Master Cylinder Caps

[Way2Fast]

Has anyone except Lamonester bothered to remove the caps on the master cylinder (located under the seat) and checked if the rubber diaphragms are partly or fully pulled out from the normal retracted position? The latest recall "fix" seems to be replacement caps with a slit cut in the rubber membrane to prevent it from pulling out when the fluid level drops due to pad wear, temperature change or some other cause. Of course the "slit" will defeat the purpose of the airtight rubber seal and evidentually allow moisture to contaminate the hydraulic fluid.

I'm thinking that due to improper design of the master cylinder, when the rubber diaphragms become fully extended, they might interfere with the floats in the master cylinder, causing an error or brake warning message on the dash.


Richard

 

[Lamonster]

I would love for someone at BRP to explain how the new caps work with the cut in them. :dontknow: :

 

[Way2Fast]

I would love for someone at BRP to explain how the new caps work with the cut in them. :dontknow: :

You and me both !!!!

I'm sure it was a money saving move and a way to avoid making the changes necesssary for a correct fix. Who knows, when BRP orders the next batch of caps from the manufacturer they may decide to save another quarter and specify caps without the rubber diaphragm !!!!


Richard

 

[matusky]

Anyone have a decent picture of the new cap with the 'slit' in them?

 

[BajaRon]

I would love for someone at BRP to explain how the new caps work with the cut in them. :dontknow: :

It is simple... they can't and they won't work (as intended). The entire function of these rubber diaphragms is predicated on a vacuum seal. If there is any way for air to get past (i.e.; cut, slit, hole, crack, poor seal, etc.) then they just can't work. The only reason to have them at all (if you're going to destroy the vacuum seal) is to give a perimeter seal with the threaded cap. An O-Ring would do as well.

The plastic cap has a pinhole in it to allow atmospheric pressure into the back side of the diaphragm which works to deploy it into the reservoir as fluid is displaced ONLY if there is a vacuum seal.

But with the plastic components (below the rubber diaphragms) occupying the same physical location as would be used if the diaphragms were deployed it defeats the process anyway. And it isn't like this is new territory. Automotive engineers have been using this approach for at least 30 years.

So the real fix is to leave the diaphragms as they are and re-design the reservoir including the sensors. Very expensive solution indeed! No doubt you will be seeing a different design on future Spyders.

The bottom line is bad design and quick fix. Then again, these diaphragms are simply an effort to overcome extremely poor maintenance (or slow failure due to leakage). If you simply check and fill your reservoir, as necessary, the rubber diaphragm issue becomes somewhat mute. Not to make excuses for BRP.

As for me (a Spyderless deposit owner), I think I'd leave the diaphragms as they are. At least they keep moisture out of the system. The reservoir is easily checked and I'd just do it more often than I might with a properly designed system. It's not all that big a deal but it is dissappointing.

 

[Way2Fast]

It is simple... they can't and they won't work (as intended). The entire function of these rubber diaphragms is predicated on a vacuum seal. If there is any way for air to get past (i.e.; cut, slit, hole, crack, poor seal, etc.) then they just can't work. The only reason to have them at all (if you're going to destroy the vacuum seal) is to give a perimeter seal with the threaded cap. An O-Ring would do as well.

The plastic cap has a pinhole in it to allow atmospheric pressure into the back side of the diaphragm which works to deploy it into the reservoir as fluid is displaced ONLY if there is a vacuum seal.

But with the plastic components (below the rubber diaphragms) occupying the same physical location as would be used if the diaphragms were deployed it defeats the process anyway. And it isn't like this is new territory. Automotive engineers have been using this approach for at least 30 years.

So the real fix is to leave the diaphragms as they are and re-design the reservoir including the sensors. Very expensive solution indeed! No doubt you will be seeing a different design on future Spyders.

The bottom line is bad design and quick fix. Then again, these diaphragms are simply an effort to overcome extremely poor maintenance (or slow failure due to leakage). If you simply check and fill your reservoir, as necessary, the rubber diaphragm issue becomes somewhat mute. Not to make excuses for BRP.

As for me (a Spyderless deposit owner), I think I'd leave the diaphragms as they are. At least they keep moisture out of the system. The reservoir is easily checked and I'd just do it more often than I might with a properly designed system. It's not all that big a deal but it is dissappointing.

I agree with you 100%.

I just received my recall letter from BRP today.....here is a quote; "Since we performed the brake inspection (first recall) on your vehicle, we have identified that some vehicles have one or two fluid reseroir caps that are unsealed. This might create a vacuum under certain circumstances (such as when it is stored in your cold garage over the winter or transported from our factory here in Canada) which could lead to absorption of air into the service brake circuits. Abnormal quantity of air could result in degraded brake performance.

