replacing brake discs

[Simon J]

In line with Don's comments above it's interesting that the Volvo Performance Brakes are promoted by Volvo not in terms of their absolute stopping power, but rather in terms of their ability to withstand repeated heavy use as a consequence of their larger (both in terms of diameter and thickness) discs. The same is obviously true of the AP set.

However it isn't correct to assume that the larger pads of the AP or Volvo kits improve the stopping power as pad area is irrelevant in relation to braking torque. (The larger pads will of course improve heat dissipation) But obviously the larger diameter discs will increase braking torque for a given pedal pressure, and this, combined with the more aggressive pads of the AP kit would undoubtedly account for their apparently prodigous stopping power. As far as I can determine, the Volvo pads are nowhere near as aggressive as the Ferodo DS2500 but Volvo decline to give any specific data on them.

And while the four piston AP calipers would logically seem to be better than the single piston Volvo ones, it's worth noting that the same type of single piston caliper as the Volvo was used by BMW on the M5 up until the latest model!

[Simon Linton]

My views on the standard brakes are well-known; the 280mm ones are dangerous on the hotter 850s, while the 302mm 70 series brakes seem to hold up well on the equivalent 70 series vehicles.

The Volvo big brake kit does appear to cost a lot for the upgrade in performance - and if I'd spent all that money I'd want a cosmetic improvement!

Tinkering around with upgraded pads and grooved discs on the standard size brakes is in my view a band-aid solution that many have found requires much tweaking and combining various flavours of pad and disc to achieve a useful result.

I recommend doing it all in one go and getting the AP kit, ideally when you are having to change the discs anyway to minimise the upgrade cost.

OK, I haven't yet had to put on new pads or discs on my AP kit so the pain of replacement has yet to arrive, but the confidence in stopping is something that I regard as essential in a performance saloon that weighs close to 2 tons laden.

But the very fact that I haven't yet had to replace either shows another advantage of the AP kit; the combination of larger swept area and greater moment arm of the larger disc diameter means that a lower pedal pressure is needed for similar retardation; thus cutting wear.

Putting high grip pads on more expensive small discs guarantees a high wear rate and frequent replacements, so the cost of ownership rises; good news for the suppliers, but bad for the owners.

I would definitely start your upgrade path with braided brake hoses; these give better response even on the standard rig and don't cost a fortune.
If and when you upgrade to a AP kit which has braided hoses, you can simply sell your new or old set.

And remember to TELL YOUR INSURANCE COMPANY WHATEVER YOU FIT. If you don't you are driving uninsured.

This last goes for any upgrade, no matter how minor; even putting Samco hoses on your engine could invalidate cover - especially if your accident involves your insurers or others in a large payout.

[Simon J]

>The Volvo big brake kit does appear to cost a lot for the
>upgrade in performance - and if I'd spent all that money I'd
>want a cosmetic improvement!

Each to their own ;-)

>>Tinkering around with upgraded pads and grooved discs on the
>standard size brakes is in my view a band-aid solution that
>many have found requires much tweaking and combining various
>flavours of pad and disc to achieve a useful result.

I agree entirely - I put a set of Black Diamond discs and Redstuff pads on my previous T5 and they were rubbish!

>OK, I haven't yet had to put on new pads or discs on my AP kit
>so the pain of replacement has yet to arrive, but the
>confidence in stopping is something that I regard as essential
>in a performance saloon that weighs close to 2 tons laden.

How many miles have you done on your AP discs and pads so far? I had to replace both pads and discs at 28K

>But the very fact that I haven't yet had to replace either
>shows another advantage of the AP kit; the combination of
>larger swept area and greater moment arm of the larger disc
>diameter means that a lower pedal pressure is needed for
>similar retardation; thus cutting wear.

The swept area is irrelevant - only the greater moment of the larger discs, and the higher coefficient of friction of the pads,makes a difference to braking torque. Whether that reduces wear by giving the same braking torque for a lower pedal pressure remains to be seen as the higher coefficient of friction could offset the effect of the lower clamping force of the caliper at a lower pedal pressure.

