I tried to fit a new set of pads to front right but they are too tight, maybe 2mm or so. Dimensions, 146mm, 54.8mm, 19.5mm. The pads are still ok on front left so I thought I could swap one pad from left to right and mix and match pads on each side.

 

I have MOT coming up and wondering if this will pass i.e having one new pad and one half worn pad on each side?

1 hour ago, Aj77 said:

he pads are still ok on front left so I thought I could swap one pad from left to right and mix and match pads on each side.

NO! Even if legal and pass MOT (not sure) you're virtually bound to introduce some sort of braking imbalance by doing this.

MOT won't care as long as the thinnest pad has more than minimum of 1.5mm (from memory) meat left.

 

Which bit is too tight?

 

If it's the pad material, have you returned the piston far enough into the calliper?

 

If it's the steel of the pad back plate and it won't fit in the carrier by 2mm, then you either have the wrong pads or a different calliper carrier.

 

It's a bad idea, in my opinion, to mix and match.  You really want to be changing brake pads as an axle set (all four pads).  If one side has worn more than the other, it would be better to find out why that is and remedy the cause.

 

Gaz

7 minutes ago, Gaz said:

Which bit is too tight?

 

If it's the pad material, have you returned the piston far enough into the calliper?

 

If it's the steel of the pad back plate and it won't fit in the carrier by 2mm, then you either have the wrong pads or a different calliper carrier.

 

It's a bad idea, in my opinion, to mix and match.  You really want to be changing brake pads as an axle set (all four pads).  If one side has worn more than the other, it would be better to find out why that is and remedy the cause.

 

Gaz

Piston fully pushed back with G clamp, I spent a lot of effort making sure it was 100% back. Surfaces all cleaned with file and wire brush back to bare metal. 

 

The gap between pads is too tight to fit over rotor, there's not much in it though I tried hammering it in but it will end up breaking something like the rotor. 

 

I may buy a grinder and just grind them down but I just need to get through MOT first.

 

EDIT: I think I see what happened, I had 54mm in my head as required pad thickness(which must be an exact size) and these pads are 54.8mm I must have assumed 54mm was rounded down but 2x0.8mm is 1.6mm so I think I'm 1.6mm over, hence I guessed 2mm originally. So I need to lose 1.6mm from them.

 

Edited 18 July, 20214 yr by Aj77

54mm is much more than a pad thickness could be, except maybe on a train.

That's very odd.  Have you got any non standard parts?

 

Is the piston top (the bit that contacts the back of the pad) level with the top of the calliper pot? - Just wondering if something is preventing the piston from fully returning.

 

Gaz 

What's probably happened here is that the discs have a rusty lip on the O/D and inside where the existing/old pads have been. The old pads will be worn so they fit between these lips where the new ones will be sitting on them (or trying to).

File the rust down and the pads will likely go in.

 

Edit...Or, you bought the pads from ECP and they sold you the wrong ones for the car? 

Edited 18 July, 20214 yr by Wino

43 minutes ago, Wino said:

What's probably happened here is that the discs have a rusty lip on the O/D and inside where the existing/old pads have been. The old pads will be worn so they fit between these lips where the new ones will be sitting on them (or trying to).

File the rust down and the pads will likely go in.

 

Edit...Or, you bought the pads from ECP and they sold you the wrong ones for the car? 

 

I've filed the rusty lip also, I had this problem with my rear disks, pads, calipers, caliper pistons, there seem to be 2 sets of everything but close in size. 

 

I'm just going to have to buy another set or grind them down with sand paper or a grinder.

 

But my question was, will the MOT tester fail it for having pads of different thicknesses on each side but that are all over 1.5mm.

23 minutes ago, Aj77 said:

 

 

But my question was, will the MOT tester fail it for having pads of different thicknesses on each side but that are all over 1.5mm.

Thought I'd already covered this.

The answer is no, it won't fail on that.

Edited 18 July, 20214 yr by Wino

Just now, Wino said:

Thought I'd already covered this.

The answer is no.

So why did somebody above say the tester wouldn't care.

He won't care because he wont fail it, the answer to your question was "no!"

It was me that said it, and I agree!

Let me edit my second answer for improved clarity.

"No, it won't fail on that".

Edited 18 July, 20214 yr by Wino

13 minutes ago, Aj77 said:

So why did somebody above say the tester wouldn't care.

Because an MOT "don't care" is either a pass or a "not tested".

Just as an afterthought for anyone and everyone reading; the current MOT test manual can be viewed online.

All via one or other link here 

 

https://www.gov.uk/topic/mot/manuals

Your pads are 19.5mm thick so are the correct thickness, you haven't pushed the piston back fully. Try opening the bleed valve (11mm ring spanner) and you should be able to push the piston back with your fingers, the piston goes well back.  Or you havent pushed the pad clips fully back into the piston when fitted, or put the wrong pad into the piston end (see below about clip identification)

 

If your pads are near the limit (under 3 or even 4 mm) you risk a failing the MOT. In practice, an MOT tester has limited time and often cannot or will not measure pad thickness accurately, they will simply look at it and use their judgement. If the disc is badly lipped and/or grooved with the pad sitting snugly in the grooves, it may appear to him the pad is too thin and simply will fail it. They cannot risk passing what is now classed a dangerous fault (you wont be able to drive the car away legally until its fixed if that's the case). It wouldn't surprise me if the MOT tester fails it for having obvious mixed pads as an unsafe or dangerous modification

 

1.1.21

(d) Braking system component modification: (i) unsafe (ii) adversely affecting braking performance

Major Dangerous

 

Old pads and discs probably are worn unequally across a face with grooves/ridges/unequal thickness from hub to edge. The pad you move to a different position with not mate with the new disc face.  So you will have a significant imbalance left/right until all pads bed back in, which at best will take a long time as worn pads are much harder than new at worst will never bed in. Not sure how an old pad reacts to having to work (hard) in the opposite direction its been used before, many materials tend to develop a direction memory.  30% imbalance = major 50% imbalance = dangerous

 

Too risky. Do the job properly and change all the pads. If you cant do it, get someone who can. An hours labour at most independents or quick fit type places if they will accept you supplying your own pads.

 

Note: Not sure what disc size you have, but on our bog standard Octavia with 280mm discs, (FSIII) the 4 pads may look at first glance identical, but are in fact two sets of 2. The spring clips on the backing plates are slightly different depending on whether its fitted on the piston side or the outer side. Get them the right way round otherwise ime you'll find your brakes develop an annoying squeel!

 

In the pic below the one on the left with the curved clips on all 3 prongs is the piston side. 

 

Edited 18 July, 20214 yr by xman

^ Nice bit of info on the difference between retaining clips, here's a photo showing the inner pad on the left, outer on right, from an angle which makes it easy to see.

 

 

 

45 minutes ago, xman said:

Too risky. Do the job properly and change all the pads. If you cant do it, get someone who can.

 

 

Someone who would look to see why the pads wont go into place, someone who is not going to hammer them into position, grind them down or mix old and new pads putting the old in different positions.