Simon's new Xantia V6 and Leaf blog

[xantia_v6]

To throw in a left-field suggestion, all sorts of issues can arise with drum brakes if the wheel bearing has too much play.

[bobins]

If it were me, I'd definitely be looking to rub down the three raised posts 'til smooth with a bit of wet 'n' dry or similar and see what happens with the brakes then. The fact that they did work fine after you first reassembled them but then reverted back to being grabby would point to the fact the grease you originally put on the posts did its work until enough of it was rubbed off and they went back to being grabby. You only need a small bit of grease on the raised posts once you refit it all - a quarter to half a pea's worth on each post would be fine.

[RichardW]

I would take the paint off - you might find it's powder coated and it's harder than you think! It seems a really odd fault though - you wouldn't have thought it would suddenly lock up on constant pedal pressure if the shoes were moving - and it it did then the pedal would sink? But perhaps the whole shoe set is rotating around and pushing one piston in and the other out so there is no change on the pedal. Given that the drums are easy to get off, might be worth swapping side to side to see if the fault moves? I wonder if one of the drums is a bit oval...

[white exec]

Ovality should show up if the drum (wheel) is rotated by hand, with the brakes very slightly on.
Experimentally, you could also lessen the pull of the hold-back springs (eg use a rubber grommet in place of the spring) and see whether the jamming lessens.

I take it the shoe edge isn't able to fall off the crest of the ear, and get stuck?

[bobins]

The thing that I find a bit odd is that there is normally fairly restricted braking effort applied to rear brakes* so they shouldn't be in a position to be 'grabby' under normal conditions. I'm wondering if the fault is further up the system ?
*- light load, light to moderate braking effort.

[lexi]

Other perusals are: Sticky wheel cylinder. Aftermarket shoes that are not spot on with size or hole spacing for springs.

[Mandrake]

I would take the paint off - you might find it's powder coated and it's harder than you think! It seems a really odd fault though - you wouldn't have thought it would suddenly lock up on constant pedal pressure if the shoes were moving - and it it did then the pedal would sink? But perhaps the whole shoe set is rotating around and pushing one piston in and the other out so there is no change on the pedal. Given that the drums are easy to get off, might be worth swapping side to side to see if the fault moves? I wonder if one of the drums is a bit oval...

My thinking is that on a single cylinder system like this you have one trailing shoe and one leading shoe. The trailing shoe will never lock up as when it grips it tends to pull it back off again. However when the leading shoe starts gripping the rotation of the drum will cause it to bite in harder. Normally if they can move sideways as well to find a "neutral" position it should remain in balance and not lock up completely, however if one of the shoes is snagging on the back rests and can't slide freely sideways when you release the brake the leading shoe may be staying where it is instead of retracting, causing it to bite immediately.

It's not that it's grabbing unexpectedly with a constant pedal position - I am very gently increasing the pressure on the pedal and then suddenly wham, the wheel locks.

What I've also noticed last night is that it doesn't grab in reverse - I can roll backwards and apply the hand brake or footbrake normally and it works fine. Then roll forwards and touch the brake lightly and it tries to lock. Roll backwards again and it's fine. Also if I briefly pull the handbrake on hard a few times while accelerating, feeling it bite but not lock, it "fixes" the problem temporarily. The next dozen or so full stop applications of the brake seem normal, but then after a while it starts grabbing again.

Good idea on swapping the drums over - that is pretty easy to do, and would at least prove or disprove whether ovality was the cause. The only problem is it might take a few days for it to play up again before I'd know.

Ovality should show up if the drum (wheel) is rotated by hand, with the brakes very slightly on.
Experientally, you could also lessen the pull of the hold-back springs (eg use a rubber grommet in place of the spring) and see whether the jamming lessens.

Wouldn't that make it worse if the problem was one shoe couldn't retract fully when the brake is released ?

I take it the shoe edge isn't able to fall off the crest of the ear, and get stuck?

