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Discussion Starter · #1 ·
What would cause a brake pedal to become stiff from time to time without affecting brake performance?

Sometimes after a hard braking where you really let into the pedal, it will get stiff for some time afterwards.

Is this something worth investigating further (ie is it a safety issue)?
 

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First ABS or not ABS? An overly stiff pedal can be a symptom of a bad Brake Booster.
 

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Discussion Starter · #3 ·
It's an ABS car

It isn't stiff all the time - and it brakes wonderfully. Even when it is stiff, it seems to have the same braking capabilities. I just thought it could be a sign of something on the way out.
 

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RB - any specific circumstance surrounding when this happens? After a panic stop, after hard braking (as in sprinting through switchbacks), when doing the heel-toe dance in spirited driving ??
 

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Discussion Starter · #5 ·
SteveTheFolkie said:
RB - any specific circumstance surrounding when this happens? After a panic stop, after hard braking (as in sprinting through switchbacks), when doing the heel-toe dance in spirited driving ??
Well, to give you an example, I first noticed it when this woman cut me off on the beltway leading to me standing on the brakes and doing a 3 or so second ABS skid (my ABS is in good working order). Afterwards, the pedal felt hard, although the brakes seemed to be working at full force.

It happened yesterday when I had to stop short for a dumbo left turner who failed to yield - in this instance, the brakes actually seized a bit to the point that starting from standstill was difficult (had to do a mild clutch drop to free them up). The pedal, again, felt hard after this, but the brakes seemed to perform as normal for the rest of the ~15 miles home. Can't recall exactly how long the stiffness lasted, but I don't think it lasted the whole ride. Normal function this morning, as well.

It does not seem to be related to high brake heat sessions (BTW the brakes are fantastic in these situations with the high heat range pads I have on them :D).

The fluid is about a year old, with no apparent leaks judging by the level in the resevoir. I think the rear pads are overdue for replacement, if that affects it.
 

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is there a check valve in the ABS accumulator or elsewhere in the ABS system? If so it might be allowing residual pressure to come back into the system (to the pedal) after a hard braking effort - now I may be all wet on this one - but that's my best quick draw shot ...
 

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When you say the brakes "feel stiff", are you referring to pedal effort, pedal travel, feedback through the pedal?
How does the pedal feel after you've pumped down the accumulator?
Is that the same stiffness you're talking about?
Will it recover if you cycle the ignition?
Does it take a long time to pump up in the morning?
Does the ABS work?

Try standing on the brakes when the car is on a very slight incline. Will the car roll when you let off the brake? Will it pass the same test when the brakes are hot?
 

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Discussion Starter · #8 ·
Jim Mesthene said:
When you say the brakes "feel stiff", are you referring to pedal effort, pedal travel, feedback through the pedal?
I'm referring to I guess some combination of pedal effort/pedal travel - The pedal provides significantly more resistance and it doesn't travel nearly as far.

How does the pedal feel after you've pumped down the accumulator?
Is that the same stiffness you're talking about?
Yes, it feels like that, although maybe not as extremely stiff, if I recall correctly.

Will it recover if you cycle the ignition?
Will test tonight, if I can reproduce the symptom.

Does it take a long time to pump up in the morning?
Does the ABS work?
No (at least that I've ever noticed) and yes, respectively

Try standing on the brakes when the car is on a very slight incline. Will the car roll when you let off the brake? Will it pass the same test when the brakes are hot?
Will test tonight as well.

SteveTheFolkie said:
is there a check valve in the ABS accumulator or elsewhere in the ABS system? If so it might be allowing residual pressure to come back into the system (to the pedal) after a hard braking effort - now I may be all wet on this one - but that's my best quick draw shot ...
I'm not sure if there is one, but that makes for good sense. The similarity of the feel to what happens when you pump the brakes with the car off is getting me thinking...

For what it's worth...when I first looked at the car the brake pedal felt stiff, but that the brakes seemed to be functioning well. Also, the brake fluid needed changing, which the guy I bought it from (saab indy) changed and bled. I figured it was something caused by air in the lines that the bleeding fixed, because the pedal felt normal when I picked up the car a few days later.
 

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Discussion Starter · #9 ·
OK - I "tested" it, but I'm afraid my frame of reference may be off - The pedal felt like it could have been stiffer than normal on the drive home (before I started hard braking to test it). When I did some hard braking on my street, it did seem to get stiffer than it was on the drive home. Turning it off an on again didn't seem to make any noticable difference, and it seemed to stay stiff for the rest of the time I was driving it (5-10 minutes). I turned the car off and tested it again about 45 mins to an hour later, and the pedal did seem softer, and then got harder again when I braked hard (btw these cars have great brakes! Thing stops on a dime everytime!). Even when it is hard, brakes perform well.

Tried to make the brakes stick by standing on it, and it did not stick at all both when hot (I got them really hot) and cold.

If I turn it off, pump the brakes till they feel "empty" and then turn it on, it seems to regain it's pressure pretty quickly, of course I'm not really sure how fast it was supposed to when the car was new, so I have no frame of reference.
 
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