The ultimate solution for clunking tranmission

[TexasRebel]

The best way to get rid of the clunk is to turn the engine off before shifting.

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[jasonstang]

Loud exhaust

 

[RedRyan98]

I certainly haven't solved the thud/clunking, but have minimized it by changing my driving style a little, especially when shifting. Normally when driving a manual I'd get off the gas and on the clutch at about the same time, or as part of one motion. When shifting like this I'd hear a thud most of the time.

However, if I get off the gas a split second before pressing the clutch pedal down I don't hear it. I still hear it in other scenarios, but as far as shifting goes I rarely do now. I'm not sure if that will help with folks with other engines or differentials but I'd give it a shot.

 

[EXP Jawa]

I've stated this in the other thud thread, but my theory is that the root cause of the thud is in the clutch. The noise eminates from the driveline and movement within the backlash, but the root of the issue probably starts with the clutch.

Here goes: there is (may be) a small amount of residual clutch drag, between the clutch disc and the pressure plate, even when the clutch is fully disengaged. As a result, when in neutral, the drag across the clutch can make the input side of the transmission spin a little since there's no load to resist it. When you put the transmission in gear, then suddenly there is resistance to that spin, causing the input shaft to stall. The inertia of the spinning components gets transferred into the output shaft of the transmission when it suddenly stops the input side from turning (now that its in gear). That inertia causes the drivetrain to wind up momentarily and release as the energy dissipates, taking up the slack (lash) of the drivetrain components briefly as it does so. That causes the "thud" noise to occur. The actual noise is the sound of the drivetrain system bouncing off of the hard stop(s) at the end of the backlash movement.

That's why, I think, that there are so many different "fixes" for the problem, none of which truly work for everyone. Because how pronounced the thud is ties to how much system lash there is in the drivetrain, how damped the components may be to movement, and of course, how much initial clutch drag there might be. It isn't one single issue, but a systemic collection of little issues. But its triggered by the clutch. That's the only thing I've been able to think of that addresses all of the reported symptoms that I've heard. But if someone were to affect an adjustment to the clutch or pressure plate such that it completely disengages when the pedal is all the way down (which might not be practical), it would probably keep the whole thing from occurring altogether.

I'm not sure if I'm conveying this well. But, in summary, the thud is death by a thousand cuts considering all of the possible sources of powertrain and drivetrain lash. But they're all responding (in different degrees) to one input, one source of energy.

 

[AZFord]

EXP Jawa - Agree 100% on this. With the car sitting still / transmission in neutral, then depressing the clutch and putting the car in 1st will cause the thud. The only source of the thud has to come from the momentum of the clutch dragging then taking up all the lash in the drive train. Makes me wonder if we'll be replacing clutches sooner on these vehicles since it never truly stops dragging.

It's been awhile since I've had a Mustang (last one I owned was a Foxbody) but is it possible to adjust how much throw the clutch pedal puts onto the pressure plate?

 

[jasonstang]

EXP Jawa - Agree 100% on this. With the car sitting still / transmission in neutral, then depressing the clutch and putting the car in 1st will cause the thud. The only source of the thud has to come from the momentum of the clutch dragging then taking up all the lash in the drive train. Makes me wonder if we'll be replacing clutches sooner on these vehicles since it never truly stops dragging.

It's been awhile since I've had a Mustang (last one I owned was a Foxbody) but is it possible to adjust how much throw the clutch pedal puts onto the pressure plate?

I bet if you push in clutch and wait long enough before putting in gear, you will not hear the clunk. Or put in gear, take it out, and put it in gear again, you will not hear it either.
Of course when you press in the clutch and put in gear right away the input shaft would be spinning before the syncro stops it.
If your clutch is truly dragging you will not be able to put in gear when stopped.
Actually, the little movement of the input shaft helps the syncro teeth to slid in smoothly. If all gears are stopped, it makes the process harder.
It's just on a car like Mustang, it's much more obvious as the drive train goes though the floor.

 

[EXP Jawa]

Possibly. But I'm not talking about a significant drag in terms of wear life or preventing gear engagement, just a very slight contact, as if the nominal clearance is set up so the faces just kiss, with no real pressure on the surface. That would be all it takes. Obviously, a great many other manual transmission cars can be put into gear without a clunk promptly after pushing in the clutch. I can put the T45 in my '99 in gear without objection. So, there is a variable there.

 

[jasonstang]

Possibly. But I'm not talking about a significant drag in terms of wear life or preventing gear engagement, just a very slight contact, as if the nominal clearance is set up so the faces just kiss, with no real pressure on the surface. That would be all it takes. Obviously, a great many other manual transmission cars can be put into gear without a clunk promptly after pushing in the clutch. I can put the T45 in my '99 in gear without objection. So, there is a variable there.

Maybe the T45 had tighter load on the bearings everything stops quickly.
Of all the RWD/4WD I have owned over the years, there is always some kind of tick or thud can be heard or felt.

 

[wimbrow]

shifter malfunction

So I've done some extensive research, and could not find a perfect answer for this. As many people know, the manual transmission makes clunks when I press/depress clutch pedal when engaging gears and a thuk/thunk noise in lower gears shift.

Here's some list of aftermarket parts I found:

1. Transmission bushing mounts
2. BG transmission oil swap
3. Blowfish shift bracket
4. Shifter bushing

Has anyone solve their clunk/thud/thunk problem to their GTs using aftemarket parts? What's really effective? I obviously don't want to spend $$$, but other than blowfish shift bracket they seem to be in good $ shape.

Thanks!

hi grey. mine only thunks on down shifting when i don't do proper rev matching blip. which is rare now. very easy to do.. anyway if i just depress the clutch it never thuds. same factory i believe. good luck, tom

 

[Gee]

The noise you're hearing:

http://www.mustang6g.com/forums/showthread.php?t=80925

Same issue here, but I did notice the noise was less pronounced after the lowering springs went in. It's still there, just less of it and not as loud. It's livable now.

 

[TexasRebel]

Possibly. But I'm not talking about a significant drag in terms of wear life or preventing gear engagement, just a very slight contact, as if the nominal clearance is set up so the faces just kiss, with no real pressure on the surface. That would be all it takes. Obviously, a great many other manual transmission cars can be put into gear without a clunk promptly after pushing in the clutch. I can put the T45 in my '99 in gear without objection. So, there is a variable there.

I don't even think it's drag on the friction surfaces. I think the drag is on the input shaft pilot bearing surface (needle bearings or bushing sleeve) overcomes the resistance in the input side transmission bearings. Especially since the pilot bearing is dry.

Then also remember that the clutch and flywheel pair, even when disengaged, form a type of viscous coupling. While the fluid between them is air, the point of minimum potential still occurs when everything is spinning together.

 

[EXP Jawa]

I could buy into that idea, especially if the pilot is bushed instead of a bearing. Either way, I think that's what is transferring drag torque into the input shaft. If someone found a way to relieve that, the "thud" would probably disappear...

 

[Jim Bronson]

I don't have much thunking, but I am starting to have difficulty shifting from first to second. It just happens once in a while after the engine warms up. It catches me by surprise and ruins the experience.

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