How many engineers do we have here?

[Nick's Comics]

Mechanical Design

[oakman29]

I'm an engineer of death,and am truly happy to Kill for profit.

[mrc]

 

Mechanical Engineer, working with ultra high vacuum, plasma assisted chemical vapour deposition carbon coating.

[jimbo_707]

I earned a B.S. in Mechanical Engineering from Kettering University (a small school in Flint, MI) in December of '99 and worked in the field from 2000—2008.

 

I've been working in education since then, but I may return to engineering because it's been tough to make ends meet in my new field. (The kicker is that if I want to renew my teaching certificate, I'll have to spend $4K this year on tuition.)

[alexmtl]

Software engineer - and work from home too.

[delorean1981]

Mechanical/ Communications Engineer

 

Texas Tech '08 - Wreck 'em!

[marvelmaniac]

I hope that by posting this I am being out of line, If I may, I have a question for an engineer.

If possible Please try to answer in "layman's" terms without getting too complicated.

 

Here is the scenario...

Ever since the car was new (1990 Dodge Daytona Shelby) the clutch cables have broken every 4-5 years and they break in the same spot every time.

Was never an issue before because they were fairly inexpensive and I just replaced it every 4 years before it broke but now the Mopar cable is discontinued and no longer available and the aftermarket cables are "JUNK" and use a "crimped" cable end that does not look like it will last long at all rather than a "molded" cable end that is used on the Mopar cable.

 

The question...

I only drive 4 miles to work but there is a lot of traffic so I am constantly on and off of the clutch.

What produces more stress on the cable end while sitting in traffic?

1)Holding the clutch pedal down

2)Constantly depressing and releasing the clutch pedal

 

The pics below show the factory cable and aftermarket cable side by side.

The arrow is pointing to the spot on the factory cable where they break.

This is the end that goes through the clutch fork.

 

 

 

CLUTCH CABLE ROUTING

 

 

[Vorpal]

Pressing/releasing the clutch will cause more fatigue, leading to eventual breakage, than press-and-hold. But this should not be happening so regularly. Have you tried talking to a shop that builds race cars about getting some custom cables fabricated? Also, is the retainer/"pivot ball" staying greased? If not, then the cable will fatigue exactly where your arrow points.

 

Cool car BTW!

[marvelmaniac]

Thanks for the quick reply.

 

So making my foot tired and holding the clutch pedal in will be less stressful, that is the info I was looking for.

 

It is not just my car but seems to be a problem with all 80's, early 90's FWD Mopars,(that is what I am extremely familiar with) the cable always seems to break in the same place.

The after market cable I am afraid to try, looks as though the crimped end will come off in no time, wish I had a way to bench test it.

 

I was also thinking that Galvanic corrosion may be a contributing factor and have been using a product called ECK since the last cable replacement on 9/15/14.

I contacted the manufacturer and explained the situation and they sent me a tube of their product for free to try, unfortunately I will not know if that was the issue or not until the cable breaks again.

 

Every 6 months I clean the cable with a battery cleaner to neutralize any acids and re-apply the product.

 

http://www.vannay.com/index.php?m=3

 

 

[mrc]

 

Sorry, but holding the clutch pedal down other than to change gear is an absolute no-no. This will cause premature wear of the clutch release bearing and is a bad driving habit. If the clutch cable is breaking there may be various reasons.

The pressure plate stiffness can vary between makes.

There may be wear or flex in the bulkhead where the cable is anchored.

The clutch may be worn out and/or the cable has run out of adjustment.

 

Sometimes it's best just to bite the bullet and buy a new (quality clutch assy.). When I lived in London I went through 3 times as many clutches compared with living in the countryside.

 

However any decent clutch centre should be able to diagnose the fault for you. Good luck.

 

 

[Vorpal]

Sorry, but holding the clutch pedal down other than to change gear is an absolute no-no. This will cause premature wear of the clutch release bearing and is a bad driving habit. If the clutch cable is breaking there may be various reasons.

 

That's a good point. The long-term solution is to address the reason that the clutch cable is failing. You say that you're treating the cable to prevent corrosion, but are you greasing the retainer/cast "ball" on the end of the clutch cable (basically that spot where it attaches to the clutch fork)? If that begins binding, then it will cause bending loads on the cable in the spot where you described the breakage occurring.

[bleh]

electrical engineer, CSUN, 2012

[marvelmaniac]

Sorry, but holding the clutch pedal down other than to change gear is an absolute no-no. This will cause premature wear of the clutch release bearing and is a bad driving habit. If the clutch cable is breaking there may be various reasons.

 

That's a good point. The long-term solution is to address the reason that the clutch cable is failing. You say that you're treating the cable to prevent corrosion, but are you greasing the retainer/cast "ball" on the end of the clutch cable (basically that spot where it attaches to the clutch fork)? If that begins binding, then it will cause bending loads on the cable in the spot where you described the breakage occurring.

 

Thanks for all of the replies, I appreciate it, however...

 

Just started treating for possible corrosion so the results are an unknown at this point.

The issue with the cables breaking at the same place each time is common among ALL Chrysler FWD vehicles from 83 - 94 so it is/was an Engineering issue with Chrysler, not the fault of the driver or environment since it happens all across the country.

