Rear brake pistons -
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Unread 03-08-2013, 08:08 AM   #1
Ideford Jeep
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2000 WJ 
Join Date: Dec 2007
Location: Devon, England
Posts: 37
Rear brake pistons

2000 4.0 WG Ltd

In the process of replacing my rear brake pads, I found that the pistons will not return into the caliper - the calipers are now off the car and no fluid in it or brake line attached so there is no prblem relating to brake line acting as a one way valve.

The pistons will go part way in before binding - there is no noticable lip on the piston or caliper. However the piston appears to be made out of some sort of fibre and not metal - has this 'crushed' slightly causing the piston to distort? Can this be machined safely? Has anyone else come across this - a search shows some problems with rear brake pistons binding but no-one has commented on the pistons.

Also, does any-one know if the WJ calipers/pisotns are compatible with the WG (European version)?

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Unread 03-08-2013, 08:52 AM   #2
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2002 WJ 
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I apologize that I don't have much to add to this, except to say that my pistons just easily slid all the way back so it's clear (to me) that they're meant to go all the way in.

I had brakes on an Isuzu that had to be "screwed" back, using a special tool (or the tips of needle-nose pliers).
Your loss.
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Unread 03-08-2013, 02:50 PM   #3
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I can't say if you can machine them (I would say it's a bad idea, myself, but I'm no expert). The pistons themselves are made of a phenolic plastic. Strong, but not shatterproof.

I don't think the pistons would deform, instead, is the bore rusty/dirty/poorly machined?
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Unread 03-08-2013, 04:23 PM   #4
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if the pistons were forced back using a c clamp and had alot of corrosive stuff all around them they might have deformed. They usually are replaceable instead of replacing the entire caliper if you are into DIY. I found that Jeep itself was selling a kit for the front Akebono calipers which has 2 new pistons and all the associated seals for cheaper than i could buy online last year. Did both fronts for price of single reman caliper myself on a saturday.
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Unread 03-09-2013, 12:13 AM   #5
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2004 WJ 
Join Date: Feb 2011
Location: Bognor, West Sussex. England. Great Britain
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I did mine recently and had the same problem. I re attached the hose to push the piston nearly all the way out then disconnected the hose and pulled the piston out using soft grips. The piston are ceramic so be careful. Everything looked ok but on closer inspections there was like a thin varnish build up on the piston and dirt in the groove that the seal sits in. A quick clean of both (and the caliper bore) with solvent and 1000 grade yet and dry paper followed by reassembly using lots of fresh brake fluid as lube to make sure the real stayed seated and the piston was I nice sliding but tight fit and works perfectly.
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