critter

Hi all,
I apologize for creating a new thread but none existing really seemed along exactly the same topic and I searched but didn't find the answers I needed.
I have an '07 GT with a 5-speed and 4.11 rear gear changed from the original 3.73. AFAIK, it has the OEM clutch.
The car is simply not as much fun to drive as it should be, one thing is that there seems like there is a long way from the floorboard to the clutch friction point. I start letting out on the clutch slowly while adding a little gas and the motor races because what has been done to it increases throttle response a lot. So at that point I ease out on the clutch a little more quickly and the clutch seems to then lock up very quickly. The clutch seems to not be linear at all. Not that I care about profiling, but it makes it look like I've never driven a straight drive at all. I'm 51 years old and have driven straight drives since tractors and 2 ton trucks on my uncle's farm WAY before I was old enough for a license. It's embarrassing as hell.
Something that is confusing to me reading posts is that my Hayne's manual says the clutch is hydraulic and some of the posts here indicate that too, but I also see a lot of references to cables. Huh? Please help me out. Which is it?
Is the clutch in any way adjustable to make it more linear?
I would really appreciate your patience with me and letting me tap into your knowledge base. My wife and I love this car and the previous owner did some really good stuff to it, it runs like a bat out of hades. But like I say, it's only so much fun like it is. Thanks.
Respectfully yours, Lee

cliffyk

I assume you are referring to the 2007 GT listed in your profile (if so this is the wrong section).

However from 2005 up the GTs use a hydraulic clutch control mechanism, this means anything that interferes with the flow of the hydraulic fluid would cause the problems you describe. This could be that:

• There is air in the system that needs to be bled;
  
  
• The fluid is contaminated (at 5 years old it should be flushed and changed);
  
  
• That "crud" has built up in the master cylinder or slave cylinder pistons/valving causing them to react slowly;
  
  
• That the slave cylinder's external mechanism is sticking;

The slave cylinder looks like this (under its boot):


The first thing I would do would be to check the fluid level in the brake/clutch master cylinder reservoir--it will probably be OK but check it anyway.

The next thing to do would be to flush the brake/clutch fluid and systems.

Worst case would be that the slave cylinder needs to be cleaned or replaced--that means pulling the transmission.

How many miles on the car? In researching the above I found some references to others experiencing similar problems around 80k-90k miles...

critter

Sorry the wrong section.
It has 66k on it if I remember right. As far as I know the brake/clutch hydraulic system hasn't been flushed. That is probably a good idea anyway. Thanks for the suggestion.
My subject line may be misleading, I don't know if the clutch is actually "inconsistent" or it's the way it is by design. If it's that way by design then it kind of bites. So there actually is no cable in the system?
BTW, what is the proper section and how do I move it?
Thank you!

cliffyk

The form moderators will move it as they see fit.

I have driven a couple of 2005+ GTs and never found the clutch actuation or release to be in any way non-linear or inconsistent, or dramatically different from the cable operated clutch in the earlier models--not that I would expect it to be. It takes "x" amount of work to throw out the clutch and it does not matter one bit how you move that work from the pedal to the throwout bearing--more about that here.

There is no cable, when pressed the pedal acts upon the clutch master cylinder to displace fluid and that displaced fluid causes the slave cylinder to expand and push against the throwout bearing so as to disengage the clutch. On release the opposite happens, the clutch spring pushes on the TOB, which pushes on the slave cylinder returning the displaced fluid to the master cylinder.

What can happen however is related to that the amount of force applied to the pedal to disengage the clutch is variable--the driver can press harder or softer as needed to displace the fluid at whatever velocity seems right. This tends to mask any inconsistencies in the force needed to displace the fluid throughout the pedal's, and master/slave cylinder's, range of motion.

On release however it is the clutch spring, a fixed force, doing the "pushing". This means that any inconsistencies in the force needed during the pedal's or master/slave cylinder's motion will slow the flow of fluid--dynamically non-linearly and inconsistently.

[soapbox]
Over the years I have had a number of vehicles with both hydraulic and cable operated clutches and can honestly say "They are six of one and one-half dozen of the other." Cable operation is complete elegance in its simplicity, requires almost no maintenance with modern cables, but can leave you stranded someplace; hydraulic operation is more complex, requires periodic maintenance, however they generally provide plenty of negative feedback prior to complete failure.

Manufacturers and engineers like hydraulic operation because despite costing more the hydraulic line is much easier to route, with no need to design anything else "around" its route as is needed with a cable.
[/soapbox]

Diabolical!

Cliff has offered some excellent information. I'm gonna chime in as well as someone who has owned two clutch cable mustangs and spent 5 years with my current hydraulic operated clutch. I can honestly say that I much prefer the cable for maintenance, but the hydraulic is a better purpose built unit in my opinion. I've changed the clutch and slave cylinder/throwout twice on my car since I've owned it. It is quite a difficult job on the S197, mainly because of the difficulty in getting the transmission and input shaft to clear the transmission tunnel and pressure plate fingers during removal and installation. When I had the stock clutch, which is a single disk, and my first aftermarket clutch, which was also a single disk, I always found that the clutch engaged too high in regard to pedal travel. After switching to a twin disk, the clutch engages at a much lower, more natural level. However, all three clutches felt linear in their performance. For what it's worth, I would change your fluid first, and if that doesn't fix your problem, I'd recommend a good twin disk clutch and new slave cylinder. The twin disk clutches don't tax the slave cylinder nearly as much as the single disks and apply force more evenly.

cliffyk

^ I am curious as to over how many miles you have changed the clutch/slave cylinder on your car--was it a needed repair or something you elected to do.

I drove early Miata's ('90 to '93) for 10 years and found the slave cylinders lasted about 65k to 70k miles before leaking, but they were an externally mounted rubber cup sealed piston design. I always had a one or more rebuilt slaves sitting on the shelf, and got to where it took longer to get the car up on jack stands than to swap out the slave cylinder...

moosestang

Hey! You stole my picture.

critter

Thanks all, for your help!

Diabolical!

The first time I changed the clutch it was elective and the odometer was at 6,xxx miles. I was doing supporting mods before installing the supercharger so I put in a SPEC 2 and I make it a habit of always changing the pilot bearing and throw out bearing when swapping a clutch (cheap preventative maintenance), so the slave was replaced.

The second time I changed the clutch was out of necessity. The SPEC 2, after about 100 or so launches at the drag strip, finally gave up. I barely got the car back on the trailer that night. I replaced it with a McLeod RXT (quite honestly the best clutch I've ever driven on). That was with 11,xxx miles on the odometer. Again, I elected to change the slave while I was in there.

Once the transmission is out, changing the slave is a cakewalk. I do advise that anyone attempting this at home ALWAYS, ALWAYS, ALWAYS bench-bleed the new slave before installing. Our cars do not have bleeder valves for the clutch, so bench bleeding the slave ahead of time makes life a LOT easier when it comes time to do the final bleeding after everything is back together.

critter

Thanks!