Brakes/Master Cylinder -Lost All Pressure?

[Jon69RagTop]

Guys

I've put 1,700 miles on this set-up since installation and have had ZERO issues. Kore 3 C5, 325 up front and 335 in back. Wilwood 7/8 tandem master cylinder, but this issue has nothing to do with the matching of components. This is a manual brake set-up, and has worked awesome since day one.

Problem is this afternoon pullling into my driveway I lost all brake pressure, and I mean all of it. Pedal went all the way to the floor. Now my driveway is a slight uphill incline, so gravity worked in my favor and the slope of the hill stopped me in time from hitting the house. As I started rolling back down the driveway, I pumped the pedal maybe three times, and BAM I have full pressure again and the brakes work like never an issue. To say this has scared the B-Jesus out of me is an understatment.

I've checked for leakes and have found none. I checked fluid level and it is full. I've checked inside the firewall for leaking on the backside of the master cylined and find nothing. I've checked for secure linkage and the pedal and clevis, and all looks good. I'm at a loss, and a little nervous to take it out again.

Now the driveway does have a slight curb at entrance, and I drove over it this time a little quicker than normal. NOt sure if that could of caused an issue, but was wondering could that jarring motion knock an air bubble loose in the master and create 100% soft pedal. I had zero pressure, and then it came back instantly.

I would appreciate any expert opinions here, and definitly will be giving Tobin a call as well. I'm confident it has nothing to do with his product, and I'm suspicious this is a Master Cylinder issue. Just not sure what to be looking for.

Thans guys.

[MarkM66]

Damn Jon, glad nothing bad happened.

If there are no leaks, I don't see how it could be anything except the master cylinder.

Also check to make sure a caliper hasn't come loose.

[Apogee]

Jonathan,

Thankfully both you and your car are okay, but definitely do yourself a favor and don't drive it until this issue is resolved.

It sounds like your MC bypassed fluid...rapidly. Usually, as a MC goes bad, it's something that starts out mild and inconsistent and then steadily gets worse, but that doesn't necessarily have to be the case. Most of the other things that could cause the pedal to drop like that wouldn't recover until they had been fixed and/or replaced. The fact that they've been working great for 1700 miles would tend to indicate that it's not an air bubble, as any trapped air would have given a soft, spongy pedal since day one.

Does the pedal slowly sink any with your foot on the brake for 20-30 seconds applying moderately heavy pressure? I would suggest contacting Wilwood about this since I think there's a new MC in your future, or at least a rebuild kit. I would want to pull the existing piston assembly from the MC you have and take a look at the seals and the bore...without finding a "smoking gun" for the problem, I'd be nervous too.

Tobin
KORE3

[Jon69RagTop]

Tobin

Thanks for your response. I will triple check tonight on the constant pedal pressure question, but yesterday it appeared to return to full working condition.

When a master cylinder bypasses all fluid like this, would there be signs of it leaking externally, or does the fluid bypass all take place inside the unit?

I agree, it's not getting driven till I find this problem.

Jonathan

[Apogee]

Jonathan,

Bypassing fluid typically implies internal to the master cylinder in the circles I run in. External leaks are just leaks and would indicate damage to the secondary cup/seal on the primary piston or the bore near that seal, whereas bypassing fluid indicates seal or bore damage between the primary and secondary pistons which doesn't result in fluid loss. If you bypass enough fluid volume, then it won't allow you to build any pressure which is what sounds like happened to you. Without any external leaks, I can't think of anything else that might cause those particular symptoms.

I'd be tempted to pull the MC piston and inspect it as well as the MC body for loose machining chips or other contaminants that maybe didn't get fully removed prior to assembly. Even a casting burr or flash of some sort...I'm guessing here. Something had to cause what happened, and you mentioned that it was immediately after hitting the transition on your driveway a little harder than usual. Maybe it knocked something loose.

Tobin
KORE3

[Jon69RagTop]

I removed the master cylinder from the firewall and disassembled the push-rod assembly and pistons from the master bore itself. As I removed the pistons, small microscopic aluminum particles were visible in the fluid, and there seems to be an imperfection in the wall of the bore as well. You can definitly see traces of the piston boots sliding on the bore walls.




One picture shows a nick in the bore wall, and the other picture shows the scuffing on the bore wall. Logic would say rubber alone can't do this, so maybe the fluid with particles present is creating the scuffs. The gouge in the wall and no other evidence on the rods leads me to think this has been like this from day one.

Considering I lost all pedal pressure with travel 100% to the floor, and the inspection of the cylinder bore, it seems most logical to contact Wilwood.

I'm sooo "thankful" this did not result in a wrecked car or injuries.

A big 'thumbs-up' to Tobin, whose customer service always goes well beyond the purchase of his products.

[Vegas69]

You are one lucky dude. That doesn't make me feel to warm and fuzzy about mine since I'm running the same master.

[aany001]

Are you running a parking brake setup?? It really sounds like the master is the culprit.Let us know how you make out.

[Jon69RagTop]

Yes, I do feel lucky for sure. I am running Tobin's rear "parking brake in hat" set-up on the rear, but have it connected to the factory foot actuated emergency brake. I'm seriously considering switching to a hand brake though.

Since the car is a manual shift, my gut says grabbing a hand actuated emergency hand brake versus jumping my foot up to the parking brake might be more natural.

NO center councel to mess with on my set-up either.

[XcYZ]

Jon, thanks for the follow up. That's some great information to have.

I would definitely contact Wilwood. I would think they would also want to know what happened and how the MC looks.