Caliper rebuild tips please.

[Simon Davey]

Now, I'm quite technically minded, and pretty happy with spanners, just recently replaced the disks and pads on my car in fact, but I've never done a caliper strip and rebuild of a bike. 

 

Any advice? 

About 200 miles ago, I topped up the brake fluid, and I find I need to do it again. 

There are no leaks at any of the banjos, and from what I can see with a torch, the pads are a bit low. 

Couple the above with my bike having sat in a workshop corner for more than a year, and I figure I should give those front calipers some TLC as there could be a seized piston or leaky seal. 

 

I thought I'd start by removing the reservoir lid and removing the bottom banjos to drain the fluid, then loosen as much as possible whilst still attached to the forks, before removing to strip and clean. 

 

[Fender1515]

Hi Simon, I have just finished calliper strip down and rebuild in prep for the sunny weather riding, umm.

So based on my approach:

Needed,

Replacement seal and rubbers

break oil, check the DOT 

Copper grease

break bleed kit, with non-return valve

break cleaner spray

Toothbrush, wire brushes

emery paper 100/120, to rub-off any glazing on disks and pads

check torque setting for calliper bolts

containers/ tray for the bits 

depending on condition, I will tend to replace bleed nipples and rubbers. just coz

mechanics gloves, many

lots of kitchen towel

Rags

A bucket of tea, barrel of patience

knee pads, i am old git

I pump the break lever after i have taken out the pads, so the piston is pushed out but not all the  way out on the first calliper I am working on, use a piece of wood in the calliper body to stop the pistons coming all the way out,  bleed the oil out from the bleed nipple using break lever before i strip down the calliper using the bleed kit, did one side at a time, I use an air pump inserted into to the bleed nipple hole to get the pistons out of the last calliper

layout pistons so they go back in same bore

check bores for scoring etc

proper clean up, to remove break dust and road grime

use lots of oil on seals before rebuild

copper grease rear of pads, bolts etc for reassembly 

make sure pistons are fully recessed after rebuild, ask me why i remember this!

Bleed up etc 

Oh, and there is one at the back 

Remember new pads will take A  FEW MILES TO BED IN 

Least ways, I think that's what I do, 

Jobs a gooden!

[Mississippi Bullfrog]

I use red rubber grease on new seals but brake fluid is fine if you don't gave any.

 

They're straightforward just work in a clean place. You don't want any grit getting in there. 

 

Worth remembering that brake fluid is inflammable. 

[Simon Davey]

 

Wow, that's brilliant, I thought I had everything @Fender1515 but I'd forgotten the darned bleed kit.

 

Cheers @Mississippi Bullfrog that's a good point about the grit, I'll use a workbench instead of the usual floor based worksurface.,

 

Thanks guys. 

[Mississippi Bullfrog]

4 minutes ago, Simon Davey said:

 

Wow, that's brilliant, I thought I had everything @Fender1515 but I'd forgotten the darned bleed kit.

 

Cheers @Mississippi Bullfrog that's a good point about the grit, I'll use a workbench instead of the usual floor based worksurface.,

 

Thanks guys. 

I snaffle the kitchen table for brake parts. 

[Simon Davey]

That would be a no, and I wouldn't have as much room as the barn 

[Fender1515]

4 hours ago, Mississippi Bullfrog said:

I snaffle the kitchen table for brake parts. 

Yep. me too, the stony silence bit, i can deal with, dirt in callipers is big no!

[Grumpy Old Git]

Brake (not break) bleed kit:  2 foot clear plastic tubing (ensure tight fit around bleed nipple). Clean jam jar, correct spanner, Fresh brake fluid of the correct specification, Ti-wrap (for brake lever once bleeding completed).

 

[Fender1515]

Brake or a break bleed kit should have a sealed reservoir container, jam jars fall over, gets messy. 

[Simon Davey]

I've bought a kit with a non return valve. 

Hope this just means I won't have to fanny about too much. 

[husoi]

The wasted brake fluid shouldn't be used again once it comes out the bleeder.

I just use a SS dog feed bowl. Heavy and wide enough to stay in place. A couple small clamps to hold the hose in the bowl does the trick.

[Grumpy Old Git]

10 hours ago, Fender1515 said:

Brake or a break bleed kit should have a sealed reservoir container, jam jars fall over, gets messy. 

