rear suspension raises when braking

[graham1701d]

Hi,
I have recently bought a Citroen Xantia HDi. I have replaced the rear spheres. One of them was totally knackered because a great big squirt of LHM shot out of it when I took it off. Changed the spheres nice soft suspension. However since I have done that the rear suspension rises up when braking and makes the rear brakes bind slightly and then they back off slowly. Have I done something wrong? How can I fix? Thanks.

Regards Graham

[RichardW]

Likely there is gas in the rear brake circuit - give them a good bleed, and see if it improves things. Most likely origin is the rear anti-sphere leaking into the brake circuit, which you probably need to change as well....

[graham1701d]

I just thought it seemed strange it started doing it since I changed the spheres. It didn't do it before I did that. I thought I may have done something wrong in depressurising and repressurising the system.

I put the suspension in low. Let the car settle. Switch off. Open the bleed valve. Change spheres. Switch on put suspension in high. close bleed valve. Suspension up and down a few times. Now I have this problem. Thanks.

Regards Graham

[Hell Razor5543]

The problem is that, while the steering and suspension are circulatory, the brakes dead end at the callipers. This means that you could have air in them. Check the bleed nipples first, and if they look bad (crusty) you might want to get hold of some Plug Gas first, and then spray them daily for a week before attempting to loosen them (you don't want a bleed nipple snapping off!). If they look really bad you might want to get some replacements (but be aware that the front nipples are different to the rear ones), and pop a smear of grease onto the threads before fitting them.

Bleeding the brakes themselves are a doddle, and does not need an assistant.

[Old-Guy]

The problem is that, while the steering and suspension are circulatory, the brakes dead end at the callipers.

and as the brakes and suspension at each end share the same hydraulic circuit, the hydraulic pressure for the brakes comes from the suspension.

This means that you could have air in them. Check the bleed nipples first, and if they look bad (crusty) you might want to get hold of some Plug Gas first, and then spray them daily for a week before attempting to loosen them (you don't want a bleed nipple snapping off!). If they look really bad you might want to get some replacements (but be aware that the front nipples are different to the rear ones), and pop a smear of grease onto the threads before fitting them.

Bleeding the brakes themselves are a doddle, and does not need an assistant.

But as the rear brake lines go all the way from the rear height control to the doseur valve (operated by the brake pedal) and then back to the rear callipers, it's essential to bleed until clean new bright green flows from the bleed nipple. Reckon on around half-a-litre in total (more from the first calliper than from the second).

[Mandrake]

I just thought it seemed strange it started doing it since I changed the spheres. It didn't do it before I did that. I thought I may have done something wrong in depressurising and repressurising the system.

I put the suspension in low. Let the car settle. Switch off. Open the bleed valve. Change spheres. Switch on put suspension in high. close bleed valve. Suspension up and down a few times. Now I have this problem. Thanks.

Regards Graham

If the spheres were punctured (or almost so) you had no suspension travel in the rear suspension hence the rear couldn't rise under braking. What you didn't realise is the rear brakes weren't working properly either.

Now you've fixed the suspension so its nice and soft and has plenty of movement, this has now revealed the rear brakes aren't working properly. The trailing arms rely on the torque reaction of the rear brakes to compress the rear suspension under braking so if the rear brakes aren't working the rear rises under braking - simple as that.

Assuming the brakes are properly bled (try that first) it means you just need to give the rear brakes a good going over. Its common for the pads to rust to the caliper frame! I had the same problem as you - new spheres then the rear started hitting the top limit stops under braking. Two of the pads were rusted to the caliper and the pistons were all seized too.

Pads out, new pads if necessary, lubricate the pistons and work them back and forth a few times, refit, bleed the brakes and it will probably be fine. When the brakes are working efficiently the rear will not rise no matter how hard you brake, in fact it may squat slightly.

[graham1701d]

Thanks everyone. Rear brakes bled and all is well. Brake pipes aren't the best though. Next job clean and grease.

[Mandrake]

Glad to hear it. Take note of RichardW's comment though - if you didn't change the anti-sink sphere (the one with the pipe going directly into the sphere on the middle of the rear subframe) and it's nearly flat or is punctured it will gradually bubble nitrogen into the rear suspension that will find its way into the rear brakes causing them to need to be bled again. (and again)

On my Dad's Xantia we were having to bleed the rear brakes about once a month to keep them working properly until we were able to get that punctured sphere changed, it seemed to have a never ending supply of nitrogen to dump into the brakes, so if the rear brakes seem to need bleeding again soon that sphere needs changing!