Clutch/Flywheel screeching on takeoff & under acceleration

[brandon_5.0h]

Good evening all,

My car, a 2019 PP1, has just recently, at 14k miles, began to make a screeching noise under acceleration. I have had issues in the past, as the clutch would make a whining sound as I downshift normally, not rev-matching. I am unsure as to if this is a flywheel issue, and it may need to be resurfaced, or a clutch issue. After a single 1-3 pull, the clutch pedal feels nonexistent or very light shifting between gears afterwards, feeling little to no engagement. It then whines even louder after said pull in any gear. It has only worsened and I was just wanting to know If anyone else has had this issue. Car is FBO. Thanks in advance for any information!

Sponsored

 

[NoVaGT]

Good evening all,

My car, a 2019 PP1, has just recently, at 14k miles, began to make a screeching noise under acceleration. I have had issues in the past, as the clutch would make a whining sound as I downshift normally, not rev-matching. I am unsure as to if this is a flywheel issue, and it may need to be resurfaced, or a clutch issue. After a single 1-3 pull, the clutch pedal feels nonexistent or very light shifting between gears afterwards, feeling little to no engagement. It then whines even louder after said pull in any gear. It has only worsened and I was just wanting to know If anyone else has had this issue. Car is FBO. Thanks in advance for any information!

What do you mean by "downshift normally, not rev-matching".

Let's make that our starting point for the discussions.

Also, you write the car is FBO. Well, assuming that means full bolt ons, and there's not specific definition of that, you'd do best putting all your mods in your sig line so we know what you've done to the car.

 

[TexasRebel]

Also, please define "downshift normally"

 

[BimmerDriver]

I'm guessing that FBO means you have voided your drivetrain warranty.

I'm also assuming that FBO excluded any upgrade to the clutch to handle the increased power.

 

[brandon_5.0h]

I'm guessing that FBO means you have voided your drivetrain warranty.

I'm also assuming that FBO excluded any upgrade to the clutch to handle the increased power.

Indeed that is correct, although, it only makes 500 wheel and should easily handle the power. I've never heard of an issue with a stock clutch going out, only them being real crappy. Also, when I say downshift "normally," I simply mean the obvious clutch in down a gear, clutch out, in order to slow the car down naturally.

 

[NoVaGT]

........when I say downshift "normally," I simply mean the obvious clutch in down a gear, clutch out, in order to slow the car down naturally.

If you're not rev-matching, you're destroying your clutch. And synchros. Maybe the synchros more.

Your car has auto rev-matching. Have you shut it off?

 

[BimmerDriver]

If you're not rev-matching, you're destroying your clutch. And synchros. Maybe the synchros more.

Actually, rev-matching saves the clutch but does nothing for the synchros. For that you need to double-clutch (clutch in, shift to neutral, clutch out, blip throttle, clutch in, shift into gear, clutch out).

 

[BimmerDriver]

I've never heard of an issue with a stock clutch going out, only them being real crappy.

What's the difference between the two?

And at 500 wheel HP, that's closer to 600 HP at the crank, which is a sizable bump from stock.

 

[NoVaGT]

Actually, rev-matching saves the clutch but does nothing for the synchros. For that you need to double-clutch (clutch in, shift to neutral, clutch out, blip throttle, clutch in, shift into gear, clutch out).

I do believe that even when using the clutch, if you don't rev-match, you're working the synchros harder.

Double clutching was for old non-synchro transmissions where you needed to match the speed of the engine and gears. But with a modern trans, that's what the synchros are for, to match those speeds. There's no need to double-clutch with a synchro trans, you just rev-match down-shifts....which these cars do for you.

I have a sneaking suspicion the OP has toasted his synchros.

Ya'll can correct me if I'm wrong in that.

 

[Balr14]

A screeching noise usually indicates a burnished clutch.

These Mustang manual transmissions must be real crap if you can wreck things by not rev matching. I have never rev matched in 60 years of driving manuals and have replaced 3 clutches with nearly 100k miles. I have never had transmission issues.

 

[TexasRebel]

I do believe that even when using the clutch, if you don't rev-match, you're working the synchros harder.

Double clutching was for old non-synchro transmissions where you needed to match the speed of the engine and gears. But with a modern trans, that's what the synchros are for, to match those speeds. There's no need to double-clutch with a synchro trans, you just rev-match down-shifts....which these cars do for you.

I have a sneaking suspicion the OP has toasted his synchros.

Ya'll can correct me if I'm wrong in that.

with the clutch disengaged, rev-matching doesn't affect the input shaft of the gearbox. The synchros will still be used to match the shaft & gear rpm. The good news, these are in an oil bath and conical. Unless you're trying to start from idle by using the synchros, they're pretty difficult to destroy. There might be excessive wear on them if you're downshifting and not disengaging the clutch all of the way.

 

[TexasRebel]

I simply mean the obvious clutch in down a gear, clutch out, in order to slow the car down naturally.

If you aren't at least bumping your RPM up to get close (rev-matching doesn't have to be spot on) you're not slowing the car down "naturally". You're slowing the car down while running the engine up and burning the clutch (with possibly way more than 600 HP).

Don't forget, a vehicle in motion is just an energy storage device... engine braking in a car doesn't work quite like true compression braking. With engine braking in these mustangs, you're working against the butterfly valve. The compression creates heat, but then pushes against the piston on the down stroke. This isn't the same as having an exhaust valve open at TDC to dump the compressed air to atmosphere (Jake Brake).

Conservation of energy says the kinetic energy of the vehicle must change form somehow. Brakes change that energy to heat. You don't want that heat on your flywheel.

 

[brandon_5.0h]

I did my fair share of both rev-matching, more so than naturally slowing the car down. I knew these aluminum shift forks on the MT-82's are glass, but have never once heard someone having an issue with the clutch, only 3rd gear lockout regarding that in general. SO, lets assume it is the clutches and they're mildly heat-spotted, what's the next best course of action? McLeod RXT and resurface the flywheel, or is the flywheel good overall? I already have Steeda's short throw in it with many poly mounts to prevent this from happening, but I guess it was not enough. Appreciate everyone's invoice for sure.

 

[Elp_jc]

I don't think you'd ever wear out the synchros if you always downshift one gear at a time (minimum difference). And also basically no wear on the clutch if you always rev-match as well, especially with the computer, which does it perfectly every time, and up and down.

 

[Avispa]

A screeching noise usually indicates a burnished clutch.

These Mustang manual transmissions must be real crap if you can wreck things by not rev matching. I have never rev matched in 60 years of driving manuals and have replaced 3 clutches with nearly 100k miles. I have never had transmission issues.

There's your answer. Fully synchronized manual transmissions have been around for more than 60 years, most of that without any automatic rev matching. If synchros are getting roasted just from what on cars only a few years older is completely normal operating, then the trans has some serious flaws.

Sponsored