clutch master cylinder failed?

[hound dog]

I didn't get any feedback on the club cobra forum so I'll try again here. I've read the thread about all the problems with clutch slave cylinders etc., but my clutch feels like it has air in the master cylinder. I've bled the slave cylinder on the bellhousing to no avail. I can pump the cluth pedal and get enough pedal to shift gears, but that's no fun! Another strange thing, when you mash the clutch pedal the level in the resevoir rises which makes me think theres air in the cylinder somewhere blocking the fluid from going where it's supposed to. Any opinions?
Thanks,
h dog:(

[Brent]

I am currently replacing my clutch master cylinder. I had a very similar situation you are having. I removed the master cylinder and took it apart. I found two flat o-rings and a very worn cup on the piston. They are only 45.00 so Wilwood no longer makes a rebuild kit for them you just replace them. If you want to take it apart just remove it from the car, pull the rubber boot forward, you will see the snap ring behind the boot. squeeze the snap ring and remove it. pull the entire piston assy. out.

Good luck
Brent

[gasman]

Brent, As I recall, your car has less than 500 miles on it. Correct?

Still no buyer?

Steve Foushee
Unique #4279389

[hound dog]

OK, what must be, must be. I've got a new cylinder coming from Summit. It just had to be the one over next to the fender didn't it? Hardest one to get to! I think I'll also take this opportunity to route the fluid line away from the header, that can't be doing things any good.
h dog

[Brent]

Steve, I think it was bad from the start.

H-Dog, It was easy to get to with the motor out of the car :D

Brent

[gasman]

Elvis, I'm liking that Avatar....:D

Steve Foushee
Unique #4279389

[spd4me]

hound dog
Elvis left the building in a Cobra! What ever you do, the best investment is to cover the lines with Thermo-shielding. You can get from Jegs or Summit.
Bob

[davids2toys]

I was doing some spirited driving/shifting, wound out third gear, letting it coast down, when I went to shift into second, my clutch pedal was on the floor, after about 5 minutes, it magically reappeared, what in the world does this mean? Worked fine, as if nothing happened...could this be my master cyl going?

[clayfoushee]

I was doing some spirited driving/shifting, wound out third gear, letting it coast down, when I went to shift into second, my clutch pedal was on the floor, after about 5 minutes, it magically reappeared, what in the world does this mean? Worked fine, as if nothing happened...could this be my master cyl going?

Could be, or more likely, your clutch lines are very close to the headers, which boils your fluid, especially after spirited driving. When that happens, you don't have much, if any, clutch pedal. I suspect it is boiled fluid from the scenario you described. If it's working fine cold, then that is your problem.

A lot of us have either relocated the lines, which is a bit of a pain on an already assembled car, or the easiest solution is to wrap the lines with that foil insulation. Mine is fine with the latter solution.

Routine fluid bleeds help too. Over time, the boiling point goes down with contamination and water absorption. Use a DOT 3 with the highest possible boiling point. Wilwood offers 570 degrees from Summit.

Some people, including me, used DOT 5 silcone, with an even higher boiling point, and that worked great for a couple of years. However, Wilwood says that is a "no-no" and will ultimately break down the seals. Even though I never had a problem, I replaced my clutch master and went back to Wilwood DOT 3.

[davids2toys]

Could be, or more likely, your clutch lines are very close to the headers, which boils your fluid, especially after spirited driving. When that happens, you don't have much, if any, clutch pedal. I suspect it is boiled fluid from the scenario you described. If it's working fine cold, then that is your problem.

A lot of us have either relocated the lines, which is a bit of a pain on an already assembled car, or the easiest solution is to wrap the lines with that foil insulation. Mine is fine with the latter solution.

Routine fluid bleeds help too. Over time, the boiling point goes down with contamination and water absorption. Use a DOT 3 with the highest possible boiling point. Wilwood offers 570 degrees from Summit.

Some people, including me, used DOT 5 silcone, with an even higher boiling point, and that worked great for a couple of years. However, Wilwood says that is a "no-no" and will ultimately break down the seals. Even though I never had a problem, I replaced my clutch master and went back to Wilwood DOT 3.

