O/S/R Brake Locked On.

While I was typing had not noted that Iain had joined in.... of course a reconditioned calliper is a far better repair process.

I shall bale out of the conversation other than to suggest..

Hope if you go that route you can free off the brake pipe,, wire brush and a spray with WD40 or similar, a few times before you try and if you are going that route best buy a proper brake spanner to give you the best chance of not damaging the brake nut if it is as tight as might be expected..?

Good luck. :thumb:

There's nothing wrong with a repair as you suggested , an airline down the nipple hole will often push out a piston ...

It will probably have a corroded bore though .. there is the cost of parts and indeed what tools you have at home... as a replacement caliper is not that expensive in the great scheme of things then that is what i went with.

It's just my opinion though and everyone should suggest what they think as i'm not keen on the posts where it is just me and the Op .. i don't know everything as i often say !

Luddite said:

With the other pad left in place, it is a simple matter of using the brake pedal to break the bond that the other piston has in it`s bore... however the amount of pressure you may have to apply to the pedal to free it, will cause the disc to be deflected to some degree by the piston that can move.... thus to stop this from happening it would be ideal if you can find something to fit between the calliper and the disc to inhibit at least some of that movement though taking care not to inhibit the stuck piston from moving when you apply pressure.

Click to expand...

Hi Luddite,

Thanks for the suggestion – I've just tried it.

Having digested your caveats and with the pads still removed, I put the special tool into the caliper with the plates sufficiently far apart that they would allow both pistons some movement without either piston being able to pop out fully or exert any pressure on the disc (as any moving piston would simply press on the plate of the tool which, in turn, could not contact the disc because the other plate would stop it moving far enough to do so).

However, the seized piston simply didn't budge after several very firm presses on the brake pedal.

As for the other piston, it did move as far as the plate would allow it but to get it to retract again took a lot of pressure via the special tool.

This "only just movable" piston will press the pad against the disc when the brake pedal is pressed but, when the pedal is released, the braking effect of that pad continues – as the piston simply won't retract.

Whatever is affecting the movement those two pistons is affecting them very badly indeed.

What a life! :roll:

deMort said:

I've never heard of a caliper being sold without pistons before so i think it's just that they are black and not seen on the small picture .

You could always email them to check but i'm pretty sure it will be complete .

Click to expand...

Thanks, deMort,

I've just emailed them to make sure their caliper is a straightforward replacement for the one I'm taking off.

Regardless of how this repair progresses, I must say I'm very grateful indeed for the helpful advice received from you and Luddite.

I really do appreciate it.

:thumb:

Iain, we operate in different worlds, well at least as far as work in the garage goes...(-: I feel that I know the kind of good hearted guy you are and believe me I have learned so much from your posts... THANKS.

I have never bought a new calliper and have brought many an old abandoned banger back to life that has lain for many a year.... However there is no arguing that a fitting a reconditioned calliper is the simpler and most effective option, but to me that requires little skill and perhaps more importantly no real need to learn about and thus understand the system and it`s likely failings.

Sure any garage business has to repair as quickly and efficiently as possible, and unit replacement is the way to go..there is no time to strip a rusty calliper down and clean it up in the hope that it will work for a while at least.... but it might not work at all... time wasted for a less than guaranteed outcome...definately not the way to go for a garage.

Me..? I was repairing my old cars a pound at a time, so if there was any chance I could repair something by stripping it down to find out how it worked, and reassemble it, then that was the way to go, sure I broke a few things trying to strip or repair them but boy did I learn a lot in the process.... That was long before the easy money or plastic debt days...Thus a measure of attitude towards self reliance was a pre-requsite and more so if I wanted to run sports cars and m/cycles on my budget..

As ever I have a story (-: ... A few years back Porsche 911 SC Sport pal who had stored his car for a while and is handy with tools, sent off his front callipers for repair/replacement, got them back all nicely painted, fitted them and bled the system, the brake pedal was seemingly as spongy as it was before he sent them off for overhaul... He sent them back as faulty, they were tested as being OK and sent back, he refitted them... same outcome.. he called me in frustration... rolling around the ground... I clamped off each of the flexibles till the pedal went hard when pressed as opposed to spongy... Just as in the case of Phils rear calliper, one of the pistons was siezed, though the other was free to operate... the spongy feel was not air in the brakes but the disc being pushed to one side by the operational piston/brake pad and the disc springing back when the pedal was released.. the disc could be seen flexing when the pedal was pressed... He just did not want to believe that could be the issue... shrug! Even on the test drive he agreed the brakes were "better" but surely that could not have been the issue...!!!

