Front Brakes locking up after 300zx BMC install

[gtsgts]

Ok, see if u can help me with this BMC problem.

Specs:
92 240sx non-abs coupe
Front 300zx 95 N/A calipers and 5 lug w/ new stainless lines
stock BMC
(everything worked fine)

Did:
Rear 300zx ebrake/5 lug/caliper upgrade (same 95 N/A)
300zx 17/16 BMC (was bench bled prior to install, no bubbles)
....

NOW: Front Calipers locking up after car warms up to operating temp

notes:
- problem resolves when car cools
- front calipers lock up slowly over time (and ONLY the fronts)
- pedal feel stays the same
- no leaks anywhere

re-bled the system and heavily re-bled both fronts.
- ran car, problem persisted

changed back to stock 240sx BMC
- problem resolves

WTF

Ok, so 300zx BMC is the problem, but whats up?
- brake booster rod too long? (tried adjusting rod 180 degrees clockwise, didnt work)
- semi-plugged middle fitting?
- What else would cause fluid not to return to master?

:ugh:

[Chaluska]

re-bled the system and heavily re-bled both fronts.
- ran car, problem persisted

changed back to stock 240sx BMC
- problem resolves

WTF

Ok, so 300zx BMC is the problem, but whats up?
- brake booster rod too long? (tried adjusting rod 180 degrees clockwise, didnt work)
- semi-plugged middle fitting?
- What else would cause fluid not to return to master?

:ugh:

sticking seal... is it used or new?

[fliprayzin240sx]

Bad BMC...

[gtsgts]

sticking seal... is it used or new?

bought it used.

[dawagarage]

if its the bmc, i suggest rebuilding it rather than buying a new one
OEM Brake master cylinder rebuild kit (Nabco 17/16") (http://www.z1motorsports.com/product_info.php?cPath=4_34_91&products_id=1914)

[Silviaracer1988]

had this issue before with a chevelle. make sure your brake lines are away from any heat. what happened with the chevelle the brake lines got too close to the headers and would boil the brake fluid which caused it to pressurize, then it would lock up when it cooled down could you use the brakes til they got hot again.

[dawagarage]

^ thats what i was thinkin... well more along the lines that trapped air was being heated up. but still, heat and/or air = bad

[jr_ss]

Does this happen when you are cruising? Is your car boosted? The one way check valve could be bad on your booster.

[codyace]

Did you follow the FSM bleeding procedure? Typically with Z master cylidners the rears lock first.


With that said, are the fronts locking with casual brake application or under hard brake application?

[zil180sx]

Dude u got to much fluid. V fluid expands on hi temps.