[sholtby]

Simon L,

How many miles have you done now with your AP brakes and what wear is there to the discs and pads?
When new the disc thickness is 28mm and it says to replace them at 27mm. After 13k miles my disk thickness is 27.2 mm and the pads have lots of life still in them. At the price AP charge for new discs I wont be changeing them until they are worn to at least 26mm if not thinner. How about you?


Simon

http://www.volvoclub.org.uk/dc/user_files/1219.jpg

[don kalmar union]

Good morning Simon,

I think that you can trade off a bit of pad depth against disc thickness to be on the safe side.

The discs on my old S70 are well shagged...I will check the thickness and post over the weekend.

Might be worth getting Pete Collen at AP to give Iain C. a write-up on brake stuff to put up here?


Don.Norchi.

www.kalmar-union.com

TME software for serious Volvo Tuning.

[Simon J]

Simon (sholtby)

I know your question was addressed to Simon Linton but thought I'd give the Volvo Performance Brake figures as well. The original thickness is 28mm, permissible wear is 2mm, and I got 28K out of the pads and, although the discs had a few miles left in them it made no sense to put new pads in and then replace the discs shortly thereafter.

The standard 280mm discs are 26mm thick and have a 3mm wear allowance.

But it's very interesting that the AP brakes only have a 1mm wear allowance. Out of curiosity, what is the replacement cost of the AP discs. The Volvo ones are now reduced (!) to £180 +VAT each.

Simon (J, that is!)

That's why we don't use Black Diamond disks and Redstuff Pads!!! We too found them totally rubbish.

However, what I can tell you is this - We had a Volvo V70 T5 Phase 2 doing over 30 laps at Donnington Park. The brakes were 302 mm Brembos and the pads were Ferodo DS2500. Not only was the car capable of out braking most of the others there, it also still managed to drive home on the very same brakes.

Now, I'm not saying the brakes were in excellent condition after this - far from it. The point I'm trying to make is that if the brakes were good enough to stop a full weight (non lightened) V70 road car repeatedly around the track, they are sure as hell more than adequate for the road. Yes the AP kit may have been better for the track, but for road use we clearly managed to demonstrate the point.

Adam.

[Simon Linton]

The 302mm brakes do seem to be much better than the 280; one good reason for getting the later high-performance Volvos - my comments on tinkering with pad and disc types were directed at the 280 option where success is likely to be elusive compared to the amount of investment.

Why would the swept area be irrelevant, however?

If we're dealing with wear rates, a greater swept area would give more pad-to-disc contact and thus greater retardation for a given clamping force - you'd also get better heat dissipation which would also help improve the braking, especially in trackday situations.

I have not used the APs in anger on a track, but I've had occasion to use them fully on the road when someone does something gaudy up ahead, and I certainly would not like any lesser braking system now that I've got used to it.

I haven't got the mileage figures on my APs at the time of this post; I'll check and post later on that one.

[don kalmar union]

I have sold a fair few sets of Black Diamond discs over nearly 10 years now, most for the bigger 5 pot cars.

During that period I have had just one complaint about a year ago from a local customer who had warped them within a week or so of fitting.

I gave the guy a new pair, returning the warped pair to BD for their judgment of the situation.

Their opinion was that the discs had been very heavily abused, causing excessive heat build up and distortion.

What did BD do...send me a replacement set free. Why, because it is a well run and honest outfit that has an interest in keeping its well earned reputation. I passed on their comments to my customer who accepted that he had not bought kit that would take such abuse as to cause the distortion.

Black Diamond do not make ridiclous claims for their product, neither do I

In conclusion, there are particular circumstances here with heavy, powerfull cars that have underspecified standard front discs.

An AP kit is the complete answer to the problem. Any other solution involving good quality standard spec. aftermarket components will make an improvement over knackered and worn parts.


Don.Norchi.

www.kalmar-union.com

TME software for serious Volvo Tuning.

Our experience with Redstuff pads has proved them to be appalling, almost to the point where they are dangerous, where the cars had zero braking force at higher speeds. No such problems have ever occured with Ferodo.

Adam.