I very much doubt the calliper bores will be corroded unless the car has gone swimming, the pressure seal stops water entering the area of the bore, though VERY old brake fluid can contain a degree of water and could perhaps cause a bore to become rusted...? Though I bet Iain has seen hundreds more callipers than I..

The more usual scenario I have come across is that the piston gets corroded, if of the chrome plated type, though these days it seems they use better quality materials or perhaps machining can produce smoother piston surfaces in times past..?

The reason I have found for piston corrosion or pitting is usually that the dust seal has failed and water/crud can access the polished surface of the piston, more so if the pads are worn and more of the pistons surface is exposed to the crud..

Another problem arises if the now slightly pitted piston is forced back into the bore in order to fit new pads, what are the chances the pitted piston will operate freely enough to release all pressure on the pad.... perhaps creating problems of a slightly dragging brake or indeed sticking on..

The other issue resulting from a damaged dust seal, can be that the area of the bore in the calliper to the outside of the seal corrodes due to the same crud entering that could have damaged the piston... and as such can grip the piston slightly adding to the degree of resistance to the piston retracting normally...? To attend to this the piston requires to be removed and the rust cut back, emery paper can achieve that.

Strange as it may seem I have in the last few weeks got round to fixing the same issue on my old and now rarely used Ford p/up truck... intermittently sticking front brake... removed the pads, extended the pistons as far as I dare, pushed back the dust covers and polished the few pits found on the pistons with fine steel wool... blew away any residue, and gave things a squirt of WD40 and pushed the pistons right back in and then back out again quite a few times to excercsise the pistons, then fitted 28 quids worth of new pads....obviously cleaned the interface area betwix pads and calliper and hit the pins with a file to clean the rust off a bit of copperslip and the job done.... Pity I am scrapping the old thing in a few months... it helped build the extension I am sitting in typing at the moment...(-:

For sure a garage would have fitted a new Calliper and I would have paid out more than the old thing was worth...perhaps.

Phil I only type this to provide alternatives for those who may not have the cash to buy new kit and like me want to understand how stuff works..(-:

Be very sure that you have that car well supported slide the wheel under if you do not have blocks or similar because if you are removing the calliper the holding bolts may be very tight. and require a fair degree of leverage to shift them.... the last thing needed is for the car to drop to the ground and worse still with any part of you under it...

So Phil, you will end up with one reconditioned calliper out of four working as new... New pads pins and springs... perhaps....brake balance...? The reality is that there will be rather a lot of bits`n bobs that could probably do with being replaced with new, as opposed to one calliper.... perhaps flexy hoses or metal brake pipes... but how far do we go... at least you have been in there and hopefully had a look around....and now decided to strip and clean all the brakes...now that you are an expert on calliper replacement..(-:

Do buy the proper brake pipe spanner if you do not already have one, if you get the brake pipe nut out... GREAT, but usually crud gets trapped betwixt the nut and the pipe and sometimes corrosion starts there temporarily bonding the pipe to the nut and even if the nuts threads are not siezed, when you begin to unscrew it, the pipe may well twist and if you continue it will twist and break... New brake pipe required.... However IF you have wire brushed the assembly and sprayed with the stuff of your choice be sure you have also sprayed in between the nut and the pipe.... when trying to unscrew it if it seems to want to twist tap the pipe a few times spray it again and turn the nut back and forward a tiny bit while doing so to encourage the bond to brake.... good luck with that.. It could affect your costs if you damage the nut to make it impossible to screw out, thus requiring the brake "specialist" to drill it out and clean up the threads, the same goes for the bleed nipple, so again it might be worth hitting it with the wire brush and spray a few times allowing it to soak a bit before putting a tight fitting ring spanner or socket on it and trying to coax it out.... again if you mess that up, you give the brake guys a harder task and reduce the value if any to them of your old calliper...?

With both of the above proven to be free, then you are handing them a calliper with a sized piston.... perhaps they can say as a result it is not worth reconditioning or charge extra... So it may just be worth making sure it will come out by following the suggested stone age procedure.... Sure Iain, an air line can be used if there is a compressor available but in this case it seems simpler to just use the braking system (?) and in so doing testing it`s pressure holding capabilities by showing up any weaknesses should they exist...?

