dvs_dave

A hopefully definitive fix for this well known and annoying issue on the 04-08 A8 D3's before they brought out a revised motor unit.

This fix tackles the problem at it's root cause; the electromagnetic clutch in the trunk motor assembly wearing out so it slips and is no longer able to transmit sufficient torque to open the trunk lid. My unit had become so weak that it couldn't even close the trunk!

There are various other fixes out there involving extra springs, solder flux paste, and a few others, however none of them were satisfactory or worked for me .

To fix a worn clutch you replace the friction material. A replacement clutch part is not available so I had to figure out a way of increasing the torque capacity of the existing unit's worn out clutch.

The solution lay in the form of a 5" 120 grit sticky backed sanding disc (pack of 5 less than $3 from Home Depot). A sanding disc is essentially very high friction and robust, friction material.


5" 120 grit sticky backed sanding discs



You have to remove and disassemble the trunk motor to get to the clutch plate (plenty of info out there on the web on how to do that) which is the part shown below.


A8 D3 Trunk motor clutch plate

Trim the sanding disc so that it fits flat inside the clutch plate.


Trimmed to size sanding disc

Peel the sticky back off the disc and then stick it onto the clutch plate.




Clutch plate with new friction material stuck on.

Reassemble the motor mechanism, re-install it in the car and you're done. Your trunk will now open and close at the touch of a button as though it were new!

Disclaimer: this is for information only and you choose to do this at your own risk. I accept no responsibility and cannot to be held liable for any losses or damages as a result of you carrying this out etc etc.

ltooz_a6_a8_q7

is struggling again, great idea, let's see how long this will last. I just bought some solid pine colophony resin to put between the friction plate.
The sand disk is working very well? The particles on the sand disc will wear off in no time and only paper left. Every time we open, the disc will slip and catch.

Cheers,

Louis

dvs_dave

2+ weeks now as I wanted to test its durability before putting it up. There is no indication of any clutch slip (no sound) and a sanding disk is pretty durable in nature. Time will tell in the long run but so far so good.

ltooz_a6_a8_q7

I think your fix is great. I'll try it when I have time. Hate to see the trunk is trying and the wife doesn't want to spend $500 for a new and hefty one. You don't miss it if never had it, but now, I do like the trunk lifted with the remote.

Cheers,

Louis

aTOMic

Haha love it! What made you choose 120 grit?
If I may suggest an improvement (as resident abrasives expert) it would be non-slip tape. It is designed to NOT wear out. It looks like sandpaper and Lowe's/HomoDepot have it.

Sandpaper/discs/belts are designed to remove material and shed the abrasive as it becomes dull on its exposed edge. Neither sounds like what we want to occur here. Especially the cheap no-name discs will wear out quickly and you'll have a coating of abrasive grit everywhere there is grease or static.

There is also friction material farm supply stores carry to cut-to-fit for making your own clutch/brake linings which would probably be the optimal solution, but I think that's too far from your original suggestion. Don't think it comes in 120 grit haha seriously it'd probably be too smooth for this.
HTH
Tom

ltooz_a6_a8_q7

the non slip tape.

Thanks for the tip,

Louis

dvs_dave

I chose 120 grit as of the range available in the store my calibrated finger told me that 80 grit was too course, and 180 grit was too fine.

I like the friction tape idea although can you get it in 5" wide rolls? If not then you're going to have to have a tape join on the clutch plate which may be problematic?

mishar

If problem is friction, which I doubt, you can have those surfaces sandblasted.

dvs_dave

What makes you think friction/diminished clutch torque capacity isn't the issue? To me it's clear that it is as when the friction coefficient of the worn clutch is modified, the motor works again as intended. There is nothing else in the mechanism to allow the mode of failure we see (gradual performance degradation as clutch wears out).

As an aside, before the sanding disc insertion, I did sand the face of the clutch faces to see if that would work. The motor was then able to close the trunk but it still couldn't open it.

mishar

My experience with that actuator, not necessarily same as yours, is that motor was not strong enough. I couldn't hear any clutch slip. Just motor dying. I believe Audi engineers came to the same conclusion and designed new actuator with much bigger motor. I didn't open it to see if the clutch is different.

Your case is obviously different if it couldn't even close the lid.