I have been trying to track down some annoying squeaks and squeals in my front brakes of late and have had some success with exercising the pistons, cleaning, greasing and bleeding (although I suspect the callipers will need to be rebuilt at some point).
During the process I have noticed that the front callipers have anti chatter clips which are not mentioned in my service manual. I suspect a previous owner may have installed them. The car has the 3 pot callipers.
Is someone able to explain to me the correct installation of these clips and what forces they apply and how they work in general? The clips don’t appear to be providing a great deal of force in any direction (except for a modest amount of force towards the centre of the hub).
I wonder if I have installed them incorrectly or if they have lost their spring over time and need to be re-bent or simply replaced. (an image of correct installation, that would be great!)
The noise should then occur without pedal application, Ed - does it…?
A lot of force is required to get any noticeable drag - basically; sticking pistons is required. While the retraction caused by the seals are indeed small - it’s nonexisting with sticky pistons. And even a small run-out of the disc will effectively kick the pads off the disk - unless pistons stick…
Absolutely correct Frank, the noise occurs without pedal application - in fact it silences it.
In the near future I will pull the callipers apart and rebuild them. (which I am very much looking forward to )
On that note, do you (or indeed, does anyone) have any opinion as to the benefit of using stainless steel pistons as opposed to the standard? They are about twice the price but it doesn’t seem like the originals fail all that regularly anyway?
I forgot to replaced them in my 83 when I replaced the pads. No harm, no noise and they work just fine…
What I did do was to clean the slides in the caliper nicely and trim the new pads just a mite so as to work smoothly. and the anti chatter tin and goop did find their way on to the job… The tin needed a bit of 'fettle" to fir smoothly…
More tricky than a pad swap in my two Fords, one a Tbird and th other an F150. My IHC Scout II shared brake types with the F 150… A hammer the prime tool!!!
The retraction of pistons caused by the seals is tiny, Ed, and not very powerful. And the retraction of the pistons do not retract the pads - but some force is required to have any braking effect.
But also; the slight amount of drag - are you sure that is not the normal resistance of the wheel bearing? Which would be noticeable while spinning the hub without the tyre. Have you checked the bearing adjustment…?
With the pads removed the wheels spins without any drag. As such, it would seem the brakes are causing some resistance. (It can be heard and felt)
In the end, I am trying to get a feel for whether some resistance always exists and if so how much?
I appreciate this may be difficult to appropriately describe online. Perhaps when I next have the wheels off I will take a video. FYI the flex hoses have been recently changed, along with the fluid and pads.
As the pistons retract, Ed - the pads do not; they are ‘pushed’ back by the rotor run-out…
The pads is held by mounting pins’ friction, and if the rotors have no run-out, the pads stay put. Adding that if piston retraction is restricted for some reason they add to pin friction. And of course; the force available to move the pistons out is immensely much stronger than the retraction force on the pistons. And ‘sticky’ pistons, for whatever reason is a fault…
As considerable force is required for appreciable braking effect; its an interesting question how significant ‘rubbing’ pads are - for all I know it is not necessarily even abnormal. Your ‘whether some resistance always exists’ requires inputs form other listers…?
And such rubbing is probably of little consequence in itself - except as a fault indication? But even light rubbing will cause heat, and heat cause expansion, which may increase rubbing - but induce the pads to move further away from the discs…
With the pads removed; try slowly pushing the pistons back, in turn, They will offer smooth resistance as fluid is pushed back into the reservoir and against the friction of the seals. But ‘little’ force should be required. You may also notice the minute ‘spring-back’, from the seals, as you let go. If there is noticeable difference in the force required to get one or more pistons moving - it implies sticking…
(Do not push the pistons very far in this test as it may cause brake reservoir to overflow. Which, having changed pads you already know… )
Another test, with the pads in place; briefly apply a heavy foot on the pedal. Then repeat the rotation check on the discs. If ‘much’ more force is required to get the discs moving it may imply sticking. After a full disc rotation you may be back to the original - the effect of disc run-out.
A deeper test is to fit worn-out pads and apply the brake to extend the pistons for some examination. They should of course be nice and shiny - discolouration or pitting, together with the other symptoms, indicates that a calliper overhaul is advisable…?