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Mushy pedal after changing to SS lines (NA)

 
Old 12-28-2017, 12:42 PM
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Default Mushy pedal after changing to SS lines (NA)

I know the likely answer to this is "just redo it" but I'm lazy and hoping there's a shortcut here. I've also bled all four corners a bunch of times and it feels like it's okay for the first couple days/weeks, but then a neuron randomly fires and it feels a bit squishy again. And I think I can get all the way to the end of the pedal if I push hard enough.

Possibly important specs/details:
- '97 NA, 197k on the chassis, 3k on the rebuilt motor
- 949 SS lines
- ATE brake fluid
- 2 Laguna Secas and ~6 autocross in the last year
- Unknown master cylinder age

I'm guessing if I redo it, I'll have do also get new banjo bolts and crush washers?

Thanks for all help in advance.
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Old 12-28-2017, 01:00 PM
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Should do new crush washers. How old is the brake fluid pretty fresh since you keep bleeding it? Could be a problem with the master or booster too. Do you have any fluid loss? This is how i would go about it.
  1. Check/Tighten all fittings to ensure system is sealed. Suck all old fluid out of master and replace with new clean fluid and then use a vacuum bleader on all 4 corners RR, LR, RF, LF
  2. If problem continues id replace the master cylinder because they are cheap-(From the sound of it im guessing this will be the issue) make sure to bleed the master before installing
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Old 12-28-2017, 03:02 PM
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If there is a trapped air bubble, pounding the pedal multiple times as quickly as you can will break it into very tiny bubbles, almost a foam, and if you bleed it again you can often get it to come out then. It's an old trick but it works sometimes.

If something else is wrong this won't help.
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Old 12-28-2017, 03:18 PM
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Thanks for the input.

I'll do another re-tightening round, I suppose. No fluid loss at all, which makes me suspect it isn't a tightening issue. I've bled it a million times already so the fluid is less than 2 months old, and most importantly, no track days.

I think I'll just **** it and replace the master cylinder and hope for the best.
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Old 12-28-2017, 03:38 PM
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Even with no visible leaks on the outside its possible that the master is leaking out the rear seal into the booster too. The master is a cheap and easy thing to try.
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Old 12-28-2017, 05:14 PM
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Rodger that. Just ordered a new master cylinder -- will let you guys know. Thanks again for all your help.
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Old 12-30-2017, 12:12 PM
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If not too late, I enjoy the 15/16" master and booster I got from a wrecked MSM. Anything with the bigger sport brakes will have it, too, but it'll have a booster with more assist, which you may or may not like - the MSM booster gives you almost exactly the same pedal effort as the stock booster with the smaller master cylinder, but with a more direct pedal. If you find good local, used parts, it's an easy and cheap swap, with just minor brake line plying required at the master cylinder. Even with paying Canadian shipping and import taxes, I feel it was well worth it. I also went from feeling like I was just about bottoming out my pedal during hard braking to a perceptibly firmer pedal. Well worth it for the <$200 and 1-2 hrs it took.
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