Spreading rear caliper

[Justasking]

Hi, I've managed to successfully change 3 sets of brake pads on my vr statesman but the last one (ds rear) will not spread open. I've read around and realise I need to undo the bleeder. I also noticed that some tell you to disconnect the handbrake and that the rears twist in. Do the vrs twist or push in and do I need disconnect the handbrake? Thanks

 

[vs-lover]

Hi JA,

There is no twisting whatsoever utilised in Holden Calipers.

I gather you are referring to the pushing back of the piston into the caliper so that the new pads will be able to fit over the disc rotor ?

If this is the case you should always push the piston back with a bleeder hose and brake fluid container connected and the bleeder valve in the open position. You should never push the piston back in without the bleeder open as this merely back pressures the master cylinder and can cause the cups in the bore of the MC to reverse. This is more so common to happen in some other brand of cars like Ford Lasers, but this is a practise that should be applied to every car when pushing the piston back in.

Now the other thing that's rather common on VB through to VS is the lower rear caliper slide seizes with corrosion causing the caliper to no longer float as it should while in service. This is now just a case to remove the complete assembly and remove all the rust on both the slide itself and the bore in the caliper housing. After that if the slide is still serviceable and doesn't require replacement it's super important to apply the correct caliper synthetic slide lubricant (not standard grease, nor Rubber grease) and reassemble. (it's available from Automotive parts stores) Also ensure that the rubber slide seals are replaced with new tight fitting units to stop the moisture from re-entering and putting you right back where you started from.


Now finally going back to the non moving piston scenario, if the piston won't move with the bleeder open then you may well have a what we call a seized piston that will not be totally parallel in the bore (wedged) and thus the only way is to pull it outwards completely from the housing and then inspect the piston itself for fouling marks on it's sides. If this is the case you are going to have to find another good piston at the wreckers etc. and buy an overhaul kit which isn't all that expensive and install that into the housing and re-install the replacement piston.

Make sure you do not allow any foreign matter into the open caliper and actually clean it out using Methylated Spirits (Metho). Then use clean new brake fluid as the lubricant to re-install the piston and seals within the piston area of the caliper.

Hope this is all self explanatory.

Cheers.

 

[Calaber]

Interesting what you say about cup reversion if the bleeder isn't released. In fifty years of working on cars and replacing pads, I have never released the bleeder. My method of pushing the piston back into the caliper is to use a G clamp and gradually screw it in, compressing the piston slowly to provide room for the new pads. This method works for stiff or jammed pistons as well as freely moving ones, and cup reversion has never occurred. The only thing I do beforehand is check the master cylinder fluid level and remove a bit if necessary.

 

[gtrboyy]

G clamp to push piston in using old brake pad...check/lube slider then slap it back together.

Sip beer & shout "You beautyyyyyyyyyyyy"

 

[vc commodore]

You can get a brake piston tool from any spare parts supplier....ie Repco, Supercheap Autobarn.....You use an old brake pad to push the caliper piston back into the caliper and place new pads in....Never had to undo the brake bleeder nipple to replace brake pads...

 

[stick3]

also get brake/ fuel hose clamps from supercheap or any parts store very handy if you want to remove a caliper or push in the piston by clamping the hose and undoing the bleed nipple i have done it this way and the other

 

[vs-lover]

Hi Stick,

You're definitely on the right track, and yes I forgot to mention the brake line clamps that I use as well to stop any force going backwards.

If there's one thing about these forums I've seen time and time again is backyarders and the heaps of s%#@t they muck around with, but then there's the people that use Penrite.........................."the better class of mechanic" that actually know what should be done so as not to have someone killed due to their short cuts and slackness.

BTW any reputable brake workshop that's worth it's weight will tell that you should never back pressure a Master Cylinder. That's why the correct tools are made for the job.

 

[Skylarking]

The brake fluid within a caliper occupies the hottest place within the brake system. Thus it has the toughest time so should be flushed.

So my process is to open the caliper bleeder valve and attaching a drain hose going to a waste container before pushing back the piston. As such I can effectively flush much of this old caliper fluid out into the external container. Then it’s just to close the bleeder valve and remove old pads and install new pads.

Just for this reason alone (part flush of caliper fluid) you should always crack the bleed valve when changing pads.

Good practice would then be to suck out much of the fluid out of the master cylinder and fill up with new clean brake fluid before pumping your brake pedal to push the new pads against the rotor. I then follow up with bleeding the brake lines.

Doing it this way makes for an easier fluid flush during the brake pad change process. I always prefer to flush new fluid through the lines as part of my pad change.

Easy on older brake systems but correctly bleeding ABS brake fluids are more complex and manufacturers recommend specific procedures often requiring specialised tools.

But whether piston seal reversion actually occurs by not cracking the bleeder before pushing back the piston I don’t know. Opening the bleeder valve and flushing caliper fluid during pad change is a no brainer to me.

As for hose clamps, I’ve never used them on brake lines as I don’t see any need. Why put pressure on a hydraulic hose in a way opposite to its intended stressing. Using a hose clamp could conceivably cause some weakness after repeated use on the same spot thus leading to potential early hose failure? I don’t remember any manufacturers workshop manual requiring such clamp methods to avoid master cylinder back pressure? May be I need to re read my old manual

@vs-lover shops worth their weight often try and make things sound more difficult and dangerous than it actually is, may be to ensure their income stream. So I listen to what they say but often take it with a grain of salt

 

[vs-lover]

But flushing brake fluid during pad change is a no brainer to me.

I can tell that you use Penrite ?

 

[Calaber]

VS. I'm no mechanic but I'm happy to stake my knowledge and experience against your backyarders any day. I've seen too much piss-poor work by so called experts, who charged way over the top, ever to consider I need their "help".
Oh, by the way, I might have misinterpreted your post, but to me, it was offensive.