Clutch Slipping on stock A91 MT...

[BrettMRC]

This just came up on my feed, 2023 MT running around 570hp.
Very curious to know from them if they've done any work on the transmission at all and whether they noticed any issues.
Reason being, in my opinion if there are no issues on this car running around +40% more power than stock, then for whoever does have issues we can be more confident in the theory of manufacturing issues.

She seems fine so far!

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[Cyclingdude723]

I don't have any photos but I did go an inspect the bearing. The inner race of the bearing was completely loose from the assembly but it did still spin fairly freely. Most concerning IMO, is the fact that the ONLY symptom I had was a VERY slight clutch burning smell when the windows were rolled down.

i guess the question is - was this failure a rare occurrence or could there be an underlying weakness. if they let you keep the bad part i'd be curious to see pics, but they may keep or return it since it's a warranty claim.

 

[kern417]

I don't have any photos but I did go an inspect the bearing. The inner race of the bearing was completely loose from the assembly but it did still spin fairly freely. Most concerning IMO, is the fact that the ONLY symptom I had was a VERY slight clutch burning smell when the windows were rolled down.

yeah, that's the kind of failure that can leave you stranded out of nowhere. glad you were proactive

 

[Adrenaldestruction]

@Spart & @NitroYellowMKV


Seconded.

The CDV drove me nuts - more than most folks, it seems. Even after removal, I am hungry to go aftermarket clutch (not until power requires, of course). That being said, the difference is not remarkable but it is (subjectively) important. It really does feel like a feature that was *meant to protect the driveline but *in practice only serves to introduce slip. There are multiple factors but for the sake of this conversation, you get the point.

The overall feeling is that Toyota hit a fork in the road: cater to the power-hungry enthusiast OR release the perfect car for a 50-something divorced physician to drive home after 2 cocktails at the north side bar. They chose the latter.

 

[DGINR8supra]

She seems fine so far!

What mods do you have done?

 

[BrettMRC]

Whitbitz Downpipe, Akrapovic mid pipes and silencer, MST intake, Forge hard pipes, Wagner cooler, Whifbitz hybrid turbo, Femto unlock, BM3 custom tune.

 

[AJRMKV]

Whitbitz Downpipe, Akrapovic mid pipes and silencer, MST intake, Forge hard pipes, Wagner cooler, Whifbitz hybrid turbo, Femto unlock, BM3 custom tune.

who tuned you?

 

[BrettMRC]

who tuned you?

It was done on the Whifbitz dyno by a gentleman called Mike Ball.

 

[AJRMKV]

I'm guessing the FX400 will be the popular option but I have a friend who went ahead and ordered the 1000 series just to be extra safe. He already put on the top mount and is finishing up on the supporting mods so lets see how these things perform with some 1/4 mile abuse. Would have been nice if Clutch Masters called out the actual torque rating for each and actually put in some time to proof read the product descriptions.

Went over to Bimmerpost and noticed that the manual G80 guys are replacing their stock clutch with FX400's and they've been problem free over the last 2 years with everything the stock turbos can throw at them... So 750 wtq ish

 

[94boosted]

@lucky phil

I am curious to hear your thoughts on why the CDV is there from the factory? If you're Toyota or BMW or any manufacturer selling a sports car with a manual transmission, would you not put in a CDV? During an aggressive launch or aggressive gear change, the CDV, by design, will delay (slightly) how quickly the clutch disengages engages, thereby reducing some of the shock the driveline sees. As a manufacturer that's likely what you'd want when selling an MT sports car to people of greatly varying ability to drive a car with a manual trans. Especially when offering a 5yr powertrain warranty. Therefore the CDV will also have, at least some, effect on how shifting feels to people, no?

Edit: Engages, not disengages

 

[BMWAF]

I know it's an unpopular opinion, but after reading countless threads, I honestly think the majority of manual transmission issues (all cars not just MY23+ Supras) largely fall back on people not really knowing how to drive a manual properly.

Despite what the automatic folk say, driving a manual correctly; smoothly and quickly (while not rocket science) does require a certain level of skill.

 

[lucky phil]

@lucky phil

I am curious to hear your thoughts on why the CDV is there from the factory? If you're Toyota or BMW or any manufacturer selling a sports car with a manual transmission, would you not put in a CDV? During an aggressive launch or aggressive gear change, the CDV, by design, will delay (slightly) how quickly the clutch disengages, thereby reducing some of the shock the driveline sees. As a manufacturer that's likely what you'd want when selling an MT sports car to people of greatly varying ability to drive a car with a manual trans. Especially when offering a 5yr powertrain warranty. Therefore the CDV will also have, at least some, effect on how shifting feels to people, no?