What you say makes perfect sense and was on my list of things to do.
I have girling MC's, brake and clutch...can I go with Dot 4 or that valvoline syntec, it is suppose to be compatible with dot4, or if i go with dot 3, why? I thought dot 3 and dot 4 were totally compatible, and dot 4 was much more heavy duty and higher temp!
While we are on the subject, all my MC caps have this crust like substance on the outside and some on the inside of the caps/rubbers.
What would you suggest my problem is here, do they sell replacement caps?
Thanks, Dave

[clayfoushee]

Girling, like Wilwood MCs, is old-school technology. The manufacturer's recommendation is to stick with DOT 3. The Wilwood 570 stuff is DOT 3. There are others with a similar higher boiling point now. Just make sure it says DOT 3 on the bottle.

I don't know what the "crusty stuff" might be........never seen that, unless the fluid is just ancient. I don't know where to get new caps either.

Wilwood MCs are cheap and available on-line from Summit. If I were you, I'd order a couple to keep on the shelf. That way, you'd also have some new caps for the time-being.

[rdorman]

3, 4 or 5.5. All should be fine. What you want to stay away from is synthetic fluids. The Syntec is a great value for the buck.... even though I use Wilwood 570. I run what ever has been sitting on my shelf the longest in the clutch. The lines go over the footbox and down the tunnel so I have never had and issue. The orange crust is from a badly neglected system. Water mixing with fluid. Make sure your caps have the rubbers on the bottoms. I would rebuild it all and flush out the lines.

[davids2toys]

3, 4 or 5.5. All should be fine. What you want to stay away from is synthetic fluids. The Syntec is a great value for the buck.... even though I use Wilwood 570. I run what ever has been sitting on my shelf the longest in the clutch. The lines go over the footbox and down the tunnel so I have never had and issue. The orange crust is from a badly neglected system. Water mixing with fluid. Make sure your caps have the rubbers on the bottoms. I would rebuild it all and flush out the lines.
Don't you mean stay away from the silicone? Synthetic is what we do want I believe.
Just getting to this job now!!! I put a new slave in last week and ordered a new Girling clutch MC tonight from pegusus racing. It is 3/4 bore.
My car has a 3/4 bore MC for the front brakes and a 5/8 bore MC for the rear, I think they are backwards, shouldn't the 5/8 bore go to the front to make more pressure???

[Naumoff]

Don't you mean stay away from the silicone? Synthetic is what we do want I believe.
Just getting to this job now!!! I put a new slave in last week and ordered a new Girling clutch MC tonight from pegusus racing. It is 3/4 bore.
My car has a 3/4 bore MC for the front brakes and a 5/8 bore MC for the rear, I think they are backwards, shouldn't the 5/8 bore go to the front to make more pressure???

No.
The pressure is not effected by bore size only the volume move by effort(pedal resistance) and stroke(pedal movement)

Does your pedal assemble have an adjustable brake bias bar? Maybe this was done to set the brake bias.
Smaller bore M/C for the rear means less volume to the rear brakes with the same amount of pedal movement.

[rdorman]

Don't you mean stay away from the silicone? Synthetic is what we do want I believe.
Just getting to this job now!!! I put a new slave in last week and ordered a new Girling clutch MC tonight from pegusus racing. It is 3/4 bore.
My car has a 3/4 bore MC for the front brakes and a 5/8 bore MC for the rear, I think they are backwards, shouldn't the 5/8 bore go to the front to make more pressure???

Glad some one actually gives some thought to what I write! Yes, silicone is to be avoided. Synthetic is fine. 3/4 front and 5/8 rear is what I have currently. And you are correct... ALL else being equal a smaller master will result in more pressure. As any good plumber should know ;)

[RJacobsen]

Don't you mean stay away from the silicone? Synthetic is what we do want I believe.
Just getting to this job now!!! I put a new slave in last week and ordered a new Girling clutch MC tonight from pegusus racing. It is 3/4 bore.
My car has a 3/4 bore MC for the front brakes and a 5/8 bore MC for the rear, I think they are backwards, shouldn't the 5/8 bore go to the front to make more pressure???

I second Tonys comment and add that front brakes usually have more and larger pistons than rear brakes, requiring them to need more fluid to move the same amount as the rear.

[JeepSnake]

System pressure is directly affected by bore size. This is the basic principle behind how every hydraulic system in the civilized (and a bunch in the uncivilized!) world works.

You have a force (F) coming from your leg.

You have the cross-sectional area of the master cylinder piston (A).

