Unanswered Hope V4 caliper/piston question

[ibgarrow]

I’ve just acquired a 2017 Levo FSR which has had Hope V4 calipers and discs fitted. Unfortunately the last owner doesn’t seem to have looked after the bike, and has damaged the pistons in the rear caliper in an attempt to free them. As a result, I can’t expel the inner pistons as one is seized and the other leaks, so not pressure to push pistons out.
if I remove the bore plugs and push out the outer pistons, is it possible to extract the inner ones? Perhaps by driving a self-tapper in and pulling them out?
this may leave damaged bores, in which case I’m looking at having to replace the whole caliper ?

 

[Mikerb]

looks like you have no other option but to remove the bore plugs and push the outer pistons out. You then have a few options for removing the inner istons by accessing them through the opposite bores..........all of which will scrap those pistons but a complete piston/seal kit is going to be needed regardless.
Firstly I would use a penetrating oil like WD40 trying to get that between the inner pistons and their bores. Leave a while then clean up with IPA.
Not sure if the piston is plastic or ally but I would be inclined to try first aralditing a rod to the piston ( clean the piston surface with IPO first) using the outer bore hole for access. If you use a rod the same diameter as the dished inner shape of the piston face you will get the maximum contact. Leave for 24 hours in a warm place to ensure a good set. You should then have the option to both rotate the piston and to pull it.

 

[ibgarrow]

looks like you have no other option but to remove the bore plugs and push the outer pistons out. You then have a few options for removing the inner istons by accessing them through the opposite bores..........all of which will scrap those pistons but a complete piston/seal kit is going to be needed regardless.
Firstly I would use a penetrating oil like WD40 trying to get that between the inner pistons and their bores. Leave a while then clean up with IPA.
Not sure if the piston is plastic or ally but I would be inclined to try first aralditing a rod to the piston ( clean the piston surface with IPO first) using the outer bore hole for access. If you use a rod the same diameter as the dished inner shape of the piston face you will get the maximum contact. Leave for 24 hours in a warm place to ensure a good set. You should then have the option to both rotate the piston and to pull it.

IPA, IPO?

 

[RustyMTB]

Isopropyl alcohol. I have a V4 caliper with this problem. You'll find if you undo the bore caps, you'll be able to tap the piston out using a dowel of some description, ideally plastic or wood, definitely nothing metal & a soft faced mallet.

The pistons are made out of phenolic resin & chip easily, they'll pop out of the bore without damaging it as thery're a much softer material. I would just buy a new set with new seals, they're cheap enough & refitting them is awkward to say the least. Hope recommend lubing them with plumbers silicon grease. Under no circumstanced refit chipped or marred pistons, they'll wreck the seals, cause fluid leaks, pestilence, death etc.

 

[ibgarrow]

Isopropyl alcohol. I have a V4 caliper with this problem. You'll find if you undo the bore caps, you'll be able to tap the piston out using a dowel of some description, ideally plastic or wood, definitely nothing metal & a soft faced mallet.

The pistons are made out of phenolic resin & chip easily, they'll pop out of the bore without damaging it as thery're a much softer material. I would just buy a new set with new seals, they're cheap enough & refitting them is awkward to say the least. Hope recommend lubing them with plumbers silicon grease. Under no circumstanced refit chipped or marred pistons, they'll wreck the seals, cause fluid leaks, pestilence, death etc.

Thanks. Yes, I can get the outer pistons out once the bore caps are off, but it’s the inners I was asking about removing. I can’t blow them out, as one leaks so badly there’s no pressure, and the other is stuck solid. someone has tried to prise them back, and has chipped the protruding part. (Glad to hear they’re resin-explains the chipping)
going to try all the suggestions so far. I’ve got new pistons and seals coming.
Ta everyone.

 

[RustyMTB]

Right. RTFQ as they say. Might work that idea. I'd be inclined to think the pistons might shatter if you try to screw into them. Might be worth asking Hope direct, they do answer queries. [email protected]

Another way would be to bleed them up & actuate the lever whilst keeping the outer pistons recessed by force but you've suggested they're too stuck for that. If it comes down to it, a V4 is about £100-£120 if you can get one, if it's just too knackered to recover. Good luck.

 

[Gary]

Hope calipers are completely strippable and re-buildable and Hope sell every single part required to do the job.
It can be a PITA job to do, requires hope specific tools and is fairly time consuming so depending on your enjoyment of this sort of job simply buying a new complete caliper may be the more attractive option.
In a shop you may well be charged more for labour and parts to overhaul, strip and rebuild the caliper than the cost of a new caliper (sans fitting/bleeding)

 

[Mikerb]

ok....if they are resin araldite should adhere OK.To increase the quality of the bond the surface of the piston needs to be grease free...hence the IPA. It may also be worth using a sharp probe to scratch the surface to give the araldite more to stick to.

 

[EezyRider]

Contact Hope, they offer a “brake service” service, not used myself (I service my e4/v4’s regularly) but a mate used them when he damaged a piston and they came back like new, with new pads, pistons etc, think it was about £60 or 70

 

[RustyMTB]

As if by magic, my new pistons turned up. A tenner all in for a freshy rebuild.