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Only fully contacting one side of rear disc
iscmatt - 15/4/10 at 06:17 PM

Picked up by my MOT man, the inside of both rear discs is a little rusty though not badly pitted suggesting that the pads are making some but not complete contact. I have had the callipers off, checked the pads and also ensured the pads are not stuck and added a little copper slip to back of the pads. Not sure that has made any difference though. Is there a possibility the the piston has seized into the calliper. How would i go about 'un-seizing' it?? do i need any special tools, do i need to rebuild the calliper as per the haynes?

any advice welcomed! Thanks

Oh on another note, anybody know what size nut the locking nut is on the track rod ends? mine are missing and there is some play in the front wheels without it.

Funny how i had an MOT and passed but then i find myself not able to drive the car!!

Thanks again

blakep82 - 15/4/10 at 06:25 PM

is the bracket spaced correctly? what type of caliper?

locking nuts on rack will be M14 if its a escort mk2 rack

Paul TigerB6 - 15/4/10 at 06:33 PM

Yep - it does sound like a seized piston but i'd check the slider is not stuck first just in case.

You could take the caliper off and clamp the piston you know is free before having someone gently press the brake pedal and see if it moves. You'll then of course need to press it all the way back in.

If its seized then probably time for a rebuild. By the time you buy a kit / red rubber grease etc, and especially given the handbrake mechanism, it may be worth investigating a replacement.

britishtrident - 15/4/10 at 07:01 PM

The caliper guide pins are prime suspects, but if you have a balance bar pedal box that is where I would start investigating.

iscmatt - 15/4/10 at 07:06 PM

Just to answer some of the points raised

they are sierra callipers.
No balance bar.
The calliper sliders are working fine.

It is looking more like a seized calliper. Is the only way to overcome a seized calliper to rebuild?

blakep82 - 15/4/10 at 07:12 PM

what do the rubber gaiters on the slider bolts look like? are they stretched right out?

iscmatt - 15/4/10 at 07:16 PM

I dont think so, not right out, if they were what would that indicate?


having looked again they do look more stretched than some photos on google.

What does this mean?

[Edited on 15/4/10 by iscmatt]

MikeRJ - 15/4/10 at 07:26 PM

quote:
Originally posted by iscmatt
I dont think so, not right out, if they were what would that indicate?


having looked again they do look more stretched than some photos on google.

What does this mean?

[Edited on 15/4/10 by iscmatt]


Possibly that you calliper mounting is not correctly centred over the disk, so the calliper is only engaged with a short length of the pin. This could be causing the pins to bind when the brakes are applied.

If the piston was seized it wouldn't apply pressure to either side of the disk, so it's more likely a problem with the pins or calliper mounting. Does the calliper twist noticeably when you stand on the brakes?

Get those locking nuts on your TREs ASAP, that's quite a dangerous situation as normal suspension movement can cause the tie rods to rotate. Did it pass like this? If so the MOT man was must have been half asleep.

iscmatt - 15/4/10 at 07:43 PM

thanks mike i will have to check that out with the pressing the pedal.

It did pass MOT but these were pointed out as things to ensure are done before driving it again.

If what you say is right then it must be to do with the pins as the disc is shiney on the outside surface just the inside surface is the problem.

I will try out adjusting the mounting of the caliper to ensure it is centred over the disc.

blakep82 - 15/4/10 at 07:57 PM

if the gaiters were stretched right out, they can't compensate any more for wear. however...

... if the INSIDES of the disc are rusty, well thats the side the pistons are on, so sounds like the piston's not moving. but it must be if they do anything...

so if the inside pad stuck, therefore its pushing agains the pad, its not moving, so its pulling the slider across and only doing the outside pad?

its a weird one. if there was 2 piston's like on the cortina calipers, you could say the piston was stuck, but this doesn't quite all add up to me!

ashg - 15/4/10 at 08:31 PM

put money on either the inner pad being stuck on the sliders or the guide pins are bent/misaligned.

iscmatt - 15/4/10 at 08:37 PM

quote:
Originally posted by blakep82
but this doesn't quite all add up to me!


eek i'm confused as it is blake!!! (hence the post!)

iscmatt - 15/4/10 at 08:48 PM

PS, thanks for your help everyone!!

JonnyS - 15/4/10 at 09:44 PM

I had this issue on the rears. The pad wasn't worn straight so contact was limited. Could be a number of reasons why this happened, but a new set of pads has cured it...

Frosty - 15/4/10 at 11:13 PM

Sounds silly, but one thing I would definitely check is that the pads are fitted correctly.

The Sierra calliper piston has a broken cross shape indented into it, and the brake pads have a notch on the edge. The brake pad notch must line up perfectly with this piston groove. If it doesn't, the brake pad will be applied at an angle instead of flat against the disc.

This image shows what I mean:
http://www.madinventions.co.uk/mojo/Images/Bigg%20Red%20Sierra%20calipers.JPG

Grimsdale - 16/4/10 at 07:16 AM

well, as an alternative viewpoint, i';ve had exactly the same issue, with the inside of the rears rusting up. It was just the amount of road salt on the road, kept driving it and it cleared up. Calipers were less than 6 months old, car used most days.

Frosty also makes a good point, i did that once accidentally, but it gave me a very long pedal, and the pads rubbed on the disc, so instantly recognisable as a problem.

[Edited on 16/4/10 by Grimsdale]

JoelP - 16/4/10 at 08:15 AM

suspicious that its both rears doing the same. If it was just one side id suspect something sticking. It could just be that when you brake, not much effort gets to the rear end.

Id sort the other issues and take it out for a hard drive, see if you can clear the rust with some hard braking.