Pressure = F/A

So, if you vary the diameter (and thus cross sectional area) of the master cylinder, you will vary the pressure accordingly.

The tradeoff is in the volume moved. You'll need a longer stroke on the small master cylinder to move the volume before you generate the pressure. For a given braking force (B), the smaller master cylinder will require more stroke, but less leg effort to achieve. Holding (B) constant, if we go to a larger diameter master cylinder, less stroke will be required, but you'll need more leg effort. (This all assumes that the caliper piston sizes are held constant.)

Here's a basic diagram...
http://www.explainthatstuff.com/hydraulics.html

Basically, it's Pascal at work.

Theoretically, you could use a tiny master cylinder with big-pistoned calipers to have "power brakes." Realistically speaking, though, we just plain run out of room for the necessary master cylinder stroke to move the volume before pressure is generated. So, we trade more leg force in order move the volume required before we bottom the pedal.

Geez - this doesn't translate into print very well.

[JeepSnake]

Here's a pretty good page with diagrams and the math behind it.

http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/Pascals_principle.html

[Ed]

Typically the pistons in the calipers are smaller or fewer in the rear ;hence the need for more volume to the front.

[davids2toys]

As usual, I am absolutely impressed and thankful for all the knowledge and help available on the different forums.I was back on the phone with wilwood and the tech dept at Pegasus Racing. They both say and recomend the smaller master should go to the front:confused:.
after re-reading what you guiys had to say, I understood bits and pieces to be honest. I am going to copy what is on my car presently.
When I bought my Cobra, the rear brakes would lock up, so I just kept turning the BIAS BAR until it stopped locking up in the back end.
I had ordered a 3/4 clutch Master, and copied what I had for a slave, I measured the bore of the slave and it measured one inch...is this good for a cobra?
Thanks all!!!

[rdorman]

You say you adjusted the bias until the rear stopped locking up. Am I to assume that the fronts now lock first? If so, where is the balance bar set in relationship to the master cylinders and brake pedal? Is it roughly centered or....... measurements will be handy. Make sure that the bar is perpendicular to the pushrods when the pedal is fully depressed, that the master cylinders can fully return and that there is no binding throughout the travel.

[davids2toys]

No, the front end does not lock up, it just nosedives!
I threaded the rod in the bias bar towards the front MC, I would say there is about twice as much threads showing on that side. I presently have no fluid in the rear MC so I can't do as you requested

[pgermond]

I got tired of crawling into the foot box to adjust the brake bias, so I installed one of these - http://www.wilwood.com/Products/005-PedalAssemblies/004-RBBA/index.asp A Remote Brake Bias Adjuster. Kind of like a quick change rear-end - works like a charm :)

[tcolley]

Phil,

I am going to order one for my FIA Roadster as I too am tired of trying to fit my "large body" into that tiny foot well to make adjustments! I've always had a brake bias adjustment in the cockpit on my other Cobras and race cars over the years but they were the "in line" variety with a tandem master cylinder rather than a dual cylinder balance bar set up.

Regards,

[davids2toys]

Yeah, that is pretty neat...what was the cost?

[pgermond]

$60, although it's been 4-years so the price has probably changed. What ever increase has occurred - it is worth it.

[davids2toys]

Thanks a lot

[RJacobsen]

I've always had a brake bias adjustment in the cockpit on my other Cobras and race cars over the years but they were the "in line" variety with a tandem master cylinder rather than a dual cylinder balance bar set up.


my car came with an "in line" type adjuster. I plan to use it again, any Pros or Cons out there?
http://www.wilwood.com/Products/006-MasterCylinders/001-PV/levervalve-LRG.jpg

[weaver]

I think all you can do with that type adjuster is change the fluid pressure to either the front or rear brakes, which ever line you install it on, it is not a bias adjuster.

Alan

[RJacobsen]

I think all you can do with that type adjuster is change the fluid pressure to either the front or rear brakes, which ever line you install it on, it is not a bias adjuster.

Alan

Wouldn't the end result be the same?

[JeepSnake]

Wouldn't the end result be the same?

Yes - result is the same. Lower pressure on the caliper pistons generates less force on the pads. Adjustable proportioning valves (like this) are used a lot on cars with "regular" tandem master cylinders - i.e. where you don't have a balance bar.

[Slither]

Geez - this doesn't translate into print very well.

I disagree... great job[thumb]!