Transmission issues 2020 C8
Advanced
Joined: Jul 2020
Posts: 72
Likes: 19
AH HA! The DCT doesn’t have a torque converter found in previous Corvette transmissions. This explains what you said about NOT using the throttle to hold the car on a hill…thus…hill hold assist! Makes perfect sense! It applies the brakes! Thanks for that clarification. Now if I could figure out why the car happily rolls along at about 8 MPH with no throttle application… I’m guessing here… NO torque converter might be the cause. Ideas??
Race Director
Joined: Aug 2016
Posts: 12,760
Likes: 10,193
From: Garden Valley CA
This is the idle creep feature to simulate how an automatic with a torque converter works. If you pull back on both paddles it will fully disengage the clutch disks.
Last edited by RKCRLR; Oct 7, 2021 at 12:24 PM.
Intermediate
Joined: Aug 2017
Posts: 43
Likes: 14
From: South Eastern USA
AH HA! The DCT doesn’t have a torque converter found in previous Corvette transmissions. This explains what you said about NOT using the throttle to hold the car on a hill…thus…hill hold assist! Makes perfect sense! It applies the brakes! Thanks for that clarification. Now if I could figure out why the car happily rolls along at about 8 MPH with no throttle application… I’m guessing here… NO torque converter might be the cause. Ideas??
There's a US patent by Ford that explains why and how idle creep can be simulated in a DCT...a good read and is found here: https://patents.google.com/patent/US8260513
In Ford's simulation, idle creep mode isn't active until the brake pedal is released. I'm not sure whether this applies to partially released brakes or whether the C8 works similarly. I must use partially released brakes and/or partially engaged clutches to decrease or increase idle creep when parallel parking along my long, wide sloping driveway. I don't find any warnings in the owner's manual against doing this...only against using partially engaged clutches to hold the vehicle at a standstill on an incline.
Advanced
Joined: Jul 2020
Posts: 72
Likes: 19
AH HA! The DCT computer is the issue. When the brake pedal is pushed and the car stops, the computer disengages DCT gear clutches to prevent wear on the them. Since a regular automatic transmission has the torque converter to absorb the twisting motion on the clutches it’s not an issue. With a DCT, when the brake pedal is released, the clutch is re-engaged to smoothly accelerate. Also, the “hill assist” allows one to take the foot off of the brake pedal and the clutch will not engage. This explains the slight jerk I feel when the hill assist releases. It also explains why pulling both paddles will put the DCT into an "electronic neutral" as the computer is programmed to see both paddles pulled as the driver wants all of the clutches released. This also explains why stop 'n go traffic (like a parade) can be hard on a DCT because the clutches are continually engaged/disengaged. Someone straighten me out if I'm off base here!
Last edited by c8winston; Oct 7, 2021 at 02:35 PM.
Race Director
Joined: Aug 2016
Posts: 12,760
Likes: 10,193
From: Garden Valley CA
Idle creep in a DCT is a feature that's designed to simulate the behavior of a torque converter automatic transmission. It helps to smoothly launch the vehicle from standstill. It may have been 10 years ago when I test drove a VW Passat diesel with a DCT and it didn't creep. So the engine speed had to be increased far above idle before the vehicle moved which I didn't expect and didn't adjust to readily.
There's a US patent by Ford that explains why and how idle creep can be simulated in a DCT...a good read and is found here: https://patents.google.com/patent/US8260513
In Ford's simulation, idle creep mode isn't active until the brake pedal is released. I'm not sure whether this applies to partially released brakes or whether the C8 works similarly. I must use partially released brakes and/or partially engaged clutches to decrease or increase idle creep when parallel parking along my long, wide sloping driveway. I don't find any warnings in the owner's manual against doing this...only against using partially engaged clutches to hold the vehicle at a standstill on an incline.
There's a US patent by Ford that explains why and how idle creep can be simulated in a DCT...a good read and is found here: https://patents.google.com/patent/US8260513
In Ford's simulation, idle creep mode isn't active until the brake pedal is released. I'm not sure whether this applies to partially released brakes or whether the C8 works similarly. I must use partially released brakes and/or partially engaged clutches to decrease or increase idle creep when parallel parking along my long, wide sloping driveway. I don't find any warnings in the owner's manual against doing this...only against using partially engaged clutches to hold the vehicle at a standstill on an incline.
Now some people are going to get concerned that this causes excess wear on the clutch plates. But wet clutches are different from dry clutches. The life reduction is probably less than one day of average driving. In fact, the clutch plates may not even be making contact during idle creep. The engagement could just be from the fluid shear between the disks, but this is just speculation.
