Binding Brakes And Pad Fitting

Been done a load of times before, I know -- but as I've just been through the mill again, thought I'd post for the benefit of anyone recently got their XM. Most of my XMs have wound up with binding front brakes at some point before I've been around them and on mine it's always been either cars with previous lack of use (don't suffer that once I have them !) or the cable clip on the lower retaining pin. As you withdraw the lower pin that keeps the caliper fastened down, you will notice it passes through a clip on the bottom of the caliper casting, apparently there to hold the pad wear wire. In my experience, this clip is the troublemaker, causing the pin to bind and I now always remove it. There are other causes for binding posted elsewhere on the forum if this one doesn't fit your bill.
If it's your first time at the pads, you have to wind the pistons in (clockwise) using either a proprietary tool or a square shaft of some sort. If very stiff, try opening the bleed nipple (engine off). Then, when you come to fit the new pads, be aware that two of the new pads will have a small lug on the rear face. These are used on the piston side of the caliper and the piston must be aligned such that one of the four cut - outs passes over the lug as the caliper is lowered down. Before you raise the caliper at the start of the job you need to unhook the hand brake cable at each caliper and withdraw the end of the outer cable slightly from the caliper body. Take as much care as possible to keep some tension on the inner cable, otherwise it may jump out at the underbody end and is then a considerable extra fiddle to replace. Once it's all back together and before replacing the wheel confirm the 'hand'brake is working correctly. If it has jumped out underneath, the pedal will hit the deck and the lever on the caliper won't move. Might sound grim, but once you have the hang of changing them it's only a 10 minute a side job. Enjoy !


MIke.

Hi Mike,

Sound advice there. The first time I changed them on the S2 it took me ages, but I did it again there in September and was finished in 40 minutes. Mind you, the first time round I did change both parking brake cables, as well as plug in and route all the pad wear wires etc, and I also managed to avoid pushing the parking brake cables out of the equalizer under the car when finishing up!
The next time, I had the pads done and pistons wound in very quickly, (thanks to my little cutting of square bar I kept after the agonising struggle last time) , but managed to dislocate the driver's side cable!

Speaking of the parking brake cable, this will sound like a very stupid question, but how do you manage to feed it through the hole in the upper caliper with its little rubber protecting grommet intact? I ended up cutting part of the end of the rubber off (stupid I know), because I just couldn't get it through the hole with the rubber bunched around it. Just more brute force needed perhaps?

Ciarán

Yea tricky, but if you pull the inner cable fully out of the outer cable it should pull out far enough to lengthen the grommet to squeeze through the hole ... otherwise its a fiddly job working it through in a circular motion.. if you can understand what I mean..

I managed to unhook the cables at the equaliser end on BOTH sides on a car once, HOW annoying..

I Really do HATE the wind-in callipers.. Why cant they be simple push back format!

Rgds
citroenxm

Hi all,
Useful bit of revision, must try omitting the springy metal clip as per onthecut and see if it helps even up the pad wear.
Two points on the parking brake cable:

1. at the lever am end under the console, any slackness in the inner cables usually causes them to spring out of their slots in the pivot arm. This can be prevented by securing a loose loop of wire around the two inners so they are restrained from moving apart but are free to slide to and fro. That way the cable ends stay within the holes in the pivot and reseat correctly when tension is restored. I leave it there permanently.

2.Feeding the rubber covers through the hole at the caliper end is made a lot easier by a liberal dose of silicone grease/spray. Line it up as straight as possible and use a narrow blunt strip of steel or stiff plastic to poke the rubber into the hole a bit at a time. (Simply pushing at it causes the rubber to bunch up and jam in the hole.) Soon as it appears at the other end use a long nose pliers to gently pull and ease it through.

Robert

Something I forgot to ask:
The rubber bellows/boot that covers the upper rod the half caliper slides on is missing on one of my calipers. Anyone know if these are available seperately as they don't seem to be included in any of the seal/repair kits and I don't see them on the parts microfiche.

Robert

Hi Robert.

I may well be misinterpreting the slide, but if you have the fiche see if you think they are included within item 9 on the caliper page. Described as 'Set Column Screw' , part number RP 4448 68.

Mike.

Hi Mike,
I had a look at the items you referred to in 9 and they are also in kits illustration 6 and 7 above that. However they seem very different in form to the rubber bellows on the caliper unless poorly drawn. I may have this all wrong but I think the items shown are the metal seals that are fitted to the caliper at eitherend of the column screw. A short rubber tube projects from each seal and I thought the bellows spanned the gap between, perhaps glued on. Still, I can see no reason to omit the bellows even if it is a universal component. Wonder if anyone has fitted one of the kits and can resolve the matter.