Hope this might help someone somewhere sometime if not you Phil.... Iain/DeMort is the expert in this area, I am just one who ever preferred muck around in a bid to be to be self reliant if possible...

Thanks for the info and advice, Luddite.

I'll certainly bear it all in mind as I proceed with my "engineering" works.

If there's one thing I do know something about, it's the danger involved when working under a car that isn't supported properly.

Many years ago, I was on the drive of my mum's house working under the back of a Jag with one of the rear wheels removed and the vehicle supported only on a scissor jack. The car came off the jack and pinned me to the ground. Every breath I took was shallower than the last as the car began to crush me. I knew I only had seconds to live.

Unusually, in that very quiet little road, there were three burly blokes passing by and my mother's cries of alarm brought them running over to save me.

But my experience with unsupported cars doesn't end there: a couple of years later, a guy I knew was working under a Hillman Imp supported only on a scissor jack. The car somehow came off the jack . . . and killed him.

I've always love messing about with cars but, as you say, it's important to have the right equipment and work in the right conditions.

Okay chaps, here's another potential problem related to my stuck calipers.

Some time ago, both rear wheels were impossible to turn by hand although both would move when driven by the engine.

In an attempt to fix the problem, I jacked up the nearside (leaving the offside tyres on the ground), started the engine and put the car into gear – relying on the differential to turn the raised wheel and hopefully unstick it, which it quickly did.

When I then tried turning the wheel by hand, it turned normally.

So far so good.

I then jacked up the offside, the side on which I now know the rear caliper was badly stuck (leaving the nearside tyres on the ground) and tried the same procedure.

The wheel turned but after a few seconds there was a bit of clanking from the rear end so I stopped immediately.

Upon then driving the car up and down the driveway, it drove perfectly normally but, upon raising the offside rear wheel again, it still wouldn't rotate by hand (which is why, as you know, I'm now replacing the caliper)

Today, I thought I'd check the nearside rear wheel again and, with the offside wheel still raised, I raised the nearside wheel and it turned perfectly normally.

However, almost as soon as I began to rotate it there was a slight "clank" from somewhere nearby. I kept turning the wheel but I could not reproduce the sound.

With both rear wheels still in the air, I started the engine and went through all five gears, taking the car up to a theoretical 80 mph: everything was fine. I then tested it in reverse and again everything was fine.

Do you have any idea what the clanking sounds might have been?

Phil, I guess you know for sure that you definately have an LSD..?

That you performed the tests as described would suggest you may have put the clutches in the diff under pressure, though to what extent..hmm.?

The idea of LSD is to detect a free spinning wheel and in such a situation provide more drive to the wheel with "grip"... Which in the situation created as you describe, it seems you may have been lucky the car did not try to drive off the jack...... and if the car was held back in some way to avoid that happening, then the clutches in the diff trying to drive the wheel with "grip" could have been slipping forcibly which seems less than ideal for their longevity..?

My old Morgan has an LSD and the guys do not test the rear brakes individually on the rollers for fear of creating problems in the LSD..

I suspect the noises you heard were related to the clutches protesting and/or the pressurising spring struggling to drive the wheel with "grip."

But that is all just me theorising... hopefully someone who really knows will jump in.

Seems despite your unfortunate experiences of the past, you may still not be entirely risk averse.. :?: :?: :?:

Luddite said:

Phil, I guess you know for sure that you definately have an LSD..?

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Thanks for the reply, Luddite.

No, I don't know whether it's an LSD.

I used the wrong terminology: I should have said "diff".

I'll edit the post to remove the reference to the LSD.

I've done a bit of work on cars in my time but, as you can tell, I don't exactly qualify as an expert. :roll:

What I really need to know is whether or not I've buggered anything up?

Phil, I suspect the sticker in the frunk would provide the info as to whether your 911 was fitted with an LSD or not when it left the factory..? You will have to search around for a breakdown of the code letters on the forum.

I can well understand that you want answers to all questions but via the interweb that seems less than likely..?

You are at risk of stressing components that have not seen normal use for some time trying to free of brakes .... As by your description you have done a bit of work on cars in your time....Perhaps just concentrate on checking and cleaning all the brakes, checking the pipes for corrosion and flexibles for any sign of damage etc, get the rear discs off and clean up the handbrake mechanism and the rust out of the drumsthough it seems you are not in too much danger on your usual test circuit...(-:

Perhaps with problem brakes and and now a duff diff to add to the list of other probable issues awaiting discovery, a tenner could buy it...? But only a fiver if it`s a cabrio.. :floor:

Luddite said:

Phil, I suspect the sticker in the frunk would provide the info as to whether your 911 was fitted with an LSD or not when it left the factory..? You will have to search around for a breakdown of the code letters on the forum.

