siezing brakes ???

[benrob]

So I did a 4 wheel disc conversionon on my 521 pickup and after 30 min of driving the brakes slowly sieze up then cool back after about a hour . Is it possible that my brake fluid could boil and press on the brakes ? Or mabye air inthe lines ?

[datzenmike]

The  residual valve(s) in your master are for drum brakes and keep about 10PSI in the lines at all times. This keeps the shoes close to the drums so they don't have to travel as far and cause lots of pedal travel.

 

Disc brakes only need a few pounds to keep them lightly against the rotors.

 

Also check that you have about 1/32" of free play on the pedal. Push on the pedal with your thumb. There should be a small clearance before the push rod starts to push against the master and there is resistance. If not set correctly the fluid cannot return to the master properly and every time you use your brakes the pressure increases until you can't move.

[flatcat19]

Did the master get replaced?

 

Should have kept this in your brake swap tread so we can see what has and has not been done.

http://community.ratsun.net/topic/44584-disc-brakes-help/

 

 

I just reread that thread. Lots of suggestions were made to do the job proper.

None were taken. At least it wasn't stated that you installed which and what parts.

 

You also had an unknown MC you were putting on there.

 

Give a quick rundown of all that was done and replaced.

[datson4life]

yea the free play that was mentioned in very important, i had same issue not too long ago, the master cylinder shaft to the brake pedal wasnt getting enough play on the return

[benrob]

I did put a new master , a 15/16 bore out of a 280 z . And there is plenty of play when the pedle is released. Another thing that ive noticed is that this still happens when I dont apply the brakes. Thats y I feel like its a heat problem.

[datzenmike]

So I did a 4 wheel disc conversionon on my 521 pickup and after 30 min of driving the brakes slowly sieze up then cool back after about a hour . Is it possible that my brake fluid could boil and press on the brakes ? Or mabye air inthe lines ?

.

Boiling brake fluid or air in the lines will not push the pads against the rotors. Remember if the brake pedal is up, andyresidual pressure in the system vents back into the master reservoirs. Expanding vapor from boiling fluid would just push back into the master. Your pedal would also become very mushy.

 

Have you raised the tires and tried turning them by hand?

[wayno]

I did put a new master , a 15/16 bore out of a 280 z . And there is plenty of play when the pedle is released. Another thing that ive noticed is that this still happens when I dont apply the brakes. Thats y I feel like its a heat problem.

 

Are all the brakes seizing, or is it just the front or the back?

Was the master out of the 280Z for disc all around, or was it a disc drum year?

Is there play in the pedal when the brakes are seized?

I had my brakes seize on the way to blue lake a few years ago on my 521 kingcab project, I was towing it, I was not even in it when it happened, but I knew something was up before leaving, so I brought a 10mm wrench with me, and half way there I opened the bleeders and let the pressure off the brakes.

[datzenmike]

 

Was the master out of the 280Z for disc all around, or was it a disc drum year?

.

Good point wayno....I assumed he meant 280zx not 280z. The zx master would have had rear disc brakes and the correct residual valve in it, but if really from a 280z it would have been rear drum. In which case....

 

The  residual valve(s) in your master are for drum brakes and keep about 10PSI in the lines at all times. This keeps the shoes close to the drums so they don't have to travel as far and cause lots of pedal travel.

 

Disc brakes only need a few pounds to keep them lightly against the rotors.

 

Also check that you have about 1/32" of free play on the pedal. Push on the pedal with your thumb. There should be a small clearance before the push rod starts to push against the master and there is resistance. If not set correctly the fluid cannot return to the master properly and every time you use your brakes the pressure increases until you can't move.

[benrob]

Im not sure about the master it was given to me and I was told is was out of a 280 , z or zx im not sure . Seems to be more the fronts than the backs and ya when I raise the tires a can't turn the wheels by hand . Dident think about checking for play in the peddle when there siezed up so i dont no . Sounds like its time for a new master .?

