Soft-ish brake pedal after big brake job

[82DMC12]

Hey guys, as part of my front and rear suspension overhaul, I did total brake overhaul as well.



New master cylinder from DMCMW (DMC logo version) - this was a few years old but still in the original sealed wrap and no sign of corrosion or anything.
Turned front and rear rotors
Brake calipers plated and new bleeders
All piston seals replaced
New SS front pistons, rears were re-used as they still looked great
New SS crossover pipes for the rear calipers
Re-used my SS flex brake lines
Castrol GT-LMA brake fluid
New pads and hardware from DMCMW
Powder coated the booster bracket and painted the booster
New check valve and grommet, installed with Girling veggie-grease, replaced the hose vacuum hose from booster to hard pipe
New seal between the master cylinder and booster


Anyway, first I installed the master cylinder and "bench bled" it using cut up old brake line and directing hoses into the fluid. I pumped a few times and no longer heard air pushing through, so then I hooked up the two hard lines and started to bleed the brakes in the order in the book (RR, LR, RF, LF). I tried a MityVac but didn't have a lot of confidence in the purge so later enlisted the wife to do it the old "pump pump pump HOLD" technique while I cracked the bleeder and watched the air come out with a clear tube into a jar. That was a lot better, and we went around the car twice. Then I went on a 20 minute test drive and I was stopping but the pedal felt a bit spongy. We tried again and I definitely got more air out and I feel like it's all purged now. The M/C never went below halfway during all this.

I have gone around the car multiple times with a lamp and I'm confident there are no brake fluid leaks.

And yet the brakes still don't feel super hard.

Any techniques I'm missing or should I bed the brakes first and then try bleeding again? I'm not doing any hard braking until I do a brake bedding sequence.

[eseethal]

Yes, sometimes there is still air trapped somewhere in the system, especially when a lot of brake parts were renewed/drained. Usually I drive around a bit and then bleed again. And again if necessary. It is astonishing, sometimes it is o.k the first time bleeding, on some cars it took me a few bleedings. Good luck!

[David T]

You could still have some air trapped in the system or you could have a bad hose. A bad hose will swell up under pressure making the pedal feel soft. The S/S braided hoses do give a stiffer pedal.

[Citizen]

My 2 cents (and I’m certainly no expert, but…)

A spongy pedal means air is still in the system.

The old “pump pump pump hold” technique should actually be “pump, hold, bleed, close, repeat, repeat, repeat, repeat. Did I mention repeat? Oh yes, and then repeat.

That is to say your helper should not release the pedal off the floor each time until you’ve had time to crack open the bleeder and let the air/fluid exit, then reclose. Only then should the pedal be released. This is because when the pedal is released, air will be reintroduced into the line if the bleeder is the least bit open.

Why so many repeats? I had done a clutch M/S job one time, and even started with a bench bleed. Still, I had to pump bleed so many times I got frustrated and was convinced something was wrong. But no, it just took lots of bleeding. Now that’s a clutch, with only one line from M to S, and only a short distance at that (master cylinder to slave, which is mounted on the transmission). Now imagine a brake system with 4 lines, each way longer in distance than a single clutch line.

And there you have it.

And just one more thing. Bleed again. Fluid is cheap.

Good luck.

…

[82DMC12]

My 2 cents (and I’m certainly no expert, but…)

A spongy pedal means air is still in the system.

The old “pump pump pump hold” technique should actually be “pump, hold, bleed, close, repeat, repeat, repeat, repeat. Did I mention repeat? Oh yes, and then repeat.

That is to say your helper should not release the pedal off the floor each time until you’ve had time to crack open the bleeder and let the air/fluid exit, then reclose. Only then should the pedal be released. This is because when the pedal is released, air will be reintroduced into the line if the bleeder is the least bit open.

