Change rear-brake pads - Vectra C

[mointainwalker]

Today I set out to do the above. It was only the second time I have ever changed rear pads on a car needing a rewind tool, and the first time I used a pair of circlip pliers as I didn't have the tool: as I recall it was laborious but went smoothly enough. Following that I bought a kit for the next time which was today.
I started off using a ratchet with the corresponding tool , rather than the T-bar tool they supply. I sat there turning and turning - and keeping as much pressure on as possible - but noting seemed to be moving. I then came into the house and looked at a video how to use the correct tool and saw my error: just not able to apply enough pressure constantly to the piston. When using the correct procedure with the T-bar and "lock-plate" everything went a lot smoother.

Two questions: I persevered initially with the ratchet because I thought that if there is a thread, then the screwing motion ought to engage it, but it didn't . Why not ?
Secondly, why is this mechanism used ? Why can you not simply squeeze the pistons back as is still the case with the front brakes ?

 

[Harry Bloomfield]

Why can you not simply squeeze the pistons back as is still the case with the front brakes ?

They are self adjusting, both constant pressure and turning is needed, to screw them back in.

 

[mointainwalker]

They are self adjusting, both constant pressure and turning is needed, to screw them back in.

Harry, doesn't answer why the piston didn't engage/wasn't engaged on the thread and therefore retract when I was sitting there using a ratchet. If it's on the thread, it shouldn't also need pressure.

 

[Mottie]

They are self adjusting

All brake callipers are self adjusting Harry.

Difficult to explain why they have to be screwed and pushed at the same time but it’s all to do with the built in handbrake mechanism.

 

[Harry Bloomfield]

Harry, doesn't answer why the piston didn't engage/wasn't engaged on the thread and therefore retract when I was sitting there using a ratchet. If it's on the thread, it shouldn't also need pressure.

It's to do with both parts turning together, unless you push and turn. The pressure stops the rear part turning in sympathy.

 

[Harry Bloomfield]

All brake callipers are self adjusting Harry.

They are now

 

[Stivino]

If it's on the thread, it shouldn't also need pressure.

That's correct, maybe it was just off the end of the thread?

 

[carmanmemoranda]

That's correct, maybe it was just off the end of the thread?

I agree but...
It often happens and you need to maintain the pressure even when it's halfway back or can just spin and not wind in.

It has to do with the ratchet type mechanism inside which allows the piston to wind out and take up the pad wear but not retract, so allowing the handbrake to keep a constant pressure, again without having to take up too much slack.

 

[mointainwalker]

Thanks everybody, I think you've cleared up my queries, however I am left with one and am uncertain whether it ought to be another thread or not.

What can you do if the automatic hand-brake adjustment isn't giving a good result i.e. lever well up but iffy hold ?

EDIT: Looked on a Vectra-C forum and found as much as I'll probably get. You can try a few things which may/may not work, but then it's a new assembly with an expensive fitting charge ( wouldn't try it myself - no garage )

 

[Harry Bloomfield]

Thanks everybody, I think you've cleared up my queries, however I am left with one and am uncertain whether it ought to be another thread or not.

What can you do if the automatic hand-brake adjustment isn't giving a good result i.e. lever well up but iffy hold ?

Usually here is some adjustment at the handbrake lever itself, to take up slack in the cable(s).

 

[carmanmemoranda]

Thanks everybody, I think you've cleared up my queries, however I am left with one and am uncertain whether it ought to be another thread or not.

What can you do if the automatic hand-brake adjustment isn't giving a good result i.e. lever well up but iffy hold ?

EDIT: Looked on a Vectra-C forum and found as much as I'll probably get. You can try a few things which may/may not work, but then it's a new assembly with an expensive fitting charge ( wouldn't try it myself - no garage )

The normal handbrake issue is either

A caliper mechanism not working

A cable sticking or trapped

A handbrake used before the pedal is pressed repeatedly after fitting new pads. Ideally release the handbrake cables, rewind the calipers, fit the pads, press the pedal until the foot brake is right and clearances taken up and then fit the hand brak cables accordingly. Using the handbrake before the clearances are taken up gives a poor foot and poor hand brake