flak monkey
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| posted on 21/5/05 at 02:10 PM |
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Best way to unseize a calliper?
It appears that I have a seized up calliper on my cortina uprights. Whats the best way to sort it out?
Any advice appreciated.
Cheers,
David 
Sera
http://www.motosera.com
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GazzaP
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| posted on 21/5/05 at 02:28 PM |
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mine were seized when i got them the best way i found was to spray wd40 or plus gas over the caliper leave it for a few hours after that i was able to
pull the pistons out of the caliper i than covered the calipers in plus gas or wd 40 using loads and left them over night after a while of working
them they were ok and are still working fine today.
hope this is of any help
www.gmpmotorsport.co.uk
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tom_loughlin
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| posted on 21/5/05 at 03:00 PM |
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I got told to connect it to an air supply if you have one, and with any luck, they should unseize. failing that, connect them to a brake circuit, and
press the pedal, which will force the piston out.
my local garage were more than happy to help out when i told them what i was building.
all the best,
Tom
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liam.mccaffrey
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| posted on 21/5/05 at 03:24 PM |
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i had a nightmar gettingmine out which was surprising as they were not corroded at all.
First of all air supply method works well but make sure you protect the piston and caliper with a piece of wood it will pop out with an allmighty
bang.
what i actually did was to screw a grease nipple in the bleed hole i think (it was 18 months ago so a bit hazy) blank the inlet then pump it out with
a grease gun, bit messy but worked well and gurantees sucess!
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clbarclay
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| posted on 21/5/05 at 05:00 PM |
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If its on a vehicle, then taping the piston in and using the brake system to force them back out useually works. Use a brass punch or similare to
avoid damaging the piston.
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Mark Allanson
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| posted on 21/5/05 at 06:24 PM |
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I hooked the caliper upto a grease gun, safer than an air line, and just pressed the pistons out. If you have twin pistons, let the first to move out
by about 1/2" and then clamp it, pust the other out completely and then twist out the first.
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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britishtrident
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| posted on 21/5/05 at 06:35 PM |
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Using compressed air isn't a good idea for two reasons;
(1) You can get many times higher pressures from the brake master cylinder.
(2) It is highly dangerous --- air is compressible and because of this at high pressures stores tremendous ammounts of engery. In contrast
hydraulic presure dosen't have much stored engergy
How easy the piston will be to free depends on how far in it is stuck -- on some P16/M16 calipers if the piston is forced to far back it can be
pretty well stuck for good as it seems to block the inlet port to the bore.
Is usually a case of soaking the piston in a a silcone based rubber lubricant (NB WD40 is not a silicone lubricant it is mainly Kerosene like
hydrocarbons use that and the seals will need replaced) and working the pistons back and forward fractions of a mm until they start to move ---
taking care not tip the piston in its bore, it helps to make a really solid "strong back" type clamp for the opposite piston.
[Edited on 21/5/05 by britishtrident]
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britishtrident
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| posted on 21/5/05 at 06:41 PM |
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I forgot to add --- to press the pistons back use a tyre lever or bar with a blade about 40 to 45 mm x 5 mm and nice rounded edges BUT don't
use it as a lever instead twist it to give a cam type action using a "Stillson" wrench or adjustable spanner on the end ; doing it this
way stops the piston tipping the bore and jamming as you try and push it back.
[Edited on 21/5/05 by britishtrident]
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Peteff
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| posted on 21/5/05 at 08:08 PM |
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I screw mine a bit back in first using a G clamp then rub some copaslip round them and pump them back out. Works for me.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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madman280
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| posted on 22/5/05 at 03:26 AM |
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quote:
Originally posted by britishtrident
Using compressed air isn't a good idea for two reasons;
(1) You can get many times higher pressures from the brake master cylinder.
(2) It is highly dangerous --- air is compressible and because of this at high pressures stores tremendous ammounts of engery. In contrast
hydraulic presure dosen't have much stored engergy
How easy the piston will be to free depends on how far in it is stuck -- on some P16/M16 calipers if the piston is forced to far back it can be
pretty well stuck for good as it seems to block the inlet port to the bore.
Is usually a case of soaking the piston in a a silcone based rubber lubricant (NB WD40 is not a silicone lubricant it is mainly Kerosene like
hydrocarbons use that and the seals will need replaced) and working the pistons back and forward fractions of a mm until they start to move ---
taking care not tip the piston in its bore, it helps to make a really solid "strong back" type clamp for the opposite piston.
[Edited on 21/5/05 by britishtrident]
Um..disagree with compressed air being higher presure. Brake fluid presures can be upwards of 2000psi. My shop air is at 150psi. There is more energy
in hydralic fluid in my opinion also. I think the bigest problem is the fact that most air guns aren't very linear and most people just push
them all the way on and give full line presure in one shot. It does do a fine job of freeing up the piston though. I would agree a piece of wood is
usfull to prevent damage. As for the fluid of choice to free them up- I wouldn't even bother if it were that bad. Not sure about where you are,
but here most remanufactured calipers are quite resaonable, so if its that bad I just get another. Considering the time it would take to free it and
clean up and rebuild the caliper properly, it makes sence to get a reman. Any time a piston is removed from the bore, providing the seals aren't
less than a few months old, I replace them. A few decades of profesional wrench turning have taught me brakes are too important to do stupid things
with.
[Edited on 22/5/05 by madman280]
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flak monkey
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| posted on 22/5/05 at 08:39 AM |
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Thanks for the replies chaps, when I get back home in a few weeks I will take a closer look and see what I can do.
The uprights are no longer on the car. The pads have been removed from the caliper that has seized as the car was being banger raced. The guy soon
found out it wanst a good idea to remove the pads and ended up in the fence.
I took a look on Brakes Int and their reman callipers are £33 each + VAT and £20 surcharge  so hardly cheap. Is this expensive? How much should I be
looking to pay for recon callipers?
Cheers,
David
Sera
http://www.motosera.com
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clbarclay
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| posted on 22/5/05 at 08:42 AM |
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When using liquid under pressure from a brake system when the piston moves the fluid does not expand (not appreciably) behind the piston. 2000psi is
rapidly lost.
Crompressed air expands a lot. 150 psi doesn't just disapate likie the fluid pressure.
The result is that the gas pressure accelerates the piston as it leves the caliper.
Another example tyre blow outs. If an unsecured tyre were to blow out the effects can be desatorous (why you should always inflate tyres when they are
attached to a vehicle or secured in a cage). 10 psi ios enough to propel half ton of wheel/tyre up 15 feet and then come crashing back down again.
In short liquids under pressure are far from safe, but at no cost under estimate the dangers of compressed gas.
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britishtrident
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| posted on 22/5/05 at 10:32 AM |
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quote:
Originally posted by flak monkey
Thanks for the replies chaps, when I get back home in a few weeks I will take a closer look and see what I can do.
The uprights are no longer on the car. The pads have been removed from the caliper that has seized as the car was being banger raced. The guy soon
found out it wanst a good idea to remove the pads and ended up in the fence.
I took a look on Brakes Int and their reman callipers are £33 each + VAT and £20 surcharge so hardly cheap. Is this expensive? How much should I be
looking to pay for recon callipers?
Cheers,
David
Thats a very fair deal --- the seal kits alone are quite expensive,.
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