Brake Master... Truly independent circuits?

[skidd]

In a functioning brake system , are the front and rear fluid circuits truly independent? I ask, because it seems in my setup like fluid from one is finding its way into the other.

I have a '93 (edit, I had '95 here by mistake) cobra R master in front of a fox booster. I have a pair of aluminum reservoirs connected to each inlet independently. Also, I have an inline proportioning valve (aka pressure reducer valve) in the front circuit. The front brakes are plumbed to the end away from the booster, the rears to the end close to the booster. SN95 disks all around, with PBR fronts.

The brakes seem to be working just fine, stop strong and feel good.

I noticed about a month ago a bit of fluid seeping out the top vent ho!e in one of the reservoirs. I opened them up, and saw one was a bit high, the other a bit low. I didn't think much of it at the time and just leveled the fluid and walked away. I don't recall which circuit it was that was high.

About 2 weeks ago, it happened again. Got me thinking about how and why its happening. So, I've been googling for answers and finding nothing. Again forgot to pay attention to which circuit.

Today... Again. This time I took note, it was the rear circuit that was over-full. Wish I could say it has always been this one, but I just don't know. Truth is, I want to say it was the front last time. Just can't remember.

The master is a new one with only about 700 miles on the whole car.

Is fluid seeping between circuits inside the master somehow? If so, is it by design , or do I have a faulty master? Looking at the factory plastic master, I see the 2 inlets share the same reservoir, with an internal separator wall. This issue I'm having would be not a problem since the fluid would just spill over to the other side.

So, do I need to think about going with an OEM reservoir? Perhaps somehow link the 2 I have now? Do one-piece remote reservoirs have a similar separator to the OEM plastic ones? I was sure I've seen others with 2 completely independent reservoirs. Has anybody else seen anything like this?

Here is a look at he reservoirs during initial mockup.
https://www.ludicrous-speed.com/zp/cache/Shanes%20Cobra/TheBuild/IMG_20170409_224236652_595.jpg

[michael everson]

I cant answer your question for sure, but it seems like they should be independent. The bigger issue is your brake line connections. Pretty sure the front brakes go in the fitting closest to the booster.
Mike

[CraigS]

I cant answer your question for sure, but it seems like they should be independent. The bigger issue is your brake line connections. Pretty sure the front brakes go in the fitting closest to the booster.
Mike
I agree on the front vs rear lines postion. Re; the fluid levels, I feel they should not be doing this but can't say for 100%. As you note the stock reservoirs are one w/ a divider wall. If this level change were happening in one of them we would never notice it. I hope someone else chimes in on this.

[rich grsc]

3x, you have the lines switched at the MC. Change them and I think it'll solve the issue.

[mike223]

In a functioning brake system , are the front and rear fluid circuits truly independent?




Yes - see illustration below - I suspect "circuit 2 front seal".

However, as you noted - with the stock reservoir you wouldn't likely notice you had a problem (until it got worse).

Not sure I'd get too worried about it unless it became a regular PITA (it might settle down with some more break in).


I agree the plumbing is reversed, but I don't think that would make a difference with this particular issue.


80801

[Jeff Kleiner]

X4, you are plumbed backwards.

Won't say it's impossible but I've never seen or heard of fluid traveling past the seal in one chamber, through the unpressurized area between front and rear and into the pressurized second chamber resulting in the level being high in one and low in the other :confused:

Jeff

[mike223]

I've never seen or heard of fluid traveling past the seal in one chamber, through the unpressurized area between front and rear and into the pressurized second chamber resulting in the level being high in one and low in the other :confused:



My theory is a little pressure from circuit 2 is leaking past circuit 2 front seal into the unpressurized area and into the forward reservoir through the (unpressurized) equalization port.


Of course, that's assuming that his particular MC is ported exactly as drawn (but it's pretty much standard).



