Brake Fluid Reservoir

[ZeeOSix]

Did a brake fluid change on my 2005 Tacoma last weekend. This truck has ABS, but no VSC (vehicle stability control). Factory service manual says to bleed the brakes the old fashioned way - pump the pedal, hold and open/close the bleed screws.

So I started the process by sucking the old fluid out of the master cylinder fluid reservoir. After sucking as much as I could out of the reservoir, the front chamber was still full of brake fluid. I had to round up a small syringe with a very small long tube and snake the tube down into the front reservoir area as the red arrow path shows in order to suck out the old fluid. After the whole reservoir was empty I filled it with new brake fluid. The front chamber didn't start filling up until the back chamber was nearly full and the fluid cascaded over the top of the separation wall to fill the front chamber. The blue arrows shows the separation wall between the front and rear chambers.

But here's the strange part. When I bleed the brakes only the rear chamber would empty. I started with the rear brakes so thought that the front chamber was tied to the front brake lines, but when I bleed the front brakes the front chamber still didn't go down at all. The front chamber fluid level never went down throughout the whole brake bleeding process.

So what's the reason the front chamber of the reservoir never goes down? It is tied to the ABS function somehow - does the ABS unit flow fluid back to the reservoir front chamber when the ABS operates?

There are only two lines going out from the master cylinder to the ABS unit - I thought maybe one line was for the rear brake lines circuit and one was for the front brake lines circuit, but that doesn't seem to be the case. Is one of those lines a "return" line from the ABS unit when it operates? I looked in the service manual and couldn't find any description of why the reservoir is chambered like it is.

Photo after sucking out the old brake fluid.

Only two lines coming out of the master cylinder that go to the ABS unit.

 

[danez_yoda]

I had the same question on my 07 tacoma. Exact same experience.

 

[atikovi]

No idea but most of the time I pull the reservoir anyway to clean it out.

 

[ZeeOSix]

Originally Posted by atikovi
No idea but most of the time I pull the reservoir anyway to clean it out.


My reservoir was pretty spotless inside, so it would have been way too much trouble to pull it off. That would have made the job much more involved for sure, just because I'd have to remove the two main lines and then bleed the master cylinder. The small tube on the syringe worked pretty good.

 

[ctechbob]

Originally Posted by ZeeOSix
Originally Posted by atikovi
No idea but most of the time I pull the reservoir anyway to clean it out.


My reservoir was pretty spotless inside, so it would have been way too much trouble to pull it off. That would have made the job much more involved for sure, just because I'd have to remove the two main lines and then bleed the master cylinder. The small tube on the syringe worked pretty good.



A lot of the time you can just pull the plastic out of the rubber grommets. I think that's what they're referring to.

 

[ZeeOSix]

Originally Posted by ctechbob
Originally Posted by ZeeOSix
Originally Posted by atikovi
No idea but most of the time I pull the reservoir anyway to clean it out.

My reservoir was pretty spotless inside, so it would have been way too much trouble to pull it off. That would have made the job much more involved for sure, just because I'd have to remove the two main lines and then bleed the master cylinder. The small tube on the syringe worked pretty good.

A lot of the time you can just pull the plastic out of the rubber grommets. I think that's what they're referring to.


This setup connects the plastic reservoir to the metal master cylinder with a roll pin (red arrow). Not easy to bang out when mounted in the vehicle, plus it would put some side impact force on the assembly which I wouldn't want to do. Using a syringe with a small long tube attached was way easier in this case.

 

[atikovi]

I just bang out the roll pins. Not a big deal but hard to believe that's the original reservoir on a 14 year old truck.

 

[ZeeOSix]

Originally Posted by atikovi
... hard to believe that's the original reservoir on a 14 year old truck.


It's only got 50K miles on it. I bought it new and it's been well cared for. Probably keep it forever as I still like it as much as I did when it was new.

 

[supton]

Originally Posted by atikovi
I just bang out the roll pins. Not a big deal but hard to believe that's the original reservoir on a 14 year old truck.

How is that hard to believe? Do you see them fail often? I don't think I've seen one ever fail, but I'm no mechanic.

AFAIK mine is original on my '99.

 

[atikovi]

I was referring to how clear and transparent the plastic is. Most cars that old it has turned white and opaque not to mention having a black coating of gunk in it..

 

[02SE]

Originally Posted by atikovi
I was referring to how clear and transparent the plastic is. Most cars that old it has turned white and opaque not to mention having a black coating of gunk in it..


I have a 22 year old 4Runner that I bought new, (which I'm considering selling) which has an equally pristine brake fluid reservoir. Periodic (every 3 years or so) brake fluid changes have kept it looking new.

 

[nthach]

Having a little residual brake fluid is a common Toyota thing, the reservoirs are partitioned for reasons unknown. I like to take a vinyl hose and suck it out with a Mityvac.