bleeding brakes

[1lo620]

Ok I have a ???.. So I had a leak on thr front brakes and lost all the fluid out of the front fluid resevoir...Now the rear resovoir still has all the fluid... my ?? is do I have to bleed the rear brakes when I go to bleed the front brakes..any help would be great.. thannks...

[72240z]

Should bleed all 4 corners.

[datzenmike]

The systems are completely separate. As long as the rears were unaffected, you needn't bleed them.

 

For the 620.... get a short length of brake line and connect to the master rear (fronts) outlet and bend the tube up and into the rear reservoir. Repeatedly pump the brakes to expel all the air in the master. Reconnect the fronts to the master. Loosen the front most bleeder on the NLSV and bleed any air until only clear fluid comes out. Now bleed the fronts in any order.

[72240z]

The 620 doesnt use a proportioning valve between the front and rear? Because if it does then its not 2 independent systems and air can travel across them at the valve. If it doesnt then yes it is 2 independent systems and you shouldnt HAVE to bleed all 4 corners. I thought the 620 did use a prop valve though which is why I advised bleeding all 4.

 

240z uses a prob valve and air most def can migrate between. Its usually always just safer to bleed all 4 if your going to anyway, I use it as a rule of thumb. New fluid > old dirty fluid and safe > sorry

[1lo620]

well the wired thing about it is I lost the brakes while driving and I had no pedal at all. Shouldnt I have had a little pedal for the rear.. ? And Like I said the rear fluid resevoir is still full.. I will probly just end up bleeding all 4 just to be safe.. wont take that long.. Have to figure out what happend first...

[ggzilla]

The brakes will be severely affected. long pefal travel and barely stop

 

If the rear brakes are out of adjustment,.they might not work until pumped up

 

Finally the rear portion of the master may be bad

[72240z]

I agree

 

What do you mean figure out what happened? Did you locate the leak?

[datzenmike]

A dual master system would be pointless if they are connected in any way. I can't see how a proportioning valve involves the front system. Would it not simply be a spring loaded valve that reduces hydraulic pressure to the rears? I have a Willwood proportioning valve and there is an IN and an OUT to the rears. It reduces pressure up to 60%.

 

Most Datsuns achieve front rear braking bias by designing the proper size rear wheel cylinders to match against the fronts.

 

The 620 does have a NLSV which allows more brake pressure to the rear drums, proportional to how much the frame is tilted down at the back due to a heavy load. It does nothing otherwise.

 

All dual systems have a low brake pressure warning system. Its a switch with front hydraulic pressure on one side and rear pressure on the other. If both systems are working normally the switch remains neutral. If the front or rear should leak or fail there will be more pressure on one side pushing the switch over to a ground contact and lighting the BRAKE warning light on the dash.

 

 

 

And yes, for optimum brake performance and hydraulic component life the brake fluid should be changed every 3 years, sooner is fine.