I always use a jam jar - Never (touch wood) falls over - Not at all messy (use of 'elephant bog roll' helps).

 

@husoi - Agree Never reuse brake fluid (unless for cleaning brake pistons).

 

[Mississippi Bullfrog]

9 hours ago, Simon Davey said:

I've bought a kit with a non return valve. 

Hope this just means I won't have to fanny about too much. 

They work very well. Just keep an eye on the master cylinder level.

 

On some systems you can get brake fluid splashing out of the open mc when pumping the lever so if yours does that cover the open mc with a cloth before pumping. 

 

If you use a jam jar you can always chuck some old nuts in the bottom to weigh it down. You'll be throwing that fluid away anyway. 

 

A tip for brake fluid. Always use a new unopened bottle of fluid. Remove the cap but don't remove the foil seal. You want to punch two small holes in the seal opposite each other. One allows the fluid to pour out in a controlled flow. The other allows air into the bottle. It makes pouring the fluid much simpler. 

[Simon Davey]

4 minutes ago, Mississippi Bullfrog said:

They work very well. Just keep an eye on the master cylinder level.

 

On some systems you can get brake fluid splashing out of the open mc when pumping the lever so if yours does that cover the open mc with a cloth before pumping. 

 

If you use a jam jar you can always chuck some old nuts in the bottom to weigh it down. You'll be throwing that fluid away anyway. 

 

A tip for brake fluid. Always use a new unopened bottle of fluid. Remove the cap but don't remove the foil seal. You want to punch two small holes in the seal opposite each other. One allows the fluid to pour out in a controlled flow. The other allows air into the bottle. It makes pouring the fluid much simpler. 

 

Many thanks MB. 

I've got the right fluid, which I've already opened, but I like your tip about the holes in the foil, worth buying another bottle just to do that, especially if I'm pouring a lot. 

 

I bought this... 

https://www.halfords.com/tools/hand-tools/automotive-tools/europat-vizibleed-brake-and-clutch-bleeding-kit-321141.html

[Phil1]

Avoid using wire wool on the pistons unless you clean them up scrupulously, a tiny strand of it can ruin the seals. Scotchbrite is better.

 

Plus the wire wool sheep are on the endangered species list now. 

Edited April 8 by Phil1

[Simon Davey]

1 hour ago, Phil1 said:

Avoid using wire wool on the pistons unless you clean them up scrupulously, a tiny strand of it can ruin the seals. Scotchbrite is better.

 

Plus the wire wool sheep are on the endangered species list now. 

 

Blimey, I was thinking of using wire wool, then blowing everything out with air pressure. 

That's a good point though, thanks. 

[Fozzie]

Big cans of brake cleaner are on offer at the moment from Toolstation. £3.99 a can. And the stuff is essential for jobs like this. 

 

I find caliper rebuilds quite therapeutic. It's delicate work on the internals. 

 

Removing them is easy, generally a couple of bolts. But I'd loosen the other bolts with it there, like the retaining pin/pins for the pads. When off pull the pin and remove the pads, also note there is often a retainer/shim at the top of the caliper that can fall out. Note it's position and make sure it gets a good clean. 

Remove the pistons with internal grip pliers, I find a slight twisting back and forth motion as I pull works them out easy enough.

 

You can pump the brake with the line still attached to push the pistons out, but usually only one pops out a lot, and you end up using a piece of wood to jam one piston and get the other moving. Soft, but solid material is best so as not to damage the piston faces. 

 

Once apart, remove the seals. Clean their recesses well with either a pick (being very careful not to ) or I use a dremel with brass wire brushes that can't harm the bore. Cleans them out nicely. Thoroughly clean everything with brake cleaner and a tooth brush, with a final spray into the piston bores with the caliper held up so it all drains out. 

 

Reassemble with red rubber grease on the seals, and a very fine smear on the pistons, almost enough to not see. Brake fluid is fine for an alternative, but I like grease for its suspension properties. 

 

Bleeding is the bugger, you can be there for ages pumping and cracking the bleed nipple before it eventually comes through. I switched to using a vacuum pump that pulls it through from the nipple. Then I switch back to the usual one way valve, but as the seal is often imperfect around the nipple, I still tighten it after the last hold down of the lever. I usually pull it 4 times, and on the 5th hold it in and crack the nipple open, close, and repeat. 

