|
Re: Can anyone check whether brake pistons move freely?
mrcheerful
. wrote:[color=blue]
> "Stuart A. Bronstein" <spamtrap@lexregia.com> wrote in message
> news:qmHOf.65951$PL5.40749@newssvr11.news.prodigy.com...[color=green]
> > "M Cuthill" <moray_dot_cuthill@v21.me.uk> wrote in
> > news:440b3e48$0$14378$6d36acad@titian.nntpserver.com:[color=darkred]
> >>> Do you know how to check that the caliper & 4 pistons move freely?.
> >> Remove pads, and check that all four pistons require a similar amount
> >> of force to push back in.[/color]
> >
> > Do they make a brake piston force guage which works on 4 piston calipers?
> >
> > I just realized that replacing the rotor and pads will not solve my brake
> > vibration problem if the pistons are sticking!
> >
> > To answer your question, I tried pushing the eight front pistons in with a
> > disc brake spreader. The knob twisting seemed the same for both sides of
> > each caliper - but I don't have a force guage in my hand to measure it!
> >[color=darkred]
> >> By Shimmy I take it you mean a vibration?
> >> Only way to check that is by using a dial gauge and checking disc
> >> run-out.[/color]
> >
> > The runout, even after indexing and cleaning of the hub mating surfaces,
> > is
> > within spec (0.0028 inches), yet there is still horrible brake judder upon
> > high-speed (over 50 mph) braking.
> >
> > I'm beginning to realize replacing the rotors and pads won't solve the
> > long-term problem if the true cause is the pistons sticking causing pad
> > material to be deposited unevelnly on the rotors.
> >
> > Here's what StopTech has to say about the true cause of brake shudder:
> > "Every case of "warped brake disc" that I have investigated ... has turned
> > out to be friction pad material transferred unevenly to the surface of the
> > disc [resulting] in thickness variation (TV) ... due to hot spotting that
> > occurred at elevated temperatures."
> > [url]http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml[/url]
> >
> > So, now it's time to diagnose the brake pistion force "Despite the popular
> > myth, brake judder is not caused by warped rotors. Judder is the result
> > of
> > a thickness variation in pad buildup on the rotors' surfaces" due to
> > pistons sticking [url]http://www.zeckhausen.com/avoiding_brake_judder.htm[/url]
> >
> > So, I think we finally found the answer as to the main cause of brake
> > shimmy! Replacing the rotors and pads will not solve the problem long
> > term.
> >
> > Is there a brake piston force guage that I can buy on the Internet?
> > Stu[/color]
>
> the easiest way for you to satisfy yourself as to the ease of piston
> movement is to strip the caliper completely, with no piston seals at all the
> cleaned pistons should be able to fall freely in and out of the caliper.
>
> the initial problem is usually a heavily worn disc or a disc that has excess
> runout, this leads to disc thickness variations which is what most people
> call warped discs.
>
> replace the discs, check that they do not have excess runout, and that the
> pistons move freely and that the pads are not tight in their locations, all
> will now be fine.
>
>
> mrcheerful[/color]
If you follow this advice, you might as well run a hone down the bores
and put a new seal kit in the calipers, assuming you can find same.
That will be the same as buying a "rebuilt" caliper from your FLAPS and
will be much less expensive
Of course, you should also clean them well and spray them with Ford Red
paint while you have the castings bare :)
After you are satisfied that everything is good and clean, but before
reassembly, you should wash all parts in ALCOHOL (nothing petroleum
based) and lube the seals with either brake fluid (will destroy your
nice fresh red paint, though) or silicone grease.
good luck,
nate
|
Linear Mode