Why so many repeats? I had done a clutch M/S job one time, and even started with a bench bleed. Still, I had to pump bleed so many times I got frustrated and was convinced something was wrong. But no, it just took lots of bleeding. Now that’s a clutch, with only one line from M to S, and only a short distance at that (master cylinder to slave, which is mounted on the transmission). Now imagine a brake system with 4 lines, each way longer in distance than a single clutch line.

And there you have it.

And just one more thing. Bleed again. Fluid is cheap.

Good luck.

…

That was my fault on the clarity. It was more like "pump pump pump HOLD" and then I cracked the bleeder, watched bubbles fluid go out momentarily, then closed the bleeder, then signaled to her she can left off the pedal. We did this maybe 5 to 8 times per wheel.

[82DMC12]

I have the Midstate DMC Goodridge stainless flex lines which I installed maybe 15 years ago. The are stainless braided with a clear vinyl sleeve over them. The only thing I can think of that might be a problem there is the tip of my propane torch flame swiped the front driver side line briefly and melted a tiny spot the size of a lemon seed so the SS braid is exposed under the vinyl. I can't believe that would make a difference since most SS lines don't even have the clear sheath on it and the current lines sold by Goodridge don't have a clear sheath. The line never got "hot", the flame just briefly side-swiped it while re-positioning torch. I assume there is some kind of flexible hose under the stainless braid and the braid is what keeps the rigidity? The sheath just keeps the stainless clean.

I could change the SS lines for the hell of it but I'd rather not if it's probably just air.

Maybe bring it to a shop who can use a power bleeder? Anyone ever use one of those?

[Helirich]

My procedure for bleeding brakes goes like this.

1. Open the bleeder valve
2. Install clear Tyson hose on the nipple and the other end in a cup
3. Pump multiple times till you have clean fluid coming out the hose

You can do all this by yourself. At this point, you should have the hose end under the the fluid surface so if there’s any back flow, it sucks up fluid. You can pump as much fluid as you want through it like this as long as you keep filling the reservoir. (Wash out the lines) The only problem at this point is every time you let off the pedal, a little air can suck through the threads on the bleeder. If you snug the bleeder slightly by finger, you may stop most of the air getting by, but it really is time to get help.

4. Now have a helper (wife) pump the brakes a couple more times. But these times, you have a end-wrench on the nipple. As she pushes slowly on the pedal, have her call out when she is nearly to the floor. Tighten the bleeder. She can let off then. As she applies slight pressure, crack the bleeder again and tighten again when she calls out. You can repeat this several times, but it normally doesn’t take but twice.

The idea is, what ever leaking at the threads is leaking out as she pushes the pedal. No air can leak in as she lets off because you have it tight.

This system has worked for me for years. It’s nice because I don’t need my wife but for a few seconds.

[painterdave72]

you can drive it to my house this weekend and we can finish bleeding it out if you like.... its supposed to be nice outside i think..

[DMC-Ron]

When you split the front calipers to rebuild, it's easy to get air in the outside caliper. This air is not easily removed because the bleeder and brake line are both connected to the inside caliper. Opening the bleeder allows flow (and air) thru the inside caliper. But there is no flow thru the outside and air will stay trapped there. Normally the trick is to fill the outside caliper with brake fluid and push the air out by depressing the piston during assembly. If the front brakes are installed and air is stuck in the outside calipers, the best option is to open the bleeder and depress the outside piston with a clamp or channel locks to push as much air out as possible. Reassemble and then continue with your normal bleed procedure.

Ron

[82DMC12]

When you split the front calipers to rebuild, it's easy to get air in the outside caliper. This air is not easily removed because the bleeder and brake line are both connected to the inside caliper. Opening the bleeder allows flow (and air) thru the inside caliper. But there is no flow thru the outside and air will stay trapped there. Normally the trick is to fill the outside caliper with brake fluid and push the air out by depressing the piston during assembly. If the front brakes are installed and air is stuck in the outside calipers, the best option is to open the bleeder and depress the outside piston with a clamp or channel locks to push as much air out as possible. Reassemble and then continue with your normal bleed procedure.