What a crock of shit......they have it backward, the "fix" they have is what is going to cause the air to get into the system and degrade brake performance. The original caps are sealed, the replacement ones are not. I am going to file a complaint with the National Highway Traffic Safety Administration. http://www.safecar.gov
and explain the entire situation to them. This is going to cost BRP !

Richard

 

[BajaRon]

... we have identified that some vehicles have one or two fluid reseroir caps that are unsealed. This might create a vacuum under certain circumstances ... which could lead to absorption of air into the service brake circuits. Abnormal quantity of air could result in degraded brake performance.

This statement from BRP makes no sense at all. If the problem is that the diaphragm is "Unsealed" how does putting a hole in it fix the problem? Come on!!!

I'm not always right and I'm open to correction. But it sounds like they are talking out of the wrong end of the horse on this one. I can't, for the life of me, figure out what they are talking about. As far as I can tell it's exactly backwards.

It is true that the diaphragms can be deployed (at least partially) by contracting air inside the reservoir (due to cold, etc.). But only if they have a good seal. If they are Unsealed (as this statments says) then the diaphragms would do nothing at all.

Having them deploy for cold weather, etc., would normally be no problem at all. For crying out loud, they are designed to be deployed by reduced fluid levels. And when the air warms up again the diaphragm's would simply return to their normal position.

I do know that fully deployed diaphragms will hit the sensors because I checked that out on Lamont's Spyder. This has to be the REAL problem. It isn't the diaphragms at all. But if you disable them then you won't get interference with the sensors. You won't get the function of the diaphragms either.

It's like turning off the water to your house because a pipe is broken. Solves the problem of leaking water but doesn't really fix what is wrong either.

BRP is a very good company and from what I've seen of the Spyder, it is very well engineered. I am still very much looking forward to getting my Spyder (which Lamont assures me will happen). Still, the best of us make mistakes (especially on the 1st try). I hope BRP comes out with a better explanation for this recall.

 

[BajaRon]

One more thing has occurred to me. If the reservoir experienced TOO much unreleased vacuum. air could be sucked past the caliper pistons into the calipers. This would NOT be good. Especially with a system that requires a computer and 6 hours to bleed properly.

The diaphragms are pretty small, and the plastic parts below the diaphragms restrict full deployment. They might not be able to relieve all of the vacuum in the reservoir. This may be the bigger issue.

Putting a hole in the diaphragms would make much more sense, in this case.

The problem with explanations that don't make sense, or are partial information, is that it keeps people guessing as to the real reason.

 

[Lamonster]

Seeing you use to own a brake shop I would say that you know more than most on this subject. :bigthumbsup:

 

[spyryder]

Did a little search on hydraulic brake systems....it appears that brake reservoirs ARE vented to the atmosphere.

Venting
In order to allow the fluid to flow into the master cylinder,
the reservoir has an air vent that allows atmospheric
pressure to force the fluid into the master cylinder when a
low pressure is created by the movement of the pistons.The
vent is positioned above the normal brake fluid level in the
reservoir and keeps atmospheric pressure at the top of
the fluid.

http://www.peterverdonedesigns.com/files/hydraulic system theory.pdf

 

[Way2Fast]

Did a little search on hydraulic brake systems....it appears that brake reservoirs ARE vented to the atmosphere.

Venting
In order to allow the fluid to flow into the master cylinder,
the reservoir has an air vent that allows atmospheric
pressure to force the fluid into the master cylinder when a
low pressure is created by the movement of the pistons.The
vent is positioned above the normal brake fluid level in the
reservoir and keeps atmospheric pressure at the top of
the fluid.

http://www.peterverdonedesigns.com/files/hydraulic system theory.pd

Yes, you could say that the reservoir has a vent because it does. The master cylinder caps are vented but in a properly functioning system the vent is separated from the fluid by a rubber accordian seal or diaphram. This "high" mounted vent (in the cap) and the flexability of the rubber seal is what keeps atmospheric pressure at the top of the brake fluid. The inside of the reservoir is not in contact with freely circulating air.....unless you own a Spyder and install one of the new "leaky diaphram" master cylinder caps that BRP is encouraging in the new brake recall.


Richard

 

[BajaRon]

Did a little search on hydraulic brake systems....it appears that brake reservoirs ARE vented to the atmosphere.