 

Probably missed a few bits in here, but trying to keep it short. 

[Tiggie]

1 hour ago, Fozzie said:

But I'd loosen the other bolts with it there, like the retaining pin/pins for the pads

 

Usually this is what I completely forget about until I've taken the caliper off 

 

So much easier to undo the bolts when its still on the forks

[Simon Davey]

5 hours ago, Fozzie said:

Big cans of brake cleaner are on offer at the moment from Toolstation. £3.99 a can. And the stuff is essential for jobs like this. 

 

I find caliper rebuilds quite therapeutic. It's delicate work on the internals. 

 

Removing them is easy, generally a couple of bolts. But I'd loosen the other bolts with it there, like the retaining pin/pins for the pads. When off pull the pin and remove the pads, also note there is often a retainer/shim at the top of the caliper that can fall out. Note it's position and make sure it gets a good clean. 

Remove the pistons with internal grip pliers, I find a slight twisting back and forth motion as I pull works them out easy enough.

 

You can pump the brake with the line still attached to push the pistons out, but usually only one pops out a lot, and you end up using a piece of wood to jam one piston and get the other moving. Soft, but solid material is best so as not to damage the piston faces. 

 

Once apart, remove the seals. Clean their recesses well with either a pick (being very careful not to ) or I use a dremel with brass wire brushes that can't harm the bore. Cleans them out nicely. Thoroughly clean everything with brake cleaner and a tooth brush, with a final spray into the piston bores with the caliper held up so it all drains out. 

 

Reassemble with red rubber grease on the seals, and a very fine smear on the pistons, almost enough to not see. Brake fluid is fine for an alternative, but I like grease for its suspension properties. 

 

Bleeding is the bugger, you can be there for ages pumping and cracking the bleed nipple before it eventually comes through. I switched to using a vacuum pump that pulls it through from the nipple. Then I switch back to the usual one way valve, but as the seal is often imperfect around the nipple, I still tighten it after the last hold down of the lever. I usually pull it 4 times, and on the 5th hold it in and crack the nipple open, close, and repeat. 

 

Probably missed a few bits in here, but trying to keep it short. 

 

That's superb, many thanks for so much detail.

Are you free this weekend?

(I'm kidding, we have the MIL over) 

[Fozzie]

6 hours ago, Tiggie said:

 

Usually this is what I completely forget about until I've taken the caliper off 

 

So much easier to undo the bolts when its still on the forks

 

I definitely forget it half the time I do it, and it's always on calipers with seized pin caps  

 

2 hours ago, Simon Davey said:

 

That's superb, many thanks for so much detail.

Are you free this weekend?

(I'm kidding, we have the MIL over) 

 

You should be fine, although worst case, if you can't manage it you can pop them in the post to me, I've done that for friends, family and a few forum members in years gone by  

[Simon Davey]

That's very generous @Fozzieand thank you.

I just bought a service trolley from Halfords and put it through our business, so I have to do it, just to avoid scowling from the missus. 

[Simon Davey]

Just to report back. 

It was all pretty simple really. 

The pistons were pretty well jammed into the crusty old seals, which had been changed before. This was evident by the plier marks on the pistons left by the previous bodge. 

The old pads were very thick, but I replaced them anyhoo. 

I polished out the marks on the pistons there were some small burrs. 

Got it all back together easily enough, went to Halfords and bought a new torque wrench 

Spent forever bleeding the brakes, and I'm still not 100% happy with the pressure, but I'm going to do a master cylinder rebuild to see if that helps. 

 

You can see a slight leak, it's where the piston had been put back in with plier marks, the burrs had damaged the seals. 

 

Thanks again for the input folks. 

 

Edited Friday at 21:55 by Simon Davey

[RideWithStyles]

the leak

Edited 12 hours ago by RideWithStyles

[Simon Davey]

1 hour ago, RideWithStyles said:

the leak? if the outside surface of the piston is to worn (from being polished to remove imperfections) or scarred from bodging, pressure might be affected so at the mo if the MC doesnt give you the results your expectating then new pistons might be a good idea.

 

There's a place in north London that does them to order. 

In fact, they do a complete refurb of the caliper if required.