RonNo way, really? I think that's actually my problem because when I got my rotors turned, I got them zinc dipped to protect them until I install them. After driving around for a bit and taking the front wheels off again, I see the zinc is totally removed from the surface that the pad touches in the rear, but not much disturbed in the front, at least on the outside, I did not check the inside. I better have an air pocket at the piston.

I ordered new stainless steel flex lines so when I installed them this weekend I think I'm just going to split my calipers again and fill them on the bench like you suggested.

Sent from my Pixel 3a using Tapatalk

[FABombjoy]

You can do this on car too once the new lines are on:

Open the bleeder and push the pistons all the way in. Close the bleeder.
Remove the pads from one corner & press the pedal slowly to extend the pistons.
They will probably not move uniformly, so be prepared to pinch/stop one side so both extend.
Open the bleeder and push the pistons all the way back in. Any remaining air should be gone now.

You might need something large & flat to help with leverage. Do both sides & refill fluid. This is what I do during a brake flush to ensure that the low points are flushed out.

[82DMC12]

You can do this on car too once the new lines are on:

Open the bleeder and push the pistons all the way in. Close the bleeder.
Remove the pads from one corner & press the pedal slowly to extend the pistons.
They will probably not move uniformly, so be prepared to pinch/stop one side so both extend.
Open the bleeder and push the pistons all the way back in. Any remaining air should be gone now.

You might need something large & flat to help with leverage. Do both sides & refill fluid. This is what I do during a brake flush to ensure that the low points are flushed out.

In what I will call your "step 1", how are you pushing the pistons in with the caliper mounted and the pads installed?

[FABombjoy]

Slip the pads out, the one benefit of these tiny brake pads is they're quick change style. I use a big pry bar. With the bleedscrew open they'll move.

[82DMC12]

Slip the pads out, the one benefit of these tiny brake pads is they're quick change style. I use a big pry bar. With the bleedscrew open they'll move.

Oh OK, I saw you mentioned taking the pads out in "step 2" but I guess you're actually taking them out first thing, right?

[82DMC12]

Now I'm questioning if I should change the flex lines. As I mentioned, I have older Goodridge SS lines installed but they are probably 15 years old. I ordered a new set of lines that will be here tomorrow. Based on the evidence that I probably have air in the front calipers, should I go through the trouble of changing these lines? The money isn't a big deal for me but I don't want to replace stuff for no reason. I'm sure they go bad but surely they last longer than 15 years?

WWJD?

[FABombjoy]

Whoops, that's right, going from memory and it's been a while w/ stock calipers. I'd edit my post if I could.

[FABombjoy]

I'm sure they go bad but surely they last longer than 15 years?
I can't imagine that a brake hose would quietly go soft & spongy. I had those same Goodrich hoses installed since '99 or 2K up until this summer. Only removed due to the installation of a Wilwood kit.

[82DMC12]

I can't imagine that a brake hose would quietly go soft & spongy. I had those same Goodrich hoses installed since '99 or 2K up until this summer. Only removed due to the installation of a Wilwood kit.

I think I'll replace the fronts since I'm messing around with those calipers anyway. I'll keep the rears for later and swap 'em out on a future brake flush. I'm doing a frame-off at some point so they can enjoy some nice new brake stays on the frame at a later date ;-)

[82DMC12]

When you split the front calipers to rebuild, it's easy to get air in the outside caliper. This air is not easily removed because the bleeder and brake line are both connected to the inside caliper. Opening the bleeder allows flow (and air) thru the inside caliper. But there is no flow thru the outside and air will stay trapped there. Normally the trick is to fill the outside caliper with brake fluid and push the air out by depressing the piston during assembly. If the front brakes are installed and air is stuck in the outside calipers, the best option is to open the bleeder and depress the outside piston with a clamp or channel locks to push as much air out as possible. Reassemble and then continue with your normal bleed procedure.