Venting
In order to allow the fluid to flow into the master cylinder,
the reservoir has an air vent that allows atmospheric
pressure to force the fluid into the master cylinder when a
low pressure is created by the movement of the pistons.The
vent is positioned above the normal brake fluid level in the
reservoir and keeps atmospheric pressure at the top of
the fluid.

http://www.peterverdonedesigns.com/files/hydraulic system theory.pdf

True, the master cylinder must be vented to allow the brake fluid to move properly. But balancing atmospheric pressure does not mean that air is exchanged. Venting simply allows atmospheric pressure to equalize. There remains a membrane (rubber diaphragm in this case) between the two air masses. Atmospheric pressure is maintained without the negative effects of air (read water) exchange.

Think about it, if air were allowed to move in and out of the master cylinder how would the diaphragms expand into the open space below them? There would never be negative pressure inside the Master Cylinder and the diaphragms would never expand.

We know what the diaphragms are supposed to do, what is required for them to work correctly and why they are installed into a system like this. So, we are back to square 1. Why would BRP put a hole in the diaphragms which disables them completely? Are they not needed? Then why install them? And why is every other similar system in use today using operational diaphragms?

There is a "Hole" in this approach by BRP, me thinks.

 

[Way2Fast]

One more thing has occurred to me. If the reservoir experienced TOO much unreleased vacuum. air could be sucked past the caliper pistons into the calipers. This would NOT be good. Especially with a system that requires a computer and 6 hours to bleed properly.

The diaphragms are pretty small, and the plastic parts below the diaphragms restrict full deployment. They might not be able to relieve all of the vacuum in the reservoir. This may be the bigger issue.

Putting a hole in the diaphragms would make much more sense, in this case.

The problem with explanations that don't make sense, or are partial information, is that it keeps people guessing as to the real reason.

It would take a mighty high vacuum before outside air could be sucked past the caliper pistons and into the calipers....if it could be possible at all. These same caliper seals are subject to hundreds of pounds of pressure (thousands ?) in a panic stop without letting any fluid escape. If I'm missing something here, please let me know.

Richard

 

[spyryder]

True, the master cylinder must be vented to allow the brake fluid to move properly. But balancing atmospheric pressure does not mean that air is exchanged. Venting simply allows atmospheric pressure to equalize. There remains a membrane (rubber diaphragm in this case) between the two air masses. Atmospheric pressure is maintained without the negative effects of air (read water) exchange.

Think about it, if air were allowed to move in and out of the master cylinder how would the diaphragms expand into the open space below them? There would never be negative pressure inside the Master Cylinder and the diaphragms would never expand.

We know what the diaphragms are supposed to do, what is required for them to work correctly and why they are installed into a system like this. So, we are back to square 1. Why would BRP put a hole in the diaphragms which disables them completely? Are they not needed? Then why install them? And why is every other similar system in use today using operational diaphragms?

There is a "Hole" in this approach by BRP, me thinks.

I agree with what you're saying....so I did some more checking. First I looked at my car, a Chrysler 300 which also has a Bosch brake system and probably similar in theory to the Spyder's system. I've owned this car for almost 4 years and the cap has never been removed from the master cylinder(the level which has gone down due to pad wear can be seen through the plastic reservoir). I removed the cap today and guess what? The diaphragm was not expanded at all! It should have if the system was a truly airtight seal. Perhaps these diaphragms have some porosity designed into them so that they will retain their shape over a long period of time.
Another manufacturer also made mention of precision slits cut into their diaphragms..... :dontknow:

 

[Way2Fast]

Could you be more specific when you say "another manufacturer has made mention of precision slits cut into their diaphragms"

I have been working on cars all my life and come from a family of auto mechanics and I have never heard of a company willfully disabling the purpose of the diaphragms used in a hydraulic brake system.

If the master cylinder diaphragm in your Chrysler is not partially extended after brake wear it is probably due to:
1. The cap had been removed and the diaphragm bushed back in...possibly during a vehicle service or oil change.
2. The diaphragm is defective.
3. The cap had not been installed properly


Richard

 

[Lamonster]

Just got mine fixed at the local brake shop here in East TN ;D :bigthumbsup:

 

[spyryder]

Could you be more specific when you say "another manufacturer has made mention of precision slits cut into their diaphragms"

I have been working on cars all my life and come from a family of auto mechanics and I have never heard of a company willfully disabling the purpose of the diaphragms used in a hydraulic brake system.

