Squishy brake pedal

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kzooman83
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Squishy brake pedal

Postby kzooman83 » Sun May 15, 2022 6:15 pm

Hello all! My wife and I are getting a 1990 Beretta GT ready for one of the Lemons Rallies this summer, and I have hit a snag with the brakes. We have replaced all brake lines, master cylinder, calipers, wheel cylinders, hoses, pads and shoes; after bleeding the brakes, I cannot seem to get a firm pedal. We have bled them several times, and I bought a pressure bleeder which I just used on it today; I put 2-3 gallons of fluid through it with the pressure bleeder and actually got some air out of the rear brake lines. I thought that did the trick, but the brake pedal still feels low and squishy. At this point, I am thinking air has to be getting in somewhere, but there is no brake fluid on the ground, ever. Has anyone ever run into a similar situation? Can you have a leak that allows air in but not fluid out?



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Rettax3
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Re: Squishy brake pedal

Postby Rettax3 » Thu May 19, 2022 7:30 pm

Hey, glad you figured out the old surging issue, but for the brakes I would say one of two things is most likely causing the problems. Either air trapped in the MC (Master Cylinder) that isn't being pulled by the pressure bleeder (GALLONS? Wow!) may have to be removed by properly BENCH-BLEEDING the MC off the vehicle. Worth a shot... Second possibility (most likely I feel) is the MC itself is simply defective. New does NOT mean good. What brand is it, and where was it sourced from? Rock Auto is a decent source, but sometimes their parts are just too old, plucked from some backwater parts store that finally went belly-up because they never moved any product, and most of the regular parts stores are just competing in the 'race to the bottom' of quality and pricing selling cheap overseas parts. And yes, absolutely a bad MC can keep drawing air in and and not show any leak, because it an just keep exchanging the volume with the fluid in the reservoir, if that makes any sense. Keep us updated how it is going, if you get the chance to post any pics of your Lemons Rallies we would love to see them!


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

kzooman83
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Posts: 7
Joined: Mon Jan 16, 2012 1:59 pm

Re: Squishy brake pedal

Postby kzooman83 » Thu May 26, 2022 9:58 pm

Update: I did an isolation test and narrowed the problem down to the left rear. Replaced the relatively new Duralast wheel cylinder with a brand new ACDelco unit and adjusted the rear brakes. Also found that the tabs that contact the star wheels on the adjusters were not actually contacting the star wheels, so I bent them slightly and adjusted them so that they are definitely making contact. Put it back together and bled the brakes again; this time the pedal is nice and firm, so I guess a combination of brakes out of adjustment and faulty rear wheel cylinder. The weird part is that the wheel cylinder wasn't leaking. Can they fail and not leak?



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Rettax3
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Re: Squishy brake pedal

Postby Rettax3 » Wed Jun 01, 2022 12:58 am

Well, that is a surprise. No, if the wheel cylinder isn't holding pressure, it will leak, period. They can fail to extend, they can fail to retract, but neither case will cause a mushy pedal. Severely out-of-adjustment brake shoes can do that, but that doesn't mean the wheel cylinder is bad, just that the shoes are out. Nice find on the adjusters though.

When I reassemble drum brakes, I always pre-adjust to have a little 'drag' on the drum when slipping it on. If the drum is worn and has a ridge on the edge, they will still need to be manually adjusted prior to going back on the road. I will then run the parking brake handle or pedal through several full-stop cycles to test the auto-adjusters (assuming they are so equipped -some older brakes, say '50s and older for sure, often don't have auto adjusters) and get them to 'finely-adjusted'.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26


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