First post. clutch question.

[Jim Kramer]

This is my first post on this forum, although I have watched it since it was new. I was also on the old 332-428 fe forum since it was new, but it has lately gotten so bad that apparently my computer and internet service can't handle it anymore making it almost impossible to read let alone post.

Anyway, my question..I bought a Ram "powermaster" , diaphragm style PP and disk for my 390 Mustang. The engagement and disengagement all takes place within about one to two inches of peddle travel. I have a friend with a similar set up and it acts the same way. Is this typical for a diaphragm type clutch. When I push the clutch down it seems to "overcenter" at the point of disengagement, making control of the process difficult. I'm afraid this will make movement in tight quarter touchy. I'm thinking the only way to improve the operation would be to lengthen the lower arm of the "Z" bar, thus improving the effective ratio. Has anyone encountered this and come up with a solution , or do I simply need to learn to live with it..... thanks....Jim Kramer

[wayne]

Welcome i can not help with your pressure plate i always run the long style 3 finger some one here will help you.I was on the old forum for years but never go there any more cant even log in now.

[My427stang]

Jim, I have run a diaphragm in my Mustang for years.  It acts very normal, no different than a Long except easy on my leg.

Did you remove the clutch assist spring under the dash?  You likely don't need or want it any more.  Also, in some cases, you may have to modify the clutch linkage to have less throw (shorten the Z bar on the bottom usually) However, I have not had to do that on a Ford

[machoneman]

Or, do the racer trick and secure a sized block of wood to the floor or pedal to limit down travel. 

Made up an adjustable metal brace for our old SS/B Camaro (oophs!) long ago after figuring out the correct distances. Bolted same to the clutch pedal and it worked fine with a diaphragm clutch. 

[Jim Kramer]

Yeah, I thought about lengthening that arm after I posted, and I think shortening it would be the answer, and I may try that but it will put the pushrod somewhat out of line. The car since I have had it always had a C4 in it, (raced as  a D/SA car), and I got it as a pile of parts 30 years ago, however it is actually a 390 4spd. car. I never did put the assist spring in and peddle pressure really isn't my problem and I can adjust the point of engagement OK too, Its just that when it does engage it seems like "all of nothing". Its hard to let it out smoothly, It "pops out", or engages very quickly ( with authority ) over the course of maybe one inch of peddle travel..........Jim Kramer 
 

[jayb]

I have a diaphragm clutch that does exactly the same thing.  It is very aggravating.  It has improved over the 6000 miles or so since I've had it in the car, but still tends to pop out and engage suddenly.  Feels like it sticks as you are slowly releasing the pedal,  and then BAM, becomes fully engaged all at once.  Also tends to feel as if it is overcentered when you push the pedal in all the way, but you need to do that to get full release.  It is a diaphragm clutch, brand is Atomic, got it from American Powertrain when I bought the transmission package from them. 

Unfortunately I don't have a solution to the problem, so I can't help you with it, but you are not the only one dealing with this issue.  Because others use diaphragm clutches with no problems, I assume it is the clutch design or a defect of some sort.

[Jim Kramer]

Yes Jay that describes what mine does pretty much exactly. What sucks is that I was deliberating between the diaphragm and the long style clutches, and remembering what a bear trap clutch my 427 Fairlane  had I decided to try to save my knees and go with the diaphragm type. Maybe a poor choice.  Thanks.....Jim Kramer

[My427stang]

Jim/Jay, do you think that you could have overcentered it immediately and bent the diaphragm (Belleville) spring (?

The clutch design works, heck almost every single car and truck after about 1985 uses a diaphragm.  The only other option I would think would be an aggressive disk material, but that doesn't sound like what you are experiencing.

I have a good buddy that also had a bad experience with a diaphragm, I will have to ask why he didn't like it, in his case, I think he just didn't like the soft pedal, but I will check.

[jayb]

Ross, anything is possible I suppose, but I was pretty careful when I set mine up.  The only real adjustment on mine was the position of the hydraulic throwout bearing on the transmission shaft (T56 Magnum).  It had to be shimmed to a certain dimension to get the right freeplay.  The whole setup came as a complete package from American Powertrain, so I assume it was matched to work together.  At some point I'll pull it out and try to figure out what the issue is, but for now the problem has diminished as the miles have gone by, and at this point it's only really an issue when the clutch is cold, and the car is stopped.  After it warms up, or when rolling, it seems to be fine.  I'm kind of leaning towards the clutch material itself as the issue in mine, but not really sure about it...

[Jim Kramer]

It is a little encouraging to think it my improve with use. Right now I have zero miles on it. I too checked freeplay before I ever even started the car, ( mechanical linkage ) and mine was this way from the first push of the peddle. Thanks to all that offered help. If I can somehow figure a solution I'll post it.........Jim Kramer

[cjshaker]

Just my opinion, but that's kind of the nature of diaphragm pressure plates. Unlike regular pressure plates, which have a linear slope of pressure, the belleville springs go through varying pressures as they travel through their arc, which is normal (I know I'm stating the obvious here). The problem with that is when aggressive materials don't jive well when the belleville spring hits the point of 'popping' past its high resistance point. When an aggressive material starts to contact at just that point, it makes for an aggressive engagement/disengagement. You can try and manipulate the point where the spring 'overcenter' and clutch plate interact, but you don't have much area to play with, and it's often just a waste of time. The easing over time is just the belleville spring losing some of its 'spring', which makes for a bit of a smoother feel. Personally, I don't want to wait years for that to happen.

I know all modern cars use diaphragm pressure plates now, but a factory system is not the same as an aftermarket that has to deal with tons of variables. Stock systems are designed with ALL parameters taken into account, and auto makers have a fair amount of money to invest in testing...to say the least.

I never liked the feel of diaphragm clutches. The sudden easing of pedal pressure as it travels over-center on the spring just makes for a weird feel on the pedal. You get used to it after a while, but I see that as a compromise, not something desired. I've used them with good success on a couple occasions, but never liked the feel. I've also destroyed a couple of them on performance situations, and will never go back to them for anything performance oriented.