 

Also the "ball" on the end of the cable never moves, it is always tight against the fork in all clutch pedal positions.

The cable is always taunt.

 

I am not an engineer but was an Automotive Service Tech for 33 years and have been ASE Certified for 37 years, the last 15 years wrenching were at a Chrysler Dealership.

I am also an Admin on a FWD Mopar site so I am extremely familiar with these vehicles.

This is not the only time a manufacturer has engineered something on an automobile that did not function properly or was able to last for any length of time and it will not be the last.

Fortunately nowadays big brother is watching and calls them out on their blunders.

 

Numerous times working on a vehicle I had to scratch my head and ask myself "what the heck were they thinking?".

IMO from 33 years in the auto industry, all automotive engineers need to spend 2 years in the field to see how difficult it is to work on these cars they have designed or some of the "stupid" things they have designed and what we have to do to correct the goof.

 

As I stated, it was never an issue until the cable became NS1 (no longer serviced) so I need to find/try ways to make them last longer.

None of the remedies (anti-corrosion, lubrication, holding/not holding the clutch pedal) will be known to work until the cable actually breaks again or not, until that happens it is all theory.

 

[Vorpal]

Sorry, but holding the clutch pedal down other than to change gear is an absolute no-no. This will cause premature wear of the clutch release bearing and is a bad driving habit. If the clutch cable is breaking there may be various reasons.

 

That's a good point. The long-term solution is to address the reason that the clutch cable is failing. You say that you're treating the cable to prevent corrosion, but are you greasing the retainer/cast "ball" on the end of the clutch cable (basically that spot where it attaches to the clutch fork)? If that begins binding, then it will cause bending loads on the cable in the spot where you described the breakage occurring.

 

Thanks for all of the replies, I appreciate it, however...

 

Just started treating for possible corrosion so the results are an unknown at this point.

The issue with the cables breaking at the same place each time is common among ALL Chrysler FWD vehicles from 83 - 94 so it is/was an Engineering issue with Chrysler, not the fault of the driver or environment since it happens all across the country.

 

Also the "ball" on the end of the cable never moves, it is always tight against the fork in all clutch pedal positions.

The cable is always taunt.

 

I am not an engineer but was an Automotive Service Tech for 33 years and have been ASE Certified for 37 years, the last 15 years wrenching were at a Chrysler Dealership.

I am also an Admin on a FWD Mopar site so I am extremely familiar with these vehicles.

This is not the only time a manufacturer has engineered something on an automobile that did not function properly or was able to last for any length of time and it will not be the last.

Fortunately nowadays big brother is watching and calls them out on their blunders.

 

Numerous times working on a vehicle I had to scratch my head and ask myself "what the heck were they thinking?".

IMO from 33 years in the auto industry, all automotive engineers need to spend 2 years in the field to see how difficult it is to work on these cars they have designed or some of the "stupid" things they have designed and what we have to do to correct the goof.

 

As I stated, it was never an issue until the cable became NS1 (no longer serviced) so I need to find/try ways to make them last longer.

None of the remedies (anti-corrosion, lubrication, holding/not holding the clutch pedal) will be known to work until the cable actually breaks again or not, until that happens it is all theory.

 

You were really holding out on us! Sounds like you have plenty of expertise. I would have taken a different approach had I not thought you were just a shadetree mechanic with a cool car! Since you describe this as a cross-platform design issue, I think that the problem probably comes from the process of casting the fitting on the end of the cable. It likely introduces brittleness in the strands of the cable (heat hardening). Maybe the aftermarket crimped versions are actually a design improvement? I know that similar things can happen with soldering copper wire. If there's movement, a crimp is better because otherwise the wire tends to break just past the soldered connection.

[marvelmaniac]

Basically my initial question was which scenario creates more stress on the cable end, holding or depressing and releasing?

 

I am very leary of the aftermarket cables...

1)The crimped end reminds me of the kits they used to sell back in the day to repair speedo cables when the end would break and that kit consisted of a universal cable and an end that you had to crimp on with a little tool they supplied in the kit.

The crimped end never held, if it lasted a week you were lucky.

2)The casings on the aftermarket cables are cheap/thin plastic and they break easily under constant use.

 

I did contact the manufacturer of the aftermarket cable and asked them what amount of stress/pressure the cable is capable of withstanding and sent them pics of their crimped cable and the Mopar molded cable.

 

The answer I received from the companies rep was...

"I see and understand your concern by looking at the pics but unfortunately I do not have those type of specs available."

 

I also contacted LUK Clutch's who made the TBI N/A car clutches for Mopar (Sach's made the clutches for the turbo cars like mine but they cannot be contacted) and asked how much force was required to completely depress the fingers on the pressure plate that fits my car.

(I gave them the part # for their part)

Their response was 400 PSI.

Sounds high to me but I do not know about the technical aspects of leverage.

If there was an inexpensive way to actually test the aftermarket cables strength on the bench that would answer all questions.

 

I have secured two more Mopar cables but soon their will not be any left in the country so I may be forced to use the aftermarket cable someday and find out for myself if it withstands everyday use.

[LazoFoundation]

Cool thread on clutches.

Thanks.

Software Engineer (Former) and studied at the University of Cal Poly Pomona, BS and MSBA.

Also, son of Aerospace Engineer if that counts. Great conversation topic.