Is this caliper plate lift?

[944psi]

Just looking at the calipers that have come of my car and can't decide if the plates are lifiting or not. The bit of the plate with the tab on (left of the pic) appears to be encroaching on the space occupied by the pads - is this normal?

When I took the pads out, they took a little bit of persuasion to pull them from the calipers, although it wasn't excessive force. Or should I just assume there is some lift and treat accordingly?

 

[Fen]

The one on the right looks like it might have lifted but it's difficult to be sure. Can you see any corrosion down the back of it?

 

[Tony Daniel]

The best thing to do is use you break pads as a gauge, the pads should fit between in the gap without using force.
Your always better off taking the plates out and cleaning them up, they are stainless and don't rust but brake dust does collect behind them causing the pads to jam.
Have fun if you have not removed them before, the retaining screws can be a pig to undo[]

 

[Fen]

They do corrode - electrolytic corrosion between the steel and the aluminium, accelerated by salt getting in there in winter. You'll see typical aluminium lumpy white corrosion pushing the plate away from the caliper if it's bad. Of you can get the screws out then great - they usually need heat. I posted an article on it to web space here: http://fen.fotopic.net/c42436.html

 

[944cabby]

What would cause a knocking sound from a caliper then?My passenger rear makes and audible knocking sound sometimes if i put my foot on the brake quickly.

 

[944psi]

Thanks for the pointer to the article - I'm not sure what they're telling you to do with the new wear-indicator wires and clips at the bottom of page 98 though []

I'll get into the garage later and try to peek down the back of the plates to see if there is any corrosion - but given the history of the car I'd be amazed if they were OK.

Phil

 

[Fen]

I never noticed that before, I'm sure it must be some technical term [8D]. Quality rag old 911 & 911 World, although at least back then they at least tried to publish some useful tech articles.

 

[Big Dave]

944cabby,
Does this knocking sound happen after youve reversed .+ moved forward again?? or vicevesa
If so ,ide say that whoever did the plate lift last time on your car took off too much alloy / corrosion, + the space the pad fits into is now slack...If you can take the pad out VERY easily or move the pad up + down in the calliper then itl cause your noise when the pedal is applied...
It could also be that you had the plate lift rectified, but the pads were previously filed down to make them fit...+ then refitted ...If you understand me.????

 

[944cabby]

ORIGINAL: Big Dave UK

944cabby,
Does this knocking sound happen after youve reversed .+ moved forward again?? or vicevesa
If so ,ide say that whoever did the plate lift last time on your car took off too much alloy / corrosion, + the space the pad fits into is now slack...If you can take the pad out VERY easily or move the pad up + down in the calliper then itl cause your noise when the pedal is applied...
It could also be that you had the plate lift rectified, but the pads were previously filed down to make them fit...+ then refitted ...If you understand me.????

Cheers dave, it's actually under normal driving conditions but only if i apply the brakes quite quickly.I've managed to get it into a local garage this friday to check all the calipers fully.I'll post their findings on the thread then.Thanks.

 

[Guest]

Hi,

I'm not sure whether you have got this sorted or not yet. I just saw the thread, so I thought that I would reply.

It sounds to me like you've got pad knock off. It's caused by the disk not rotating true, and it pushes the pads back away from it. When you hit the brakes quickly, the pad has to travel a little way to take up the slack before it makes contact again. That's the slight knock that you hear.

Knock off is usually caused by a warped disk (it can also be caused by a dodgy wheel bearing, but if this was the case, the bearing would be making quite a noise by itself).

Big Dave's analysis of the pads being shaved or the pistons being modified is a red herring. It wouldn't happen. The brake calliper automatically takes up the slack of pad wear.

James

 

[944Turbo]

I think Dave was refering to the practice (bodge) of filling down the ends of the pads so that they can be inserted once the plates have started lifting. If this is excessive then the pads will have some movement in the direction of rotation - rather than in and out towards the disc which as you rightly say will be taken up by the pistons.
Tony

 

[Big Dave]

James H
Red herring hey.?????
I think not.....
As it happened to me....
I am only trying to pass on some info that i have "gleened" over the course of owning a 944S2 + 2 968,s + working on them myself....

Were your callipers the 4 pot type.???

