piston out of brake caliper, worth a cleanup? with pictures

[xpress]

here's the inner piston out of the front n/s caliper ..

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popped this inner piston out with a bike footpump, the outer pistons either side aren't siezed, if they're not seized would you leave them as they are and only change the seals and dust cover on the inner pistons each side?

do you think this is worth cleaning up and fitting new seals and dust seals with? the rust seems to be surface with no pitting, the actual caliper bores might be a problem tho, haynes says to use brake fluid or meths to clean then with, could i use some cif mild abrasive/autosol/wilco paint polish and then another clean with brake fluid?

should i clean them and then see how they look?

seems that the lip and the piston was just caught with a bit of this rust, i have seen this sort of thing with the dashpot on a carb, needs a little polish and a clean and then it's smooth again.

what do you think? just thought i would post it up.

[sarran1955]

Hello,

I'm doing the same job myself , the van had been towed at high speed with no servo on the brakes, so the disc pads were cooked and the pistons siezed in place. I am going to use Solvol Autosol metal polish, (if it's good enough for Rolls Royce.....), and fit new pads and outer seals. I use a brass 'toothbrush', and lint free cotton to polish. Clean everything in methylated spirits. When absolutely dry, use brake fluid as lubricant, (wear nitrile gloves). If there is any doubt about the condition of your bleed screws (7mm), now is the time to change them,
and fit the little rubber caps.

Cordialement,

[xpress]

hi sarran, just back from looking at some guides on polishing the pistons on the internets.

it's the inner pistons on my van that are sticking, i am just going to replace the seals and dust covers on these only for now, i am going to try and buff with a durable rag and brake fluid since it's corrosive and that should polish what you see up to a shine hopefully, if not then maybe some 1500 wet and dry very carefully in a circular motion then buffing with the brake fluid.

next job is to look at the bleed screws, being careful because they're brass! the brake pipe spanners have been a godsend as was a breaker bar in this job. i have ordered some rubber caps for the bleed/drain screws! six in total, two two and one for each piston on the back.

[H-G]

It may be worth using scotchbrite (the rough bit on one side of a washing up sponge) rather than emery which will rub away the metal on both the piston and the cylinder. I would also consider replacing the bleed nipples with stainless ones while you are at it.

[R0B]

where are you getting the seals and dust protectors from?

[xpress]

gsf!

[sarran1955]

Hello,

Brass bleed screws,

Standard VW was steel, worth getting in stainless,especially the lower, balancer ones. Where will you be getting your parts from, I may well use Serial Kombi.

I'm staying with Solvol Autosol for deoxidising and polishing,

As you say , there is only a bit of edge corrosion, in my case due to lack of dust seals, there's a moral somewhere...

Cordialement,

[xpress]

bad news i think i have spotted some damage to the caliper bores right at the back on either side, otoh, i can't see where the channels are that let the brake fluid in, and these might be it. pics coming in a sec.

[xpress]

here we go .. on the bright side, the piston came up a treat. as for the lumps out of the piston bores, i know that if there's a scratch on the piston that goes across the seal then brake fluid can come out, so should this affect things being at the back?

[sarran1955]

Hello,

Your job seems to be going ok

As a matter of interest, there are a pair of Girling T25 calipers NOS on ebay

Item number: 250689357806.

However, watch out when you remove the cylinder seals, as if there has been water in there may be corrosion, and this must be removed before you fit new seals, Keep going as you are, as I said, use plenty of brake fluid to slip the piston back in, old will do as long as its clean, wind the piston in gently.

My pistons have been gently persuaded in the past with a hammer, so I'll be going over the outer edges with a Dremel b4 refitting dust seals.

Who are you using for parts

Cordialement,

[sam_seed]

can't see the scratches dude... all i see is the bleed hole and the fluid line hole

[croc]

My take on this is that the outer surface of the piston must not be pitted as this is in contact with the seal ring and forms fluid seal as piston moves.
The inside of the calliper is not important except for the groove where the seal goes and to lesser extent where the dust boot goes. Internal passages must be clear. Brake fluid washes off well with hosepipe water but make sure all passages etc completely dry with compressed air or pressurised air duster can.
Inside of calliper can be gently sandblasted to clean rust and other gunge.
Do both pistons while you have calliper off as seal kit will contain seals for both the inner and outer.
Also do both (front) wheels at least with same set of matching pads.
I have cleaned piston with brake fluid and 1000 wet/dry and sand blasted inside callipers on my own vehicle and had good result.
Brasso or similar to finish pistons is ok too.
Bleeding is quite easy with a one man bleeder - soft rubber tube with plug and a slit in the end from motor factors. Can watch fluid level too while bleeding.
Bottom line - your life depends on these brake components, do the job right!!

[xpress]

definitely echoing the taking the time and doing the job right.

there's defintely two nicks out of this piston in opposite sides of the back of the barrel. not sure if this is normal. i thought one was, but two?

[croc]

Just looked at your photos again.
The pistons should be quite shiny almost like a chromed finish, in the photo yours looks quite satin finish. Could someone else have had-a-go before you with coarse wet & dry? Also brasso ~ T-cut.
Don't know about the nicks you mention in piston, did you mean calliper barrel?? The calliper has several drillings for fluid in/out, to bleeder and to other side of calliper.
You can blow through the ports inside calliper to see where they go, using a straw or small tube to your mouth.

Cheers
jon

[xpress]

thanks jon. t''other day i suddenly had an eureka moment when i was walking along and realised that the brakes are servo adjusted. therefore there must be a "push" port and a "pull" port for the fluid. there was some sort of dried up crud in one of these drillings, not the one without the little brass type "pin" that i presume sprays out the fluid, the other one. i presume it is the "pull" fluid port. this caliper was seized "on", which concurs with the suck port being blocked, could have been sediment from the piston sliding in the caliper bore and also old oil breaking down. i was a bit hesitant because the holes looked a bit handmade, but i guess they're drilled. i have two ports. i will try and blow through them with a straw and if it goes somewhere then they're obviously ports! thanks for the help.