I honestly don't know precisely why CDV's are fitted. Some are a simple restrictor and hence operate in both clutch engagement and disengagement modes and some are a check valve restrictor style that operate in the clutch engage mode only. I've looked for information on their function but only found "opinion" not information from a powertrain engineer or patents..
My personal view is that they are there to provide better modulation/feel at the clutch friction point during clutch engagement to make the actuation at that point more progressive and a little more forgiving for the average driver. I'm not inclined to believe they prevent transmission shock theories by others simply because there are already two mechanisms in the driveline to cover that. The sprung hub in the clutch friction plate and the tail shaft rubber drive coupler. I'm a sceptic by nature and combined with my passion for engineering I tend to look at the "easy task world beating result" stuff you get on internet forums with a prove it to me kind of view. I've also spent many many years troubleshooting aircraft and racing motorcycle technical "issues" and can tell you now I've probably spent more time working on the area between a pilots and riders ears than the actual machinery. Everyone wants the easy, simple, quick spectacular do it yourself "game changing" result. Remove the CDV and you'll achieve shifting nirvana. Well, I've been around forums long enough to be pretty sceptical about this sort of thing and my experience of automotive testing and design albeit second hand backs my view. People sometimes confuse "different" with "better". Remove the CDV and it's way "better", or is the clutch action just a little "different"? As I've mentioned previously there's a simple CDV influence test people can do to help them decide. Warm up you Supra and stop on some flat ground, bring the engine rpm up to maybe 1500 or even 2000 rpm in first gear and side step the clutch. If the CDV has the influence on clutch engagement people say it does then the car should not stall and move off. I wouldn't expect it to smoothly pull away of course but it shouldn't stall. Unless it passes this simple test then I'll remain sceptical and remain of the view that it's just an aid to better modulate the clutch release at the critical friction point. Remember the movement of the pressure plate of the clutch from the friction point to fully engaged is around 1/2 a mm or less actual travel. All that clutch pedal travel moves the pressure plate face around 2 mm or so at most.

Phil

 

[kern417]

Sure, manufacturers know that driving feel is important to selling cars to enthusiasts. But enthusiasts make up a small portion of their market share. Especially for a $60k+ car.

I had a car in the past that I took the bait from forum recommendations and did all solid bushings etc. in the shift linkages. Honestly it ruined the experience for me. Everybody has different preferences and most german buyers want smooth shifting, and a CDV aids in that for daily driving. It can be raced, but it's not built with racing as a priority.

I always thought CDV was kind of a german engineering default for manual trans. The same thing is in VW/Audi manuals. I think the only car that can get away with prioritizing driving feel and fun is a Miata.

 

[94boosted]

I honestly don't know precisely why CDV's are fitted. Some are a simple restrictor and hence operate in both clutch engagement and disengagement modes and some are a check valve restrictor style that operate in the clutch engage mode only. I've looked for information on their function but only found "opinion" not information from a powertrain engineer or patents..
My personal view is that they are there to provide better modulation/feel at the clutch friction point during clutch engagement to make the actuation at that point more progressive and a little more forgiving for the average driver. I'm not inclined to believe they prevent transmission shock theories by others simply because there are already two mechanisms in the driveline to cover that. The sprung hub in the clutch friction plate and the tail shaft rubber drive coupler. I'm a sceptic by nature and combined with my passion for engineering I tend to look at the "easy task world beating result" stuff you get on internet forums with a prove it to me kind of view. I've also spent many many years troubleshooting aircraft and racing motorcycle technical "issues" and can tell you now I've probably spent more time working on the area between a pilots and riders ears than the actual machinery. Everyone wants the easy, simple, quick spectacular do it yourself "game changing" result. Remove the CDV and you'll achieve shifting nirvana. Well, I've been around forums long enough to be pretty sceptical about this sort of thing and my experience of automotive testing and design albeit second hand backs my view. People sometimes confuse "different" with "better". Remove the CDV and it's way "better", or is the clutch action just a little "different"? As I've mentioned previously there's a simple CDV influence test people can do to help them decide. Warm up you Supra and stop on some flat ground, bring the engine rpm up to maybe 1500 or even 2000 rpm in first gear and side step the clutch. If the CDV has the influence on clutch engagement people say it does then the car should not stall and move off. I wouldn't expect it to smoothly pull away of course but it shouldn't stall. Unless it passes this simple test then I'll remain sceptical and remain of the view that it's just an aid to better modulate the clutch release at the critical friction point. Remember the movement of the pressure plate of the clutch from the friction point to fully engaged is around 1/2 a mm or less actual travel. All that clutch pedal travel moves the pressure plate face around 2 mm or so at most.

Phil

Appreciate you sharing your thoughts. I certainly don't think that removing the CDV is some sort of a transformational experience, but if removing it does in fact remove some of the delay in the operation of the clutch, it may be a worthwhile change to make. I do respectfully disagree that in some small part it isn't reducing driveline shock during aggressive launches/shifts. Simply due to the fact that it's delaying, slightly, how quickly the clutch disc can engage the flywheel.

Once the snow melts and I take my car out for a drive I'll happily try your suggested test, if I remember, maybe I'll shoot a quick video.

 

[Spart]

It's really simple.

Regardless of what happens when you side-step the clutch, the CDV acts as a damper.

The spring pressure you feel comes from the diaphragm spring on the clutch. That spring transmits force hydraulicly to your foot. The clutch delay valve limits the flow of that hydraulic system, and below a certain rate of flow provides almost no limit at all. So while you may feel the same pressure with the clutch pressed to the floor, how much of that pressure persists at your foot will change based on the speed you move your foot.

It is that variability that leads to drivability issues when you switch from driving casually to driving aggressively. Your brain expects the clutch to move a certain way based on the pressure applied or released by your foot, and it gets a result that's unexpected.

Removing the CDV makes the operation more intuitive - that is to say your brain gets what it expects.

Just ignore Phil. He admits he's never tried this. He doesn't speak from first-hand experience. A whole bunch of the rest of us do.

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