Click to expand...

The only sticker attached to the underside of the front lid is a little one that tells me that breathing asbestos dust is bad for my health.

However, I have found the appropriate sticker inside my service book.

Apparently, an LSD is option number 220 but I don't have that number.

Instead, I have:

286: intensified windscreen washer

288: headlamp washer

330: cassette-radio Blaupunkt Toronto SQR 46

340: seat heating, right

341: central locking system

383: sports seat left, electrical height adjustment

387: sports seat right, electrical height adjustment

439: electric soft top

462: securiflex windscreen

975: luggage compartment velour carpet

Despite the absence of an LSD option, it's interesting to note that with both rear wheels raised, if I turn one wheel by hand the other wheel moves in the same direction.

I've always thought the effect of a normal differential was to make opposite wheels turn in opposite directions when one was turned by hand.

In any event, if you look at option 439 in the above list, you'll see that my car is only worth a fiver – which is, I have to say, a bit disappointing. :?

OK, OK, so I went out to the garage jacked up the rear of my old sports car with a LSD, and spun each of the wheels, regardless of the direction I spun either of the wheels there was zero effect on the other....

@ Luddite . Bless you .. i was like you as well .. i started in 1981 and in those days we used to fix items .. strip .. repair and refit ..

It's a different world these days i'm afraid .. i must say i've had many a happy day repairing components over the years .. but it's just not cost effective these days .. companies do it for far less than what i can do it in .


I'm going to have to be blunt here as well .. no offence caused i hope ..


I do this for a living so technically if i give the wrong advice i could be held liable .. i'm a professional saying what you need to do ..it's risky for me .

I also have to consider the skill of the person i'm talking to .. i'm afraid i have no idea there and so i tend to take a safe line ..

A replacement of a part as in this case is easy enough .. yup i know there might be issues with pipes not coming undone etc but that's a separate matter and we will deal with that if we need to , a caliper refurb and you will still need to remove it .

A replacement part is far simpler .. not a huge cost in the scheme of things so it's what i decide is best after weighing up all the Alternatives .

i don't post a complete list of why i've said what to do .. i weight it up and post what i think is best .

You and me .. old school .. yup we repair .. most people here are not us though .. again no offence phil .. one old guy explaining things to another

@ Phil ..

i helped a member here take his engine out of a 996 .. first thing when i saw it was i put his wheels under the car .. if it comes down we have a safety barrier .. i've seen a car come off a ramp .. luckily no one was hurt ..

I've recently been shown a video of a car coming off a ramp with mechanics under it .. i REALLY wish i hadn't seen it .. 1 dead the other injured .

This job may seem easy .. a piece of cake but there are consequences if you get things wrong ... if i don't pay attention at work then it could well be me .

A car on a ramp HAS to be balanced correctly or you can remove a wheel and it's just enough to tip it .. that's what i saw .. can't comment further on that but it was a close call shall we say .

ref the noise .. dont worry about it .. noises when driving and under a load are what counts .. you cant damage a diff by running each wheel in turn .. they are designed to slip on a standard diff and a clonk is not unusual .


These are not new anymore .. the gearboxes / diffs do make noises .. the box itself is old school .. shall we just say more play and leave it at that .

If it had LSD then one wheel on the ground and not the other it wouldn't want to turn , maybe by hand but that's not driving it ... if you tried to drive it then it would shoot forward .. LSD = single wheel drive as all the power goes to the non slipping wheel .

In short .. once the brakes are sorted then drive the car and see .

I did kinda speed read the posts a bit so hopefully i've not got anything wrong .

Again .. no offence meant by what i have posted .. it's just better if i post what i think .

Different strokes for different folks, as they say.

They also say there's more than one way to skin a cat which, I think, means the same thing.

At the end of the day, however, it's great to have advice from kind people who clearly know what they're talking about.

Believe me guys, I appreciate every word from both of you on this thread. :thumb:

It's a bit of fun for us and gives you different alternatives on fixing your car ..

For me ..

That's what this forum is all about .

I still say you need a replacement caliper though