broken brakes.

[411blackbird]

having random brake seizures.

can be driving along, brakes working fine then for some reason when i hit the pedal the brakes will lock on solid (often when pulling into a service station) and nothing, even a decent amount of power from the engine will get her to move again, until i physically open the bleed valve on the master cylinder removing a good amount of brake fluid through my engine bay, only to get a few more miles and it happens again.

iv had the brake shoes replaced, wheel cylinders honed and refitted all brake lines replaced even the master cylinder has had all seals refitted.

what have i missed or done wrong?

has anyone else had this problem?

[datzenmike]

Wasen't there a similar post?

That answer was that the brake pedal push rod was adjusted too long and the M/C pistons can't return to their rest positions and release the fluid back into the reservoirs.

[411blackbird]

legend, as far as i can tell that's fixed the problem, won't know for sure till it's back on the road.

[411blackbird]

still hasn't fixed it, just got it back up and running and drove it back into town, brakes are still seizing after being used a few times.

[hang_510]

assuming that the hardware was too...springs specificlly.

maybe a little lube on the plate where the shoe moves.

 

old fluid fushed out?

pedal return spring?

MC rod adjusted? (mikes ?)

:confused:

[datzenmike]

Front or back? Is it a single M/C?

 

The M/C piston has to return fully in order to release all the pressure. The brake pedal should have a small free play in it.

[GLOZANO67]

Yea, I'm currently having the exact same problem right now. I drive my 620 for a couple of miles and little by little the brakes start to seize up on me till they stop completly. Then the only way to release the pressure is to open up a bleeder screw from m/c. This is a list of items that I have changed to fix the problem but have had no luck.

- rebuilt m/c

- adjusted rod several times

- replaced all 4 calipers

- replaced all 4 brake lines

- flushed out fluid to dot 5 synthetic

 

seems like I'm out of options, someone told me that the booster may be holding pressure on the m/c therefore holding pressure on the calipers does anybody know if that can be a possibility? need help thanks

[banzai510(hainz)]

Maybe pop a drum to make sure the brakes are not gummed up by Hydralic fluid(if MC needs top off all the time)

 

maybe a wheel cylinder is sticking? But you said you rebleed it then fine so I dont think that.

 

 

My 521 I have a 5 yr old Tawan Brake Master and push on the brakes and it would go to floor. Wont leak but I seen airbubbles from inside the resivoir. Believe it or not it was bad. This would help your situation but mayeb swap it out. there isnt much to these things. I was lazy and didnt want to do it but had another and it was fine after that.

 

also if you have a vaccum ass(power brakes) ck in to that also maybe diapram is not releasing.

Im only guessing now

[GLOZANO67]

It has 4 wheel disc brakes, woundering if anyone knows if the booster can be the culprit (problem) that is the only thing that I have not swaped out. someone told me that they can hold pressure once they have gone bad, is this true? :mellow:

[67411sss]

having random brake seizures.

can be driving along, brakes working fine then for some reason when i hit the pedal the brakes will lock on solid (often when pulling into a service station) and nothing, even a decent amount of power from the engine will get her to move again, until i physically open the bleed valve on the master cylinder removing a good amount of brake fluid through my engine bay, only to get a few more miles and it happens again.

iv had the brake shoes replaced, wheel cylinders honed and refitted all brake lines replaced even the master cylinder has had all seals refitted.

what have i missed or done wrong?

has anyone else had this problem?

 

I had a similar problem with my 411, the master brake cylinder was letting fluid past the plunger and leaking into the rubber boot. I guess after a while it would return to the original position and be fine but i always thought the plunger was getting stuck down the cylinder and applying pressure until the fluid was out from the other side of the cylinder, once gone then the brakes would release.

[GLOZANO67]

Does anyone know how to check a booster, to make sure that it is working properly?

[Guest Rick-rat]

I just went through this with my 620 with drum brakes, finally put on new master cylinder and it works fine now, as far as drum brakes go

[Z-train]

It's not the booster.My money is on the MC.

[GLOZANO67]

The m/c has already been rebuilt and its a 15/16 bore.

[BJW's FiveTen's]

Here is something I found. I had a booster problem on a car that drove me crazy, wish I had known this before.

If the booster is working correctly, it should have no noticable effect on the engine, but if it is leaking, it will cause big problems. Use the following procedure to check yours.

 

Things you need:

 

Vacuum guage

Cap for vacuum port on the intake manifold

Friend to work brake pedal

Pencil and paper

Procedure:

 

Hook up the vac guage. Start the engine. Note the reading. This is your "base" reading.

 

Stop the engine, disconnect the booster vacuum line and cap the port on the manifold. Start the engine, look at the guage. If this reading is substantally higher than the base, you have a leak in the system, probably in the lines leading to the booster.

 

Stop the engine, remove and test the one-way valve (should be able to blow into it one way but not the other). Air should only pass in the direction indicated by the arrow printed on the top of the valve (make sure to reinstall it in the correct direction).

 

Reconnect the one way valve and vacuum line to the manifold and start the engine. Watch the vac guage as a friend depresses the brake pedal. It should dip as the pedal is depressed and return to the base reading. If it drops slowly, but returns, you have a blockage/collapse in the vac line. If it falls and does not return, you have a torn diaphram in the booster. Especially indicative of a torn diaphram is a hissing when the pedal is depressed.

 

Hope this helps.

Thanks

Bryce

[banzai510(hainz)]

Rebuilt cylinder?????????

 

I rebuilt a Slave cylinder and it worked for a few days. It would not leeak but suck in ai. Would have to blled it every few days. I got a new one then was OK.

 

if a brake booster bad it might suck in brake fluid and look like a bad head gasket. But Im only guessing here as ai never owned a Datsun w/power brakes.