Technical changing brakes (both discs and pads)

[matty23]

Hi,

I have just ordered some new brake pads and discs (both Bosch) for my Panda. The big question regards pushing back the pistons on the calliper and how I should properly go about doing it.

I understand that the ''official'' way is to use a C-clamp (or G-clamp) and wind the piston back. I don't have these items and I recently watched a video on youtube of a chap who pushed the piston back using the arm of a hammer. Obviously the removing the brake master cylinder cap will help dramatically and I'd like to know if using a hammer to push the piston back is a good idea? I'm not so sure.

I'm sure you've all got some good tips.

Matt.

 

[jrkitching]

and I'd like to know if using a hammer to push the piston back is a good idea?

It's a very bad idea. Don't do it. If the piston is not pressed centrally and evenly it could ruin the caliper seals, and then you'll have to buy a new caliper, which will cost you more than the discs & pads combined.

Just go buy a G clamp; even a cheap secondhand one will do (probably £1 or so at your local market).

Also buy a brake hose clamp.

Before trying to push the piston back into the caliper, first put a brake hose clamp on the flexible hose above the caliper. The attach a piece of tubing to the bleed nipple and loosen the nipple, so that the excess fluid is released when the piston is pushed back. This most important step prevents any fluid inside the caliper (which may be contaminated) being forced back through the brake lines. If any contamination finds its way back into the ABS modulator, it could ruin it - and they're not cheap. Another benefit of doing it this way is it eliminates any risk of the master cylinder reservoir overflowing when the piston is pushed back.

You may need to top up the brake master cylinder when you've finished. Personally I like to change the fluid when replacing pads, just in case any contamination has been dislodged.

Doing stuff like this yourself saves you a great deal of money; make it easy on yourself by buying the proper tools.

 

[A3jeroen]

Frontcalipers can be pushed in by hand.

gr J

 

[Sweetsixteen]

Before trying to push the piston back into the caliper, first put a brake hose clamp on the flexible hose above the caliper. The attach a piece of tubing to the bleed nipple and loosen the nipple, so that the excess fluid is released when the piston is pushed back.

Can't agree with the clamping bit, but otherwise sound advice.
Any unnecessary flattening of flexible hoses weakens them. For the same reason you will find that when advice is given on changing calipers or discs it is stressed that you should not allow the caliper to hang loose but tie it up so that its weight is not taken by the flexipipe.

Brakes are your lifeline, and you do not want to do anything that might create a future weakness in such a flexible component.

Just open the bleed nipple wide when you compress the piston into the cylinder, and the fluid will run out without a problem. Discard it, because it will be the fluid in the system with the most contamination.

Apologies to JR.

 

[daveofkent]

You can push it in by hand and you could use a hammer handle but its so much easier and controllable with a clamp. You spent the money on branded parts and a perfectly good g clamp for the job is £2-3 off ebay including delivery and its such a useful thing to have.

 

[jrkitching]

Apologies to JR.

No apology needed - we're all entitled to our opinions here.

I'd agree it's important not to unnecessarily stress brake flexible hoses. They should always be properly supported when the calipers are removed - I've seen far too many cars in workshops left with the calipers dangling, sometimes even in franchised dealerships .

Brake hose clamps are specifically dsigned not to stress the hose more than is absolutely necessary; IMO the risk of damaging the ABS modulator is greater than the risk of damaging the hose providing you use the proper tools. If the hose does crack when using a good quality hose clamp (and you should check after removing one), it needed replacing anyway (ideally all the flexible brake hoses should be replaced every 10 years, but this almost never happens).

Obviously if you do use hose clamps, you need to take proper care not to overtighten them.

As you say, opening the bleed nipple alone should ensure that most, if not all, of the fluid in the caliper is expelled from the system but personally I prefer not to take the chance.