Rotational Torque And Weight Transfer = Manual Transmission Shift Issues

Five.0GT

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Mar 24, 2016
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This may be a bit long, so bear with me. I have a 2016 Ford Mustang GT with 6-speed manual, non-PP.


I have noticed on several other forums and even Edmonds.com and Road and Track (I believe) had articles dealing with complaints of Manual Transmission on the S550 ('15+) and even the prior generation for that fact were experiencing 1-2 and 2-3 "clunkiness" or shift issues. I have noticed this in mine as well. But I have found the root cause (I believe) and a solution, which I wish to share with the community. It can most often happen when in Normal or Sport mode, and shifting anywhere over 2800 RPM's.


During acceleration shifting from 1-2 or 2-3, there is a higher strain (drag + friction + gravitational effects on an object moving from a standstill) on the engine, transmission, driveshaft, rear-end, etc. It takes more effort, in other words to get a mass that is stationary to move than it does to move an object that is already in motion.


There are also rotational forces working with the torque and rotation of the engine crank & cams, as well as the drive shaft. These forces tend to upset the frame and suspension components (ie wheel hop & front end sway). These forces also act upon the manual transmission when shifting, in a negative way. Some folks say that a more rigid mount can be used, but I'm not into that. I only have 4,000 miles on my S550 and don't want that expense.


I did fix some of the front in sway and shifting by install the 2-piece Ford Racing Strut Tower Brace (mine is non-PP). This helped a lot at first. But then I noticed the "clunkiness" or mechanic "thud" still occurring from 1-2 and 2-3 shifts. Then I finally had it !! The other day, I took my 10 year old to the store. She weighs around 85 pounds, soaking wet. The Mustang, just smoothly accelerated and shifted each and every time !!. Then the thought occurred to me (as I had been trying to trouble-shoot and diagnose the "cluncky" shifting issue for the last 5 months) - The suspension components are the same in the Manual as they are in the Automatic. I just so happened to read an article dealing with the Porsche Cayman GT4 and the new 2017 911, which have the Stick shift back in them. The Porsche guys have recently designed a Manual Stick Shift that mechanically and functionally works the same as the PDK - they talked about weight between the 2 as being very small as compared to other manufacturers that have a large weight disparity between the Manual Transmissions versus their Automatic offerings.


So back to my daughter's drive to the store…..I noticed the difference in ride, acceleration and shifting on every stop and start going to the store. I then asked her how much she weighed (I had no idea) – she replied 85 lbs or so. The Mustang needed to be Balanced Laterally to counteract the Rotational Torsion forces caused by clockwise rotation of all the engine and drive shaft components. The Automatic has this extra weight and has no ill effects (as well as not having to be manually shifted). Once the extra weight of the automatic is removed then the suspension issues cause the "clunkiness" of the manual. Since the majority of cars sold by Ford are Automatics, it can be safely assumed that Ford designed the suspension components of the S550 to be best suited for 2 people and a Full tank of Fuel to comfortably cruise on the US roads. When you put the Manual Transmission option into the mix, that decrease in weight causes the suspension components to ride higher in their range and the balance is somewhat lost, causing the disruption to the Perfect Shift.


I have a background in motorcycles for some 25+ years and am very keen on suspension setups and perfect shifts and the relationship between the engine-drivetrain relationship which can be compromised with a poor suspension setup or weight balance.


My solution, upon returning home was to load a backpack with 85 pounds of free weights. I then placed that backpack in the floor board Behind the Passenger seat. This mimicked my daughter sitting in the seat. I truly believe a formula could be calculated using the driver's weight which would yield a more precise number of pounds which should be placed on the passenger side to perfectly counterbalance the suspension disruption due to the effects listed above. I'm thinking it would probably be and ½ the weight of the driver. So, at 190 pounds, I should actually place about 95 pounds. Let me know what you think. I know some Ford reps monitor these posts, so please let me know from an engineering standpoint if my conjecture has validation. Thank you
 
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Bullitt347

man bewbs please...
Mar 23, 2007
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So why do you suppose this issue arises in this model year car, that by all accounts has more torsional stiffness and chassis rigidity than any other prior Mustang? And not in the earlier weaker more flexible platforms? I have a 89' Foxbody Mustang with an 8 point cage in it. It is said that the S197 chassis has a more stiff chassis than my Foxbody Mustang with a 8 point cage. Over double the torsional stiffness. Why did my 89 Mustang not exhibit this concern? And yet the S550 chassis is even better than the S197. BTW, My 08' Bullitt Mustang does not do what you describe, even after 67K miles.
 

Five.0GT

New Member
Mar 24, 2016
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I do believe it has to do with the mounts and the Chinese manual transmission as well as the Independent Rear Suspension (IRS)
 

Ikeaman

Member
May 13, 2016
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That is very interesting, sounds like an issue you would have with a 70s car with a torsion bar suspension, like an old olds or Buick...
 

84Ttop

They make new pistons every day, so why worry?
Mod Dude
Jul 2, 2009
5,329
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The shifter is mounted to the body, not the transmission... I have seen most of the issues clear up with a shifter such as bartons that is mounted directly to the trans. This does however increase NVH
 
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