Stops but no pedal resistance after brake swap

Took a couple of test drives after bleeding several times over the week. The pedal has no resistance for what feels like the first 20-30% of travel then I get some and it wants to send my face into the windshield.  It is slowing down in that area of travel though.

Main suspicion is a hidden air bubble in the lines. I've experienced that before but it felt like I had a lot less braking until the pedal went down far enough. I did gravity bleeding and used a homemade pressure bleeder over the week then last night did the 2 person method.

The other possible culprit is the 2 rear brake hoses from hard line to caliper, they're probably 10 years old. The rest (3) are new rubber. Since everything else is new maybe they're the weak link and swelling. I'd experiment with my wallet but I'm kinda sick of brake bleeding at this point.

Details: My brake swap is pieced together to mimic the 3rd gen RX-7's caliper and master piston sizes with a similar sized dual diaphragm booster. Front calipers are 4 piston ones from the 2nd gen, rear are single piston from the later first gen, all were rebuilt by me a couple years ago. All with new StopTech Sport pads. Master cylinder is new from Centric and booster is rebuilt from Cardone.

Any ideas?

Photo for flavor:

Did you bench bleed the master?

In reply to preach :

I did not. Would it make a difference after this much bleeding?

Though if there's an air bubble trapped in there, not much to lose except more sweat.

I had a similar issue on my rx7 after a master cylinder swap.

It ended up that there is a "reaction disk" in the booster that was dislodged and caused the brakes to have a soft pedal, but had crazy aggressive bite.

wvumtnbkr said:

I had a similar issue on my rx7 after a master cylinder swap.

 

It ended up that there is a "reaction disk" in the booster that was dislodged and caused the brakes to have a soft pedal, but had crazy aggressive bite.

Came here to say two things:

1. Cardone is on the Hennessy Honda of Woodstock diet in my book.

2. If booster and master were separated, sounds like reaction disk is missing, dislodged, or perhaps installed backwards.

More booster info than you knew you wanted

I just tried driving it with the vacuum line disconnected to the booster and plugged. Pedal travel shrank from the go and of course was a bear to stop.

I guess Cardone struck again?

Also looked up reaction discs and how to extract them, most of the boosters people are taking apart have a star washer retainer in the front that's easily removed. I've got a dual diaphragm booster for 2001-2005 Miatas in the pic below and can't find a guide for them. Anyone familiar with these? Or should I just get a single diaphragm one like a normal person?

In reply to AngryCorvair (Forum Supporter) :

Nerd interest intensifies!

Not helping me not want to put hydroboost on Colin.  I have a new in box unit from Summit for $cheap, making the lines will be the hard part

AngryCorvair (Forum Supporter) said:

1. Cardone is on the Hennessy Honda of Woodstock diet in my book.

The purveyor of the parts most likely to be voted "the invoice says [whatever car part] but reality says 'scrap.'"

CV axles with no grease caps and splines that were specially treated by being shipped in a big bin of other axles.

Sorry to reduce the signal:noise ratio, but if it saves one person a fiasco...

Just searched my receipts and the last time I bought anything from Cardone was the booster I just removed, installed in 2015.

Any opinions on SKP? Their part photos on RockAuto show them painted as opposed to bare metal like Cardone's boosters, that already looks more promising.

In reply to j_tso :

No personal knowledge or experience with that brand. Maybe Google can tell you who owns them?

j_tso said:

Any opinions on SKP?

I have had a not so good experience with them. While doing a Ranger 2.3 timing belt I ordered a T-stat housing (SKP brand) and a temp sensor. The housing has a fitting for the temp sensor. The new one looked the same but . . . When I went to attach the wire connector - no room for it to fit like the original did. An up close look, while attached, showed the slight, but significant, difference. I cleaned up the old housing and finished the job.

Later I looked into getting a correct housing. SKP has / had at least 4 different part numbers for the exact same application. I have no idea what or why there would be a difference. I am now at least leery of SKP parts.  

Jesse Ransom said:

AngryCorvair (Forum Supporter) said:

1. Cardone is on the Hennessy Honda of Woodstock diet in my book.

The purveyor of the parts most likely to be voted "the invoice says [whatever car part] but reality says 'scrap.'"

CV axles with no grease caps and splines that were specially treated by being shipped in a big bin of other axles.

Sorry to reduce the signal:noise ratio, but if it saves one person a fiasco...

Dirty secret: Most of the parts store reman anything are rebadged Cardone.

Not all CVs have caps.  VWs usually didn't.

In reply to Pete. (l33t FS) :

Well, heck. That definitely confirms I'll be avoiding reman anytime I can get new or DIY the remanufacture... It's only a savings if the rebuilder makes a good faith effort to provide a usable part, and I don't think Cardone is setting their bar that high.

FWIW, these were E30 axles and had caps, which were not readily moved over without damage and not available separately (but in the end were moved to the extent possible of necessity, IIRC. It was a while back...) The spline damage alone should have rendered them untenable. I spent a bunch of time cleaning them up to get them good enough to almost get them so stuck I couldn't finish seating them in the hub splines with a 1/2" impact. That may have been the thing that drove my impact upgrade...

Rolled the dice on another reman booster 2 weeks ago and the issue of "sudden bite" is gone, so that appears to be solved.

Getting tired of brake bleeding, at least in this heat because I have to wake up early to do it. Since the master cylinder had to come off to replace the booster it was another couple rounds, but the pedal is still too soft for my liking. With the engine off I can pump out the vacuum and the pedal will get stiff and not sink further, but it initially sinks a little further than my last setup. Going to do another morning round of bleeding this weekend before I start suspecting the master cylinder was defective as well.

Replaced the master cylinder with one for a Miata and the brakes are back in business. The old one was also new but for a Protege, don't know why it wasn't working. Same piston sizes but went with the Miata for the brake line locations.

Looking forward to no more bleeding until the weather is cooler. Got to at least replace this cheap DOT3 fluid before the next trackday.