Front brake refresh ... glazed inner disk surface ?

[BenF]

A few weeks back, I was getting a little steering vibration under heavy braking which I put down to warped disks.

Given a set of Pattern disks + Toyota Pads is just over £100, I decided to replace the lot - the brakes last time I did that were great afterwards.

Looking at the outside of the disks, everything looked normal with an even swept shiny disk


However, I was shocked when I got the disks off the car to see this on the inside surface :





The disk appeared to be completely glazed over, by 2-3mm of material. The brake pad surface looked 'normal' but had worn down more rapidly than the outer pad, as you'd expect on a MR2.

Looking at the material on the disk, in some areas you could see where it had flaked off :







It looked like there were only small bands of ~5mm on the inside (RHS of the below pic ) of the disk where the disk was 'bright' and actually working with the pad - not surprising that I was getting vibrations under braking with the uneven heating.



I've had mild scoring on the inner disk before which was what I was expecting as is common on Mk3's - but has anyone seen a layer of glaze like this on a Mk3 brake disk ?

Most of my driving is around town, with the occasional country roads run where everything gets hot. Prior to doing the brakes, I'd also taken the car for a few runs to see if getting the brakes hot cured the vibration under braking.

[Ekona]

Jo's brakes looked similar to those when I changed them the other month before we sold the MR2, although she had an incredible amount of scoring on there as well as the glaze. Hers looked bad on the outside as well though, not just the inside like yours.

I bet they feel a bit better now, eh?

[tonigmr2]

Blimey! That's standard toyota pads you say?
Are they pattern discs?

[afennell]

that is bad

[BenF]

Blimey! That's standard toyota pads you say?
Are they pattern discs?

Yes, Mr T pads and my local motor factor's pattern disks - have been fine in the past. I've had a previous set end up with some fairly heavy scoring ( as Dan describes ) but nothing as bad as this.

[BenF]

I bet they feel a bit better now, eh?

That plus some new DOT5.1 brake fluid and they're feeling good again. Much more stopping power for much less brake pedal pressure.

Much as MrT's pads are great all rounders for road and light track use, it does make me wonder about trying other pad materials.

[tonigmr2]

Is it not the quality of the disc then? It looks very degraded, how old was it?

[BenF]

It was only 12-18 months old. The outer face looks absolutely fine, which was why I was so surprised at the state of the inside surface of the brake disk.

I don't think the disk material / quality was a problem here - the last set from the same supplier didn't have this problem, and I've used pattern disks with MrT pads on a variety of MR2s over the years without seeing this.

[Fozzy]

Looks to me more like you have a seized caliper so its not applying any pressure to the inner pad. Without regular contact with the pad the surface of the disk has just corroded up. Id be taking a good look at the calipers and slider pins

[greglebon]

+1 on that....

Classic symptoms of seized caliper / piston....

Had the same on my Mk1 a couple of years back.....

[excalibur1814]

Mk1 Mr2 - Over the years replaced all four of them
Mk2 Turbo - Over the years replaced all four of them
Mk3 Roads - Over the three years I've replaced one... so far.

Damn calipers!

[BenF]

Looks to me more like you have a seized caliper so its not applying any pressure to the inner pad. Without regular contact with the pad the surface of the disk has just corroded up. Id be taking a good look at the calipers and slider pins

.. apart from the inner pad had worn down more than the outer pad! There was about 1-2 material left on the inner pad, and 3-4mm on the outerpad.

I'm going to do a service on the car in a few weeks so I'll take another look at how the replacement disks and pads are doing.

[BenF]

Just to update, I suspect the issue is that the calliper's sliding pins were not working, causing the inner pad to do more work.

The replacement pads and disks I fitted back in October I've swapped in March as they were also showing some scoring again.

I re-assembled them using Red Rubber brake grease from a local motor factors - I'm going to check the brakes ( weather permitting ) one day soon to see if the red brake grease has solved the issue ...

[HighwayStar]

I had the same problem with the original toyota disks at Miches last service. 6yrs old and about 33,000 miles. Don't recall needing pads though. I guess I'd better be checking the calipers too although it still feels fine under even heavy breaking.
Hope yours are sorted Ben...

R.

[BenF]

Yep, if not then the only other greases are white lithium grease or CV joint grease - I'll give the spray on white lithium grease a go, as primarily its just needed to keep water out rather than do any heavy / high load lubrication.

[BenF]

Just thought I'd update on this thread - it looks like its quite a common issue on Roadsters.

Last April, I noted the inner surfaces were glazing up again on new disks and pads, and the sliding pins had seized up.

As a temporary workaroud ( pending some parts arriving ) I found I could sandpaper the surface of the disk to remove the pad material glazed onto the disk to get back to a metal surface, and file the pad surface to again to remove the glaze. That, plus re-lubing the sliding pins with Red caliper rubber grease much improved the breaking power.

However later, I found the pins had seized again, and cleaned and re-lubed with spray on Lithium grease.

The '2 recently passed its MOT but with an advisory for scoring on the disks - so I ordered up some Pagid Pads and Disks from Euro car parts for £76 delivered to see if it was a Toyota pad material issue possibly causing this.

Taking it all apart this afternoon to fit, the Lithium grease had dried out - having tried all the different greases you can get locally ( I can't get specifically sliding pin grease ) , I've ordered up from Bigg Red some high temperature silicon grease for sliding pins - http://r.ebay.com/kDiIfo

The Pagid disks looked good - much better than the pattern parts I've had before, and they were painted up with what looks to be something rust-resistant.

The Pads are 'standard' items but I noted that the edges of the pads are chamfered at quite a shallow angle so that on the new pads only about 2/3rds of the total pad surface is in contact with the disc.

I've got to bed in the new pads and disks, but they do work acceptably well from being installed, but oviously are wearing off the surface coating.

[toxo]

Just to add this into the mix... I used pattern discs on my MK2 Turbo and noticed the inside of the front pads were wearing unevenly. They had loads of meat left towards the outside of the disc (so upon inspection through the gap in the top of the caliper looked perfectly serviceable) but towards the inside of the disc the pads had completely worn down. This happened on both sides at the front, on calipers that were entirely free-moving. I assumed that the construction of the disc had lead it to be tougher or more dense or whatever near the centre of the disc. Switched to genuine Toyota discs and it never happened again.

That's clearly not what happened on yours, but it's interesting nonetheless!