Not as far as I can see, no. It's pretty constrained where it can move. The only thing it might be getting stuck on that I can see is the backplate rests with the groove worn into them. It's primarily the top backresets - from memory the bottom one doesn't have any wear and the middle one has a slight amount - its the top two that seem to be worn right through to the metal as depicted.

The thing that I find a bit odd is that there is normally fairly restricted braking effort applied to rear brakes* so they shouldn't be in a position to be 'grabby' under normal conditions. I'm wondering if the fault is further up the system ?
*- light load, light to moderate braking effort.

I don't see how the fault is further up the system - I can reproduce the same problem with both foot brake and hand brake, so its definitely the rear, and of the two rear wheels its always the one on the left.

One other thing I've noticed is after reassembling the drums and manually setting the auto adjusters to where I thought they should be, they stayed put for an hour or two of driving and then fairly suddenly both auto adjusters at the rear have pulled themselves really tight. But I'm not sure what I can do about that - I can't stop the auto adjuster from adjusting! The auto adjuster mechanism itself seems fine and in perfect condition, but again I wonder if one shoe is snagging on the backplate whether that could cause the auto adjuster to over compensate.

[Mandrake]

Other perusals are: Sticky wheel cylinder. Aftermarket shoes that are not spot on with size or hole spacing for springs.

Both sides of the cylinder seem well lubricated and not sticky at all. No way to be sure they're not aftermarket shoes but I think it's highly unlikely the rear brakes have ever been touched on this car until now so I'd wager they're the original factory shoes.

[Mandrake]

The hold-back springs will pull the shoes towards the backplate, where (normally) one of two arrangements are designed:
- either one or more raised flat pads, which the shoe edges slide across (when the brakes are applied),

This is the system used in this car. The metal edge of the shoe sides rests on raised flat pads, three for each shoe, and the top pad for each shoes is gouged right through the paint to the metal.

Here's a dump of all the pictures I took when I had the drums apart, some of which I posted earlier, just so everyone is clear what we're talking about. Most were taken during disassembly so are before cleaning etc:

These are the top two raised sections which are the most badly scored back rests:

You can see all 6 backrests here with copper grease before reassembly:

This is a picture of one of the shoes after I had chamfered the ends:

That's all the pictures I have.

Before I disassembled them the shoes were not free to move sideways at the top with the drum removed - they were pretty stuck and seized. After cleaning everything, greasing the backplate support pads and putting everything back together they are able to move sideways at the top (cylinder) end relatively freely compared to before, but I can definitely still feel them "snagging" on a sharp edge as they slide across. I'm thinking (hoping) that this snagging when trying to move sideways is the underlying cause of the problem, especially when the problem comes and goes. (Maybe when you press the pedal hard it jumps onto the other side of the snag for a while)

I think sanding the pads back to a smooth flat surface is the only thing that will help but once I do that I can't undo it so I wanted to be sure I was on the right track. The only other thing I can think of is perhaps the edge of the shoe material snagging on a lump of rust on the drum edge itself - swapping the drums between sides might help prove or disprove that possibility.

[Mandrake]

Just came across a quote in this article:

http://www.brakebleeder.com/rear-brake- ... um-brakes/

Shoe Lands or Bosses

The shoe lands or “bosses” are an often overlooked item when looking for the cause of a rear wheel lockup condition. The shoe lands keep the brake shoes square with the drum and provide a friction surface for the shoes to move against. Over time the bosses can become grooved and corroded as in Figure 61.6. This grooving can allow the brake shoe to hang on either the apply or release of the brakes which can cause lockup. The shoe lands should be checked during the inspection and if rear brake service is performed they should be cleaned and lubed.

Quite what kind of "cleaning" they are talking about if they are grooved I'm not sure...I reckon it will take wire brushing!

