Swirl Arm low cost repair!
 

Hi, I'm new to the forum and some this will help some of you! I have had the dreaded Swirl arm problem and many attempts at a repair left the parts so loose the the assembly only lasted a few miles before coming apart. I noticed the initial problem (broken link) was caused by the stepper motor being "overdriven" in order to calibrate the mechanism about every fifth time the engine was stopped. This is quite a common technique (I am an electronic engineer) for this type of arrangement. Anyway, the torque of the motor (when being overdriven) is sufficient to cause the linkage to break in time.
Once I understood this, I came up with the following solution, which has been rock solid for 6 months/10,000 miles.
(I hope the photo has uploaded OK)
Basically, I went to B+Q and got some right/angled aluminium extrusion and a rubber "foot" as a buffer. I cut a short length and drilled a hole in it so that the part could be fitted using one of the motor fixing points. I filed the hole so that it was a slot so that the position could be adjusted.
Next, I fitted the rubber foot as a buffer.
Finally, I fitted the part and adjusted it's position so that, when the calibration (overdrive) of the mechanism occurred, it used my part as a "bump-stop", instead of straining/breaking the mechanism. It is important the position is adjusted so that correct calibration is achieved, i.e. it stops the mechanism when fully extended, but JUST before it strains the arm.
No more trouble, simple to fit and costs only a couple of pounds.

Additional information
 

Forgot to mention - you can just see on photo that I fitted a small washer on the ball joint where the arm clicks in. This helped on an earlier repair attempt as it stops the arm rotating laterally when moving.

Swirl arm calibration
 

Hi Bic,

Very interesting to read your post, i noticed on my D5/185 that the arm at the swirl arm end had come off and although it was still attached to the motor/actuator end wasnt doing much !.. a bit of investigation revealed that one of the four tiny "clips" inside the socket thats on the engine side had broken, and it seems likely having read your post that its when it tries to calibrate the movement, pushing the link toward the front of the car fully, that it must have broken the socket end. I also noticed the first time I re attached the plastic linkage (with hand crafted bracket that holds the ball into the socket on the engine side) it moved the linkage over its full range before returning to normal position. I did wonder if this only happened if the link wasnt there, but perhaps as you say it does it once every number of cycles.

Does it rely on the resistance of when the link hits its end stop to detect its reached full travel? im guessing it must unless it has some other way of measuring the position, seems a bit crude either way, as the linkages dont seem to stand up to the strain.

Ive attached some pics of the linkage, it looks a bit different to the one in your pics, what year is yours? The elastic band in the pic is only to see if it would work before glueing the bracket in place ! (pics to follow)

How did you work out where to position the stop? having the link disconnected doesnt seem to throw up any fault codes, or perhaps it does but you cant see them?.

Hi.
The motor is known as a "stepper motor" and is driven by a series of voltage pulses or steps. The software in the system knows the position of the motor by applying a known number of voltage steps to the motor. In normal operation, the motor can "slip" i.e. the motor shaft position relative to the number of pulses can shift - hence the need to routinely re-calibrate.

This is done by applying enough steps to the motor to guarantee it will be in the end position, known as overdriving. The mechanism will mechanically stop the motor at the end of it's travel whilst voltage steps continue to be applied. This occurs at every 5th switch off of the engine.

Unfortunately, the torque of the motor eventually results in the mechanism breaking as a result of this calibration procedure. (Try holding the motor still during this process and you will see what I mean!)

The bump stop position is easy to set, just move the mechanism to the end of its travel by hand and set the stop in that position. My linkage is broken in the same way as yours but this fix has been fine for many months now and just works by taking the strain out of the system.

Someone on this forum took the idea and made a much better stop than mine (electronic engineers make rubbish mechanical designers!!), you should be able to find it if you do a search.

Hope this helps.

Bump Stop
 

Hi Bic,

Also read about a modified arm kit that volvo do, presumably this is a lot stronger and less likely to break? Apparently the actuator can be calibrated using the volvo computer thingy I wonder what this does ? as it sounds like it wants to calibrate itself every 5 switch off's.

Do you mean you can move the stepper "arm" manually without any damage? to see where to set the bump stop?

Did you find any messages come up on the dashboard, or any fault codes need resetting when the arm failed on yours?

Thanks for the info,, v useful :)

Hi,
I have not seen the modified arm, but in theory any stepper motor driven mechanisms can "slip", i.e. not move physically when a pulse is applied.

This is only really an issue when no additional position sensor is fitted.(The software controls the position of the arm by applying a known number of voltage "steps".)

A good example of the calibration procedure is on some modern speedos where the clocks travel to max as switch on, then return to zero. Looks very nice, but this is actually the stepper motor calibrating itself by overdriving the needle, in the same way that the swirl arm is calibrated.

My fix just uses a physical stop to hold the mechanism when being overdriven, rather than letting the arm take the strain. Provided the stop makes contact JUST before the mechanism runs out of travel, it is a perfectly good fix and will save the arm taking any more excessive stress, which causes it to break, in time.

For this reason, I would think that, even with a new arm, the software would still require routine re-calibration.

The issue seems to be that the motor is VERY (possibly too) powerful and, as I found, when you strengthen one part, it was a matter of time before the next weakest part in the mechanism broke! I was concerned that, in the end, I would have to strip part of the engine down to repair internal parts of the linkage. The idea behind the bump stop is to eliminate stress in the setup, and to date, this has worked well.(You could always combine a better linkage with the bump stop, if you want).

Hope this helps!

Sorry, forgot to tell you the error I got.

When the arm broke, I would get the message "Engine Service Required" on the DIM, usually under hi throttle/revs when accelerating. This would clear and re-appear, I guess depending on driving style and the position of the swirl flaps when the mechanism failed

Looks like ill need to try the mod kit
 

The fix i had come up with to hold the ball joint on the plastic link into the butterfly on the flap control end doesnt seem to be holding up too well ! even with a bump stop as bic suggested, it certainly takes a bashing when it decides to "calibrate" every 5th to 6th engine off.

So im going to have to try the mod kit that volvo do, im not entirely sure how it works but seems you have to drill a hole in the butterfly? has anyone else fitted this mod ? ive heard comments on here that it also might not last too long but im hoping it will (but then i might just be being over optimistic!)

Has anyone had to resort to stripping the linkage down to fix it should this not work?

P/N for the mod kit is 31293291 apparently

I am just about to fit the mod kit to replace a previous mod I did with a split pin. The part numbers required are 8692676 for a new Swirl Arm (£1.99) and 31293291 for a Pin and retaining washer (unbelievably £4.95). You will need to drill a whole through the Ball Joint on the new Swirl Arm large enough for the pin to pass through. There is already a hole started through the ball as supplied, so just pass the drill through this hole until it passes out through the top of the ball ( I did this by hand with a small 2 to 3 mm drill bit). The next bit is very tricky, you need to make a hole in the socket where the ball joint connects, on the arm under the oil filler. I used the same drill bit here, but heated the drill to red hot and used the heat to melt a hole as it is just about impossible to get to. This hole needs to be in the centre of the socket in order to pass the new pin through, the arm and then through the newly drilled ball on new swirl arm and then fit the washer that comes with the kit.

Hi Rob, Could you post a pocture of the modification please. Brian