Rear brake pad uneven contact.
Discussion
I think I might have posted on this before, but I can't recall, so excuse me if I have.
My rear brakes squeal. They have new pads and new rotors as of the rebuild. You can visually see that the outer of both rears has full brake pad contact on the rear disc and the inner isn't contacting as much. This puzzled me and after a bit of Googling and curiosity, I jacked it up, took the wheels off and had a look. Nothing looked untoward, but I greased the calipers sliders with rubber grease for good measure. No real improvement.
It's sprung into my mind today that it could be something to do with the handbrake? The handbrake is cable operated and attached to the inner of the rear brake calipers. Could this tie in at all? The handbrake after rebuild has more pull to lock it on as it were, but I wondered if this might tie in why it's the rears and just the inners of them...?
Please excuse the annotated pictures. I've used pictures from Alcester Racing Sevens page as I didn't have any suitable.
My rear brakes squeal. They have new pads and new rotors as of the rebuild. You can visually see that the outer of both rears has full brake pad contact on the rear disc and the inner isn't contacting as much. This puzzled me and after a bit of Googling and curiosity, I jacked it up, took the wheels off and had a look. Nothing looked untoward, but I greased the calipers sliders with rubber grease for good measure. No real improvement.
It's sprung into my mind today that it could be something to do with the handbrake? The handbrake is cable operated and attached to the inner of the rear brake calipers. Could this tie in at all? The handbrake after rebuild has more pull to lock it on as it were, but I wondered if this might tie in why it's the rears and just the inners of them...?
Please excuse the annotated pictures. I've used pictures from Alcester Racing Sevens page as I didn't have any suitable.
The handbrake shouldn't affect pad contact as it pushes the piston, so its action is exactly the same as the footbrake.
Are the pads fitted correctly? Some have pegs on the backplate which must fit into the slots on the face of the piston; if they are not properly located pressure will not be applied centraly to the pad.
Are the pads fitted correctly? Some have pegs on the backplate which must fit into the slots on the face of the piston; if they are not properly located pressure will not be applied centraly to the pad.
Ahh, as just a hope! Must just be fluke that it's on both rears, and the insides of both. I did think the hand brake would effect both sides, but I thought due to the similarities, there might be something in it.
How do they work as such? The piston is behind the pad which you can not see. The pad you can see obviously has no piston behind it. How does the pad that you can see in the picture get draw onto the rotor? I'd have thought the inside pad would be acted upon more directly.
Car mechanics isn't my for front. I might take them off again and look at the piston for the rear calipers. Could it be gummed up? Worth taking a look and to see if it could be cleaned? Maybe I'll have to find a rebuild kit and a local firm to sort it out. I could get the seals sent over from Bigred if nobody else is local.
How do they work as such? The piston is behind the pad which you can not see. The pad you can see obviously has no piston behind it. How does the pad that you can see in the picture get draw onto the rotor? I'd have thought the inside pad would be acted upon more directly.
Car mechanics isn't my for front. I might take them off again and look at the piston for the rear calipers. Could it be gummed up? Worth taking a look and to see if it could be cleaned? Maybe I'll have to find a rebuild kit and a local firm to sort it out. I could get the seals sent over from Bigred if nobody else is local.
The handbrake cable operates a lever that forces the piston to press its pad against the disc.
One half of the caliper is free to move on the pins ('A' in your pic)& this movement allows both pads to contact the disc.
Be a little careful with handbrakes of this type & ensure it's fully applied as there have been instances of cars rolling away due to the cooling of the disc reducing the grip of the pads on the disc. (As my wife found with her 307) I advise leaving it in gear in addition to the handbrake.
One half of the caliper is free to move on the pins ('A' in your pic)& this movement allows both pads to contact the disc.
Be a little careful with handbrakes of this type & ensure it's fully applied as there have been instances of cars rolling away due to the cooling of the disc reducing the grip of the pads on the disc. (As my wife found with her 307) I advise leaving it in gear in addition to the handbrake.
Edited by paintman on Saturday 20th June 12:45
Are the sliders completely free? These very commonly seize up, causing the entire caliper to twist under braking which would cause uneven contact.
The other thing to check is that the pin on the inner pad is correctly aligned with the slots in the piston. This pin is to prevent the piston rotating when the handbrake is applied. If not carefully aligned when the pads are fitted, you'll end up with a wedge shaped inner pad.
The other thing to check is that the pin on the inner pad is correctly aligned with the slots in the piston. This pin is to prevent the piston rotating when the handbrake is applied. If not carefully aligned when the pads are fitted, you'll end up with a wedge shaped inner pad.
Another thing to add, if you've got the rear brakes particularly hot then you may have killed the seal and removed the piston fallback. If you can find a rebuild kit and have an airline to pop the piston out with then it's actually a pretty straightforward job to change it.
That all said I'm not sure how it would only affect the inner pad, typically uneven wear on a sliding caliper like that will be down to the sliders themselves. Perhaps also worth checking that any slider/abutment clips have been fitted to the pads and pistons otherwise they will bind.
That all said I'm not sure how it would only affect the inner pad, typically uneven wear on a sliding caliper like that will be down to the sliders themselves. Perhaps also worth checking that any slider/abutment clips have been fitted to the pads and pistons otherwise they will bind.
I popped into a garage this arvo and they had a quick look. With the car on the ramps, the wheel off and me pressing the brakes. You could see the caliper twisting, when I say caliper twisting, I believe there is play in the sliders, so it's causing a slight twist.
I've been told you can normally buy new sliders and so on, so up to me to find what I need.
I've been told you can normally buy new sliders and so on, so up to me to find what I need.
Play in the sliders is unlikely to be the underlying cause of the caliper twisting under load.
If the pads are correctly fitted and parallel with the disc, then there should be no twisting forces at all. Twisting on the sliders usually means one of the following:
1) The sliders are seized (most common)
2) Bent or incorrectly mounted carrier (i.e. caliper no longer held parallel to disc)
3) Inner pad has been fitted incorrectly (anti-rotation pin not aligned with notch in piston).
4) The inner pad is partially seized, or a badly fitted anti-rattle clip is obstructing it.
If the pads are correctly fitted and parallel with the disc, then there should be no twisting forces at all. Twisting on the sliders usually means one of the following:
1) The sliders are seized (most common)
2) Bent or incorrectly mounted carrier (i.e. caliper no longer held parallel to disc)
3) Inner pad has been fitted incorrectly (anti-rotation pin not aligned with notch in piston).
4) The inner pad is partially seized, or a badly fitted anti-rattle clip is obstructing it.
Mr2Mike said:
Play in the sliders is unlikely to be the underlying cause of the caliper twisting under load.
If the pads are correctly fitted and parallel with the disc, then there should be no twisting forces at all. Twisting on the sliders usually means one of the following:
1) The sliders are seized (most common)
2) Bent or incorrectly mounted carrier (i.e. caliper no longer held parallel to disc)
3) Inner pad has been fitted incorrectly (anti-rotation pin not aligned with notch in piston).
4) The inner pad is partially seized, or a badly fitted anti-rattle clip is obstructing it.
I'll try and jack it back up again and stick my head back under.If the pads are correctly fitted and parallel with the disc, then there should be no twisting forces at all. Twisting on the sliders usually means one of the following:
1) The sliders are seized (most common)
2) Bent or incorrectly mounted carrier (i.e. caliper no longer held parallel to disc)
3) Inner pad has been fitted incorrectly (anti-rotation pin not aligned with notch in piston).
4) The inner pad is partially seized, or a badly fitted anti-rattle clip is obstructing it.
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