With regards to "piston" modification...READ the post as i havnt mentioned anything about piston mods....[][][]
To be honest , its common sense that if when the plate lift is fixed + youve filled off too much alloy then the pads will be "slack" in the callipers...Causing them to move back + forth when you move the car forward or bacwards...+ then brake.....Which would then cause a knocking sound....OR if the previous owner/servicer has cut corners + filled the pads down to make them fit...

 

[Guest]

Hi Dave,

I'm not cirticising. I just think you've got the wrong end of the stick. You were takling about the caliper piston having material removed when it's cleaned up. I just abreviated it to modified. Sorry for the misunderstanding.

However, what you were saying about pads being filed down to make them fit or the piston being shaved causing slack is actually wrong. What happens when you put your foot on the pedal is that the pad is pushed hard onto the disk. When you release the pedal, the pressure is released, but the pad isn't pulled back from the disk. It just sits there. If you reduce the thickness of the pad (either by filing down the back or through pad wear) it makes absolutely no difference. You won't see this effect.

The only time that you will see this is if the disk isn't running true, for whatever reason. In that instance the disk pushes the pad back, and you get the slack.

James

Edited to say - I think I've just figured out what you meant by the pads being filed down. Do you mean the SIDES of the pad? Blimey, if somebody has done that to make them fit, I'd be stripping the brakes completely and rebuilding them.[8|]

 

[hartge bob]

ORIGINAL: JamesH

Hi Dave,

I'm not cirticising. I just think you've got the wrong end of the stick. You were takling about the caliper piston having material removed when it's cleaned up. I just abreviated it to modified. Sorry for the misunderstanding.

However, what you were saying about pads being filed down to make them fit or the piston being shaved causing slack is actually wrong. What happens when you put your foot on the pedal is that the pad is pushed hard onto the disk. When you release the pedal, the pressure is released, but the pad isn't pulled back from the disk. It just sits there. If you reduce the thickness of the pad (either by filing down the back or through pad wear) it makes absolutely no difference. You won't see this effect.

The only time that you will see this is if the disk isn't running true, for whatever reason. In that instance the disk pushes the pad back, and you get the slack.

James

I can't see where Dave mentioned anything about doing anything to the piston.

It is a well documented problem that when the plates lift some people have been known to remove material from new pads, not in thickness, but from the vertical length of the pad, to make it fit into the reduced space in the caliper (vertical dimension)

 

[Guest]

ORIGINAL: hartge bob

It is a well documented problem that when the plates lift some people have been known to remove material from new pads, not in thickness, but from the vertical length of the pad, to make it fit into the reduced space in the caliper (vertical dimension)

Yes. Just figured out what he meant now[]

 

[Fen]

Yep, was going to post that it was you who had the worng end of the stick James but I think you have it now. The problem is that corrosion develops between the stainless plate and the alloy caliper at the top and bottom of the pads thus pushing the plates away from the caliper body and binding the pads so they don't move properly. A bodge (or someone unable to figure out what has gone wrong even) is to file the top and bottom of the pad to make it fit. Alternatively if fixed "properly" too much material can be taken off in cleaning up the corrosion with the effect that even full-size pads rattle around.

 

[Guest]

Certainly. It does sound like a bit of a bodge. I haven't had any brake problems with my 944 (but then it's only just back on the road for the first time since I had it).

The symptoms described in the original posting still sound more like pad knock off, although it is notoriously hard to diagnose car problems over the internet [8|]

 

[Big Dave]

Finally the penny drops.....[8|][][8|][][8|][][8|]

 

[Guest]

I am suffering from this plate lift on one of my rear capillers (same as the one pictured at the top of this thread). I think its causing the pad to bind on the disc occasionally which plays a very annoying tune when moving at low speed in traffic. I tried to fix it with some copper slip yesterday afternoon and ended up having to take the calliper off to get the pad out.

What's the correct solution? Do the plates come out of the calliper for cleaning behind?

 

[Diver944]

ORIGINAL: DougBewley

What's the correct solution? Do the plates come out of the calliper for cleaning behind?

Hi Doug, welcome to the forum []

You've diagnosed it exactly. The plates have to come off, then grind down the corrosion behind before replacing. Unfortunately its the small screws holding the plates in place that are a devil to get out[]

Have a look at the article that Fen has hosted in the 4th message of this thread