Citroen XM Forum

As this is a Left Hand Drive car, the brake valve is not mounted under the scuttle and does not have the pivot mechanism that causes problems on RHD cars. The brake valve is mounted on the firewall below the LHM tank and is directly operated by the brake pedal.

Hi folks - still looking for help on this one I'm afraid.

Have been successful in sourcing 2 callipers (one from Germany and one from Holland!). They've been fitted.....but.....problem remains with squealing brakes.

Apart from being really cheesed off with mechanic for probably getting me to change 2 callipers that were ok (for a total cost including the parts of c. £400).......he says now that he thinks that it might have something to do with the front sphere which pressurises the brakes.
Could this be a possibility?
Although I am really passionate about my hydropneumatic cars, I don't know enough to know if this is possible.

Any ideas?

Squealing brakes are usually caused by either lots and lots of gentle braking (deliberate firm braking sometimes cures it), or by the brake pads not being properly 'acoustically coupled' to the heavy brake calipers.

Only fairly lightweight items are capable of high frequency vibration (eg squealing or ringing), because they have to move (vibrate) fast.
A large and heavy brake caliper cannot do this.

Coupling the brake pads to the caliper (so that they behave like one big heavy mass) is achieved by the anti-squeal shims between the pad and the caliper, and by making sure that the contact surfaces of both pads and shims are smear-coated with a heavy copper grease.

Front brakes on XM are not known for squealing. Rear brakes (which do very little work on these cars) can squeal, when hot after lots of light braking.

The front spheres will have absolutely no effect on the front brakes.
Some types of after-market pads can be prone to squeal, but copper grease normally shuts them up.
If the front discs are heavily polished (mirror-like), this doesn't help; some deliberately heavy braking is normally enough to deglaze them.

I’ve just taken the hub/disc/calliper assemblies off my V6 and the brakes didn’t squeal. Car is being broken after failing its MOT earlier this month. If they’re any use to you drop me a PM.

Cheers

Marc

My suggestion would be to fit a new set of brake pads of known quality brand.

I presume that the bakes we are talking about here are the 283 mm version?

Were the old calipers actually seized? I suspect not.
Brake squeal is the interface between the friction material and disk causing a resonant frequency, which the pad backing, caliper body and disk then vibrate to.

Most new pads have chamfered edges and rubberised backing to stop this, but sometimes the makup of the friction material still encourages it.
The traditional fix was/is to use copper grease on the back of the pad and caliper contact points.
Obviously don't get any grease on the friction surface, or disk.

The sphere can't have any effect on brake squeal.

Time to start DIYing your car servicing.

It would be worth checking the caliper slide bolts aren't worn, allowing movement.

Caliper slide bolts should be well greased (standard grease, not copper) - also helps the acoustic coupling.

Hello again folks. So. It would appear that the problem has been resolved by Salters Garage.

On my first visit there, in addition to loosening bleed nipple, they thought that the near side front brake was seized and replaced the 'new' calliper with the 'old' one that was still in the boot and thought that brakes were no longer binding - note - no real road test of vehicle at this stage. When examining car they say that handbrake not operating on off side front wheel - cable disconnected on pedal yoke so this was also fixed.

However,
On my drive home after about 15 miles squealing brakes again.

Booked in for the week after....

Just collected my car again just now from Salters after explaining (again) nature of the problem and requesting that they field test car to diagnose problem as it appears to only happen at temp before they give it back to me again.

The rear brakes were squealing at 10+ miles - they cleaned and de-glazed them. LHM getting too thin at temp and pushing past doseur internals causing light braking to be applied. They sampled LHM fluid and the flow/return filters and saw they were dirty. They cleaned filters and reservoir, flushed system with Hydraurincage (1 unit £49.80), flushed/clean doseur and filled with fresh LHM. Have just driven 30 miles from garage this morning and all seems to be ok. Fuel consumption looks better than before, no squealing approaching lights and no tell-tell catching of brakes on drive off.

Hopefully this is it.

Thought I'd let you know how it went.
Thanks for all your help - this is a great resource

Maybe. Hopefully.

JFI, Hydraurincage is NOT meant as a "quick clean", but for the car to run on it for 1500-5000km (3000 miles). It effects a very gradual cleaning action on the internals. Shame they couldn't have left it in, especially as it wasn't cheap.

If the garage actually stripped and cleaned the doseur valve that has probably fixed this issue.
I suspect the valve was sticking and not allowing fluid to return to the reservoir, thus binding the brakes.

It seems strange that they didn't leave the Hydrarincage in the system.
You could always recover the fresh Lhm, fill with Hydrarincage then change back to Lhm again in 3000 miles time.