The front brakes are normally bled first then rears but on my car I had a lot of trapped air in rear hydraulics after replacing steering rack and disconnecting pipes and entire accumulator and regulator. It doesn't hurt to bleed entire system anyway and it's good practice to bleed brakes/clean up calipers and slides whenever pads are changed - especially rears as the brakes are particularly biased to the front on Xantias which is why the rear calipers and discs/pads can rust and seize up quite easily if the car doesn't tow or carry any loads. The bleed sequence is LH front, RH front then LH rear, then RH rear.
I forgot to carry out the classic Citerobics first to fully prime the hydraulics after the rebuild and the rears didn't bleed at all. :-[So fully cycle the suspension from service hi to low at least five times before bleeding. Haynes say bleed fronts first. On a 'normal' car you bleed the brake furthest from the master cyclinder which should be the rear. On the Xantia you do fronts first then the rears. I did the rears first simply because the MOT said the fronts were excellent but low on rears and since I couldn't get any LHM to bleed I attacked this end first.
1) Carry out citerobics - five times should be ample
2) Put in service hi setting
3) Loosen rear wheel bolts
4) Jack up and support on axle stands (photo to follow)
5) Remove rear wheels
6) Place scissor jack under both rear arms. USE CAUTION. I use a section of rubber floor mat to protect arm. The jack is only to apply some upward pressure to allow rear height compensator to flow LHM under pressure into calipers. Older and/or high mileage Xantias will be easier to bleed using this method. Sometimes you only need to put in service high and then bleed.
7) Clean around bleed nipple with wire brush and apply some plusgas to threads especially if bleed nipples haven't been touched in a long time. Put some clear pvc pipe (from DIY stores, Aquarium/pond suppliers etc) over nipple and make sure you have container to catch fluid.
Start up engine - allow to idle. Place section of wood or similar to keep the brake pedal pushed down.
9) Open bleed nipple half a turn and watch LHM fluid flow out. Should be bubble free. Nip up the nipple and remove clear pipe. Put cloth or tissue around to prevent spills. Do the same with other side. It does help to have two scissor jacks as both rear suspension arms have to have pressure on them at the same time. Release brake pedal, switch off engine. (car will still be in service high mode)
10) Get ready to bleed the front brakes. Loosen front wheel bolts, raise car using trolley jack under front cross-member that lies just behind rear of sump. Support on axle stands then remove front wheels.
11) Start engine again, wedge brake pedal then put clear pipe over nipples. Undo half a turn and make sure fluid flows out. When bubble free, tighten up bleed nipple then do opposite side.
12) Put wheels back on, gently lower car to ground just in case front suspension sinks/drops which can happen on older high mileage Xantias with weak pumps/knackered accumulators/regulators)
Make sure the big red stop lamp has gone out then check LHM levels with car still in service high mode. If okay, put car in normal ride height and test car brakes. Brakes need about 100 miles to bed in so no heavy braking.
I actually prefer to work on an XM as the bigger car generally means more space to get to various components.
Next stop sorting air-con out. I've got leaky gas refill ports.