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

[borrone821]

Hi Everyone,
I finally "finished" up my disk brake swap on my 68 Cutlass convertible.

4th gen F-body calipers/rotors/pads, BRP spacers for the F-body brakes, completely new NiCop lines, a 2229NC Booster and Duralast NM1749 Master (disc/disc for 70s corvettes where outlets are on driver side), and a Willwood proportioning valve.

Finally took the car out for a test drive today around the neighborhood and absolutely had to stand on the the braked pedal to get it to stop.... way worse than original manual drums that I took off it.
I know I'm getting vacuum to the booster, pedal feels like booster is working (how it feels when turning car on and off).
With the engine on or off though, it feels like I can push the pedal a lot farther than I should, and with the car off, I can't really build up pressure to the brakes where the pedal point is way higher than when running.

I do know when I bled it I had a b$tch of a time getting fluid through, bench bled the master multiple times, and got solid fluid (no bubbles) at all 4 wheels. Only thing that I know is that when I was bleeding (son in car pushing pedal and I had a clear tube on bleeder going into container) there was solid fluid, but it never actually really flowed into the container like the other brake jobs I've done.

Is that the master isn't pushing enough fluid or fluid fast enough?



I'd rather targeted troubleshooting at this point rather than getting the car back up on jacks (was on them for months) and re-bleeding to get the same stuff.


Thanks in advance
Jim

[Vimes]

Perhaps this will help.

https://mpbrakes.com/what-causes-soft-brake-pedal/

The one that stands out to me is the master cylinder vs the calipers. You'd want to make sure that the MC for a 1970 car with the much smaller calipers can still move enough fluid to work larger calipers.

It could also just be a defective master cylinder out of the box. It's been known to happen, and is extra frustrating because you tend to mentally rule out new parts.

[borrone821]

The thing that really gets me is the bleeding process and the fact that pushing the pedal didn't really move a lot of fluid. Car off one bleeder at a time it didn't have bubbles but didn't feel pressurized.
That feels like the MC to me.

[borrone821]

And there is zero fluid leaking anywhere and the pedal will not stay up

[Vimes]

How well does it build pressure if you pump the brake pedal a few times? Will it get less spongy feeling after a few strokes, like 5 strokes in 10 seconds? I'm thinking you have a bad master cylinder here.

The only other things that come to mind (from a thousand miles away) is if you used the car's existing metal lines that there might be corrosion inside the lines from the master down. Brake fluid is hydroscopic, and any water inside the line will turn it acidic and will eventually corrode the brake lines. This is a bigger problem on cars that sit (such as being restored) and a corroded line will expand the metal inwards for reduced flow. What's bad is the outside of the line can look brand new despite being a corroded mess on the inside. Disconnect the brake line from the driver front caliper and have someone pump the pedal, and the brake fluid should squirt like a porn star. If it dribbles like an old man, you may have a corroded line. In this case I'd move to the master cylinder output and do the same test. Same results, bad master, but take care since brake fluid will eat your paint quickly. Make up a brake line stub that you can install into the master cylinder that will let you direct the fluid to a catch can.

Really I'm leaning towards a bad master, as corrosion will have a small chance of affecting both sides equally and you didn't say anything about it jerking the car to one side when braking.

[Hotwire]

Did you move the push rod on the brake pedal to the assisted setting vs leaving it at the manual hole on the brake pedal arm?

You should have the correct setup for the Camaro brakes, right master, etc. Should be 1 1\8" bore.

Did you remove the factory proportioning valve from the system when you ran new lines?

Did you replace the rubber lines going from frame to rear, frame to calipers?

[cdrod]

Jim:

You're current set-up is providing less braking force than the factory disc brake system. There are 2 holes in the brake pedal arm for the booster pushrod. With a dual 9-inch booster, a 1" master cylinder and using the lower, power brake hole in the brake pedal arm you should have approximately 30% more brake force than the stock disc set-up. I have a dual 9" booster/1" MC set-up in my '72 442 convertible with C5 front calipers and Hawk 5.0 pads. The C5 calipers have a smaller piston diameter than the LS1 calipers you're using so you should have even more front braking force than my set-up. My pedal was firm using the power hole in the pedal arm but I wanted a bit more, so I drilled another hole in the brake pedal arm mid-way between the 2 stock holes providing approximately 5:1 ratio (the stock power brake hole is approximately 3.4:1). I'm pretty happy with my set-up with good pedal modulation; the only thing that would provide me with more brake force would be a hydro-boost set-up or more engine vacuum as I only have 15 inches of vacuum at idle. I hope this is helpful info.

Rodney

[borrone821]

Hi guys, thought I responded last night but apparently didn't post.

Using brand-new lines except the flex lines at the caliper itself and the rear to rear end T.
Prop valve taken out and replaced with a Willwood (most expensive part of brake system).
I'm on the lowest pedal hole position and that's definitely not the issue; i have very little braking power... it's worse than my manual drums by a wide margin.

I'm convinced it's the MC since I cannot build a firm pedal with the car off. I can get it firm enough, but it never raises the pedal up.
After thinking more and more about the last however many weeks I spent here and there working on this, bleeding the master (did it a few times when I wasn't getting good fluid at the wheels) never resulted in enough pressure to really move the fluid.

[Hotwire]

Only other question, is the booster push rod matched to the master cylinder piston? Ie is the booster able to apply full stroke to the master?

[dhutton]

I would replace all rubber hoses. They can swell over time and restrict flow. Common problem.

