Manual Trans. Thud when shifting

[TexasRebel]

People talk about it being a driveshaft issue, a rear end issue, a transmission issue. And you see some situations of replacing a part and it going away for one guy, but not another. Here's my best guess / theory.

The root cause may be there's some amount of drag across the clutch, even when disengaged. This causes the input shaft of the transmission to spin slightly when in neutral, but being in gear obviously provides enough resistance to stop it. When you're in neutral and move into gear, the inertia of the input shaft transfers to the transmission output. Depending on how much backlash is in all of the downstream components, you'll get a thud of varying degree as that inertia is transferred down the drivetrain and all of that lash is used up, forcing the input shaft to stall. More combined lash means more thudding.

So, if you have low lash in the axle, but a bit in the 2-piece prop shaft, putting in a 1-piece shaft reduces the lash - and the inertial movement - enough to make the thud less noticeable. But if there's also excessive lash in the axle, then you don't make enough reduction in system lash to change how the thud feels. It might be more noticeable off the bat in PP cars because 1) the 3.73:1 gears multiply the axle back lash more than the taller gearsets do, and 2) the Torsen lacks a preload spring, which masks the differential gearing lash in the clutch plate diffs. So, more perceived lash comes from the axle. But you can get it in other axle combinations if the prop shaft or transmission system lash is also high enough. You don't get it in A/T cars because the transmission obviously sidesteps the issue.

I could be completely off base on this, I'm just an axle guy. But this is the only thing I've been able to come up with that addresses all the facts as I understand them. You can chase various aspects of drivetrain back lash and improve the situation, but I'd bet that if the clutch could be set up so the clutch disc more fully disengages the pressure plate, the problem would disappear. At least that's my thinking...

This is what I've observed also. The only time I get the "thud" is if I've been sitting in neutral and quickly engage a gear. The location and nature of the sound seem to be the pressure plate and input mass coming to a quick stop by the synchros. Does anyone have the breakaway torque/preload specs for the input of these transmissions?

Some say different oil in the transmission eliminated the thud. A more viscous fluid would cause more resistance to rotation as the input rotates the lay cluster.

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[skytop1]

Fully disagree with you and the previous long post. Your supposition is clearly unbased and in error.
Even standing still with clutch fully dispressed for say, 5 seconds, put into ANY gear THUMP! Move from 1 to 2nd to 3rd to 4th to 5th to 6th, THUMP, THUMP, THUMP, THUMP, TUMP, THUMP!
When moving, I get the TUMP.
I have experienced this issue since brand new.

I am also FED UP with the insane center stack design of tiny squeezed to together controls that are virtually impossible to adjust while driving because one must look down the stack to see where the teeny tiny desired button is. Super dangerous and amateur design from Ford.

I am tired of the gremlin in my security system that locks me out and refuses to open the trunk or opens the trunk by itself.
Yes, my next 2018 car will NOT BE A FORD.

 

[Dave2017GT]

Mine did it as well I did the BG fluid change and it is almost gone. I say almost because the notchyness is gone but on occasion it does thud just not as bad as it was.

Whats the BG fluid change? Transmission fluid?

 

[TooSoonJunior]

Whats the BG fluid change? Transmission fluid?

Yes, the fluid properties of the BG fluid seems to tame some of noises from the MT82 as well as improve varying temperature performance. I noticed some noises right away when I purchased my Florida car and drove it in 30 degree new England weather, when I asked the previous owner he was honest and said he never experienced the same noises. My next step I ordered the fluid kit and will be doing the change over in a few weeks.

That said, I have spent the better part of 3 weeks going through these forums and honestly have come to the conclusion that most of the "issues" and "thumping" people hear and raise concerns about are all personal preferences and opinions. My brother got behind the wheel and rowed through the gears and thought it felt heavenly, best 6 speed he has driven (coming from a bunch of GM vehicles). So I have to go with the old saying, opinions are like @ssholes....EVERYONE HAS ONE...

 

[Bhoris]

So I have to go with the old saying, opinions are like @ssholes....EVERYONE HAS ONE...

And they all stink!

 

[Coconut]

Mine thuds if you shift it super quick into gear from neutral. Slowing the shift down a bit and I don't get the thud. My S2000 had this thud as well. To get smooth shifts from your MT82, don't manhandle it.

 

[skytop1]

When I shift that slowly, I tend to become weary but then the car behind me blast his/her horn.
Shifting at all speeds producing the thunk in my Mustang GT. Today I was noticing I have do have the thud in all gear when stationary or while in motion. Unacceptable and very aggravating. I hold Ford responsible fully for causing such frustration during my ownership of my car. No more Fords for me.

 

[S550bsessed]

Quick history on me, i have approx 20 years experience driving manual transmissions (Mostly FWD), and I was in the automotive trade (Service Advisor) for 13 years...recently moved on.

So I have had my car for a month...and I have approx 1500 miles on it. I am finding that clunk/thud noise is pretty normal to me, it feels like driveline play to me.

What concerns me is that - For me I am finding that when the transmission is cold, I can really feel the syncros grabbing/pulsating back into the gear selector?? This is under normal driving conditions in the city, shifting around 2500 rpms.

To me it almost feels like the syncros are not bringing the gear up to speed fast enough.on the 1-2 shift and 2-3 shift.

My shifts 3-4/5-6 are very smooth and I don't feel the syncros grabbing.

I am wondering if this BG Syncro Shift Fluid would help with this?

OR

Is it possible that Ford put beefier syncros to withstand the beating of harsh driving/accelerating that most of of bought the car for.
It would make sense to me that seeing as people typically are beating the crap out of the transmission when shifting 1-2 and 2-3.

Thoughts??

 

[16s550]

The bg fluid will help out a ton. Also a new shifter would be good too. Stock one sucks. I have also noticed the transmission shifts funny when cold but once warmed up it feels normal. As of now with all the mods I only have the this once in awhile. I Also changed to a stainless braided clutch line.

 

[ZIGZGT]

I switched to the BG fluid as well. It may be slightly better than before, but it isn't what I had hoped for. That being said, I will stick with the BG instead of the stock fluid for future changes as well.

 

[16s550]

I switched to the BG fluid as well. It may be slightly better than before, but it isn't what I had hoped for. That being said, I will stick with the BG instead of the stock fluid for future changes as well.

Are you still using the stock shifter? I suggest swapping that the clutch line and maybe the white line or Steeda insert bushing for transmission mount. I also put BMR motor mounts not sure if that helps but I did notice easier shifting after not sure if it was coincidence

 

[16s550]

And now that I remember also the differential bushing inserts

 

[wildcatgoal]

Ford apparently improved the syncros in S550 MT82. Didn't last for Steeda's race car, haha.

 

[16s550]

Ford apparently improved the syncros in S550 MT82. Didn't last for Steeda's race car, haha.

Yeah I think it could be hit-or-miss on the durability depending what fluid you use in the car and the skill level of the driver. I'm taking the car to the track and beat on it a lot so far holding up great knock on wood. If it ever goes south in the future I just going to have to go with the Tremec.

 

[ZIGZGT]

Are you still using the stock shifter? I suggest swapping that the clutch line and maybe the white line or Steeda insert bushing for transmission mount. I also put BMR motor mounts not sure if that helps but I did notice easier shifting after not sure if it was coincidence

I still have the stock shifter. I will probably switch and try that clutch line, but I'm not interested in the inserts. Most reviews say it increases the NVH and this is my daily driver so I don't think I'd like that very much.

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