Mine has 252mm no doubt being the 255mm ( is it usual to be a few mil out ? My measurement is correct)
The caliper i presume would be identical to an abs model ?
The brakes have always been very good and passed mot’s fine.
On stripping to clean everything i notice the front face is perfect and why thought they looked fine and also fully swept however the back of the disc the outer 20mm maybe has not been getting used/swept and is in terrible condition, too bad to clean up maybe, the pad has a chamfer to match.
When i bought the car in the boot was a new unopened set of pads identical to those on the car now size wise, so my thoughts were, why has the unswept area occured on one side of the disc ( can’t access the other side brakes yet ) could it be linked to the incorrect diam. fitted ?
Are the pads different for abs cars ? The disc condition generally and pad thickness suggest they have not been on many miles.
Need to replace so once you nice members throw a few facts back i can make my choice as to what to fit.
My sizes quoted come from a Haynes manual for this model, strange thing is that there are three diameters mentioned and these are obtainable which is why i believed the manual was factual.
So the big brake model is one 270mm leaving two other sizes 255mm and 235mm
One for all the 1.6 Mk1 cars approx 235mm or what ever, do not go measuring to the nearest mill just are they about that size.
Virtually all Mk2 and Mk2.5 cars are about 250mm or so.
A very small number of Mk2 cars and some Mk2.5 cars had the 270 mm discs.
The inner front pads and the inner surface of the front discs can get in a mess after say 10k miles on these cars when the outer surface and pads are OK as you have found.
That is even when you make sure the pad sliding wings are lubed and the slidding pins are done with red rubber grease.
Just accept that the front discs and pads are inexpensive and are a consumable. The rear last a lot longer.
The MK1 1.6 use a specific front pad. The MK1 1.8 and all the normal brake MK2’s and Mk2.5 use a slightly taller and slightly thicker pad.
The big brake cars 270mm disc cars use another different set of pads.
Were all the springs and shims in place when you removed the front pads.
In my experience it is because the caliper is not sliding correctly.
These are single pot (piston) calipers and they work very much like a G Clamp with the load being applied from one side and the other, (rear on the brakes case) being pulled outwards to put even pressure on both pads.
The caliper slides on two pins. It is not a precision fit and one runs in a rubber sleeve. If one or both pins gets sticky, siezes or any other of many scenarios that can cause the caliper to “cock” over then you will get an uneven contact patch, possible even a longer brake pedal. The front pad is better operated because the piston is pushing it directly and it is less affected by any twist.
Your bang on, no clips or shims, not even a screw from disc to hub…i know when i bought the car they were totally clueless with cars, or appeared…they got everything done at a local garage as they were quite rural so makes me think that it was a bit of lax place…personally i haven’t faith in many places ive seen in my life.
The wire springs pull the pads back from the disc when the pressure is off the pads.
The yellow bracket things give a sliding surface for the pads and stop a bit of rattle.
The backing shims are to stop rattle, some pads come without the shims, some like Greenstuff have a cushion rubber shim attached to the backing plate during manufacturer. Mazda pads used to come with shims but no longer come with the shims or slidey yellow things.
Three reasons not to supply the shims with new pads.
1) It adds to the cost and all aftermarket, non-specialist pads are on a race to the bottom on price.
2) The vast majority of mechanics throw them in the bin as not being needed.
3) As piston seals harden, the pistons take up space because the hardened seals do not pull the pistons back into the calipers as they used to when new.
If that happens on a punter’s car, the punter will complain of hot brakes because the mechanic has damaged the brakes at the pad renewal and go mental at having to pay for a caliper rebuild that is necessary as their last garage did not rip them off for that.
Therefore, a brake pad supplier does not supply shims that may in an older caliper if used, reduce noise but may show the car needs a caliper rebuild as they take space in the caliper that is lost due to hardened seals and everyone wants a quiet life.
Very few brake pads for the MX5 come with shims but I think that I got some recently with rear pads for a MK2 but maybe not!
Do not use copperslip in the slider pin rubbers, Mazda advise red rubber grease in these rubbers get a tube or a tin of it.
Very few mechanics will bother to use red rubber grease in these slidder pin rubbers that as advised by Nick above does not help with the inner pads / disc surfaces. No such issue I have come accross in the MK3 to date.
Stay well clear of that stuff [in my view] all it does is stick everything together And reduces movement [which its designed to do] but that’s not how the brakes were made to work.
Use red rubber grease on slider pins [but even that hardens off] so I use silicone rubber grease
Use a touch of copper grease on the caliper pad ‘ears’ slider support
Always file a bit off the pad ’ears’ and surfaces that’s rest on the caliper as they do expand with heat and so rely totally on the springs to retract them - I prefer them to be a loose fit and have never ever suffered from brake squeal with standard road based pads.
Use copper grease between pad shims and pad and on the surface of the piston and the opposite ‘fingers’ This allows free shear movement which prevents the chattering vibration known as brake squeal. It offers a number of options for pads and callipers to slide/separate.
Importantly when installing the slider pins always always lube the rubber internals and NOT the pin. Many have been packed with cr*p over the years and they 1) remove all your lubricant when inserting - ooooh matron - and 2) lift the rubber off the pin when inserting/tightening to prevent ‘hydraulic lock’
In summary the brakes are designed to flap about enough to relax and not chatter, hence my advice above.