Stuck brakes

[1fstdat]

Dont know if you guys have had this problem but I just did the passport/hardbody disc brake conversion, and now the front brakes drag, and once they get hot they stick. I have changed calipers, brake lines, and the master cyl. I have removed the valve in the master so I wont hold presser in the lines, but still after I drive it they stick on and if I crack a bleeder or line anywhere on the truck a burst of fluid comes out and the brakes work fine. Could it be the small factory master? Im dont think I can go with a longer master because under the hood is cramped.

[BEEBANI]

Could be you have a bad master. Did you put new calipers on there?

[jesusno2]

pistons are not retracting or their not sliding. If their new id take em back. if ya just slammed them on from a junkyard they may need cleaned up and rebuilt. The master cylinder shouldnt have really anything to do with them sticking, that's all in the caliper itself.

Edited October 15, 2008 by jesusno2

[datzenmike]

Your pedal has no free play. There should be at least a 1/4" of pedal travel before the push rod begins to move the master cylinder piston. If not the master cylinder piston can't return fully and allow the pressurized fluid in front of it to vent back into the reservoir. Each time you add a little more pressure until the brakes stick.

 

Look up under the dash at the brake pedal and you'll see the push rod that goes into the m/c booster. The pedal end has a pin and a cotter pin. Remove the cotter pin and then the push rod. Loosen the lock nut and turn the end in to shorten the rod length. Re-install and depress the brake pedal with your fingers to get just under a 1/4" of play. When set, remove rod and tighten the lock nut, insert pin and DON'T FORGET THE COTTER PIN. YOU DO NOT WANT THE PIN TO FALL OUT!!!!!

Edited October 15, 2008 by datzenmike

[yello620]

I agree with Datzenmike here. You have a fluid pressure problem and not a sticking piston problem.

Adjust the freeplay in the pedal to the booster... as Mike described. You could also search about this adjustment, as it has been dicussed before.

 

Jason

[1fstdat]

Its a 521 so there is no booster and has the orig. master, Im on my 2nd new master, and this new one is adjustable as the original andmy fist new one where not, I have adjusted them all the way back and still have line pressure... got me going crazy, the first calipers where off a '92 is 2wd pickup they where junk yard ones but looked good and I cleaned them up, the piston moved ok, but a 2wd must have a solid rotor that is thin. so I swapped them out for a set of pathfinder 4wd calipers again they looked good as with the 2wd ones. has anyone run a disc brake setup with a 521 master cylinder? could it be the calipers take more fluid to move in and out then the master cylinder can move, unless pumped, and you cant un-pump so it just get stuck? Any ideas are great help Thanks guys.

[moparvwfreak]

upgrade to a Z master? i have heard thats something you need to do when doing the conversion.

[Llittle_Llama]

i know its different, but just some insight....i had rthe same issue on my 90 240sx about 2 weeks ago, disconnect the check valve and air would woosh, yes woosh from the booster. check valve was sticking. had to drive about 12 miles home full boost just to keep it going. i would spin the back tires till about 15 miles an hour before the fronts would break free and roll. thank the LORD i had the RB20, the ka would NEVER have moved it, lol

[1fstdat]

Hey I just took a master cyl out of a currier... I know Ford parts on a Datsun, Anyway its only an 1" or so longer then the stock one and is a dual reservoir unit bolted in with few mods but I will hook up the rest later tonight. Would have ran the z one but the construction biz is slow got to go cheap... all the time just no money. Thanks for the help

Edited October 16, 2008 by 1fstdat

[Llittle_Llama]

all the time just no money. Thanks for the help

 

welcome to RATSUN.NET :D:lol:

[moparvwfreak]

all the time just no money. Thanks for the help

 

i know that feeling. good luck with the truck man.

[ariascarlos1990]

Your pedal has no free play. There should be at least a 1/4" of pedal travel before the push rod begins to move the master cylinder piston. If not the master cylinder piston can't return fully and allow the pressurized fluid in front of it to vent back into the reservoir. Each time you add a little more pressure until the brakes stick.

 

Look up under the dash at the brake pedal and you'll see the push rod that goes into the m/c booster. The pedal end has a pin and a cotter pin. Remove the cotter pin and then the push rod. Loosen the lock nut and turn the end in to shorten the rod length. Re-install and depress the brake pedal with your fingers to get just under a 1/4" of play. When set, remove rod and tighten the lock nut, insert pin and DON'T FORGET THE COTTER PIN. YOU DO NOT WANT THE PIN TO FALL OUT!!!!!

 

wait... you can adjust the adjust the rod length?

[datzenmike]

yes

[ariascarlos1990]

yes

 

I wonder if thats what wrong with my friends brakes?? :confused:

[1fstdat]

The master cylinder I removed and the first new one where not adjustable, but the 2nd one was, so not all are adjustable.

[ariascarlos1990]

I'll check.

 

Thanks alot.

[datzenmike]

The master cylinder I removed and the first new one where not adjustable, but the 2nd one was, so not all are adjustable.

 

It's not the master that has the adjustment. It's adjustable where the pedal meets the push rod under the dash.

[1fstdat]

Yea thats what Im talking about also, the push-rod right?, I have had 2 with fixed ends on the push rods and 1 that was adjustable, and none of the push rod would come out with out removing a snap ring and a retainer plate in the end of the master cylinder, its diffrent then most I have seen maby its a 521 thing?