Removing and rebuilding front brake caliper

[Mark101]

Hi,

I have an O4 R1200GS ABS with servo assist brakes

A piston in a front caliper has stuck and I need to remove it from the bike for a rebuild.

I've rebuilt calipers before on other bikes, but I gather the servo assist on the GS makes it more problematic.

I've checked out the info on flushing servo brakes but wondered if anyone can give me some pointers or things to watch with regards removing a caliper completely

Cheers

 

[Boxerboy55]

I haven't done it on a GS, but do not imagine that the mechanics of removing the caliper and overhauling it with genuine parts will be any different from any other caliper. Don't cut any corners with brake parts.

However, "bleeding the brakes" on a servo bike is a little bit different. Again, I didn't do it myself, but watched an Indepenent change my brake fluid a while ago.

(a) he'd done it before
(b) he had the trick funnel and connections to do each of the braking elements in turn

But hey, you're only breaking the one hydraulic connection to the caliper. But is it time for a full fluid change?

Personally, I'd get hold of a new or recon caliper and get along to someone who could swap it over and bleed the fully system for you in one hit.
Peace of mind all round.

 

[Bendy toy]

The caliper swap idea makes sense. Make a clamp from two lengths of steel strip and long bolts to hold a piston into place and use a block of wood between the other two pistons. Compressed air should move the one free piston. Remove the seals clean everything and replace the piston with new seals if needed. Move the clamp to the just done piston and repeat. Eventually you will have all four cleaned up, or with new seals and ready to go.

 

[Mark101]

Hi,

Thanks for the advice.

I think I'm going to sort the caliper out then flush the whole brake system. I doubt it's been flushed for a couple of years.

I need to suss out if removing the caliper will allow the fluid to drain from the servo - I gather letting it run dry is not a good idea.

Cheers

 

[BBB61]

Over on Advrider they have a section in their Hall of Wisdom about bleeding the brakes on a servo bike which you might find useful.

 

[alex_rsa]

Bleeding a servo system is very easy as the servo does all the work for you.

It looks daunting and that scares most people off but there are quite a few "how to bleed servo brakes" write-ups out there. I have done it twice without any fancy funnels.

Make sure you have the brake fluid in something you can easily top-up the small brake fluid resevoir (big syringe) and just keep topping it up as it bleeds.

You will have more problems getting the stuck piston out of the caliper!

 

[Bendy toy]

You will have more problems getting the stuck piston out of the caliper!

The easiest to shift a stuck piston is compressed air. If you dont have a compressor make up a banjo fitting that you can connect a foot pump or stirrup pump to. It means a bit of forward planning, but a cycle stirrup pump can generate a very high pressure and with a special banjo is a lot less costly than a compressor.

It might be possible to use a tapered connector as used for footballs and gym balls into the caliper bleed hole, but you may need another person to sharply push down the pump handle. And - a suitable bolt to plug the banjo bolt hole.

 

[Mark101]

Bleeding the servo system does seem scary but after reading up is seems relatively straight forward. I guess you just have to be methodical.

I'm in the process of bodging up a funnel with an old rubber bung I have form which seems to seal quite nicely. If that doesn't work I'll get a top up helper

I've had hours of fun grumbling and wresling with stuck calipers but found connecting to an air compressor has not let me down yet - there is always a first time!

Cheers