The Haldex diff is the first of the rear diffs. It’s the one that the prop shaft connects to. Internally, it’s a series of plates in “oil”. And there’s a small filter inside. Originally Saab claimed it was sealed for life.
However, it soon became clear that after around 50,000 miles it stopped working correctly and the take-up of the drive would get clunky. The Saab fix was to replace the whole unit at a cost of £3,500, plus labour.
Outside of the Saab franchises, independents developed a service procedure. Then Saab offered a “service kit”. With a recommended service interval of 35,000 miles.
The service is straightforward, if fiddly. The side cover of the unit is removed (I’m not sure if it can be drained first) and the inside cleaned of all the sludge that’s formed of worn bits from the internal clutch plates. The filter is also changed. The cover is refitted with a new gasket, and the unit filled with fluid.
The fiddly bits are that you may need to lower and hang the exhaust out of the way a bit, and that filling with fluid needs two or three goes. Fill until it reaches the hole in the side. Run the car around the block to get the fluid to all the places it should go. Undo the plug and top up. Run the car again around the block. Come back and add another 10 to 15ml of fluid through the vent pipe on the top of the diff. If you don’t, it’s almost certain that, about 10 miles down the road, you will get a “bing bong” and a message on the dash saying “XWD failure. Contact service”, or similar.
The symptom we had in the Carlsson the first time it was serviced was a jerk at takeoff from a standing start when warm. Most noticeable on a Sunday evening in the stop-start traffic jam on the M25 after a run up the M3 from a visit to the grandchildren in Southampton. The road surface was smooth, but when trickling along at 1 or 2 mph, the rear jerked slightly when you touched the accelerator to go faster. It felt like it does when you drive over a joint in a concrete road. The service cured it, but it was in the early days, and I had to go back to get the 10ml top-up.
You can also get judder from a Haldex when reversing uphill around a corner. This is another sign of the need for a service.
I got the Haldex service done this time as I had just started to feel the odd “clunk” and recognised the symptoms. I didn’t want to find it became a real problem when we go to IntSaab in the Alps in August.
The small filter and gasket set is available at a typical SaabParts “finger in the air” price, as is the special Haldex fluid, which is rumoured to be derived from unicorn pee. No doubt available outside the SaabParts supply chain, but because of the warranties, etc. my guy will, quite reasonably, only use official parts.
