Spongy brakes - 4th gen F-body swap onto 68 Cutlass

[Hotwire]

Glad to hear it's coming around. I'm running an M2072 master from Napa, 1970 Corvette, been working great for 8 years. Looking at the specs I can't see any difference in the 2? Wondering if all the master push rod stroke is the same length?

[cdrod]

Glad you got it sorted out.

[borrone821]

just wanted to give an update (just got back from vacation. yellowstone with the kids = very highly recommend).
I still have a non-linear pedal feel. I have no problem stopping the car, but pressing down at the bottom of the pedal doesn't really lock them up. Still feels like something is wrong.

Is there a way to test the flex lines going to each caliper?
Driver side front when bleeding does not produce a lot of pressure; no bubbles when opening the bleeder and i get some fluid, but it's not enough to get through the hose into the fluid container.
I cannot think of anything else. Calipers are brand new.

Any help would be greatly appreciated. I'm going to keep driving it for the summer in Massachusetts, but really want to figure out what's going on

[dhutton]

https://www.summitracing.com/parts/l...SABEgJA-_D_BwE

[Hotwire]

One question does come to mind.. what fluid are you using?

[borrone821]

Might be the time to invest in the pressure gauge.
Pretty sure I'm using DOT3 but will check when I get home

[borrone821]

So I'm using DOT3 fluid.

The pressure gauge is only going to tell me I have "an issue" or not at the caliper since I screw into the bleeder, right? I can't test at the banjo bolt to differentiate between the caliper and lines to caliper, and I know there is "some" kind of issue on the driver front. Passenger and rears are flowing much stronger so I've narrowed it down to a particular wheel which is all the gauge will do, correct?

Only sources I can think of that don't have common components are the hardline from prop valve to flex line, flex line, and caliper. Is there a way to test these individually?
Caliper is a re-man unit. Am I at the point where I should pull the caliper and put compressed air through it to see how the pistons move? I don't know enough about the caliper internals of the "fluid pressure to mechanical piston pushing"

[Hotwire]

I'd start loosening connections from caliper towards master, push fluid at each connection to see if you can feel where the obstruction is. Bad caliper? Collapsed hose? Pinched tube?

[borrone821]

so all i needed to do was actually read the 2nd post and the link that was posted.
In there they mention essentially the "little movement" pedal followed by deadening the pedal w/o real pressure. They said to get the booster pushrod measurement tool and ensure the booster pushrod to MC cup was ~0.020".
Turns our mine was close to a 0.25" and when I was pushing the pedal, the booster pushrod would fully extend, but that would not depress the master cylinder.
SO, the NM1749 MC is NOT a direct fit into the 2229 Tuff Stuff Booster. In order to make it work, you need to get a new booster Pin and grind it down to get the spacing between MC and booster in the 0.02" range.



So I've now got solid brakes on my 68 Cutlass for short money relative to kits and learned a TON about brake systems in the process (painfully so)