Seized pistons in P1800 front calliper

[Alan Beckett]

Does anyone know of any tricks to free up the pistons inside the front brake callipers? I have the girling four pot callipers on my '68 - three pots are free on the nearside, only one free on the offside.

Is compressed air the answer, or is there some form of solvent that will deal with the rust / oxidation without having a harmful effect on the rubber seals?

[Citizen.Agfa]

Yup, compressed air is the boy, with lots of "agitation" (hitting the side of the caliper with a girt big 'ammer, whilst the air is on) and loads of WD40 or equivalent.
As for the seals, if the piston is siezed they're probably shagged (technical term) so solvent damage isn't much of an issue.
Hope this helps, Nick H.

[pookie]

" Big Al " Beckett who used to shoot a bow and arrow ?

[Andrew (UK)]

Actually the most effective way is to connect up a hydraulic system (eg your brake system complete with master cylinder) if possible, you can get a far higher pressure that way and when they do move they won't go shooting out.
If they are badly seized then you will probably want to replace the pistons or else they will destroy the seals and seize again quickly and it would be criminal not to do the seals anyway. If you do use any petroleum based lubricant eg WD40 you will need to thoroughly remove all trace of it afterwards with something like meths or brake system cleaner.

Andrew

[Alan Beckett]

Pookie,

Yup, that's me. Kit still in the box, intending to get back to the club, but fixing up this car got in the way. Are you still shooting? PM me with more details

Citizen Agfa / Andrew,

Many thanks for the suggestions. Brake fluid runs to the callipers through the new brake lines I have put in, I'll try and bleed the system and then force the buggers out. I have a new seal and spring kit in stock with enough spares to fix up the duff pots. Many thanks guys.

[amazondean]

If the piston has siezed it's usualy because the piston has started to rust. There is no answer other than a new piston, otherwise you will be doing the same job again in time. Once the crome plating starts to come off thats the end of it. You will probably find that the other pistons are on there way as well. Stainless pistons are one answer. I can make stainless pistons if anyone is interested.

Dean.

Alan, I had this problem on my amazon, used wd40 and a good push on the break peddal and as far as I remeber a slight and carefull bit of leverage. There was slight rust damage but this hasn't caused a problem for the last 12 months.

I only noticed the sieze when i had to change the pads.

Good luck
Ian

[Alan Beckett]

Thanks for all the responses. Having bled the brakes, and applying some gentle persuasion, I managed to get all the pistons moving. However, slipping a set of pads in the callipers and then pressing the pedal a few times resulted in the pistons moving against the pads but not retracting. Time for some more leverage to get the pistons used to moving in both directions. Who knows I may even have the car off top the MoT man by the end of the month! Time to go and let the pigs out for their evening flight...........

[mike gilbert]

Instead of the pads try using progressively thinner and thinner bits of wood in the calipers. This will allow the pistons to come further out without risking them popping out altogether. The further you get them out the easier it will be to lever or push them back in. Repeat the process a couple of times and they should work fine,,,,for a while.
Mike

[Alan Beckett]

Once again, thanks to all for the hints and suggestions. I have bottled out and bought two reconditioned calipers. A cop out, I know, but hey, in for a penny, in for a pound (or several thousand).