Leaking piston, pedal feel and NA6/NB8A caliper swap

[deags]

Hi,

To start-
I wanted to fit NB8A rotors and pads to my NA6. I received a set of NB8A calipers, pads and brackets but was unable to push the piston out of one of the calipers so ended up using the NA6 calipers on the front that were already fitted. While doing this upgrade I also installed braided lines. The first one I did was the rear right with the splitter box in the lines - I had huge difficulty installing the braided line and it took far too long and I lost all of my brake fluid.

Here is a photo of the fronts:
https://imgur.com/a/ryR7K

Some questions:
Previously a mechanic has diagnosed an 'internal leak' on a rear caliper - but it was corrected to get the car going and I was told it would keep working. This was following my complaint about a soft pedal feel. When replacing the rears I did not notice anything odd - however when I compressed my FL piston it leaked brake fluid from the piston dust cover. I intend to replace it now when I can find a replacement part, but would this be the cause of sh*t pedal feel? There is no fluid leaking when the brake pedal is pushed hard. I am unsure what an 'internal leak' is? I've replaced both rears but suspect it is actually the FL caliper with the issue.

I've bled and rebled all the calipers - is it possible I have air in my master cylinder since I did lose ALL my brake fluid changing the rear right line?

I've read mixed info about NA6 and NB8A/NA8 calipers - most places say they are identical, others give slightly ambiguous answers. Some places mention flipping the sides around on the front, this is only needed if fitting NB8A calipers? They are certainly different, which I discovered after taking the wheel off an NB8A and seeing the smaller/bigger slide pins are different (lower and upper end of the caliper). I am a bit confused.

Some places discuss the length of the 'fingers' on the NA6 calipers as being too short - see my second and fourth photos I am not sure if this is a problem?

Currently the car drives OK - I have pushed pretty hard from ~60-70km/h and the wheels did not lock which I would like... my main concern right now is even after doing all this the pedal feel is quite soft but I am not certain what the cause is.

Cheers

[hks_kansei]

NA6 and NA8 calipers are different.

NA8 and NB8A are the same.


As far as side/fitment, the bleed nipple must always be at the top.


Internal leak would be referring to one of the seals inside the caliper itself, they consist of the metal casing, with a machined bore where the piston sits, behind the piston are a few clips and rubber seals, over time these can start to leak, meaning less pressure on the brake (and less braking, crap pedal feel, etc etc)

[93_Clubman]

Previously a mechanic has diagnosed an 'internal leak' on a rear caliper. I am unsure what an 'internal leak' is?

An 'internal leak' on a rear caliper (often the rear passenger side on a RHD MX5) may also refer to seepage around the internal handbrake adjustment mechanism: https://www.miata.net/garage/ebrake/index.html

I've bled and rebled all the calipers - is it possible I have air in my master cylinder since I did lose ALL my brake fluid changing the rear right line?

Yes - for example when fitting a new brake master cylinder, 'bench bleeding' may be required before actual fitting. However, I've found the MX5 NA to be generally forgiving in this regard, but some other cars aren't.

[RS2000]

however when I compressed my FL piston it leaked brake fluid from the piston dust cover. I intend to replace it now when I can find a replacement part, but would this be the cause of sh*t pedal feel? There is no fluid leaking when the brake pedal is pushed hard.

I presume you are saying that fluid came out of the dust boot when you pushed the piston back to fit new pads. This indicates a worn/damaged piston seal (or piston), & fluid has leaked into the boot. Since the work, you say there is no fluid leaking when the brake pedal is pushed hard. But perhaps there is a small leak into the boot, which is yet to appear externally.
Cheers

[deags]

Thanks everyone - internal leak is just a leak within a single component, ez

RS2000 - I didn't consider there might be fluid accumulating in the boot, that makes sense.

If using the NA6 calipers with NA8/NB8A brackets+pads is ok, I will try rebuilding my front left and seeing if that helps. I have half a rebuild kit already so it will only cost time and more heartache

I fitted rear calipers from an NB8A to the NA6 so if there was an issue with one of the rears then hopefully it is fixed now and the front is a new issue.