brake flushes were just done with a Porsche version of a motive bleeder and abs was never cycled.


Also average people are morons, I had a person get mad at me because they thought 2 year brake flushes were a scam.

[Norm Peterson]

Originally Posted by Gasoline_Farts

I worked in service at Porsche, even there brake flushes were just done with a Porsche version of a motive bleeder and abs was never cycled.

I'm sure the thinking runs along the lines of it being extraordinarily unlikely to be boiling fluid inside the ABS HCU. You'd have bigger problems sooner.

I think people have gotten the word that other system flushes really aren't necessary, so after that they figure that none of them are.


Norm

[NickyRacerBoy]

I personally use this bleeder and its VERY well made!
I prefer Castrol over Mutol but ALOT more $.
Also I will purposely activate my ABS and then flush again.


https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1