Robert.

I have the remains of a calliper repair kit in my garage which may have the piece(s) you want. Let me know your needs - there is no call to buy the whole kit.

Hi techmanagain,
Thanks for the offer. My problem is in identifying the rubber "boots" on the microfiche from my recollection of what is missing on the caliper, they dont look like what I expected. I refer to the two items on the right of illustration 9 page 794, also included in two other kits on the page it seems.
I will be changing the pads soon and will investigate in more detail and report back.
Robert.

I would have thought you were referring to Item 6 on Page 794. No doubt we shall both know in all good time!

one mod I've done is to add springs to the cable behind the actuator lever on the caliper. Halfrauds were selling off odd brake bits so I paid 50p for a bag that had a few springs in.

on each side, I slipped 2 springs (to make up reqd lengh) over the end of the cable (suitable size to slip over the little gaiter) and re-attached to the arm. Now the pad wear is even on both/both sides, so seems to help the problem of the cable causing the caliper to drag against the disc and hence wear on pad in the pair quicker.

regards
Dave

Hi Dave.

Interesting mod. I've always thought the lever arm seems pretty well sprung itself, but I can see on a little used car where the cables may have suffered water ingress and corrosion it could help to overcome the tendency to stick.
One thing I always do is ensure the cables are not over adjusted --- I set them on full lock with the cable at maximum stretch and I tend to leave a bit of slack even then. It's noticeable how you can set them so the handbrake bites anywhere from having the pedal so high your knee is under your chin, to pretty much on the floor. I reckon having a bit of travel helps keep the inner cable free (obviously not to the extent of compromising the function of the brake, of course).

Mike.

Hi all,

Not wanting to appear controversial but I've always been of the opinion that the return spring mechanism is very poor and undersized given the amount of work it has to do.

The spring hidden behind the big rubber boot on the caliper is a torsion spring made from approx 3mm diameter spring steel. The radius of the lever its attached to is only 10mm at best. To get any torque at that small radius needs a large force or conversely with only a given amount of torque available it only produces a small amount of tension in the operating cable.

Think of the work that spring must do. When you release the parking brake it must pull the inner cable through the sheath from both wheels back from the compensator in the centre of the car underneath next to the exhaust. It must then pull on the centre rod of the compensator and rotate the pivot. The lever on the other side of the pivot must then pull on the inner cable of the common cable which goes back through the bulkhead to the pedal box. The inner cable then pulls on the parking brake pedal on the opposite side of the pivot from the pedal itself and the pedal itself is raised against gravity. The pedal length is not inconsiderable compared to the lever length with a ratio of about 4:1. The pivots all the way from the pedal to the caliper are all geared to provide maximum mechanical advantage to your foot and leg when applying the brake. This obviously works in reverse when pulling from the caliper end. Now the caliper spring is fighting against all those pivots at a mechanical disadvantage. Each pivot represents a frictional resistance and each inner cable sliding inside its sheath provides more frictional resistance. As the wheel and of each cable is subject to road salt and water it rusts and frays the end resulting in even more resistance.

In order for the self adjusting mechanism in side the caliper to work properly the actuation arm MUST return COMPLETELY back to its stop. Only then with the coarse threaded internal screw turn to take up the slack. In order to get back to its stop that very inadequate torsion spring must overcome all those cable resistances, pivot resistances and raise the pedal against gravity. Thats a tall order and the fact that it does so at all is luck rather than good engineering. As things corrode and become stickier the spring is simply not man enough and two things happen; the parking brake drags when driving quickly wearing down your pads and decreasing your mpg and the parking brake doesn't adjust properly resulting in the car rolling down the hill when you park it.

Dave's suggestion of the additional spring to help the one in the caliper is an excellent idea. So good in fact I'll be looking at this tonight. My parking brake is atrocious so I have to leave it in gear when I'm parked.

Cheers

noz

must say I can't take total credit to the idea - was suggested by Lez a good while back as a mod that might help the uneven wear.

As I was near to changing the pads, thought I'd give it a shot and it hasn't done any harm. Only possible negative could be that the brake would release quicker than before perhaps, so you lose a little of the advantage of a sliding caliper when releasing the brake on a hill, where a slight drag helps ease the hill start (for us manual box drivers that is).

regards
Dave

I don't presume to your level of expertise Noz, but I have to say the parking brake is one area (excepting obviously naff cables) that I've never had any bother with. Without wishing to sound insulting are you sure you haven't got one cable seized off, leaving the parking brake just on one caliper ? Unless a cable has given out, I've never had one as bad as you describe.

Mike.