[dhutton]

A brake pressure gauge can be an invaluable tool when troubleshooting brake problems.

[borrone821]

Aright replaced the master and bleeding pressure was much better with the clear tube going back into reservoir.

Still can't get a firm pedal though once I connect it. I have no fluid leaking anywhere.
I'm going master sending front and rear to the prop valve which goes to 2 fronts and 1 rear. The rear splits at the rear end to go to both tires.
I'm running 3/16"s everywhere, everything feels tight. I can get fluid with no bubbles to all wheels, but none of the are really pushing fluid.

How do I test each connection individually? are there block-off ports to check each wheel line?

[borrone821]

Re-bled everything. Again, no leaks anywhere but not a completely firm pedal.
I took it for a really short ride around my neighborhood and the braking seemed to get better. When driving, slowing down wasn't bad, but the stopping power just isn't there.
I have to stand on the pedal to stop and even then, it takes some time. I expected the power discs to really provide some stopping power.

Are there specific hose clamps you can get at harbor freight or somewhere to negate one wheel at a time?

[Hotwire]

That setup should put you through the windshield. Do you have the vacuum hose connected on your booster? I've locked up all 4 tires on my car and striped them when someone pulled out in front of me.

Il

[borrone821]

Exactly what I was thinking. Is air getting in? Everything is as tight as I can get it. I guess I'll go to Harbor Freight tomorrow and get some hose clamps and go one by one. Not sure exactly how else to be troubleshooting

- - - Updated - - -

Yes have the vacuum line hooked up. Issue is definitely not in the booster as I can feel it helping and I can't get a firm pedal with the car off

[Vimes]

You reused the same flex lines? That might be the problem. Water will set in on the line brackets and rust inside where you can't see, crushing the lines, although I would expect uneven braking with that unless only the rear is affected. Come to think of it, I used to have a Tahoe that had terrible braking because of the rear drum design - they wouldn't auto-adjust so after a few hits of the pedal they stopped being in play. Old lines will also deteriorate and stop being able to hold the pressure, so they'll expand a little bit and there goes the stopping power. Stainless lines from Earls or the like would be the solution if this is the problem.

Reread the link I sent, on #1. It's possible that there is still air in regardless of how much bleeding was done, and might require removing the calipers and hold them so the bleed screws are the highest point. If you resort to this, a clean piece of wood the same thickness as the rotor should be used in place of the rotor to keep the piston from going full extension. Keep them fingers clear too, the caliper will squeeze a finger off so fast you won't realize it's gone till you pick your nose and nothing happens. An old coat hanger can be used to make a holder to keep the wood in place.

The only other thing I can think of is, you switched from a Cutlass to a Corvette master/vacuum booster? I saw you're connected to the lower hole on the pedal, but is the rod you connected long enough? Perhaps it isn't long enough and isn't engaging the master correctly although I don't know how to measure that to be sure.

Oh, and just to throw this out there, the order of bleeding is right rear, left rear, right front, left front, furthest from the master to closest. If you happen to be going the other way you won't clear air out.

[borrone821]

the 2229 has a threaded rod and I bought an extension with the clevis so it's adjustable. I have it almost as far out as it can get.
Right on about the order; I follow that religiously even if it's not called out. Given that I have the adjustable prop valve, I honestly doubt that order is that important but I do it anyway.

So I got frustrated and decided to put the mityvac on and make sure there was nothing in any line cuz I could not think of anything else.... low and behold, I pulled out a LOT of bubbles.... did that to all 4 ends, then had my son finish with the 2 person method. This was after I bled the lines a few different times ,found leaks in flares I made or didn't tighten down enough, rinse, repeat, etc.
Now I have a much much firmer pedal!! Just went for a ride and it's pretty good, but never gets to the point where I think i'd lock them up. I still have to push down very hard to get full full stop quickly but driving around is now manageable.
I have to press very hard to get a quick stop which I don't think is normal.
The pedal becomes so firm at the bottom and I'm not close to locking them up which I would've thought would be likely.
Any idea what might cause that?

[rallystyle]

When i did my corvette front and ls1 rear setup i used the same 2229 booster with a s10 master. to get all the air out of my system after i tried doing a vacuum and pushing on the pedal bleeds. i had unbolted my master from the booster. leaned the master forward so the fill ports in the master where the highest point. then performed and reverse bleed and i could hear the air coming out from the ports in the master during the process. i did also find that at first there was a spacer in the booster that caused the booster to push on the master very lightly and cause the fronts to drag. after all that work the new brakes where very solid but didn't stop the car very good at first. after some heat / bedding them in. they will now lock the wheels up if i want them to. i did get new brake lines from Tobin at kore3 also. i just remade one of my front brake lines with nicop also. did my brake bleed process and every thing worked awesome again.

[borrone821]

That's actually why I went with an older master instead of the S10 (which is now way overpriced).

Definitely felt like it was getting better as I was driving but at the end the pedal gets wicked hard and it doesn't really stop hard (at least not what compared to any other disc brake setup I've used).
Will try some more driving after work and see if bedding helps more

[borrone821]

Just wanted to give everyone an update that I've got probably 100 miles on it and still going strong. I need to rebleed to soften up the last inch of brake pedal but the 2229 does in fact mate well to a NM1749 Master and works well with 4th Gen F-body brakes. I could not find out online whether this worked or not, so I wanted to let everyone know this is in fact a good setup for anything that can take a 4th gen f-body setup