|07-30-2015, 07:25 AM||#1|
S13 with Z32 brake swap, brake bleed problem
I have searched a few dozen threads and it seems like this is a common problem. However, I can not find any resolution to this issue so I'm putting up a new thread asking for help. I have a track day in 48 hours and I've been working my these brakes easily for a week now with no resolve.
I purchased my S13 from a fella who did the Z32 swap on all 4 corners. No ABS and stock master cylinder. Two weekends ago I wanted to do a brake upgrade. I rebuilt the front two calipers because one was sticking, then replaced all rotors and pads, upgraded to speed bleeders, and I bled all of the old fluid out of the system in exchange for Motul 600.
After about 3 hours of bleeding I had moved a good 3 pints of fluid through each wheel. Yet the pedal pressure was still lax to nonexistent. I could close the bleeders, then pump the pedal. After 5-6 pumps the pedal would get hard and hold. However, if I let off of the pedal then came back in a few seconds the pedal would go down almost to the floor with only a little resistance. (this is all while the car is off)
Fast forward a few days and I decide it's my master cylinder. I replace the master cylinder, bench bleed it thoroughly, then put it on the car. I spent 3 hours last night bleeding each wheel and moved easily 3 pints of brake fluid through each bleeder. I pumped and pumped and pumped; fast and slow and made sure that each piece of tubing was bubble free and clean.
However, I am STILL having the same problem. Again, I can close the bleeders and pump and pump and pump and the pedal will get hard. Yet when I let go of the pedal and get back on it, the pedal goes almost to the floor.
If I crank the car up and try to drive it then the pedal immediately goes to the floor. You have to pump super fast to get the brakes to work and even then they just barely seem to work.
When I put the car up in the air I can press the brakes and each corner grips the pedal fine. I have no leaks whatsoever and I have honestly spent 5-6 hours bleeding the brakes on my car. The calipers were rebuilt correctly, the bleeders are on TOP of the caliper, and as far as I can tell I'm not leaking a drop anywhere on the vehicle.
Any thoughts? I'm using speed bleeders and the only doubt I have about the whole system is that the LR bleeder weeps a little bit of fluid when I first crack it open for a bleed. None of the other wheels do that, as they will only start to weep when I open them then push the pedal.
It's ****ing frustrating. I've done brake jobs on dozens of other cars and this is by far the worst experience I've ever had.
|03-19-2017, 01:02 PM||#3|
Join Date: Nov 2010
Trader Rating: (7)
Feedback Score: 7 reviews
try adjusting the clevis for the brake pedal. if that makes no difference, your BMC is toast
|03-20-2017, 12:20 PM||#4|
I'll adjust the clevis this coming weekend.
I believe the LR caliper is just so old that the gap around the bleeder thread is causing air leak. I've tried using grease and teflon tape but to no avail. The vehicle stops fine (scary enough is that I track it) but the pedal just feels very soft all of the time.
I'm pulling the car out of storage next week and plan on buying new calipers to see where that gets me.
|03-20-2017, 02:14 PM||#5|
Join Date: Mar 2012
Location: erith kent england
Feedback Score: 0 reviews
you may well need the larger bore z32 300zx BMC to match the larger fluid volume
of the 300zx calipers and get rid of the long pedal travel
the stock smaller bore BMC can only deliver so much fluid,so has to over stroke to
get the pedal firm and working the pads onto the disc's
there are three z32 BMC bore sizes 7/8th,1",and 1 1/16th
(and not sure what you can got on the USA spec cars)
I went with the 1 1/16th version to match my 8 pot K sports and z32 rears
you may be better with the slightly smaller bore sizes as can over do it
and end up with a sharp and hard to modulate pedal (easy to lock up)
the K sports are for my 13 but tried them on my 14a as a test
with stock rears+ stock BMC
and pedal needed a rapid second dab to keep it from sinking away
the UK 14a has 4 pots and a bigger bore BMC than a 13 on single piston/sliders
but not enough for the extra fluid volume of 8 pots
just stuff I found when searching on what others have done
|03-20-2017, 02:52 PM||#6|
Thanks Andy, I will definitely look into these options.
|03-20-2017, 07:29 PM||#8|
The previous owner did the brake swap and before I changed pads and rebuild the calipers, the pedal was much better. Would there be any reason why the rebuild could have messed up my brake bleeding abilities? Again, I think it's leaking from around the bleeder threads on one caliper when I'm bleeding the brakes.
I've tried to bleed them with and without speed bleeders (Mity-Vac) but the results are still the same with a spongy pedal.
|brake bleed, s13, z32 brake|