testing brakes

Bukowski · 05-10-2013, 09:47 AM

87 944 NA w/ original brakes (Porsche or Ate I think, single piston)

planning a brake caliper rebuild. need to test them afterwards - besides the obvious (does your car stop, are there no squeals/leaks/pad break-in smoke), what specific things does one look for in a careful brake system function test after a caliper rebuild? I know I can look at the reservoir, cylinder, clutch stuff - but specifically what? any good tests while the wheel is off? etc.

djnolan · djnolan's Garage

Basically, when you are done the pedal should be rock hard, and braking should be smooth and even, there should be no vibration. There should be no fluid leaks.

The biggest improvement will come from machining or replacing the rotors if they become out of round or unevenly worn over time.

The caliper rebuild itself can be as simple as cleaning the piston and bore, and replacing the seal and boot if the bore is not worn badly. If the bore is worn you may want to look for a rebuilt one.

Also if the caliper seals have gone bad, the caliper pistons could be rusty and seized and not retracting after braking. This causes the inner and outer brake pads to not apply evenly, causing uneven wear on the pads and rotors and rough braking. (outer pad will wear more than the inner pad reducing stopping ability)

Uneven pad wear can also be caused by the caliper slide rails being seized from lack of grease. If the grooves in the caliper are badly rusted may need to be wire brushed or gently filed with a small triangular file so the caliper can slide freely again. Grease these will with synthetic caliper grease.

And of course replace the flexible hydraulic lines and properly bleed the system. This takes an assistant or a motive power bleeder.

marko · 05-10-2013, 03:30 PM

I'll be doing this very soon also. Are there any good write up's or how to video's out there?

John_AZ · 05-10-2013, 03:52 PM

A good-really good caliper PDF by member Exitwound:

http://www.theexitwound.com/944/brakecaliper.doc

Bendix Q&A FAQ
Bendix :: Tech Corner : Tech Bulletins / FAQ

Videos --youtube?

J_AZ

marko · 05-10-2013, 04:18 PM

Thanks John. Looks like a very good write up from exitwound. It looks that I spoke to soon, although, I didn't pay attention that Bukowski has the single piston calipers. I have the brembo calipers.

John_AZ · 05-10-2013, 04:25 PM

Maybe...??

DIY Brembo Front and Rear caliper rebuild - NASIOC

GL
J_AZ

John_AZ · 05-10-2013, 04:28 PM

I found a Porsche video !!

Link:
http://www.youtube.com/watch?v=HCLqUREvKm8

marko · 05-10-2013, 04:50 PM

EXCELLENT!!! thanks!

Bukowski · 05-11-2013, 03:13 AM

Is there a good way to measure the pitting of the piston or bore?

Also Jürgen aka Dr944S2 has a great video on YouTube doing Brembo brake service on his 944S2. Username is Irina-something-or-other.

Bukowski · 07-07-2016, 02:41 AM

Follow-up ... Off the top of my head ... had calipers plated by ... that place in Utah - excellent service. They even re-did one or two and AFAIK covered shipping back. Highly recommended.

Resealed, reassembled - get piston correct rotation or your life is miserable esp. w/o an air compressor ... greased sliding surfaces. The big clip thing - shaped like a wishbone was seized in but no worries.

Well, hundreds of miles later, and - w/o another teardown - brakes are obviously good. Rotors look ok. Caveat - cylinder, most lines are new. Just another thank you to the forum members here, hope this helps the next 944.

... check off one follow-up - so many. It sucks reading threads like this that just end abruptly. One day, I'll plow through...