Clutch Slipping on stock A91 MT...

[FuzzyRev]

The f***ing Good Idea Fairy strikes again.

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[puppers]

Curious if a JB+ is enough to make the clutch slip or if it was the CDV all along.

Thanks for the link on the slave cylinder. Just ordered. Like my previous BMW's, the clutch pedal was the most inconsistent feeling thing and that has translated to the MT Supra. Glad that it has been reported to change the feel, for the better.

 

[kingdooksdb]

Curious if a JB+ is enough to make the clutch slip or if it was the CDV all along.

Thanks for the link on the slave cylinder. Just ordered. Like my previous BMW's, the clutch pedal was the most inconsistent feeling thing and that has translated to the MT Supra. Glad that it has been reported to change the feel, for the better.

Before I partially unlocked my ECU the JB4 didn’t slip my clutch but my turbo wouldn’t spool after 5k rpm’s…. Fucking overboost hesitant acceleration very lame

 

[BMWAF]

Curious if a JB+ is enough to make the clutch slip or if it was the CDV all along.

Is a JB+ enough to make the clutch slip?

 

[lucky phil]

I'm sorry but I'm an engineer and I need data to believe stuff or at the very least a double blind test. So here's a test for the std clutch actuation system. If you depress the pedal and then sidestep the clutch pedal does it instantly return without delay? If it does then the restrictor is having no influence. Yes I know the Master cylinder has a return spring on the piston but that's a lightweight spring with no impact in this scenario. If the restrictor is having an influence on the pressure plate speed of returning to the engaged position then it will be reflected in the speed of the pedal return when you sidestep the clutch as the return of fluid to the master cylinder will be the controlling factor in the pedal return speed. Just try it with the engine off and see if the pedal returns immediately or if it retracts noticeably less quickly than it should.
I notice all these supposed problems are always the "easily fixed by the home mechanic" sort of thing. Like oil threads are oil threads because the average Joe can do an oil change so everyone has an opinion or theory on what's the best oil. Not many opinions and theories on conrod bolts and conrods or valve seat cuts and angles around. Just an observation.
Phil

 

[Spart]

I'm sorry but I'm an engineer and I need data to believe stuff or at the very least a double blind test. [...]
I notice all these supposed problems are always the "easily fixed by the home mechanic" sort of thing.

Just google search "clutch delay valve delete" and look at the thousand or so threads about it with regard to other BMW vehicles. I don't know how much more data you need.

Or just ignore this thread and keep your CDV. My Tacoma still has it, and it's never caused me any issues on that vehicle to include daily heel-toe. I suspect Toyota's implementation is less aggressive than what BMW does, I only really notice it doing anything when it's sub-zero outside. (Then your test of side-stepping the clutch results in a VERY lazy pedal return, almost comical.)

The BMW implementation made this car almost impossible to heel-toe consistently, and the 1-2 shift was pretty inconsistent also. It was the first negative I thing I noticed after getting out of my GT350 (which is a dream to heel-toe, like playing a fine musical instrument) and getting into the Supra, which literally felt broken and/or unfinished. Now it feels normal.

 

[kyle9]

I'm sorry but I'm an engineer and I need data to believe stuff or at the very least a double blind test. So here's a test for the std clutch actuation system. If you depress the pedal and then sidestep the clutch pedal does it instantly return without delay? If it does then the restrictor is having no influence. Yes I know the Master cylinder has a return spring on the piston but that's a lightweight spring with no impact in this scenario. If the restrictor is having an influence on the pressure plate speed of returning to the engaged position then it will be reflected in the speed of the pedal return when you sidestep the clutch as the return of fluid to the master cylinder will be the controlling factor in the pedal return speed. Just try it with the engine off and see if the pedal returns immediately or if it retracts noticeably less quickly than it should.
I notice all these supposed problems are always the "easily fixed by the home mechanic" sort of thing. Like oil threads are oil threads because the average Joe can do an oil change so everyone has an opinion or theory on what's the best oil. Not many opinions and theories on conrod bolts and conrods or valve seat cuts and angles around. Just an observation.
Phil

You want people to double blind test this? Good idea, enjoy setting that up 🫡

 

[robotvoice]

Just google search "clutch delay valve delete" and look at the thousand or so threads about it with regard to other BMW vehicles. I don't know how much more data you need.

Or just ignore this thread and keep your CDV. My Tacoma still has it, and it's never caused me any issues on that vehicle to include daily heel-toe. I suspect Toyota's implementation is less aggressive than what BMW does, I only really notice it doing anything when it's sub-zero outside. (Then your test of side-stepping the clutch results in a VERY lazy pedal return, almost comical.)

