Question About Rear Caliper...

You can certainly remove the pistons and clean them up. Use a fine metal polish NOT wire wool or a wire brush on both pistons and bore. Light use of a nylon pan scrub is just about ok. You would be well advised to replace the seals while you are at it and the banjo washers (or anneal the old ones). The brake hose may also be showing its age,

Those underslung calipers attract dirt and benefit from a periodic deep clean and polish of the brake pins. Re-assemble with brake grease and bleed vertically before you reassemble on the carrier.

 

If you remove the pistons you will need a seal kit, they are sometime svery tricky to get back on after cleaning without the right press or tool.

What I do for the race bike is use a 'G' clamp to hold the piston one side in place, then gently pump the brake lever forcing the piston in the other side out a bit, be careful not to go too far, then gently clean the piston with wire wool & brake cleaner, I normally use a tiny bit of silicone grease on the piston before releasing the clamp, then push the clean piston back in & repeat the process on the other side. When you have done both then clean excess grease off with brake cleaner then refit the pads.

 

I have just done similar on my 97 Sprint, rear caliper stuck, total loss of back brake (not that I use it much).

I looked for a second hand spare... There were a few in the US, but none in the UK, there was a guy offering rebuild and recondition at about £80 on ebay...

I bought a set of stainless pistons and seals, kit included stainless bleed nipple and brake grease.

After removing the caliper, there was no way the pistons were coming out easy... I used piston pliers to pull them... They weren't too corroded, but I replaced them anyway. The reason they were corroded and stuck was because the previous owner hadn't fitted the outer seals, and the pot was full of brake dust and crap.

It was actually an easy job to do. I have done plenty of car wheel cylinders, but this was the first caliper I had done. It was a very pleasant surprise!

Sticking on has put the rear disc slightly out of true, so looking for a replacement for that. My mot tester says it's not bad enough to be bothering with, but, brakes man, brakes!

 

Parts from here, by the way...

https://www.squaredeals-ltd.co.uk/

Very fast service, and parts were really good quality. I'm happy to recommend them!

 

The caliper is mechanically very simple. Lump of metal, two big holes, pistons and 4 seals (2 main plus 2 outer dust). A small hole at the back admits brake fluid.....

The key parts to polish are the bores and the pistons. Brass polish works very well. It is very finely abrasive and will polish away corrosion. Replace the seals and lubricate with brake fluid to re-install pistons.

We’ll get to bleeding later!

 

I think one very important part is to make sure that all parts that should move can move.... Mine has a part that moves in and out (think its a slide its called) on two pins. Ideally I should have replaced the rubber thingies (haha, I said 'rubber thingies' I mean boots, I guess ) but couldn't get any, so just a damned good clean, and plenty of red rubber grease in the boots. Coppaslip on the back of the new pads, and a bit on the antisqueal plate.

It was a bit fiddly getting the pistons in, but I have carrots for fingers, and I managed it!

 

I did have a wonderful video of the following but seem to have deleted it.

Can you see what is going on in this photo - for stuck piston removal?

If you can "get in to" the piston, then this hasn't failed to work (well...only once and that was on a piston that was totally corroded in).

Put a standard socket in the piston, and also the square end of a socket driver. It needs to be a close fit. As you then rotate the driver the 'cam effect' should all lock the socket into place, and as it does so you should then be able to rotate the actual piston. If you can rotate the piston gently pull up (or pull on the piston) as you continue to rotate...pulling the piston out.

You may need to play with socket/driver sizes to get a good fit.

As others will testify, I ain't not no expert...but I managed full caliper strip down. clean and rebuilds on my 955 Triple...sincerely, if I can, anyone can!

 

here is it in action! From 3m50s

 

I used these....

https://www.amazon.co.uk/dp/B00487UO1G/ref=cm_sw_r_cp_apa_fabc_ranUFbW56V13Q?_encoding=UTF8&psc=1

Especially as I had decided to fit new pistons anyway.

To be honest, I read about using the air line, and I doubt that would have worked, didn't fancy pushing them out by hydraulic pressure (could see one coming out, but the other refusing) so opted for those pliers. @DanielB's idea is cool though. True improvisation.

 

My immediate go to are water pump pliers followed by a grease gun for control you can’t achieve with an air line. If nothing is disconnected use the hydraulics and block each piston in turn til they’re both nearly pushed out.

 

You're welcome....it is a pleasure to share. When I first did it I couldn't stop smiling...there was such untold joy in something so simple!

 

Just as an addition...and I did feel like my calipers refurb turned in to "Triggers Broom"; but whilst I was this far in and upgrading bleed nipples, banjo bolts, pad pins etc all to SS....it seemed a shame to spend a lot of time trying to tidy up slightly pitted and now 18yr old pistons. They really didn't cost much to buy new.... And I didn't get ss pistons either. I felt 'the normal ones' lasted 18yrs....so some new normal ones will do the job perfectly.

Again, as you're this far in, be sure to have a better clean than you think of the veins that feed the piston reservoirs. The tiny veins that actually run inside the caliper ...Mine where full of a waxy jelly type muck that didn't 'wash' out but needed to be mechanically cleared. I found 'interdental brushes' perfect for this....