Soft, mushy clutch after hard acceleration--thoughts?

[xclusivecar]

My clutch pedal feels great when tooling around but if I get on it a bit and either accelerate from a stop aggressively or down shift to accelerate aggressively the pedal becomes very soft and mushy. After only a minute the pedal returns to normal, feeling nice and tight. I had the pedal assembly replaced 4 months ago and am experiencing no slippage when driving normally. Everything feels "normal" otherwise. Only after a hard acceleration does this happen. Thoughts?

[deliriousga]

Have you ever changed the brake fluid? It could be boiling when the temp rises due to condensation. That would make it gas out a little and you would loose pressure.

[RandallNeighbour]

Hey John, what's his brake fluid got to do with a mushy clutch?

[MNBoxster]

Originally Posted by RandallNeighbour

Hey John, what's his brake fluid got to do with a mushy clutch?

Hi,

The Brakes and Clutch share a common Fluid Reservoir. As John quite rightly points out, excess moisture in the Fluid will Boil with Hard Use and display the classic symptoms the Lister is experiencing. If he were to get on the Brakes just as Hard, he'd find that they too would show noticable Fade and Sponginess.

A Flush, Fill, and Bleed are definitely in order...

Happy Motoring!... Jim'99

[RandallNeighbour]

Wow. The clutch uses the brake fluid? Is this what you're saying?

I'm learning something new today. It's a good day when I learn new stuff about this car.

[MNBoxster]

Originally Posted by RandallNeighbour

Wow. The clutch uses the brake fluid? Is this what you're saying? ...

Hi,

Yep, two separate Master Cylinders, but both draw their Fluid from a Common Reservoir located on the Brake Master. As the Fluid ages and accumulates moisture, both systems are adversely affected. Even greater reason to adhere to the Two-Year Change Rule. Hope this helps...

Happy Motoring!... Jim'99

[xclusivecar]

Originally Posted by deliriousga

Have you ever changed the brake fluid? It could be boiling when the temp rises due to condensation. That would make it gas out a little and you would loose pressure.

Funny you should ask! I bled the brakes last summer and had a hell of a time getting to the clutch, so skipped it. After brainstorming I figured maybe some air pockets were in the clutch line and heating up and then cooling down, quickly restoring the clutch feel. A buddy and I were going to reconnect the power bleeder, get the car up high, and bleed the clutch to see if this is the problem.
My brakes feel great and I didn't notice much, if any, air while bleeding them last summer and can't figure any air would have been trapped in the clutch line. MNBoxster--after reading your post though...because they are 2 different systems this could definitly be possible (air or water) in the clutch line. I'll try to flush this weekend and report back.

[eslai]

Originally Posted by MNBoxster

The Brakes and Clutch share a common Fluid Reservoir.

Oh wow, learn something new every day! That seems rather odd to me, but I guess it wouldn't be a problem--if you're boiling your brake fluid you've got work to do anyhow, eh?

[MNBoxster]

Originally Posted by eslai

... That seems rather odd to me, but I guess it wouldn't be a problem...

Hi,

It's not odd at all, in fact, it's rather innovative. There's actually no reason to have two separate reservoirs, both supplying the same Fluid, albeit to different circuits.

And, it reduces Production Costs because Porsche doesn't have to make two distinct Inspection Covers for the Tip S and Manual Cars, nor do they have to purchase a separate Reservoir and Cover for the Clutch. This makes the Clutch Master smaller, making it easier to locate it closer to the Pedal eliminating a bunch of Linkages. Plus, it saves a tiny bit of weight as well...

Happy Motoring!... Jim'99

[eslai]

I say it's odd because it then links the clutch hydraulics with the brake hydraulics. If one fails due to fluid problems the other system is now exposed to that failure, that's all. But again, if you're having fluid issues, leaky lines or what not, you're going to have to fix something anyhow, so I can see how it's not a big issue. Cost cutting wins in this case I guess.

I can appreciate simplifying a system, but you gotta weigh the costs. Not saying it's a bad idea, just something I hadn't seen before.

[denverpete]

Originally Posted by MNBoxster

Hi,

It's not odd at all, in fact, it's rather innovative. There's actually no reason to have two separate reservoirs, both supplying the same Fluid, albeit to different circuits.

And, it reduces Production Costs because Porsche doesn't have to make two distinct Inspection Covers for the Tip S and Manual Cars, nor do they have to purchase a separate Reservoir and Cover for the Clutch. This makes the Clutch Master smaller, making it easier to locate it closer to the Pedal eliminating a bunch of Linkages. Plus, it saves a tiny bit of weight as well...

Happy Motoring!... Jim'99

While innovative, it's hardly unique to Porsche. In fact, as I've recently discovered it's a pretty common setup. I'm definately going to keep in mind your advice about changing out the fluids!