Brake imbalance Xantia 1995

[nh51]

I have had the following MOT failures;

1) Nearside front parking brake recording little or no effort

2) Front brakes imbalanced (39%)

After being assured by the garage that a new front passenger side caliper would sort out the problem I fitted one (bought from a scrapyard - it does work).

The old caliper was definitely jiggered it was a very stutturing movement to pull/push the two sides of the caliper apart/together when removed.

After fitting the caliper and bleeding the brakes i submitted the beast for a retest, failing again but ONLY the brake imbalance; handbrake is now fine.

Any ideas? I am sure the caliper is fine mechanically otherwise the handbrake would still not work.

Any ideas will be greatly appreciated!!

[DickieG]

What condition are the pads and discs in?

[nh51]

they seem to be OK - I checked both discs and pads about 3 months ago and they seem evenly worn, and obviously passenger side when changing caliper but will do another check.

Could it be pad positioning? Copper grease job?

[DickieG]

Check the inside surface of the discs as they suffer rusting far more than the outside. It'll be worth removing the pads and cleaning the surfaces where the pad touches the caliper and checking that the caliper slides easily across the disc. What side is under performing?

[nh51]

Passenger side underperforming. Results of brake tests as follows (from retest)

Left (kgf)

179

Right

265

Imbalance

37%

[addo]

Teeing into the brake lines for a pressure gauge, might shed a bit of light.

You do know the caliper piston is a right hand helical thread?

[nh51]

Yep, there doesn't seem to be any undue difficulty winding the piston back in. The lever arm section seems fine and smooth (unlike the old one).

[addo]

If it's an ABS car, are the sensors all working correctly, or has the system been hoodwinked to cover a deficiency?

First thing I'd be doing, is bleeding it all again really thoroughly with the wheels on the ground.

As a side note, I renewed my front flexes last year as they seemed to be getting on a bit (1999 car). Yours might be further deteriorated, but I am yet to see an LHM flex hose form internal blockages like a DOT4 flex hose.

[nh51]

Pretty sure the hoses are old but ok - certainly no blockages, nearly had a green bath when my assistant pressed on the brake gently during bleeding.

[handyman]

Did you replace the caliper with the same type? There are two diifferent sizes of piston, 54mm amd 57mm. I would also suggest getting the brakes vacuum bleed as there is an air pocket that gets trapped in the calipers.

Handyman

[nh51]

thanks for all the replies, greatly appreciated and keep them coming!

Sounds like I might have to bleed the entire system?

[DickieG]

I would also suggest getting the brakes vacuum bleed as there is an air pocket that gets trapped in the calipers.

Is that likely with the pressure that a Hydropneumatic Citroen produces in the braking system? I'd have thought that bleeding the system in a closed loop back to the reservoir with the nipples wide open would remove any air in a Xantia system. I've never heard of anyone coming across a problem with air pockets in a Xantia at the front, rear maybe but again using a closed loop sorts those out in my experience.

[Derekofpriory]

Hi all, no-one has mentioned it yet but are the pads bedded into the discs, a few sessions of heavy braking should guarantee full contact between pad and disc, only if both sides have equal contact area and pressure will the brakes be balanced.
Derek B.