If the master cylinder diaphragm in your Chrysler is not partially extended after brake wear it is probably due to:
1. The cap had been removed and the diaphragm bushed back in...possibly during a vehicle service or oil change.
2. The diaphragm is defective.
3. The cap had not been installed properly


Richard

Here's one site I found:

Title:Assured venting master cylinder diaphragm apparatus and method Document Type and Number:United States Patent 4987740 Link to this page:http://www.freepatentsonline.com/4987740.html Abstract:A diaphragm for a vented master cylinder reservoir which further includes means for opening the slit thereby assuring venting of the master cylinder reservoir is provided. The slit opening means are configured in such a manner that contact of the slit opening means with the master cylinder cap will cause the diaphragm to be stressed and to elastically deform, therefore assuring the opening of the venting slit.

As far as my Chrysler, I'm the original owner and the only person who's done any service on it...that's why I thought I'd mention it. I can assure you that everything is as it should be. Also, the cap looks identical to the Spyder's caps....but there is only one cap and a fairly large reservoir. That diaphragm would be way too small to compensate for the amount of fluid in there. Also, older cars were all vented directly to the atmosphere anyways, so I can't really see a big problem with moisture.

Now the Spyder...perhaps all of them were supposed to have that V shaped slit in the first place?.....Why are some of them on the recall list and not others? I'd like to see a cap from one that isn't on the list and compare the two....see what the difference is. :dontknow:

 

[BajaRon]

It would take a mighty high vacuum before outside air could be sucked past the caliper pistons and into the calipers....if it could be possible at all. These same caliper seals are subject to hundreds of pounds of pressure (thousands ?) in a panic stop without letting any fluid escape. If I'm missing something here, please let me know.

Richard

What you may be missing is that the cups (the rubber seal between the caliper bore and piston) are specifically designed to seal against pressure from one side only. They are tapered in towards the fluid side. When pressure is applied it actually works to press the rubber seal against the piston (or in some cases the caliper bore). The harder you press on the brakes the harder the fluid presses against the rubber seal and the tighter the seal is. Very effective.

However, it works in the opposite way from the reverse side (the air side in this case). If you looked at the seal you would see what I mean. I could not find a good picture of what I'm trying to describe so I made one. Pretty ugly I'll admit. But if you can get by that I hope it demonstrates what I'm trying to describe. The seal can go on either the piston or the bore. This picture is a piston mounted seal but it's the same thing either way.

The seal goes all the way around the piston, of course. But for demonstration purposes I just show the seal as 2 tapered wings (plus the fact that I can't draw well enough to do more than this anyway). The clearance to the caliper bore is much less than this and distorts the seal somewhat.

As you can see, when fluid pressure is applied it pushes against the rubber expanding it against the bore giving a great seal. The opposite effect is true when pressure is applied from the opposite side. Any negative pressure inside the caliper will try to equalize by pulling air past the seal. It takes a relatively small amount of pressure differential to allow air to sneek past the seal. The seal simply is not designed to seal against much pressure from the air side. Nor does it need to in a properly working system.

The other problem here is that soon, Lamontster is going to tell me to take this to the Tech forum! :joke:

 

[BajaRon]

As far as the "V-Slit" issue goes I have no explanation.

If you put a hole of any kind in the diaphragm it ceases to be a diaphragm.
If you are going to have a non-functional diaphragm, why have a diaphragm at all?

I'm sorry, I just don't see the logic.

The purpose of the diaphragm is to prevent air exchange inside the brake system. Moisture is very bad for brakes. When you exchange air you get a new load of moisture with every application. Additional moisture is accumulated even when the system is not being used.

This moisture will condensate from the air and over time you end up with liquid water in your system.

Water is heavier than brake fluid so it will sink to the bottom of the reservoir where it is promptly taken into the brake lines and then finds its way into the caliper where it can cause all kinds of problems.

A working diaphragm is the better way to go.

 

[spyryder]

As far as the "V-Slit" issue goes I have no explanation.

If you put a hole of any kind in the diaphragm it ceases to be a diaphragm.
If you are going to have a non-functional diaphragm, why have a diaphragm at all?

I'm sorry, I just don't see the logic.

The purpose of the diaphragm is to prevent air exchange inside the brake system. Moisture is very bad for brakes. When you exchange air you get a new load of moisture with every application. Additional moisture is accumulated even when the system is not being used.

This moisture will condensate from the air and over time you end up with liquid water in your system.

Water is heavier than brake fluid so it will sink to the bottom of the reservoir where it is promptly taken into the brake lines and then finds its way into the caliper where it can cause all kinds of problems.

A working diaphragm is the better way to go.

Here's a pic of a Bosch diaphragm....the slit would normally be closed until vacuum were applied to it. It appears that all diaphragms need to be vented in this manner.