Why three reservoirs?

[VIRGIN MIKE]

I started this thread on my build page by, mistake - sorry.
Seems to me, each MC holds enough fluid to work properly without sucking fluid out of the reservoir(s); a failed or leaking system syphons needed fluid from the reservoir - this shouldn't affect the other MC(s) before realize you have a problem; or am I missing something?firewall.jpg

[miller7448]

In the aerospace and space industries we use risk analysis all the time. Basic concept is what is the risk of something happening and what is the potential consequence. In this case you are saying in your opinion the risk of a hydraulic failure is very low. Then we need to look at what the potential consequence of loss of brakes is. In my opinion that would be loss of life. Based on this analysis the extra cost/effort of three reservoirs vrs one is off the charts. Anyone recommending one would be fired.

[jayguy]

The same reason that all the auto makers have built in split reservoirs in their brake MC's since the late 60's/early 70's. With only 1 res, a leak anywhere in the system will eventually drain the res if it goes un-noticed and then you will have no brakes/clutch whatsoever. So for safety, unconnected systems for front, rear, and clutch (hence 3 reservoirs) are the safest bet, if you get a leak in one, you will still have working brakes on the other set and be able to stop safely, if not quite as quickly.

[NAZ]

I'm with miller7448, and have done a lot of Failure Mode and Effects analysis on various system to understand the importance of looking at the potential for failure and the criticality of one. And having had actual life & death brake failure experiences, when it comes to safety systems, I prefer a robust design with redundancy.

At minimum, you need reservoir capacity to accommodate fluid expansion and contraction from temperature changes and to have sufficient surplus for pad wear. That's the bare minimum, and that's close to what you get when using one common reservoir. But what about fluid leaks? If you have your pay attention eyes and ears on, you may notice small fluid leaks, a sign of incipient failure before a catastrophic failure actually occurs. But a minimal reservoir capacity will likely not give you that opportunity. Then again, if you're not the kind that pays attention it really won't matter if you have a gallon of brake fluid you'll only see the problem when you press the brake pedal and the car doesn't want to stop like it should. These are the kind of folks that engineers design idiot lights for warning of low fluid conditions. Even that doesn't persuade some as I know of one woman that taped here business card over a fault indicator because it bother her seeing the red light illuminated on the dash.

Be safe, it's not just your life at stake -- passengers and other drivers on the road don't get a vote but can surely be affected by how you build your car.

[Jim Schenck]

The real reason for giving three is only perception. A single reservoir with a line that y's into two lines feeding 2 seperate masters is functionally the same as a factory single reservoir (which is on almost all OEM cars) that has a small divided section at the bottom feeding each individual piston if the level gets too low. A lot of people confuse the mandated split braking systems with split reservoirs and they are not the same thing, the split braking system provides a seperate piston to actuate the front and rear brakes seperately in case one side fails but both still share the same builk of the fluid in the reservoir. If you were to have a brake failure in a system with one reservoir you still have the complete second system to get you stopped as the fluid in the master and in the section of line after the "Y" keeps that side functioing seperately.

[NAZ]

But Jim, there are many here that believe the Wilwood Tru-Bar (balance bar dual M/C) system y'all supply with their kits does not have braking redundancy so for them it doesn't really matter the size of the reservoir, if they lose the front system the rear will not work anyway (or vice versa). So their braking system is virtually the sames as on an early 60's car with only a single master cylinder.

[VIRGIN MIKE]

When I installed my brakes, the big deal was bleeding them - In my case I opened one system (read fail) to purge the other; the side being bled had plenty of pedal to purge the air (or stop stop the vehicle). I ran a tube from the bleeder valve back to the respective MCs, the open side just recirculated while I purged the other, no reservoir involved - To me that indicated I had redundancy even with the balance bar in play and a catastrophic failure front or rear wouldn't prevent half the dual system from working. The only thing I see the reservoir doing is buying time until you get around to fixing a slow leak. I think that agrees with what Jim is saying. In my case the balance bar did not allow the pedal to bottom before engaging the working MC

[NAZ]

When I installed my brakes, the big deal was bleeding them - In my case I opened one system (read fail) to purge the other; the side being bled had plenty of pedal to purge the air (or stop stop the vehicle). I ran a tube from the bleeder valve back to the respective MCs, the open side just recirculated while I purged the other, no reservoir involved - To me that indicated I had redundancy even with the balance bar in play and a catastrophic failure front or rear wouldn't prevent half the dual system from working. The only thing I see the reservoir doing is buying time until you get around to fixing a slow leak. I think that agrees with what Jim is saying. In my case the balance bar did not allow the pedal to bottom before engaging the working MC

I agree Mike, if your braking system is designed correctly and the balance bar pedal assembly is installed and set-up correctly it will provide braking redundancy. Mine does. I've tried to explain this to folks here before but there is this belief that if you lose one system you lose them both. That tells me they have an installation or adjustment issue.

And Jim has stated his position on the single reservoir here before and I agree with his operational system failure assessment, but I am still solidly in the camp that want's the extra capacity to extend the chance you will catch a leak during a pre-flight cursory inspection before one side of the system fails to function. On the motorcycle it's easy to see leaks, on the car it's a bit tougher so a larger puddle may help you spot one. I've lost half the braking system before and once lost the braking system on all four wheels in an older car and it results in moments of max pucker factor until the ride is over.

[Jim Schenck]

The redundancy with the balance bar is similiar to that of a tandem master cylinder in that whichever end has has the failure must be fully compressed before the remaining side will begin to get pressure. This results in a lower pedal height for sure, but still enough travel to get the car stopped. In fact the balance bar often will bind before allowing full compression of either cylinder making it work even a little before the faulty side bottoms out completely. (This is what makes it tough to bleed the system without cracking a front and rear at the same time)

To the original point though, I don't see how having two seperate reservoirs would have any bearing on how the mechanical part of the system functions? If the issue is you are not comfortable with the function of the balance bar that is a completely seperate from saying it needs a whole second reservoir to be able to perform a single emergency stop. How would having an additional reservoir have any affect on stopping if the balance bar can't push the second master cylinder?

[Jeff Kleiner]

...To the original point though, I don't see how having two seperate reservoirs would have any bearing on how the mechanical part of the system functions? If the issue is you are not comfortable with the function of the balance bar that is a completely seperate from saying it needs a whole second reservoir to be able to perform a single emergency stop. How would having an additional reservoir have any affect on stopping if the balance bar can't push the second master cylinder?

Ding, ding, ding! Thanks for bringing logic to the conversation Jim

Jeff

[NAZ]

Thanks Jim. Sorry I baited you but you have made your point on the single reservoir before and while doing so, alluded to the redundancy factor built into the Wilwood balance bar system without clearly stating that if one side fails the other will continue to work. That is the part I hoped you would have expanded on. I fully understand the balance bar system and know it’s designed to be a true redundant system. I’ve tried to explain that in this forum before. But there is still a belief among many that if one side fails the other one won’t work.


I suspect most builders have never worked with these systems before so it’s not intuitive. You have a tremendous amount of respect on this forum so I was hoping to see you state that fact clearly as you have now done. Perhaps the folks that are experiencing a different result will start looking at their installation and set-up – not an inherent design flaw of the equipment y’all provide. Something as simple as the pedal hitting the floor before allowing the M/C full stroke can defeat the redundancy built into the pedal assembly.