Incorrect brake pad size...

[rusty244]

Hi folks,

Last year I had new pads and discs all round when my car was in for service at my trusted mechanic. Immediately afterwards there were a couple of issues once the brakes have some heat in them:
-a rotational clack noise from nearside front wheel
-massive squealing when approaching a stop from the same wheel

I went back and was fobbed off with "it will need new callipers" without him even taking a look at it. Only really covered a few hundred miles since as the car is no longer my daily and no point in subjecting it to salty roads but the problem remained.

Anyway met up with a couple of forum regulars earlier this year and they correctly suggested the pads might be too big. I had the front wheel off last week after getting the brakes warmed up and lo and behold there was no way the pads could move, they were wedged solid against the disc. Confirmed calliper working correctly and pistons fully retracted so that was good news. I shaved a little off the corners and top/bottom of the pads and they no longer catch which has improved things:





However, the disc has warped very slightly due to the heat so will likely need a new one (or pair).

My question as follows- the pad on the outside of the disc is able to travel a decent distance along the pins back/forth but the inner pad on the other side of the disc pretty much has nowhere to retract to, so even though it is no longer jammed due to me shaving the edges down it remains in slight contact. Is this normal? It is right up against the rubber stoppers that the pistons come out of. I'm thinking maybe there is too much material on the pads?

Stupidly didn't take a photo of the disc/pads in situ but will do next time I have the wheel off.

[c_lee]

Hi James,

I run a pencil around the perimeter of the old pads when I first change them on a newly acquired car thus leaving a pad outline on one of the blank pages in my workshop manual.

That way when I receive new pads I can make a comparison with the old pad shape before removing wheels etc.

Just on the off chance that the new ones aren't right.

Colin

EDIT: As an afterthought, I presume you do wire brush the caliper machined flats that lie adjacent to the pads short edges to remove any slight corrosion or build up of pad dust there before fitting the new pads so that they are 'free running'.

EDIT No 2: Also, being that the 240 front calipers are 4 pot, if one pot is sticking it will cause the pad to move to the disc with full pressure only in line with the unsticking pot and so present a very slightly wider pad profile between those machined surfaces on the caliper. The way I used to check all pots were free running was to put a 2 mil feeler gauge between the pad and the pot, my Mrs then operate the brake and I check that the gauge was held firm, then release the brake and check that the gauge could be removed easily. The very slightly tapered piston seals are what should cause the piston to retract ( but only slightly ), if the piston seals are fitted with the taper in the wrong direction the pistons will not retract properly. That procedure should be used on each piston to be sure all is well.
I think the Haynes manual gives the maximum and minimum pad thickness.

Something doesn't sound quite right though with your description of the movement of the outboard pad, but maybe that is just the way you have worded it.

[Derek UK]

You usually have to take a file to the callipers to get rid of the dirt and rust. The pads should then be able to move freely but with minimum slop. A smear of copper grease on the sliding parts a good idea but don't get any on the pad material. A good smear on the metal backing also good where it contacts the piston. There may or may not be a thin steel anti squeal shim between the pad and the piston. That also needs some copper grease.

[classicswede]

It is very common to need to clean back the caliper or even shave the pads to get the clearance needed.

The how to could do with updating to cover this

http://www.volvoforums.org.uk/showthread.php?t=119478

[Clifford Pope]

I know this isn't your current immediate problem, but I recently found that I had to machine back quite a lot of poorly-cast metal when fitting new front caliers and disks. The calipers where OK with the old worn disks, but the inside corners were not machined square enough and rubbed on the thicker new disks.

I've often found similarly on other cars that I have to do a bit of trimming to get new pads to fit properly. New Triumph pads for example had too much lining material - OK with an old disk, but too thick to go in the slot with a new one.

It seems as if replacement components are not generally now made to very exact specifications. Best to treat them as useful blanks, which you then have to finish off to get them to fit properly.

[rusty244]

As usual excellent guidance, thank you very much all.

So checking operation of each of the pots, filing debris within the calliper, a little copper greasing and trimming of the pads/edges seems to be the order of the day. I will work on this and report back any improvements.

Very poor really that the garage fitting the new pads and discs didn't do this, should really be bread and butter work for them. This and a couple of other half a**ed jobs make me think it's time to switch garages next time I need anything garage like doing.

Meanwhile I took the offside front wheel off today to see what's what. No squealing from this side so I assumed all ok but in reality the pads are pretty well wedged on this side too so I will action the above on this side too.

Curiously, the inboard pad does have plenty of room to move in/out on this side (if it wasn't wedged in at the top and bottom). Pin locating clips removed prior to me trying to remove the pads for inspection in case you were wondering.


The same pad on NSF is flat up against the disc and the caliper with not a spare mm to move back and forth on the pins. Photo next time I have this wheel off.

[c_lee]

Looks like you have a sticking piston or air in the top RHS cylinder there James - the pads should be parallel.

I found that if looked after, those front calipers are really good, especially being 4 pot on dual circuit ( on pre ABS 240's ).

I wish the standard calipers on my V70 were as good instead of the 1 pot sliding pad mount type.
My V70 fronts are not as good as the old 240's were.

Hmm, thinks - I actually have 2 spare 240 front 4 pot calipers in my garage removed from the 240 Auto I broke a couple of years ago.
Unfortunately the V70 is not dual circuit though like the 240 or I might have been tempted into an upgrade.

Colin