Wilwood master cylinder failure and safety concerns

[defilade]

My car: Gen 1 coupe completed in 2012, 6400 miles, Wilwood pedal box and master cylinders (.625 and .75). I am the third owner.

The problem: Hopped in the car to start it up and the pedal brake pedal went to the floor. Hmm. So I opened the front clam, got back in and pressed the brake pedal and I could see brake fluid coming out of the vent hole in one of the reservoirs. I pulled the access panel over the master cylinders and had a friend push the pedal and I can see one of the masters going all the way in while the other goes nowhere. So I'm guessing this is master cylinder failure, where the the fluid is sneaking past the piston. The failed one is the .75.

Am I off base here?

Safety: Separate but related issue. I understand the reason for the balance bar setup with two separate masters, in that it allows you to set the f/r bias correctly. But there's zero redundancy in this design: Yes I have two circuits, but if one fails, the other one will not take over because of the pivoting balance bar. So it's not a "dual circuit master" in the sense of providing redundancy if one circuit fails. This doesn't seem optimal for a street car. Has anyone come up with a way to address this?

Video:


https://youtu.be/yxXWU6v45VI

[Dave Tabor]

Ok, so cylinders fail - this has been in the forum before - fine.

What's disconcerting is the loss of brakes when the balance bar loses leverage to the side the still has pressure. This can happen whether it's a master cylinder failure or a failure anywhere else in the system (hose, caliper, etc.).

ChatGPT, when presented this scenario, suggests some sort of travel limiter on the master cylinders and/or that the issue is using the compact master cylinders with short travel.

This to me is a big safety issue and liability as well.

Dave
Gen III #17

[Jeff Kleiner]

Safety: Separate but related issue. I understand the reason for the balance bar setup with two separate masters, in that it allows you to set the f/r bias correctly. But there's zero redundancy in this design: Yes I have two circuits, but if one fails, the other one will not take over because of the pivoting balance bar. So it's not a "dual circuit master" in the sense of providing redundancy if one circuit fails.

Precisely! And this is the point that I and a few others have been trying to make when some builders think that they need to have two reservoirs "for safety".

Jeff

[lewma]

Keep your emergency brake handy ;)

[RoadRacer]

Precisely! And this is the point that I and a few others have been trying to make when some builders think that they need to have two reservoirs "for safety".

Jeff

100%

[defilade]

Keep your emergency brake handy ;)

Right? Unfortunately it's not reachable with my harness on!

[defilade]

I found a "stop nut" solution mentioned in a video from Acton Customs. I think this is the way to do it. He's showing an original-style Cobra pedal box with bottom-mounted pedals, but the principal of the overtravel stop is the same.

He discusses the stop nut at 4:10 if you want to skip the background info on the pedal box setup.


https://youtu.be/L_EWceoApj0

[Bart Carter]

I found a "stop nut" solution mentioned in a video from Acton Customs. I think this is the way to do it. He's showing an original-style Cobra pedal box with bottom-mounted pedals, but the principal of the overtravel stop is the same.

Has anyone tried this? Looks like the perfect solution.

[PNWTim]

Interesting this has come up. I was/am aware of this concern and it's primarily why I opted out of the electronic e-brake. In a conversation with another member, he brought this up and after mulling it over I decided I liked the idea of a good, old fashioned backup.

[Dave Tabor]

I run a cable-actuated e-brake and practice with it now and then.
It's not very effective, lol.

Dave
Gen III #17

[defilade]

Has anyone tried this? Looks like the perfect solution.

Carroll Shelby did. ;-) My understanding from Nick Acton is that a similar bell nut was used by Shelby on the original Cobras. They used bottom-mounted pedals so the pedal box setup was different, but the Girling remote-reservoir MCs they used are similar to the Wilwoods most of us are using.

The more research I do on this, the more I'm perplexed as to why such a critical safety feature is not included with the kit.

[RoadRacer]

I’d be very careful. I suspect the reason this isn’t “factory” is that it can make things worse too, under normal usage.

If you constrain the bar too tightly:
• It may not self-equalize correctly
• It may preload one circuit

It’s something I’m going to look into, but it’ll ultimately be up to an individual setup how to do this

[defilade]

Just to be clear, this approach doesn’t touch the balance bar. You’re limiting overtravel with a nut mounted on the piston rod, between the clevis and the MC. You do want to make sure it’s positioned correctly, so that it doesn’t affect normal range of pedal travel.