[SaabGuy30]

2002 Saab 9-5 2.3 turbo. Replaced front brake pads as inner was low, rotors near wear limit ~23mm (Min thickness Spec is 22mm), slight ridge on inside and outside of rotors. Pumping brake pedal before starting car felt normal, but holding pedal down while starting, pedal goes dangerously close to the floor. Drives OK, stops straight, just excessive pedal travel. (Pumping once or twice gets good pedal, so we bled brakes, no change.) Removed caliper, filed off outer ridge on both sides of rotors. No change. Pedal feels fine before starting, but goes to floor once car starts.

What next? The shop mentioned replacing rotors of there would be excessive travel, does this make sense? Should I replace rotors or just drive it to bed-in the new pads?

 

[JohnLear]

Hmm,
New pads on a worn rotor can cause a soft pedal because the pad is only contacting part of the rotor surface, and when the pads are forced hard against the rotor the pad material can become locally compressed at the points where they are contacting the rotor, then uncompressed when the force is released. Time will tend to wear them in.

The rotor itself may be thinner toward the outer edge than it is further in, the effect of which is effectively similar to the pads having taper wear toward the outer part of the pads. This would cause lost motion as the pads are moved into full contact with the rotor faces (also tends to 'tilt' the piston in its bore).

Are the calipers sliders moving freely? If seized (or partially seized) then this can cause caliper distortion, which manifests as pedal movement.

Regards,
John.

 

[dosmie]

I would replace the rotors. If you are at or near the limit now, you will be past due by the time you replace pads again. If you still have pedal issue you could always bleed the system, or even better flush the brakes.

 

[SaabGuy30]

Thank you, Yes, Examining pads showed contact only on part of the pad, and I did notice that the caliper 'tilted' a bit as they were applied.

I'm guessing things would improve as the new pads 'bed-in', but I'm going to end this 'science project' and just get new rotors.

Regards, SaabGuy30

<snip> ...

The rotor itself may be thinner toward the outer edge than it is further in, the effect of which is effectively similar to the pads having taper wear toward the outer part of the pads. This would cause lost motion as the pads are moved into full contact with the rotor faces (also tends to 'tilt' the piston in its bore). ... <Snip>
Regards,
John.

 

[mayhem]

Whenever I see a ridge on my rotors I just replace em, the new ones are inexpensive enough, even for good ones that its just not worth NOT doing it in my opinion.

I'd be a little troubled that your old inner pads were worn more than the outers and would be taking a good look at the calipers to be sure you don't have any corrosion on one of the pins or a sticky piston.

 

[bahrm4]

Flush the brake lines. Sounds like air to me.

 

[SaabGuy30]

New Rotors = Problem solved

Firm pedal, normal pedal travel. I've never been afraid of rotors worn 'close to the limit' (Enough people I know did it on race / rally cars...), never saw such uneven wear... Oh well, the 'experiment' ends, new brakes, flushed fluid, should be ok for awhile!

Thanks for the speedy replies!

 

[philselmer]

Did you make sure your calipers were on the right side of the car? When I put mine back on, I put them on "upside down" (passenger side went on the driver side) so the bleeder screw was pointing down. This left some air in the caliper even after 4 bleeds.

 

[porsche996]

One of two things:

1) Totally normal, and should work itself out after the first couple times you pump the brakes; it's just pushing the pads down to make contact with the rotors. If it does this after 2-3 pumps, then,

2) Bleed the brakes. You have air in your brake lines.

That's really all it could be. Now, there's always a chance you broke/cut/tore a brake line while you were doing the job, but that's pretty unlikely, and easily noticeable by looking for brake fluid coming out somewhere...

Rotor thickness and/or un-eveness isn't going to be felt by "extra" travel in the brake pedal. You can feel it when actually stopping by either vibrations in the pedal, or worse, vibrations in the car. But the pedal travel distance isn't really effected either way.

 

[JohnLear]

That's really all it could be. ........

...........Rotor thickness and/or un-eveness isn't going to be felt by "extra" travel in the brake pedal. You can feel it when actually stopping by either vibrations in the pedal, or worse, vibrations in the car. But the pedal travel distance isn't really effected either way.

I have to disagree. Taper wear on the rotors (rotor thinner toward it's outer edge, typically due to the greater speed with which the rotor passes between the pads further out) and taper wear on the pads (either thinner toward the outer edge of the pads, and / or thinner toward the trailing edge, parts of the pad that run hotter than toward the inner edge and leading edge) can cause unwanted piston movement before the pads fully 'engage'.

In either case there is a gap between the pads and the rotor surfaces, i.e. the thicker parts of the pads and / or rotor will be in close proximity to the rotor and / or pad, leaving a gap where the components are thinner.

When the piston moves good contact will first be made where the components are closest (thickest), but before any real pressure can be exerted the piston must 'tilt' in its bore in order to exert force across the whole piston (and thus the pads). This movement is manifested to the driver as a slight delay in retardation, and most obviously as excessive pedal motion.

The piston doesn't remain tilted when the hydraulic pressure is released, but rather is partially retracted and 'untilted' by the hysteresis in the elastic piston seals. When the pedal is re-applied the clearances must be taken up again.

Reluctance for a floating brake caliper to slide on the pins (i.e. full or partial seizure of at least one pin) causes strains and flexure in the caliper bracket, which is manifest as pedal motion (and often as one pad wearing much more than the other).

Typically one pin will be more seized than the other, so as pressure is applied the caliper will slide more on one pin than on the other, resulting in the caliper becoming tilted, especially as the pads become more unevenly worn. Note that this creates elastic flexure in the bracket, so as pressure is released the bracket resumes its 'as manufactured' shape, which pulls the pads back away from the rotor.

I've encountered all these problems when chasing down the cause(s) of excessive pedal movement. I'm sure that a well known search engine will easily find pages explaining all this more fully.

Regards,
John.

 

[8pack]

Are you sure you put the spring retainers on properly. If they are seated in the wrong way you will get a soft pedal. If you search on here you will find others who made the same mistake. Compare to a picture you can find on line to make sure you got it right.

 

[JohnLear]

Neglected to mention that another cause of intermittently excessive pedal movement is wear on the slider pins. Clearance here allows vibration to cause the caliper body move on the worn pins, and the nature of this movement can cause the pads to back off slightly.

With the wheel off, grab hold of the caliper body and try to move it toward the centreline of the car and then outward in the reverse direction. If the caliper body 'wobbles' in this plane (moving because of pin to pin bore clearance) then its mass coupled with the vibration can be enough to push the piston back a little into the bore, possibly enough to be felt as additional movement at the pedal next time the brakes are applied.

Regards,
John.