Worn Out Clutch Pressue

I like to drive cars with a standard (manual) transmission. It's fun to rev the engine up and make noise and squeal the tires. Maybe I'm still a teenager at heart - so be it. Over the past few years, my 2007 Mustang has gotten harder and harder to shift. Generally the clutch disengages but sometimes the gears stick. This sounds like something is fishy with the clutch. Also, the clutch pedal is getting harder and harder to press and is causing pain in my knee. This puts a damper on my running hobby (addiction?).

So I decided to visit the dealer. My question was simple - "can you make the clutch pedal easier to press". It seemed like an easy fix. They might open the hood, look for the knob that says "adjust clutch pressure" and turn it 8 degrees clockwise. Imagine my surprise when they said "yes, we can improve the clutch press - give us a small pile of cash and we will replace your clutch". Hmmm.

Now I consider myself engineering savvy and a bit of a mechanic - why it was only 30 years ago that I rebuilt a 1967 Mustang from scratch. The suggestion that "replacing your clutch" would be a viable countermeasure to excess clutch pressure sounds all wrong to me.

Trusting the dealer, and verifying by testing the clutch pressure in a new Mustang, I asked them to make the change. It should be finished in a few days so I will report back then.

Not wanting to be in-the-dark on why a new clutch would help, I turned to the web. A few keyword searches including "clutch clamping pressure" and "belleville spring" turned up what I think is a reasonable answer.

As many people know, the job of the clutch is to apply or remove pressure from the pressure plate which connects rotational force from the engine flywheel to the transmission. What I didn't know is how the spring that applies that pressure works. This article describes a diaphragm clutch as a Belleville spring. This article describes Belleville spring characteristics (look at Force Adjusting Bellevilles).  This article describes what I'm sharing below. Dig in if you want more.

The 2007 Mustang uses a diaphragm clutch.  Given the discoveries mentioned above, it appears that as the pressure plate gets thinner, the force required to disengage the clutch goes up before it goes down. Once the pressure plate is too thin, the clutch will start to slip and it's game over.

This graph tells a good story but it needs some explanation.

When the pressure plate is "normal" thickness (e.g. brand new) the "pressure plate travel" in the above graph is zero. Reading from the above graph, 4,500 Newtons of pressure are required to release the clutch. As the pressure plate ages and wears thinner, the spring expands and the clamp load goes up. Spring expansion is shown in the above graph as a negative number for "pressure plate travel". The increased clamp load (i.e. pressure) is good because it delays the clutch slippage. Unfortunately, this also translates to a significant increase in force required on the clutch pedal. That's why my knee hurts. 

So, given the above findings, it seems reasonable that a new clutch with a thicker pressure plate will improve my driving fun and reduce knee pain. Stay tuned for actual results. May the running continue!

Running For Yourself

I've been running for myself for years. Friends run with me and sometimes ask for tips on how to run faster or farther. Here are a few of my favorites.

1. Be consistent. I've gotten better results through consistency. Typically I run 5 or 7 days per week - sometimes twice per day. Keeping a log helps with consistency. Setting a target pace and using a watch also helps.
2. Be realistic. In my mid 40's I have come to expect a long recovery time from injuries. This has taught me to be humble. If I can't run a super-fast mile today, maybe I can work up to it in 3 or 6 weeks. If I push too hard now, I'll pay for a very long time.
3. Short stride. A long stride will burn out your knees. Keep your strides short and your footfalls quiet.
4. Be forgiving. Poor sleep, high pollen count, sudden weather changes, and time away from running all have significant impact on results. Training takes time - avoid harsh self-criticism when you are having an off day. A poor start followed by a strong finish is better than a poor start followed by an early quit.
5. Get strong. The single most helpful non-running activity I do is core work. This includes push-ups, sit-ups, and pull-ups. There are many core exercises to help running - find the ones that work for you and start a regiment. 3-5 minutes of core work every day before you shower is a great way to improve your running game.
6. Finish negative. Finish your training and your races at a pace 10% faster than your starting pace. Starting out too fast will ruin a race. This is known as a negative-split.
7. Go easy. You'll have bad days. You'll have good days too. Don't push so hard on the bad days that your next good days gets delayed. If the day is bad, throttle back and save your strength for the next day.
8. Run walk. Mix running and walking to increase your speed or your distance. I've done very long runs with 1/4 mile of walking for every mile of running.
9. Be bold. When you are feeling strong - push it. The last 100 meters of a 1/2 mile run is a great time to speed up. Even if I only pick up the pace by a little, I always feel good finishing with a kick.
10. Run for you. Yours is the pace that matters. Run your race at your pace and focus on your own goal.

There are lots of other tips that have helped me. These are just a starter.

Run well. 

Run often.