Audi TT TransmissionPosted on: 27, January, 2019
No one wants to hear that there is something wrong with their car, especially when it comes to the transmission.
The owner of this 2010 Audi TT Quattro 4-cylinder TFSI 2 L started to feel a difference in the shift pattern when driving, and so he promptly brought his car to us with some concern. A test drive showed the somewhat erratic shifting, almost as if the clutch was slipping, and an unusually long delay between park and reverse, as well as park and drive. Our technician, Craig, got straight down to diagnostics to get to the bottom of this issue.
Our scan tool revealed fault codes for a gear malfunctioning from the DSG control unit. A Direct Shift Gearbox (DSG), or dual-clutch transmission, is an automated transmission that is capable of delivering more power, control, and speed than its traditional automatic or manual counterparts. The dual-clutch transmission was an improvement on the Sequential Manual Transmission (SMT), eradicating the delay between shifting gears by introducing two separate transmissions with a pair of clutches between. One transmission takes care of first gear, and the other transmission provides second gear, and back to the former transmission for third, and so on.
The fault codes retrieved from the DSG control unit lead to a technical service bulletin published by Volkswagen. The gear box needed to be removed and the clutch needed to be disassembled for further inspection. After draining the transmission fluid and disassembling the clutch, it was discovered that the snap ring that is meant to lock the drive plate to the clutch assembly had popped out entirely. This allowed the drive plate to turn and jam itself into the grooves where the clip is meant to sit.
Because the drive plate was not sitting properly, it had loosened off from the disc assemblies, letting off appropriate tension and badly wearing some of the clutch discs in the process. When installed, the drive plate is meant to have a specific amount of tension to ensure that the contact between the disc, steel plates and friction disc is adequate. If there is too much tension, the transmission will not shift well, getting hung up in gears. If there is not enough tension, slippage and engagement delay occurs.
Not only had the drive plate shifted, but the drum assembly had moved toward the inside of the bell housing on the transmission, causing wear on the transmission casing. When a clutch assembly is installed into a gearbox, there are a series of measurements that are taken in order to set the depth of the whole assembly on the input shaft. When set correctly, there should be a certain amount of clearance between it and the transmission. The failure of the snap ring clip eliminated any clearance that had been there, resulting in wear and minor damage.
Luckily, the owner of this Audi TT Quattro was attentive to the change in the shift pattern and diligently brought the vehicle in right away. When the DSG fluid filter was taken out, all the metal filings from the contact between the drive plate, clutch discs, and casing were caught in it and no major metallic content had remained in the transmission fluid. Had the owner ignored the symptoms and left this issue unchecked for much longer, metal filings would have, contaminated everything inside the transmission, and could have meant replacing the entire gearbox. Because of his quick action, our certified technician Craig was able to replace the parts that had prematurely worn from the rogue snap ring and reassemble the gearbox.
Although this is not a common failure for this type of transmission, there are some issues to keep an eye out for. One common problem is a faulty Mechatronic Control Unit. One symptom to be aware of when it comes to this is partial or full loss of getting your car into reverse. Faulty park/neutral switches are also common, which can result in a no-start issue.