Im trying my best to get my datsun drivable as a daily while using it as a daily. not smart on my behalf.

Ok so its a Datsun 1200 ute. Disc Front and drum rear.

Pedal was going to the floor and master brake cyl was leaking.I researched on net and decided that a 120y 11/16 one was suitable so i bought one from ebay. The original one on car was 3/4 for some reason.

http://www.ebay.com.au/itm/Brake-Mast ... ories&hash=item2564d71a76


Installed it no worries, Bled up no worries, went driving no problems but after 5 or so minutes the brakes lock up. The Pedal goes hard and smoke starts coming off the front brakes.

Crack pressure off at the brake master and all is good again for 5 mins then locks up again.

The pedal is set correctly.

If i leave the car for a few hours the brakes go back to normal.

The calipers are not siezed.

I am confused.

Please help. Would love some suggestions to try tonight.

Mike

Your sure there's no residual pressure valve in the master or lines? Drum master cyls have them. Sounds like you might in the front ones

I took the brake master out earlier today.




Thinking there was a one way check valve for the front brakes i took out the spring and rubber for the front brake section which is similar to pic above 12,13,14,15,16.

Didnt make any difference :(

Perhaps i buy the wrong Master?
I had to reuse the original 9,10,11 from old master could this have been different to what i need?

using a 120y master should be perfect for you
9, 10, 11 should be fine

i would suspect you have been delivered the wrong master (for drum front) but you have removed the part that would cause the problem with that 12, 13, 14 etc

how do you know you don't have a seized piston now? maybe you have bent a brake line and crimped it over by accident when changing the master?

perhaps you installed new pads and they are holding slightly, causing them to heat/expand and grab over 5 mins? (happened to me two weeks ago with handbrake left on)

good to know

I dont think its a siezed piston because if i release the fluid pressure at the master cyl then the pistons retract and i can drive again.

Have not touched anything else to do with brakes. Ill check lines over again carefully but i would be suprised if anything happened to them.

I have to assume its the MC preventing the fluid returning the the resevoir. #OOPS#ed if i can figure it. Il check pedal play again.

Definatly a pushrod clearance issue

The back piston can't return properly and won't compensate thru the port so the brakes are holding
You need to address this problem before you worry about anything else


So its a 1200 ute... .that never had disc fronts thats been converted
Does it run a booster ?
That master you have doesn't suit a boosted system ... so if its on a booster its preloaded and causing your issue
If its not on a booster your clearance is due to the pushrod in the back of the master

dattoman_1000 is most likely correct

B210 uses a different length pushrod to match the different pedal setup. If put on a 1200 and the pushrod length not modified the brakes will stick.

hazerb30 - i had the same problem but mine would build up pressure over 40 mins and then the rear brakes would lock on, i got some advice on here and there were some shims (i used really thin plastic washers) that you could place between the master cylinder and firewall. This spaced the master cylinder that extra mm and allowed for the push rod to release all the way out.

Also if you are using a bolt in the brake pedal where it activates the brake lights, i found that that was stopping the push rod releasing all the way so i changed the bolt to a screw that is used in a countersunk hole (this allowed it to sit flush in that brake pedal hole, againg allowing more room for push rod to release)

hope that made some sense

Yep yas were on the money. i think i have it solved now but ill have to wait till tomorrow to test properly.

The problem was the pushrod. kind of. I had used the old one so i thought it would be no problem, length was good and lined up with pedal perfectly. But.. the problem is where the pushrod clips on with circlip it was too long in there. Well... not too long on the pushrod really, there was no 'cup' on the piston on 120y master cylinder for the pushrod to seat into making it too long.

I ended up grinding the pushrod flat and when testing with air its now able to return to the resevoir.

Hard to explain. pic might help. The half ball at the end of the pushrod was not able to seat into the master cylinder because there was nowhere for it to seat into like on the old one making it longer and putting pre load onto the piston.

Attach file:

---

  2012-05-29 21.13.22.jpg (94.42 KB)