They also echo Richards suggestion of trying swapping the drums for a one wheel lockup condition:

Brake Drum Condition

Brake drum condition should be factored in when determining the cause of rear wheel lockup. An out of round brake drum or drums that vary in diameter too much from side to side could cause a one wheel lockup condition (Figure 61.8). Measuring drum runout or out of roundness is not easy in the field. Current micrometers do not allow a repeatable measurement to be taken. Using the brake lathe and a dial indicator is only accurate if the lathe and adapters are in the proper condition. If you suspect the rear brake drum is causing the problem install it on the other side of the vehicle and test drive the vehicle. If the problem moves to the opposite side then you are on the right track, if not continue your quest.

[bobins]

Here's a dump of all the pictures I took when I had the drums apart, some of which I posted earlier, just so everyone is clear what we're talking about.

I am, quite literally, out in the field right now so have no reference material to hand, but.....

......second picture down : is that 100% guaranteed the correct routing for that spring ? It looks like it's connecting the shoe on one side to the adjuster mech on the other, is there a way it could connect shoe to shoe and miss out the adjuster mech ? As I say, I'm away from any good sources of reference material so what you've got may be the correct route.


Edit : Having got home and had a proper look at the photos on a grown-up computer, and referenced DocBackup, your spring routing is - indeed - correct. The spring on the 'outside' of the shoe goes from the shoe on one side to the mech on the other, whilst the spring 'behind' the shoe goes directly from shoe - shoe.

[white exec]

......second picture down : is that 100% guaranteed the correct routing for that spring ? It looks like it's connecting the shoe on one side to the adjuster mech on the other, is there a way it could connect shoe to shoe and miss out the adjuster mech ? As I say, I'm away from any good sources of reference material so what you've got may be the correct route.

Return (pull-off) springs normally link shoe-to-shoe.
In that picture, the RH end of the spring does seem to be pulling on the adjuster (or is it the handbrake lever?), but where it pulls is so close to the pivot that it will be pulling on the shoe as well, I guess. Perhaps that one spring is made to do two jobs: shoe return and handbrake relax.

Simon, a latest photo above does show six (copper-greased) pads.
I'm puzzled by this photo, though. Not sure what I'm seeing there. Looks almost as if a pad had been partly ripped away, and turned upwards. Can you clarify? I'm certain those pads should all be flat.

[bobins]

All finished, and pretty successful I think!

<much snippage>

I used normal lithium grease in the thread of the self adjuster, which was a bit gummed up with a dirt/dust/grease mixture. I also sanded the rusty lip off the inside edge of the drum where the edge of the lining would touch, and chamfered the trailing and leading edges of all the shoes slightly.

Put it all back together and adjusted the handbrake adjuster so that the hand brake started applying at 3 clicks and was on hard by 5.

Just to clarify from a previous post of yours - the book method of adjusting the shoes up is to put it all back together then....

C-zero rear brake adjustment - PSA, fair use

The notched wheel (at 13) that they refer to is what you, I think, refer to as the self adjuster.

[lexi]

The tilting of the shoes was an oft found thing on drums when problems of operation arose. If you tourniquet or cable tie the brake shoes in a circle, so that wheel pistons don't pop out, then get an assistant to gently press pedal with that drum off, as you press the shoes in, it may just give an indication of what is happening when it starts to operate. Maybe try a finger nail inside the drum for any raised wear or scores. If there is, a flap disc in a drill would feather it down even as you go round. I used to rub the drums inside with 120 grit to rough up( with new shoes anyway)
Adjusters normally fail for fun on the Jap drums like Honda, but it is usually that they don't keep up with wear and you have to turn them manually. Yours may be Akebono system, with it being Japanese derived car?
Ah well, no cause without reason, it will come to the fore in a Eureka moment! Weather is not playing ball mind you for rolling around on ground.

[CitroJim]

Adjusters normally fail for fun on the Jap drums like Honda

And, in my experience, on Pugs and Citroens of a certain age too... I used to have lots of 'fun' with them on various 205s and 206s...

Touch wood, the Saxo is OK...