Ron

Ron, if I go all out and remove my calipers to correct this condition, would this be the best route to go:

1) Remove caliper and pads, split the halves on a bench
2) Lay the outer half down, piston-up, on the bench
3) Remove the dust cover and pry the piston out
4) Fill the bore with a couple ounces of clean brake fluid (below the inner sealing ring)
5) Carefully press the piston back inside the bore completely, which will then force some of that fluid out of the hidden hole that joins the two halves but also push air out
6) Reinstall the dust cover
7) Lay the inner half of the caliper over the outer half and install the four bolts to re-join
8) Press in the inner caliper's piston and then reinstall the pads on the bench
9) Reinstall the caliper and bleed normally

Should I do anything to the inner caliper to re-fill it on the bench, or is filling it via bleeding after installation to the knuckle good enough?

Andy

[DMC-Ron]

Ron, if I go all out and remove my calipers to correct this condition, would this be the best route to go:

1) Remove caliper and pads, split the halves on a bench
2) Lay the outer half down, piston-up, on the bench
3) Remove the dust cover and pry the piston out
4) Fill the bore with a couple ounces of clean brake fluid (below the inner sealing ring)
5) Carefully press the piston back inside the bore completely, which will then force some of that fluid out of the hidden hole that joins the two halves but also push air out
6) Reinstall the dust cover
7) Lay the inner half of the caliper over the outer half and install the four bolts to re-join
8) Press in the inner caliper's piston and then reinstall the pads on the bench
9) Reinstall the caliper and bleed normally

Should I do anything to the inner caliper to re-fill it on the bench, or is filling it via bleeding after installation to the knuckle good enough?

Andy

Andy,
Yes, your description is spot on for getting the air out during a rebuild as you assemble the front calipers. But you can also get the air out without splitting them. First, you need to have brake fluid in the pistons. This can be done by (cautiously) pumping the outside piston with fluid using brake peddle before you disconnect the brake line. You need to pull the pads on the outside caliper and watch piston position to gauge how much fluid enters the piston. You don't want the piston to "pop out". You can insert a piece of wood trim to serve as a stop. Once you have the outside caliper full of brake fluid, disconnect the brake line and seal the brake line port with a spare bleeder valve. Now you can remove the caliper from the wheel. The advantage you have when the calipers are in your hand is that you can rotate them to direct the air out. Orient the caliper so the brake bleeder is up (the internal connection between the calipers is on the end with the bleeder valve). Open the bleeder port. Compress the outside piston to push the air out the bleeder port. Once you feel all the air is out of the outside caliper, compress the inside piston and observe any air coming out the bleeder port. Now that you have the air out, close the bleeder and reinstall the caliper. As best you can keep the outside caliper on the downhill side to avoid inadvertently introducing air back in as you reinstall on the wheel. Assemble and bleed.

It's not always easy to describe a tricky procedure. I've given it my best shot. Good luck.
Ron

[82DMC12]

Andy,
Yes, your description is spot on for getting the air out during a rebuild as you assemble the front calipers. But you can also get the air out without splitting them. First, you need to have brake fluid in the pistons. This can be done by (cautiously) pumping the outside piston with fluid using brake peddle before you disconnect the brake line. You need to pull the pads on the outside caliper and watch piston position to gauge how much fluid enters the piston. You don't want the piston to "pop out". You can insert a piece of wood trim to serve as a stop. Once you have the outside caliper full of brake fluid, disconnect the brake line and seal the brake line port with a spare bleeder valve. Now you can remove the caliper from the wheel. The advantage you have when the calipers are in your hand is that you can rotate them to direct the air out. Orient the caliper so the brake bleeder is up (the internal connection between the calipers is on the end with the bleeder valve). Open the bleeder port. Compress the outside piston to push the air out the bleeder port. Once you feel all the air is out of the outside caliper, compress the inside piston and observe any air coming out the bleeder port. Now that you have the air out, close the bleeder and reinstall the caliper. As best you can keep the outside caliper on the downhill side to avoid inadvertently introducing air back in as you reinstall on the wheel. Assemble and bleed.