For that matter, even if it didn't have the equalization port, as soon as circuit 1 piston moves forward (to build pressure in circuit 1) the unpressurized area vents to circuit 1 reservoir port...

[DaveS53]

Tandem master cylinders have a volume ratio, usually 2:1, with more fluid going to the front. In the normal position, the front port goes to the front brakes. Hot rods like mine with an under floor mounted MC have the MC pointing backward, so the back port goes to the front.

http://www.wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-14241-BK

[mike223]

In the normal position, the front port goes to the front brakes. Hot rods like mine with an under floor mounted MC have the MC pointing backward, so the back port goes to the front.




lol - that seems certain to cause some confusion...






Tandem master cylinders have a volume ratio, usually 2:1, with more fluid going to the front.



True - a better wording would be more (circuit) volume is (usually) allotted to the front calipers.

This is the rear circuit on the OP's MC and installation.

[skidd]

Initially when I researched into the correct plumbing for this master, I was confused by the number of places I found that indicated the 93 cobra master was 'backwards' from typical plumbing. That the rear port goes to the rear brakes and the front port goes to the front brakes. Would have been the 1st time I saw that.. but.. ok. Now, I think I found out how/why it happened.

I used this conversion kit from LMR as a guide to what port is supposed to go where, when doing a standard conversion.
https://lmr.com/item/MM-MMBAK8/87-93-Mustang-Brake-Lines-For-94-95-Cobra-Master-Cylinder

Looking at install instructions, and some pictures, I could clearly see that the rear port on the master, goes to the "rear" inlet on the proportioning valve.
https://2d25888cf6c27e301379-f489e8ff80a7f2e3001280df7038db01.ssl.cf1.rackcdn.c om/mm-mmbak8_3417.jpg

Then.. I looked at the ports on the mustang proportioning valve to confirm.
http://i723.photobucket.com/albums/ww234/fivodude/94proportioningvalveports.jpg

When I read the text "Master Cyl Rear".. I assumed that meant, master cyl rear brake circuit.. not just rear-port on the master.
The over use of the word "rear" to describe 2 different things.. I think totally threw me off.

That said.. I'll switch the ports around and see what happens. Though... I have my doubts it could cause this strange fluid transfer issue I'm seeing. Only 1 way to find out though.

[Packer fan]

Did you ever think that it may be the presure reducer that is changing the pressure in the 2 chambers of the master cylinder and fluid is trying to move from the high to low pressure sides.
Just a thought.
Jim

[skidd]

Actually.. yes.. I did think about that.. and I can't discount that as a possibility. Not sure quite how that can occur.. but.. I supposed it could. I know the device is just a simple spring internally that takes up some of the initial pressure. But, also, initially, I had that pressure reducer set to 0, or.. max pressure.. or.. no reduction.. how ever you want to word it. When it was setup that way, was the 1st and 2nd times I encountered the "seeping" issue. Only in the last week have I actually gotten around to tuning my brakes by backing off the front brake pressure in an effort to gain better back brake traction. Seems to have worked pretty well too. I was able to dial it back enough to get all 4 ties to lock up almost at the same time, then I added back some more front to ensure they always lock up first.

[Jeff Kleiner]

Tandem master cylinders have a volume ratio, usually 2:1, with more fluid going to the front. In the normal position, the front port goes to the front brakes. Hot rods like mine with an under floor mounted MC have the MC pointing backward, so the back port goes to the front.

http://www.wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-14241-BK

The OP told us that he has a '95 Cobra master cylinder Dave. Your statement that the front port goes to the front brakes is wrong.

Jeff

[skidd]

I miss-spoke/typed... sorry... not sure if it matters.. but.. it's actually a '93 SVT Cobra R master cyl. 1" bore if memory serves.

[DaveS53]

The OP told us that he has a '95 Cobra master cylinder Dave. Your statement that the front port goes to the front brakes is wrong.

Jeff

Wouldn't be the first time. I just assumed a Wilwood MC from the looks.