Changing Brake Pads

[TorqueVR]

Is is necessary to undo to the cap on the brake fluid reservoir when fitting new brake pads?

I've promised to help my son fit new discs and pads to his car today, but's hit a deer and the bonnet lock's busted.

[fausTVR]

In short, yes. Pushing the pistons back to allow in the thicker new pads will force fluid into the reservoir.

[s p a c e m a n]

Doe!

[MajorProblem]

How badly damaged is the car if you can't get the bonnet open?

[JakeT]

MajorProblem said:

How badly damaged is the car if you can't get the bonnet open?

Could be a Focus with the stupid key operated (and very breakable) bonnet catch?

[TorqueVR]

10/10 Jake!

[GreigM]

Yes, you can push it back without removing the cap. The reason for removing the cap is nothing really to do with pressure, its to make sure there is enough space for the fluid - IF you have been properly maintaining the car the fluid would have been topped up as the pads wore down, so pushing the piston back would make this extra fluid spill out - you remove the cap to provide extra space in the reservoir and so you can remove fluid to stop it overfilling and spilling out.

Contrary to popular belief, the reservoir is not pressurised, it will have air holes to allow air in as the fluid level drops. It may be a bit more difficult to push back the piston as you are effectively squeezing air out smaller holes, but it will move.

[Sensibleboy]

You shouldn't push the pistons back with the bleed nipples closed on an ABS or ESP equipped car. Always open the bleed screw rather than push fluid backwards through the system.

[GreigM]

Sensibleboy said:

You shouldn't push the pistons back with the bleed nipples closed on an ABS or ESP equipped car. Always open the bleed screw rather than push fluid backwards through the system.

I discussed this with a very experienced mechanic once. He did say that almost all manufacturers of ABS equipment recommend that the bleed nipples are opened when pushing pistons back - however he also said that almost no garages inc main dealers will do it this way as in reality there's way more chance of breaking the bleed nipple than any issues with the ABS developing, but theoretically the above is sound advice.

[anonymous-user]

Fix the bonnet first...

[TheInternet]

GreigM said:

IF you have been properly maintaining the car the fluid would have been topped up as the pads wore down

Never known a car that could go from max to below minimum due to pad wear, seems unlikely on any run of the mill cars with single piston calipers.

[Andyjc86]

GreigM said:

I discussed this with a very experienced mechanic once. He did say that almost all manufacturers of ABS equipment recommend that the bleed nipples are opened when pushing pistons back - however he also said that almost no garages inc main dealers will do it this way as in reality there's way more chance of breaking the bleed nipple than any issues with the ABS developing, but theoretically the above is sound advice.

This.

If your just doing one set of pads then you should be ok. Removing the cap just makes it easier. But if your concerned about damaging anything, then just crack off the bleed nipple

[jamieduff1981]

Conversely openinh the bleed nipples every now and then helps prevent them from seizing in the first place

[eltax91]

Got to local pond supplier
Buy 2ft hose and one way valve
Spline 1 way valve in 6 inches along hose so it won't get pressurised.
Attach to bleed nipple
Crack nipple
Push pads back
Tighten nipple

Done

[Oldandslow]

But what about after? New pads fitted and you pump the pedal to get them seated. The fluid level drops and you've still no clue how much is in the resevoir except you KNOW it's less than it was before.

Get the bonnet sorted/opened.

[Piersman2]

Oh my word, what a bunch of ninnies.

Just lever each of the old pads back with a long screwdriver, extract and drop in the new ones, Repeat 4 times.

Done.

[t400ble]

I always remove the cap, pads on my little Peugeot Bipper van when pushed back took the fluid level right to the top

[nickfrog]

Piersman2 said:

Just lever each of the old pads back with a long screwdriver, extract and drop in the new ones, Repeat 4 times.

Do cars have 5 calipers ? ;-)

Either way, that's exactly how I do on my bike. Except I only have to do it twice.

[eltax91]

Piersman2 said:

Oh my word, what a bunch of ninnies.

Just lever each of the old pads back with a long screwdriver, extract and drop in the new ones, Repeat 4 times.

Done.

Yeh. And if they are wind back rears? You've just given him a recipe for a lot of wasted effort. And since he's included in that bunch of ninnies you talk about maybe he will damage the caliper trying not to be one.

[Piersman2]

eltax91 said:

Piersman2 said:

Oh my word, what a bunch of ninnies.

Just lever each of the old pads back with a long screwdriver, extract and drop in the new ones, Repeat 4 times.

Done.

Yeh. And if they are wind back rears? You've just given him a recipe for a lot of wasted effort. And since he's included in that bunch of ninnies you talk about maybe he will damage the caliper trying not to be one.

Was the OP asking about wind back calipers etc...? No. He asked if he needed to worry about taking the top off his brake fluid reservoir whilst fitting new discs and pads. Let's not over complicate things eh!