New rear brake pads - bedding in period?

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sharrar
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New rear brake pads - bedding in period?

Post by sharrar »

Hello All,

I've recently needed to replace the rear brake pads and discs. My usual mechanic mentioned the replacement pads were a little bit thicker than he expected - creating some rubbing / heat. I bought them new through SJ - is this just a case of letting them wear in? Anyone experienced anything similar with new pads or anything can be adjusted on this?

I've a NCT (MOT equivalent) re-test on Saturday so it would be great to get through that - I can then forget it for 2 years :lol: . If the brake pads need bedding in possibly a good excuse for a nice drive?

Thanks.

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Jason.goad
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Re: New rear brake pads - bedding in period?

Post by Jason.goad »

sharrar wrote: I've recently needed to replace the rear brake pads and discs. My usual mechanic mentioned the replacement pads were a little bit thicker than he expected - creating some rubbing / heat.
That statement smells a bit like the back end of a bull to me.
The main problem will be either the piston not retracting fully or more probably the sliders not moving. It's essential the slider moves the caliper easily, if it doesn't you effectively halve your braking efficiency.

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Re: New rear brake pads - bedding in period?

Post by MrCoolA »

I’m sure that I read somewhere probably on here that either replacement disk or pads were slightly different in depth so when replacing both there is an issue. . Have u tried a search on this forum?
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Re: New rear brake pads - bedding in period?

Post by Hawaiis0 »

MrCoolA wrote:I’m sure that I read somewhere probably on here that either replacement disk or pads were slightly different in depth so when replacing both there is an issue. . Have u tried a search on this forum?
seconded - Liner thickness has been mentioned before
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Re: New rear brake pads - bedding in period?

Post by Hawaiis0 »

Nothing is fool proof. Fools are clever!

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Re: New rear brake pads - bedding in period?

Post by sharrar »

Thanks All, The closest I found to my issue is viewtopic.php?f=25&t=1133&p=7843&hilit= ... hick#p7843
My mechanic has filed down the pads a small bit to reduce the rub. He mentioned it's on the one side predominantly which made me think callipers but he assures me they are fine. Possibly just small variances in thickness.

My MOT re-test is Saturday so fingers crossed!

Now I did hear a small squeak on the way home I've never heard before - any ideas on that? It's only the brakes the car went in for - anything related to this that cause a squeak a low speeds?

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Re: New rear brake pads - bedding in period?

Post by barker_001 »

It's funny you should bring this up - I recently noticed that one of my rear brakes is getting a little warm - after a run it gets about as warm as you would expect the front wheels to be (where you would expect a bit of heat). I had fitted new disks, and the pads, as per the other post you found, were the EBC standard "Ultimax" pads. The caliper and sliders all seemed very free when the brake was dismantled too.
Perhaps with new disks, the EBC pads result in a build up of tolerances that the caliper can't accommodate.
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Re: New rear brake pads - bedding in period?

Post by bash »

I recently changed pads etc but I also 'popped' the pistons out to have a look. Perhaps a combination of a couple of small issues are creating an issue where the piston isnt going all the way back. On mine there was a small ridge of grot on the piston, not rust but dirt, that came off with some 1000 grit wet and dry, there was also a small amount of corrosion prior to the seal in the caliper that wasnt easyily seen with the dirt bellows on. Again I very carefully cleaned this off, reassembled with the existing seals and everything feels much better. If your dirt bellows are ragged its worth replacing them at this point, I took mine out to make sure all the dirt was gone and I didnt want to rip them putting it back together. If you do this they are held in by a circlip type of a wire that can be an arse to dig out without ripping the seal which isnt easy but I did it so its not rocket science.
Another possibility might be related to the age of your flexy hoses, I havnt come across this on an Excel but I have on a few other cars. Whats happens is that the hose cats arse ( full technical description ), the internals of the hose can slightly collapse and when you push the brake pedal the high pressure overcomes the 'arse', but the only thing that returns the piston is the action of the cylinder seal flexing back, which isnt enough to get past the obstruction so some pressure is retained on the piston and you get a dragging brake.

Good luck

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Re: New rear brake pads - bedding in period?

Post by Phantasm »

NO Expert here, but isn't it possible the new discs are out of spec? (Too wide/thick). What is the spec for the disc? That could be measured with a caliper.
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Re: New rear brake pads - bedding in period?

Post by DavidOliver »

I agree with Bash. When pistons have been part way out for a time, that is with partially worn pads, they can rust/crud and it is not clever to simply squeeze the piston back to point zero. Mind you a mechanic might do this otherwise he has a long job for which he might not get paid.
For a recently acquired car or knowingly long period since maintained I suggest if you change pads you also fully dismantle the piston and install new seals and dust covers. This is a long job, you obviously have to bleed everything, why not, and get all crud and moisture removed?

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Re: New rear brake pads - bedding in period?

Post by Phantasm »

in truth, replacement calipers aren't expensive since they are Toyota parts, if you are okay with the aftermarket quality. probably less time swapping them out thean fiddling with the restoration. I replaced my fronts in this manner and never looked back. (my left front was sticking , super heating the wheel, and causing steering shudder)
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sharrar
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Re: New rear brake pads - bedding in period?

Post by sharrar »

Thanks Lads for the feedback. I have some good news - the car has passed it's NCT (MOT) so that's something to celebrate anyway!.

The flexi hoses were replaced a few months ago with the SJ alternatives so should be ok there but I'll get the pistons checked over.

The car drove well but out of curiosity I measured the temperature of the rotors with a infra red thermometer. The Front two were around 25 C, the rear passenger was 35 C and rear driver side was 60 C. A good bit hotter :twisted: and the alloys on that wheel were quite toasty too. This was after a 20 mile drive.

I expected the rears to be potentially hotter because of the brand new parts and the pads being a tight fit but would you say that is too hot / safe to drive?

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Re: New rear brake pads - bedding in period?

Post by AndyC »

I'd say use it for sort runs such as the distance you have, that will wear away any excess material, but if it continues for too long then it's more like a sticky caliper than one not retracted enough.

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Re: New rear brake pads - bedding in period?

Post by sharrar »

Thanks Andy, that's sound advice.

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Re: New rear brake pads - bedding in period?

Post by DavidOliver »

In my opinion you need to investigate the hot wheel.
Query.. Does the NCT (MOT) show handbrake effectiveness?
If you jack up the offending wheel and turn by hand you can tell whether the friction is from the caliper or the handbrake, which can stick partially on.
With the wheel off and when turning the hub you should see if the pads are rubbing against the disc.
As the other rear wheel seems to run OK, if the pads are rubbing it suggests inadequate piston retraction or sticking guides.

I recently bought front brake calipers from Brake International at very reasonable price, probably cheaper than paying a mechanic to renew seals.

Dave the cog.

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