It's not always easy to describe a tricky procedure. I've given it my best shot. Good luck.
Ron

Damn this is complicated!

[DMC-Ron]

Damn this is complicated!

OK. Here's a simpler version to do a similar purge without removing the caliper:

1. Remove the outside brake pad and push out the piston with the brake peddle (insert a piece of wood trim where the brake pad was to keep the piston from coming out too far and to protect the disk).
2. Open the bleeder and push the piston back in to expel the air (the wood will also serve as a way to leverage the piston back in).
It may take several repetitions to get all the air.


Ron

[82DMC12]

WELL, that was a pretty eye-opening experience tonight in regards to brake bleeding. Today I received new SS front brake hoses to replace a couple of fairly old Goodridge hoses that have been on the car for at least 15 years. I decided to change them since I was going to be messing with the front calipers anyway and one of the two hoses had a bit of exterior vinyl damage. Thanks to DMCMW.

I also received from Amazon a Motive Power Bleeder tank with the European 45mm adapter which works perfectly with our master cylinders.

I was thinking the theory here was correct in that the front outer caliper is air-locked because the bleed screw can't get the air out as it's on the inside half of the caliper and the outer piston and air pocket is basically "around the corner". Evidence as follows:

Here's my freshly-turned rear rotor which was dipped in zinc before installation. I took one test drive and as you can see the rear pads have been wearing down the zinc coating exposing the fresh metal as you would normally expect to see on a rotor.

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Now here's my front rotor. As you can see, the outer pad was barely putting any pressure at all on the rotor. Probably full of air and causing poor brake feel.
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First I changed the SS lines in the front and then tried out the power bleeder. Damn this thing is so simple but works great. Pump it up to 15 PSI and then go around and crack your bleeders in the correct order (RR, LR, RF, LF) and you will definitely push air out. I followed a tip I saw on the Amazon page from a review that said the user didn't bother to fill the tank with brake fluid because he didn't want to clean it out afterwards. Instead he just used it to pressurize the reservoir. I did the same and it worked amazing. Just make sure you keep topping up the reservoir before it hits MIN - I let it get too low and had to do it all over again - learning experience. Highly recommend power bleeding over brake pedal bleeding. In fact I'm going to get the adapter for my clutch reservoir now too to make the crap job of bleeding the clutch easier (and get a remote clutch bleeder kit). By the time I was done with this, I was sure my rear brakes were perfect and my front brakes were now air-free up to the calipers.

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I followed Ron's advice and took the outer pad out of the caliper, then used a couple of wood shims zip tied together to make what I believed to be about the correct thickness to keep the piston from popping out and set that against the rotor. Since I was doing this as a one-man job, I just used the Motive bleeder box to hold the wood up in position so I could get inside and pump the brakes a few times. That closed the piston over the wood. Then I pulled the wood out, opened the bleeder and connected a hose and jar to it, and then pushed the piston back in. I was almost able to just squeeze it with my hands but I resorted to a round-edge pry bar/alignment tool to carefully push the piston back while the air and fluid escaped. Then I closed the bleeder and repeated this about five times until I was sure only fluid was coming out as I squeezed the piston in. Then I re-installed my pads and hardware. Repeat on the other side of the car.

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Another view of the same job.
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Anyway, next time I would use a plastic pry bar because my metal pry bar put a few tiny pinhead-size divots in my rotor. Oops. I was gentle but I guess the rotors aren't as strong as I thought they were. Well, I went for a test drive and the brakes feel quite a bit better. I could be spoiled by my 2019 Audi's brakes and even my wife's 2014 Honda Civic brakes because the DeLorean has more pedal travel before the brakes bite. But at least I'm stopping confidently now with zero shimmy or pull.

Next job is to get an alignment (replaced a tie rod end tonight also) and then I will go out on an empty straight road and do a good brake-bedding procedure. Then.... This project should be done!

Thanks to all for pointing out the outer piston problem, I would never have figured that out otherwise.