JeffHs
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| posted on 3/10/08 at 03:52 PM |
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Seized caliper - Silicone?
Any ideas? I have rebuilt good M16 calipers with new seals and they are both showing signs of seizing (cooked pads after a very short drive).
I've just spent an hour trying to move 1 of the pistons back - a lot of brute force including hammered steel wedges between disc and caliper but
no movement.
I'm baffled because I've rebuilt similar calipers in the past with no problems at all. The only difference this time is the use of
silicone fluid - from first fill. Could this be the problem?
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mookaloid
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| posted on 3/10/08 at 04:02 PM |
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Wouldn't have thought that Silicone Fluid would cause that to happen. More likely to be a bit of crud or some corrosion causing the pistons to
jam.
I would strip the calipers and inspect for the above.
Cheers
Mark
"That thing you're thinking - it wont be that."
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blakep82
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| posted on 3/10/08 at 04:03 PM |
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did you unscrew the bleed nipple before trying to move the piston back? sure you did, but just checking
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Mr Whippy
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| posted on 3/10/08 at 04:19 PM |
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both seizing at the same time can't be crud
neither can it be anything to do with blead screws, calipers are meant to be retracted with the screw closed, the seals do this normally.
one possible cause it that the silicon has caused the hoses to swell, thus preventing the fluid returning, to check loosen the bleed screw and if the
pistons then move that's the problem.
don't use silicon on a road car as it absorbs water even worse than ordinary fluid, use the normal dot 5 etc as there's nothing wrong with
it.
]
[Edited on 3/10/08 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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flak monkey
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| posted on 3/10/08 at 04:39 PM |
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Normal caliper seals arent compatable with silicone brake fluid, it causes them to swell, then the calipers wont retract properly when you lift your
foot off the brake.
As Whippy says, just use normal dot 5, its plenty good enough.
Heres a quote:
quote:
The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the
introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing
with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to
DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with
DOT 3 or 4.
If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create
a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to
DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system.
Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to
insure that there is no water in the calipers.
David
[Edited on 3/10/08 by flak monkey]
Sera
http://www.motosera.com
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JeffHs
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| posted on 3/10/08 at 06:31 PM |
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I still don't understand this. Every component in my system is new - has never been in contact with DOT4, The car has only been driven for 20
miles (it's still not registered - DVLA problems). Google research suggests that there is no problem at all with new seals and silicone .... and
yet!
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britishtrident
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| posted on 3/10/08 at 06:36 PM |
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The fuid wont't be the problem --- sounds like a master cylinder problem --- piston isn't going back far enough as blakep82 suggested
crack open a bleed nipple if the pistons go back look at your master cylinder pushrods and pedal adjustment.
--------------------------------------------------------------------------
Just to clear up some confusion that might creep into the thread DOT5 is Silicone fluid, DOT5.1 is normal fluid as is DOT4.
DOT5 silicone fluid should not harm any seals (at least in theory)
DOT5 fluid dosen't absorb water so any moisture (water) in the system tend to collect in pockets.
DOT5.1 absorbs water -- which reduces the boiling point and causes corrosion. It is more hygroscopic than DOT4 fluid so has to be changed more
often.
WD40 or even trace contamination of mineral oil will drastically reduce the life of brake seals.
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Mark Allanson
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| posted on 3/10/08 at 07:12 PM |
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Rear shoes back pressuring the system due to the adjusters not locking in correctly?
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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TOO BADD
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| posted on 3/10/08 at 07:38 PM |
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Used silicone in mine since new ( 5 years 7000 miles ) without any probs.
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zetec7
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| posted on 4/10/08 at 06:00 AM |
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This might sound silly, but...did you open the filler cap on the reservoir? Some of them don't breathe (or, if so, is the breather hole
plugged?, or is the reservoir full to the cap, with no room to expand?), which will put continuous pressure on the system (pressure will build and
build each time you put the brakes on), as though you had your foot on the pedal... I've seen this happen.
[Edited on 4/10/08 by zetec7]
http://www.freewebs.com/zetec7/
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