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Sherlock Ohms

Balancing Efficiency and Comfort in a Ford

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tekochip
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What about manual?
tekochip   12/10/2014 1:29:47 PM
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Does a manual transmission slip during cruise?

Critic
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Re: What about manual?
Critic   12/10/2014 2:15:27 PM
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Good point, Tekochip.  Although I am not one of the authors, I have enough experience with Fords to safely answer your question:  no, a manual transmission does not utilize a torque converter or lock-up torque converter, so no, the transmission and its associated clutch do not slip unless the clutch is worn out.  The cars that are equipped with manual transmissions are generally not the top-of-the-line cars, in which NVH would be more important.  Interestingly, you can't get a manual transmission in an F-150 anymore.   

Critic
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Re: What about manual?
Critic   12/10/2014 2:22:56 PM
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I should add that in the case of a manual transmission, the driver has control of the clutch slippage, so if he/she wants to accelerate, he/she could slip the clutch and downshift to prevent lugging.

tekochip
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Re: What about manual?
tekochip   12/10/2014 2:58:25 PM
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I've never owned an automatic, so I was a little uncertain, and even with 250K miles on some cars, I've never worn out a clutch, so I was a little confused.

Yes, I push in the clutch (all the way) to prevent lugging and will also push in the clutch sometimes when going over bumps.  Here in the USA manual transmissions aren't that popular, but even the ultra high-end cars use them in Europe.

I had some German clients visiting once and they had never driven an automatic.  These guys were engineers, but simply backing out of a parking place was nearly impossible.  Speaking only a little English, they had no idea what PRNDL stood for or what the normal placement of the different gear positions would be.

 

wbswenberg
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Re: What about manual?
wbswenberg   12/16/2014 7:22:05 PM
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Yes, a manual transmission can slip.  I have a 1995 K2500 4X4 with about a ton of camper in the bed.  It has a 350 cid and manual 5 speed.  If I push it too hard the clutch heats up and vaper forms (i believe) in the hydraulic clutch.  Can't take it out of gear.  Hopefully I can pull over and kill the engine.  After it cools off a few minutes I get the clutch back.  I've had to start it in 1st grear and it will walk away.  With a fully syncronized transmission I do not have to push the clutch in every time just back off the throttle and I can shift it.  Needless to say I try to stay away from this condition.

OLD_CURMUDGEON
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Re: What about manual?
OLD_CURMUDGEON   12/17/2014 10:43:34 AM
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I wouldn't recommend the frequent use of relaxing the accelerator & shifting up with a synchro-meshed manual tranny.  The synchro gears were (are) made of hard brass, which wears significantly quicker than the steel gears in the transmission.  Continued use of this "trick" will only shorten the life of those synchros.

I've owned many vehicles with standard shift transmissions in my long driving career.  And, I've had clutches slip, especially when extremely hot either due to ambient weather conditions or load.  IF the flywheel face OR the clutch disc gets "polished", they are more likely to slip, even under moderate loading, and gone a re the days when the clutch disc was an asbestos plate, which could take the elevated temperatures from the high frictional component of the drivetrain.

RFI-EMI-GUY
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Re: What about manual?
RFI-EMI-GUY   12/20/2014 10:58:42 PM
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tekochip;

I had a 1967 MG 1100 sports sedan (manual 4 speed) that I drove from Maryland to Chicago one year. Things running really well until halfway through Ohio I heard an "airplane buzzing me" louder than the radio. Checking again I found the revs were way up on the engine and the car was slowing down. I pulled over and found engine oil (interstingly the gearbox shares same oil/sump on this model) pouring out of the clutch housing and some awful smoke.

That ended my trip at that portion requiring Greyhound the rest of the way.

So yes a "manual transmission can slip during cruise" but is never a good thing to happen.

I learned from owning a British car that failure occurred always without prior notice.

tekochip
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Re: What about manual?
tekochip   12/21/2014 8:24:50 AM
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I knew slipping was a failure mode, I was just curious if it was considered normal to slip a little during cruise.  Sliding friction is always much less than static friction, so I thought it would be a bad idea to design in some intentional slipping.

I had a motorcycle that would slip from time to time.  It was a really old two-stroke, I think an F7, anyway I'd be driving along and there would be a sudden surge when the clutch slipped, "eeeeee WEEEE eeeeee".  The bike had a loose chain too, and one day the chain slipped off and wrapped around the axle, locking up the rear tire.  That's another story, though.

RFI-EMI-GUY
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Re: What about manual?
RFI-EMI-GUY   12/21/2014 3:23:45 PM
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Some motorcycle clutches are wet clutches. They are designed to be exposed to engine oil and should not slip unless there is excessive wear, weak springs or an adjustment problem. Two stroke engines can have very peaky torque curves, so most likely you were running under a condition where the throttle was at peak power and the load was increasing.

tekochip
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Re: What about manual?
tekochip   12/21/2014 4:29:45 PM
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The little bike had about 70K on it at the time, the clutch was badly worn and I kept snapping off clutch cables from the excessive pull.  The clutch only slipped during cruise, in 5th gear, on level terrain, between 30-50MPH, so the sudden surge was quite noticeable.  The brave little 125 could hit 70MPH, though, and got about 90MPG.

It was a `72, orange, F6 that made its rounds through the neighborhood.  I swear everybody in town owned that bike at some point in time.  I had it about two years and after I sold it the original owner came around to buy it back.  I gave him the number of the new owner and he did get his bike back.

Critic
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Sales Pitch
Critic   12/10/2014 2:27:53 PM
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I was wondering how this qualified as a "Sherlock Ohms" article at first, but later realized that it is the software that helped solve a problem, and this amounts to a software sales pitch.

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