Odd Brake caliper issue

[Freebird]

Hi everyone

The offside front caliper on the Vitesse is diplaying an odd behavior and I thought I wiould bleed (scuse the pun) your brains before I dive in and strip it down.

I fitted Capri discs this time last year, so they have Canley's spacers in them. Whilst doing that I replaced all the seals too, the pistons were fine.

After the winter layup I find the offside caliper is binding. The inner pistion does not want to move back into the caliper whereas the outside one moves back fine. The fact the outside one moves back suggests the flexi hose (braded in my case) is not acting like a valve as they sometimes do. If I release the bleed nipple, which is on the inside, the inner piston moves back easily and fluid comes out of the nipple.

So both pistons come out fine, the outer one goes in fine, the inner one goes in only if the bleed nipple is released so that path is clear.

it sort of acts like there is a one way blockage betweeen the piston and the connetion for the brake hose which is also on the inside, right next to the offending piston. Very stange.

Answers on a post card please.

[Nick Jones]

How odd.  Evil spirits?  :-/

Sorry I can't think of anything more useful but your fault appears to defy logic.....

Nick

[GT6 M]

the only thing that pulls a piston back is the deflection on the rubbers.
So if there a wee bit of stickeenesss in the seals then it wont come off.
the coming of with the bleeds open, maa little flow in the right direction to unstick em.

Try this,  tek oot pad on offending piston, and pump pistionee as far oot as it will go, then press back in,
dee this a few times,and lube the piston with fluid and clean off any thing that looks like stuck on grot.
after a few pumps, re try it see if it ok.

I got one dooing this on my MX, and it gets sorted by the above way.

Some ones just had it on a PI on here, but he got new calipers I think,
just needed a good clean oot.
Lack of use is generally a culprit,along with olde fluid getting water in it, rusting the metal around the seals thus making em too tight to work.

M

[Freebird]

Thanks Marcus

I have been trying the "in, out, shake it all about" routine without any luck.

Solid as a rock with the nipple tight (stop it Smithy), push it in really easily with it undone.

Glen.

[Nick Jones]

Does it take noticeably more pedal effort to pump the inner one out?  Might be worth trying a different bleed nipple as I have a vague memory that the various internal drillings meet at the bleed nipple and I wonder if the one to the inner piston is partially obstructed by the bleed nipple itself?

Nick

[Goody]

I think you problem is most likely, crud, rust, dirt or just plan old fluid.   Look close at the caliper cyl. Is it rough, pitted of less then shiney?  Black spots?  Then check the same on the piston.   If piston then I suggest a re build kit.   If it the cyl then a quick run through with a hone.  No hone?  Use fine grit emery cloth.  All you want is to take the glase off.  

[Pete Lewis]

dont forget to check the master cyl is returning fully and the recuperation port is not being un covered  covered , ie seized pedal pivots  broken wavy wahser in the tail of the M cyl  etc.  

just a obscure view it may be a fluid build up rather than stuck piston   ...

Pete

[Freebird]

peterhlewis wrote:

dont forget to check the master cyl is returning fully and the recuperation port is not being un covered  covered , ie seized pedal pivots  broken wavy wahser in the tail of the M cyl  etc.  

just a obscure view it may be a fluid build up rather than stuck piston   ...

Pete

Thanks Pete, but the outer piston moves back OK so I don't think it can be that.

[GT6 M]

If its still going on after all above advice,
split the caliper, and use a prodder to prodderlate doon the passages ,
as some thing may have got in there and acting as a one way valve.

And iit could weel be very near the bleed nipple too.
Its  the only thing left.  it teks nowt to spilt em.

good luck  M

[Freebird]

Thanks M, that's my plan.

I split them Dec 2011 to fit the spacers for the vented discs, so it will be easy this time.

Won't be able to get round to it for a while tho. Mucho elso in front of it in the "stuff to do" queue.

[Freebird]

Well, the symptoms were misleading.

I got a bit of time this afternoon to split the caliper and it turned out to be a slighly rusty piston and also rust at the mouth of the caliper bore. I suppose opening the bleed nipple made the fluid return path that much easier than having to go back to the reservoir.

The chrome plating on the piston has breached in one area causing it to corrode, cleaning it up has effected a short term cure, but I will fit new pistons, or maybe whole calipers soon.

Thanks for all the advise as always chaps.

[GT6 M]

told ye it be sheite aroond the rubbers expanding / sticking them
It seems too that the fluid cant get to the parts to lube it, so meks it stick even moer.

this is what keeps going on with me MX, fronts and backs,
But think I got it sorted noo, filled the rubbers up with  rubber water proof grease, had no issues all winter .
















and on sliding calipers this darn pin gits stuck too





M

[Freebird]

Yukky M, but a nice clean up job.

So what calipers have I got? Type 16P or 16PB, deffo not metric.

[Nick Jones]

Will be 16P or PB - can't quite tell from your pics.  Difference is in the dust shield rubber shape.  If they are held on by a metal spring ring they are PB, if tucked inside the main piston bore (and a complete b'stard to fit) they are P.  Probably cast into the body also.

Have a seal kit for PB surplus.....

Nick

[Freebird]

Nick_Jones wrote:

If they are held on by a metal spring ring they are PB,

Have a seal kit for PB surplus.....

Nick

They are PBs then. I'll take the seal kit off your hands too. ;)