Xantia Front Disc Thicknesses

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Kowalski
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Xantia Front Disc Thicknesses

Post by Kowalski »

Does anybody know off the top of their heads what the minimum thicknesses for pads and discs on the front of a Xantia should be?

The car in question has the 283mm estate / 16v front discs, i.e. the ones that the parts catalogues say it shouldn't have. The Haynes manual I have (first edition) only covers the 266mm discs and the bigger discs are thicker.
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Post by Kowalski »

I've had a bit of a search about the forum and 22mm seems to be the new thickness, I'm guessing minimum would be something like 20 but I would really like the exact figure. It was stamped into the rim of my discs but there has been a bit of corrosion since manufacture and it isn't there any more.
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Post by JohnT »

The correct info is 20.4 and minimum is 18.5.
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Post by JohnT »

That is for a Xantia 1993-98 all models.
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Post by Kowalski »

JohnT wrote:The correct info is 20.4 and minimum is 18.5.
Thats correct for the 266mm discs, the one my car is supposed to have but doesn't. My car has the 283mm discs which the estate and 16v petrol models are supposed to have. I've found the figures of 22mm new and 20mm minimum for the thicker 283mm discs, these are round figures, I remember that the numbers stamped into the edge of the discs were approximately similar but not round numbers.

In any case, I've got rather more thickness than the 20.4, more like 21.5, I'm off to measure them properly with the micrometer...
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Post by Mandrake »

I've got the original Citroen data for the discs up to '98, and for the larger 283mm discs, it still depends on the model -

Saloon - 16V, 2.0i 16V, 1.9TD - maximum 22mm, minimum 20mm
Saloon - Turbo CT, 2.1TD - maximum 26mm, minimum 24mm

Estate - 1.8i, 2.0i, 2.0i 16V, 1.9TD - maximum 22mm, minimum 20mm
Estate - Turbo CT - maximum 26mm, minimum 24mm

Maximum runout for all 283mm discs is 0.05mm and maximum thickness variation is 0.01mm

JohnT's figures of 20.4mm and 18.4mm are correct for 266mm discs.

The figures for estate pads are maximum thickness 11mm, minimum 2mm, and height 55mm. I have the other pad figures if anyone needs them...

Hope that helps.

Regards,
Simon
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Post by Kowalski »

I've measured my discs now, they're 21.08mm thick. The discs have done 37k miles since new, as have the pads which didn't get down to minimum thickness even after that mileage.

My front left brake had been a bit noisy but only at certain speeds, I thought it may have been because of pad wear or sticking slides but as it turns out the pads had rusted and weren't very free in the caliper. I've replaced the pads even though there was a bit of life left in them since I didn't fancy taking the whole lot apart again to replace pads in a couple of months.

Just to contradict what you've posted about the disc sizes Mandrake, my '94 Xantia TD has the 266mm discs where as the '97 TD has 283mm discs, both of them are phase I hatchbacks with anti-sink, the second one does have ABS that the older car doesn't. Whenever I've gone for brake parts for the later car, I've usually been offered the smaller disc size and had to specifically ask for the larger ones, in fact all of the specs I've seen for the TD say it has 266mm discs. Somebody did mention on here about late pre-facelift cars getting larger brakes a while ago but there didn't seem to be any good reason for it.
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Post by Dave Burns »

All the brake info you require.

http://am.brembo.com/

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Post by Mandrake »

Kowalski wrote:I've measured my discs now, they're 21.08mm thick. The discs have done 37k miles since new, as have the pads which didn't get down to minimum thickness even after that mileage.
So most likely they are the ones that are 22 max, 20 min, and are still fine...
Just to contradict what you've posted about the disc sizes Mandrake, my '94 Xantia TD has the 266mm discs where as the '97 TD has 283mm discs, both of them are phase I hatchbacks with anti-sink, the second one does have ABS that the older car doesn't. Whenever I've gone for brake parts for the later car, I've usually been offered the smaller disc size and had to specifically ask for the larger ones, in fact all of the specs I've seen for the TD say it has 266mm discs. Somebody did mention on here about late pre-facelift cars getting larger brakes a while ago but there didn't seem to be any good reason for it.
Ok, I've just had another look at the data I have - the figures I quoted all came from one of the update "supplements" for later years. (which usually, but seemingly not always include the older data too)

When I look at the original book, dated February 1995, it does indeed say the 1.9TD uses 266mm discs, while the later supplement dated November 1995 says the 1.9TD uses 283mm discs, so it looks like the changeover point is in 1995 some time.

Before 1995 only the 16v petrol has the 283mm discs.

Doesn't seem to be related to the facelift changes at all....just one of the many things they changed during the run of the model.

Regards,
Simon
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Post by JohnCKL »

If we're to improve braking power, how much improvement we get if we swap the 266 with 288 disks? Besides different calipers, what else need to be modified?
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Post by Kowalski »

JohnCKL wrote:If we're to improve braking power, how much improvement we get if we swap the 266 with 288 disks? Besides different calipers, what else need to be modified?
Braking power isnt affected by changing the size of the discs, the smaller brakes will easily lock the wheels. What is affected is that the bigger discs are able to get rid of more heat and do more braking before they get too hot and stop working.

As far as I'm aware there isn't a different doseur valve for each size of discs, so the calipers, pads and discs are all that need changing. No doubt somebody who knows better will be able to confirm that.
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Post by JohnT »

Not sure if I follow that bigger disks and pads will not create more breaking?
The greater the surface area if accompanied by relative force will result in increased braking power?
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Post by Mandrake »

JohnT wrote:Not sure if I follow that bigger disks and pads will not create more breaking?
The greater the surface area if accompanied by relative force will result in increased braking power?
Thats true - but braking is ultimately limited by the tyre grip, and if the smaller discs and pads can already - with the ABS disabled - lock the wheels on dry tarmac (which they easily can) then it follows that the larger discs wont let you stop any faster.

But they will be able to dissipate heat better which means much less chance of fading with prolonged or repeated use of heavy braking. It also probably means longer pad and disc life.

Regards,
Simon
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Post by zzf00l »

Just replaced my 1.9td front discs with Brembo.... sorry didn't measure them as apparently 'size doesn't matter'. But I notice that the surface of the discs are drilled to a certain depth which I am told by GSF staff is the 'minimum depth' indicator.
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