How does a DIY check that brake caliper & pistons move freely.
In a related thread on how to diagnose high speed braking induced wheel
shimmy in a 98 Toyota 4Runner and in a variety of brake shimmy articles it
was suggested I check that the 4 pistons move freely in each caliper.
... (eg http://www.eurac-group.com/technote4.htm
http://journals.pepublishing.com/index/77665U68739575J1.pdf
http://www.babcox.com/editorial/bf/bf100326.htm
http://www.estech.co.jp/list.pdf/%20customer/cust41.pdf etc) ...
Unfortunately, neither the $20 Chilton nor the $200 Toyota Repair Manuals I
bought say ANYTHING about how to check the pistons & calipers for free
movement.
Each caliper has 4 pistons (which the Toyota shop manual says to separate
with a MONKEY WRENCH!).
Do you know how to check that the caliper & 4 pistons move freely?
"M Cuthill" <[email hidden]> wrote in
news:440b3e48$0$14378$[email hidden]:
>> 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.
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!
> 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.
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."
http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml
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 http://www.zeckhausen.com/avoiding_brake_judder.htm
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
Stuart A. Bronstein wrote:
> Do you know how to check that the caliper & 4 pistons move freely?
I believe this will be modelled in Racing Legends. Just wait a short
while...
