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A look at the Dual Clutch Gearbox

This manual transmission will send even the most experienced techs looking for a refresher course.
Monday, June 30, 2014 - 07:00
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There is an approximate two-by-one-inch gap in the clutch housing to allow air to enter for cooling. But it has proven to be insufficient as clutch temperatures can reach as high as 392°F, resulting in the upper layer of the clutch lining to glaze causing the judder. They usually see failures as low as 13,000 miles to a maximum of 62,000 miles with gas powered vehicles. In an attempt to improve the life, the dry clutch assembly has undergone six different design changes. These encompassed design changes from the clutch arm to the friction material.

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Due to the assembly design of the dry clutch, this transmission is inherently noisy. When you are driving on a bad or bumpy road with the windows down, you can hear what sound like pieces of metal in an empty paint bucket echoing off the passing houses. Some of these noises can be attributed to loose internal mechanical end play clearances causing shift levers to hit the gearbox casing. Other issues causing this noise can be play in the flywheel and play in the dampening springs in the clutch (which are identical to what you would find in a manual gearbox clutch assembly).

FIGURES 4-6

Damage to these parts increases the noise especially when traveling in seventh gear; engine rpm can be as low as 1,150 rpm making it just right for it to rattle. A slight change in the programming that TVS offers alters the rpm by increasing it to 1,400, which is enough to eliminate this vibration spot. Curing this under rpm problem not only assists is lengthening the life of the clutch, it also improves the performance of the vehicle. Additionally, they changed clutch pressure control and eliminated the 2nd gear hold bringing the transmission down into first when it should make the downshift. All of this is designed to alleviate premature failure of this easily overheated dry clutch assembly.   

This DQ200 also experiences bearing failure causing the gearbox to wear producing excessive metal (Figure 7). The magnets used as shift fork position sensors begin to attract this metal. If there seems to be about 15 mm of buildup, VW recommends a new transmission as changing these bearings may not produce the desired repair (Figures 8 and 9).

The DQ250 on the other hand does not seem to experience the same frequency of bearing failures. TVS builds about 1,000 of these transmissions in a year and they might see as many as five of them with bearing failures. The complaint they do experience frequently with this transmission is that the shifts get clunky due to synchromesh ring wear. This is a tough problem to deal with due to the fact that these synchros are not sold separately. In fact even rebuilding one of these transmissions can be challenging. More times than not you have clunk issues with Drive and Reverse engagements.

The double wet clutch drum assembly can be a troublesome area as well. It is known to develop a shudder on acceleration from as early as 2nd gear on up through the gears. It comes in at around 2,000 rpms when the turbo kicks in at max torque. It is the type of shudder that can feel like a fuel or injector problem. Changing the complete clutch assembly in some cases resolve this problem while reprogramming the computer with a modified slip program has a higher ratio of success reducing future failure.

Ronald made a point to say that though one might have 20, 30 or 40 years experience working on manually shifted transmissions, working on these automatically shifted manual gear boxes is a whole new experience.

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