Compressing brake piston

jsmoke

jsmoke

jsmoke

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Joined
17 Jun 2012
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When changing pads you need to compress the piston, do you use a specific tool or can you do it with screwdrivers, other common tools etc?
 
As a rule of thumb a front one can just be squeezed in, a big pair of adjustable grip pliers is often the tool of choice.

Rear ones where the handbrake is integrated often need a special tool which pushes the piston back and screws it in at the same time.
 
For front ones I've often used a spanner and a g-clamp, for rears more often than not a tool is needed to wind them back.
 
just to add on whats been said if its rears and you have a electric hand brake it can get complicated. I know the audi we have its a plug in to the computer task to wind the piston back. Some you can bodge with a battery, but its probably not worth it.
 
To add, don't try and use a clamp or plyers on only one side of the piston. Make sure (as someone mentioned above) put something solid over both sides of the piston so the pressure is evenly distributed, basically means all the force is pushing the piston straight in, and not any force to the side.

It's actually really easy to damage a brake piston by clamping it on one side only and trying to force it back in.

You shouldn't need THAT much pressure either, to give you an idea on my motorcycle I can actually do it by hand, without any tools. A car not quite, but if you are really having to put huge force on a clamp you are doing it wrong.
 
You wouldn't have any braking with no pads in, when you pressed the pedal you'd just push the pistons all the way out and spray brake fluid everywhere.

You'd still have the other brake circuit which would stop the car but it'd be a hell of a mess.
 
For the fronts, once the caliper and old pads have been removed, I've used the old pads back in the caliper and then a screwdriver to back the pistons. Just make sure the screwdriver only touches the old pads and nothing else.

For the rears, I've crafted up a tool made from an old steel plate, shows my idiotness but didn't realise that the rears need to be pushed and screwed back, so having my wifes car apart on a Sunday afternoon left me no option but to craft something up :D
 
jsmoke said:
Worst case scenario you can't get the pads in how undrivable would the car be without a brake on a rear wheel?
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‘Worst case scenario’???

If you don’t know what you’re doing, don’t do it. You could seriously hurt someone. Give it to a mechanic...
 
jsmoke said:
Worst case scenario you can't get the pads in how undrivable would the car be without a brake on a rear wheel?
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Not sure if joking...
There's a very high chance you'll crash. And if you do you will be liable.
Worst case is you put the old pads back in.

My Lexus pistons just pushed back in, think I used a piece of wood each side and two g-clamps.
Rear pistons on the other half's Mini needed a wind back tool.

Just remember to undo the cap on the brake reservoir! Otherwise you're trying to compress the air/fluid in there as it's a closed system.
Also. If the brake fluid has been changed or topped up since pads were originally fitted, when you push your pistons in the fluid will probably pour out the reservoir. Brake fluid is nasty stuff, you don't want to be mopping it up out of your engine bay. Instead, remove some excess with a syringe before pushing the pistons. You can always top it back up again after if you take too much out.

Good luck.
 
Dont forget to clamp the flexible brake pipe and open the bleed nipple to make it easier to push the piston back and stop any damage to the brake master cylinder.
 
bobuk said:
Dont forget to clamp the flexible brake pipe and open the bleed nipple to make it easier to push the piston back and stop any damage to the brake master cylinder.
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I'm sure this might be the absolutely belt and braces way of doing it, but I have never ever done this, nor have I seen any garages do this and IMO, it's completely unnecessary - just wind/push back the brake caliper piston gently and slowly and you should have no dramas. I've heard about the whole "seals getting inverted" in the master cylinder from pushing fluid back in, but can't help but think this would only happen on very old cars which are likely to have perished seals.

I usually just use a G clamp and use the old brake pad against the piston so it has evenly distributed force
 
jsmoke said:
So I'll have the bleed the brakes at the end also?
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Honestly, don't worry about that. I've lost count of the number of brake jobs I've done on my driveway and you don't need to do this. I get the feeling it's a hangover from the 70s or something.
 
Gaygle said:
I'm sure this might be the absolutely belt and braces way of doing it, but I have never ever done this, nor have I seen any garages do this and IMO, it's completely unnecessary
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Agree.

Done it this way several times on 3 different cars and 2 different motorcycles and never had an issue.
 
So final question, to torque or not to torque. So do you torque anything like calipers, caliper carrier, location bolt. I should say I will be replacing the disc also(rear).

Most things I read are not to bother with torquing, it would mean buying a torque wrench.
 
jsmoke said:
So final question, to torque or not to torque. So do you torque anything like calipers, caliper carrier, location bolt. I should say I will be replacing the disc also(rear).

Most things I read are not to bother with torquing, it would mean buying a torque wrench.
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Are you only replacing one side??
 
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