Bad/failing MC, is this the symptoms?

281pony · Aug 31, 2010

i have bled my brakes several times. here is the setup;

13" front cobra, 11.65" rear.
m2300k kit MC, i think its a 93 cobra?
stock booster
ss brake lines.

with the car off, the pedal is FIRM about 20% travel.

with the car running, the pedal seems to sink and sink and have some fade to it. i can let off it and "pump up" the pedal as i go and stopping is drastically improved.

if i have an "oh $hit" stop and instantly smash on the pedal it most of the time is firm as it should be, WITHOUT pumping it up.

so is this a failing mc?

Mustang5L5 · Aug 31, 2010

Ha, the irony. The pedal in my daily driver behaves like this. Tried to have it fixed under warranty but they claimed it was normal. Had the same symptoms. Pedal firmed up when car off, but sinks when running and sometimes pumps up. But in panic stops, I have good brake response.

To be honest, I would suggest air in the lines, but I too have bled and bled with no result. Someone suggested this situation is caused by an internal seal in the mc failing allowing fluid to seep internally. Of course only way to verify is to swap out the master cylinder. If this was my mustang, I would have done it already, but infinitis are a little more tricky. I am convinced it is the mc. It's actually a common issue on g35s

SMOKEDYA · Aug 31, 2010

I would say the seals are bad also,or POSSIBLY the booster.But i'm leaning to the MC one of my opels did this.So i went and bought a rebuild kit and all was good again!I do have a brand spanking new 93 cobra one for sale.peace

john

Mustang5L5 · Aug 31, 2010

Btw, the mc included in the m2300k kit is a 1993 Cobra 1" mc.

Dino Dino Bambino · Sep 1, 2010

Mustang5L5 said:
To be honest, I would suggest air in the lines, but I too have bled and bled with no result. Someone suggested this situation is caused by an internal seal in the mc failing allowing fluid to seep internally.

That someone has hit the nail on the head. If the seal inside the MC fails, it allows air to get into the system causing a spongy pedal feel. The cure is to replace the MC.

281pony · Sep 2, 2010

i forgot i have a v6 master cylinder i pulled awhile ago. im going to throw that on and try it. especially since the oreillys locally cant find me a 93 cobra mc for less then $220

SMOKEDYA · Sep 2, 2010

281pony said:
i forgot i have a v6 master cylinder i pulled awhile ago. im going to throw that on and try it. especially since the oreillys locally cant find me a 93 cobra mc for less then $220

I told ya i have a 93 cobra brand new for $90. I could meet ya in longview again or you pay shipping also and i'll ship it.I could head up that way saturday?Sorry i ment to respond to your text that day.peace

john

Mustang5L5 · Sep 2, 2010

the V6 MC will work, but if it's the 94-98 style, the pedal will be firmer

281pony · Sep 2, 2010

i actually prefer a firm pedal feel. it's a mustang, if your scared to push a clutch/brake pedal you shouldnt be driving one imo.

gonna throw it on tonight and see how it feels.

Mustang5L5 · Sep 2, 2010

Let us know.

I actually like soft pedals. I'm swapping out my 93 cobra mc for a smaller bore 94/95 cobra mc just to get more of that "suck your eyeballs out with no pedal effort" feel. I even have an sn95 booster and just not soft enough

281pony · Sep 2, 2010

well i am not sure what to think here. the brakes just dont feel as strong as they should stopping power wise. the pedal is now FIRM, but it seems to engage pretty low. i'd bet it is rock solid just past/right at half travel.

with the car off, the pedal barely moves and its rock solid. it drops down another inch or so with it running before its solid.

the good; the pedal no longer pumps up. it is solid, car stops ok with no leaks on the new MC. i bench bled it, then went over each wheel twice. solid streams of fluid.

i am gonna play with my proportioning valve some. im wondering if i had too much rear bias and it wasn't stopping as well?

TenorPlayinGuy · Sep 2, 2010

I know you can adjust the where the brakes are by way of the rod that the brake pedal and MC connect to the booster (someone elaborate as I haven't done it in such a long time)

I will be doing this on sunday myself... wish me luck as well.

Mustang5L5 · Sep 3, 2010

I'd adjust the booster rod. Might be slightly on the loose side which is what is giving you that little bit of travel before they firm up. MM has a good write-up on how to do this.

As for the pedal firmness...that's the difference a 1/16 increase in bore size can make. It comes down to personal preference. I didn't like the feel at all when I ran a sn95 gt mc...and still not loving the cobra 1" MC. Gonna go to the 94/95 cobra mc soon

TenorPlayinGuy · Sep 3, 2010

I'm gonna go ahead and get the sn95 gt myself, gotta find one in stock nearby

Shaolin Crane · Sep 3, 2010

Mustang5L5 said:
I'd adjust the booster rod. Might be slightly on the loose side which is what is giving you that little bit of travel before they firm up. MM has a good write-up on how to do this.

As for the pedal firmness...that's the difference a 1/16 increase in bore size can make. It comes down to personal preference. I didn't like the feel at all when I ran a sn95 gt mc...and still not loving the cobra 1" MC. Gonna go to the 94/95 cobra mc soon

the pedal with my 94-95 cobra MC is PERFECT!

Shaolin Crane · Sep 3, 2010

TenorPlayinGuy said:
I'm gonna go ahead and get the sn95 gt myself, gotta find one in stock nearby

I got a brand new one, only bench bled. Needs a res. but i think the fox one will work. PM me an offer...

TenorPlayinGuy · Sep 3, 2010

If you can beat $34, and local deliver from your desert to mine, you've got a deal

haha.

Thanks but, I've gotta get this done in the next few hours.

Shaolin Crane · Sep 3, 2010

TenorPlayinGuy said:
If you can beat $34, and local deliver from your desert to mine, you've got a deal

haha.

Thanks but, I've gotta get this done in the next few hours.

Ah alrighty.

Mustang5L5 · Sep 3, 2010

I actually have one too.

I have all three MC's.... SN95 GT, SN95 Cobra and 93 Cobra. So far, don't like how two felt. Lets see if 3rd time is the charm.

281pony · Sep 3, 2010

it seems my car is doing the opposite of what your thinking.

going from the 1" bore to the v6 mc, which is a 1 1/16 IIRC, made the pedal SOFTER. it is soft for roughly 1/3 travel, then it has a slightly "thicker" feel for a little bit, then its solid and doesn't compress anymore.

it drives fine and stops fine, so i guess ill see how it goes from here. i wanted to bleed it completely once more, so ill adjust the rod at the same time.

Bad/failing MC, is this the symptoms?

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