Brake pads bedding in

[handi_andi]

Hello All
Just a quicky. I picked up my plus 2 from the garage today complete with her MOT, only required a couple of minor things to pass. The most serious being a worn trunnion and the least serious the horn button falling out during the test.

Anyway, I took her for a bit of a drive and was not very impressed at the brakes at the moment. I fitted new pads a couple of months ago and she hasn't done very many miles since. Hence, I was wondering how long it took for new pads to bed in, i.e. how much should I drive her before I start thinking about checking out the callipes etc

Cheers

Andy

[Jason1]

Hi Andy

No easy answer I'm afraid, it depends how worn your discs are.

I don't want to teach you to suck eggs but, the reason the pads need to bed-in is because discs wear greatest in the middle of the contact area and leave a high/lip around the edges. So if you fit a new perfectly flat pad to the worn disc the pad has to wear lots at the edges in order to make a perfect mating surface or the pad just sits on top of the lip.

You can speed up the bedding-in by removing the edges from the new pads so they mate better. But it will depend on how hard the pad material is, how badly the discs are worn and how often you apply the brakes.

Sorry, but I hope this helps.

Jason

[handi_andi]

Thanks Jason, no it is helpful as I am now inclined to remove a wheel tomorrow and see what's happening. She is stopping but not in a seatbelt tyre skidding sort way. The pads ahave probably got about 50miles on them now maximum, although some of it was hard braking on and off due to the lvoely roads aorund here that are suited to playing with an Elan even at night.
Andy

[Jason1]

Hi Andy

If you have the time I would take the pads out and rub the edges off with course emery paper and try them again. If the discs are badly scored or very worn then you may not get very good contact between pad and disc.

With modern cars I change the discs to every second pad change.

Good luck

Jason

[handi_andi]

Jason

Have just been out and checked and there is no discernable lip on the front discs, and only just on the rear discs to the touch of the finger, so I think they must be fairly new discs, which just deepens the mystery.

Andy

[Ross Robbins]

Andy,

If the pads are new they are usually glazed a bit from manufacturing resins which will outgas when they get hot. They will have a "shine" to them, and not very good friction. So they do need to be bedded in.The way I always used to bed in race pads was to go out in a practice session and warm them up with a lap of moderate stops, then two laps of hard braking, followed by two laps without braking at all to cool them down. Then I'd come into the paddock and let the car sit for at least an hour before going out again.

So to relate that to non race methodology, find a road without traffic, make a dozen moderate stops like from 50 to 20mph (80-30kph), then do about twenty hard stops from 70 to 20 then cruise home for at least ten minutes using just the gearbox to slow the car. Park it for at least an hour WITHOUT the park brake on! Just leave it in gear. That should make a big difference.

[Jason1]

Hi Andy

I think most people that remember brake linings containing asbestos will agree that since it was removed brake materials have become a lot harder. It may just take longer to bed in.

I also think that the surface on new pads are harder than the rest of the pad, it seems that new pads even on new discs take a while to work well, or maybe it's the driver slowly getting used to the new brakes?

I agree with Ross that agressive braking will help bed the pad to the disc but as he says be careful where you do it, pulling up the handbrake on the high street may not be popular with the cars behind.

But if you have the time I would still say take the pads out and rub off the edges.

Jason

[mikealdren]

Andy,
what is actually wrong with your brakes? I suspect that they are not stopping you as well as you want/remember/expect.

If your disks are ok, pads should not take too long to bed in and you should not expect a big difference in stopping performance, after all, owners of new cars don't complain about their brakes. Bedding in is the process of matching the pads to the disks and this gives better performance for brake fade as it spreads the heat transfer to the pad more evenly. Without going into too much physics, the frictional performance is proportional to the load on the pad and the coefficient of friction between the pad and disk, it is independent of the contact area. Yes, the coefficient of friction will change slightly as the pads bed in and the surface changes but it's not that big a difference.

You are more likely to lose performance if the pistons are sticking and you are not getting braking from all four pads. This is especially likely of the car is only used occasionally as the pistons rust and (unfortunately) the solution is to take off the callipers and clean/replace the pistons with new seals and dust covers.

Ridges on disks are either caused by wear or corrosion. With older (original) pads, the edges of the disks corrode and the disks are often thinner at the edges than the wearing surfaces. More modern pads are abrasive and tend to keep the disks clean but wear them more. The disks wear to give a raised surface at the edge of the wearing surface. As long as the mating surface of the disk isn't grooved, the disks should be ok.

I would have a look (with the wheels off and an assistant to press the pedal) and make sure that all the pistons are moving freely.

Mike

[handi_andi]

Hiya
OK, so basically I have been doing the correct thing to bed the pads in then, so I think I can safely say they are bedded in which starts pointing to something else being wrong.

Essentially iI press the brake pedal fully down at say sixty, the speed is wiped off but with no urgencey. You go into a corner wondering if the speed will come off when u hit the brake pedal. Have also noticed something that I dont remember happening before which is that when I brake hard the engine revs up. I thought initiaqlly my foot must be catching the accerator but its not, it is more prenounced when the clutch is down.

I am starting to wonder whether the servo is playing up and what I am getting at the moment is non-servo assisted braking despite the fact that the valve on the servo is moving nicely in relation to the brake pedal being applied and let off.

Cheers

Andy

[Robbie693]

Hi Andy,

The engine reving whilst you brake could be the pedal shaft is worn. I had the same thing on my car - the brake and accelerator pedal were twisting on the shaft and this caused the throttle to stick slightly when braking.

Not sure if this could cause the brakes to not work properly though, so it could be the servo too...

Could be a combination of the two?