8 replies to this topic

[daniel_johno]

Ive just stripped, cleaned and repainted my 8.4" calipers and yesterday tried fitting my new seals and pistons i got for it.

I got the pistons and seals really cheap off ebay, (£20ish all in) and found it really hard fitting the new pistons. The seals fitted in easy enough but when the piston was fitted it took a hell of a lot of force.
I used WD40 to try lubricate the rubbers to help the pistons slide with more ease but now one is in it just wont move back out again. Unfortunately its not on the inside of the caliper or i could have prodded it out by putting a screw driver in the brake hose hole.

I have split the caliper and tried putting compressed air down the passage way the brake fluid takes yet it moves a few mm then then goes back in again.

Im thinking the second seal has twisted or lodged out of place and now i wish i used some grease when fitting them.

Anyone else had this problem or know how i can remove the piston?

Thanks for looking

Dan

[TOMMO0302]

Hmm,

we had a similar discussion yesterday and it was decided that it is not a good thing that you have to use so much force to get them back in, also, its not a good idea to ever split the caliper.....(although i once did it years and years ago as i thought they were the bolts onto the hub , fitted them back together and all ok.)

Im very surprised that compressed air wont get it out....you could fit other new piston and use the hydraulic pressure or carefully mole grip with protection if they are still sticking out at all?

I'm also not sure about the reaction between wd40 and brake fluid? Although obviously not an issue yet

[pikey7]

WD40 is very very bad for small seals. it tends to make them expand and you get problems like this. The only lube to use inside calipers is brake fluid. no grease, nothing. Brake fluid only.

as was said,splitting the caiper wasn't a fantastic idea, but in the heat of the moment and all that... you'll need to source some new seals and new nuts & bolts for them now. I'm not sure of a source for them, but I'm sure someone will know. Maybe contact AP directly? I'd also suggest that for the piston seals! at least they are guaranteed to be "original" then!

As Tommo says, rebuild the caliper, put the bleeders in, then hold one of the pistons closed (duct tape, tie wraps or something) and then try the compressed air. Once one seal is 90% out, tie wrap that one in position and pop the other out. That should leave you something to grip to get the first one fully out too.

[exscousedave]

Hi,

I got some new seals (not original manufacturer but replacements) for calipers from the local motor factors and the only way to get the piston in was with too much brut force. The result was that the seal was being damaged by the piston - there is a post on this from earlier this week.

Replacement seals have arrived from Minispares and I'll be fitting them tonight...hopefully they will be OK. I'll keep you posted

[TWICEmonkey]

I was gonna say, pikey....doesn't WD40 and other oils perish rubbers?

[pikey7]

I was gonna say, pikey....doesn't WD40 and other oils perish rubbers?

Perishing is down to the rubber drying out. I've found that while WD40 will initially make the seals swell, they will over time also harden, thus making it easier to perish. Basically, "silicon oils" and rubbers don't mix! I used to use it on door seals until I had to replace an entire set of seals on my old Corrado. That was a few quid!

[TWICEmonkey]

Oh I know they don't mix...I suggest using the water-based lubricants, used for fitting tyres, to lubricate your rubbers...works a treat (not that I nicked any from college )

But not in places like brake seals, of course

[pikey7]

Oh I know they don't mix...I suggest using the water-based lubricants they use in tyres for lubricating rubbers...works a treat (not that I nicked any from college )

I couldn't agree more. But not for brake seals! Water... brake fluid...... Definately not best friends! Hence the use of brake fluid as a lubricant for re-assembling calipers!

[TWICEmonkey]

I added that above in hindsight, LOL