The BMW implementation made this car almost impossible to heel-toe consistently, and the 1-2 shift was pretty inconsistent also. It was the first negative I thing I noticed after getting out of my GT350 (which is a dream to heel-toe, like playing a fine musical instrument) and getting into the Supra, which literally felt broken and/or unfinished. Now it feels normal.

The clutch pedal feels fine in my MT. I have no issues with rev-matching, heel-toeing, etc. You want to feel a an actual trash clutch pedal, go drive a mk7 Golf R. Supra is WORLDS better than that.

 

[lucky phil]

You want people to double blind test this? Good idea, enjoy setting that up 🫡

Pretty easy really. Give your friend who is experienced in manuals a drive of your car stock and ask him a dozen questions about various things relating to how the car drives, ie steering, suspension brakes, CLUTCH ACTION, gearshift smoothness etc. Then pull the restrictor and offer him another drive and aske the same questions again without signalling you've done anything to he car. See if he/she immediately notes \or comments on a better clutch/shifting action etc. Not strictly a DOUBLE blind test but useful non the less.
Sometimes tuning bikes for racers they get a bit OCD about things and you know it's just their head so when they ask for some adjustment or action you know is silly and you don't want to waste your time you just tell them you've done what they asked for and out they go for a practice session and come back telling you how much better the bike feels. Often the lap time is also better and as the tuner you've done precisely nothing to the bike. Sometimes there's more to gain tuning the head than the machine.

Phil

 

[Chong]

See if he/she immediately notes \or comments on a better clutch/shifting action etc. Not strictly a DOUBLE blind test but useful non the less.

I actually had a friend ask to drive my Supra before and after the CDV delete (not a blind test), and he noted that the 1st, 2nd, and 3rd gears were easier to engage smoothly. Aside from that, you won't really feel the difference from the CDV unless you're doing aggressive shifting in gears 1-4.

The CDV does help with quicker clutch engagement in situations with aggressive shifting.
I do think you can burn the clutch out rather quickly if you don't adapt to the CDV and continuously shift aggressively.

 

[puppers]

Is a JB+ enough to make the clutch slip?

I want to try it, but then again, I don’t since the reports of clutch slippage on stock power lol.

 

[UYCR]

Curious if a JB+ is enough to make the clutch slip or if it was the CDV all along.

Thanks for the link on the slave cylinder. Just ordered. Like my previous BMW's, the clutch pedal was the most inconsistent feeling thing and that has translated to the MT Supra. Glad that it has been reported to change the feel, for the better.

I would say yes. The clutch pretty much starts slipping before you have maxed out the stock turbo and JB4 is more than capable of doing that with a custom tune. If you keep it under control with the OFT maps you should be okay for a bit but these cars are to new to know how the stock clutch would hold up long term on a mild/oft tune.

 

[Spart]

Sometimes there's more to gain tuning the head than the machine.

Right, but you yourself have never tried this, so what exactly what the f*** do you know?

You just wanted to come here and s*** on people and tell them they're making stuff up? Okay...

 

[BMWAF]

Sometimes there's more to gain tuning the head than the machine.

I think a lot of people here need their heads tuned mate.

 

[Spart]

The clutch pedal feels fine in my MT. I have no issues with rev-matching, heel-toeing, etc.

It's always hard to tell what people are actually doing when they talk about it online, so I'll explain myself more.

I should note that whenever I do a heel-toe downshift, I'm very aggressive with the clutch pedal speed almost all of the time. This isn't the only way to do it of course (there's a million ways to drive stick and only most of them are wrong) but if you're trying to stay sharp for occasional track driving like I do, you want to be on the aggressive side because your downshifts are happening in quick succession when you're braking hard.

The way I've seen some people downshift or heel-toe, the car would slow down too quickly for there to be much point in them attempting it at track speed. Assuming they were actually braking hard of course. And to put you in my headspace, I'm picturing a relatively sharp turn after a long straight where you're well into triple digit speed, and 2-3 downshifts in a row are required. Turn one at RPM comes to mind.

The CDV is going to make itself known the more aggressively you work the clutch, such as scenarios like that.

I'm not pointing fingers and maybe you've just successfully learned to drive aggressively around the CDV (in 1000 miles, I had gotten better with it but nowhere near 100%) but for me, it made an immediate difference. Before, I had no confidence in taking this car to a track without the stupid automatic rev-match turned on, lest I toast the clutch or something else. And not being able to heel-toe my way around a track would really suck the joy out of it for me. Now I have that confidence, and I'm looking forward to getting this car on track for the first time.

If you get the chance to drive another modern BMW with a CDV delete, do it and see if you can tell the difference as well. Maybe you don't know what you're missing out on. I came to the MT Supra from another track-capable car that does not come with a CDV from the factory (S550 GT350) and the difference is very obvious to me. I would say that after the CDV delete the Supra shifts more similarly to the GT350, whereas before they were a world apart.

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