[flatcat19]

Maybe you have the lines crossed from the master to the corresponding circuits. 

 

Brake pedal push rod adjustment is something to check also.

 

 

Wayno made a good call with lifting the truck to see which wheels are locking up.

[datzenmike]

The forward part of the master is for the rear brakes and will have a large R cast into the body of the master. F for fronts is at the rear.

[wayno]

The forward part of the master is for the rear brakes and will have a large R cast into the body of the master. F for fronts is at the rear.

 

It really depends on what master you have, I have a master in front of me right now with the front/forward being for the fronts, and the rear being for the rear brakes, I have no idea what it was for.

You need a master for disc brakes all around, but it still will have a front specific circuit, do not get them mixed up.

[datzenmike]

Or go to the wrecking yard and pull the residual valve from the F section of a Nissan car or truck with front disc brakes. It's located in the body of the master just above or behind where the hard line comes out.

 

This is all you need...

[devilsbullet]

shouldnt need a new master. he said it was a 15/16, zx came with 15/16, z's(front disc rear drum) came with a 7/8. that being said, what 3/4 master came with 4 corner discs? my 510 goon has a disc swap in the rear, but seems to still have the same MC, PO did it and told me most of what he did to the car, didn't say anything about messing with the brake master.

[wayno]

shouldnt need a new master. he said it was a 15/16, zx came with 15/16, z's(front disc rear drum) came with a 7/8. that being said, what 3/4 master came with 4 corner discs? my 510 goon has a disc swap in the rear, but seems to still have the same MC, PO did it and told me most of what he did to the car, didn't say anything about messing with the brake master.

 

I have front disc brakes on my 521 work truck, I also have the stock type 521 M/C, but it is defective, the residual valve doesn't work, so when the rear brakes get out of adjustment, the pedal starts going down a ways, and I have to start pumping it, when I put the 521 kingcab onto the 720 4X4 frame setup I made with front disc brakes, at first I kept the stock 521 master, the first time I drove it, I did not even make it half a mile before I turned around and tried to make it home, I got within 4 blocks when the driveline bolts sheered off and the truck skidded to a stop, I ran to my friends house for help, then ran home and got a 10mm wrench, while my friend connected the chain to tow me home, I released the pressure off the brakes by opening the caliper bleeder.

When changing over to disc brakes that are not stock, you either have to mess with the residual valve, or get the proper M/C, but sometimes we get lucky every once in a while, and start out with a defective master that still actually will work.

If I had been driving a gas truck that day, it would not have sheered the bolts, because I would not of had the torque to keep it moving, but that truck is a diesel, and it had the torque to keep it moving till the bolts sheered from mass stress.

[devilsbullet]

I have front disc brakes on my 521 work truck, I also have the stock type 521 M/C, but it is defective, the residual valve doesn't work, so when the rear brakes get out of adjustment, the pedal starts going down a ways, and I have to start pumping it, when I put the 521 kingcab onto the 720 4X4 frame setup I made with front disc brakes, at first I kept the stock 521 master, the first time I drove it, I did not even make it half a mile before I turned around and tried to make it home, I got within 4 blocks when the driveline bolts sheered off and the truck skidded to a stop, I ran to my friends house for help, then ran home and got a 10mm wrench, while my friend connected the chain to tow me home, I released the pressure off the brakes by opening the caliper bleeder.

When changing over to disc brakes that are not stock, you either have to mess with the residual valve, or get the proper M/C, but sometimes we get lucky every once in a while, and start out with a defective master that still actually will work.

If I had been driving a gas truck that day, it would not have sheered the bolts, because I would not of had the torque to keep it moving, but that truck is a diesel, and it had the torque to keep it moving till the bolts sheered from mass stress.

looks like I may have to play with the MC for the 710 here then...damn the bad luck.

[flatcat19]

But he really has no clue about master.

It may be a 15/16", but condition is unknown.

 

There are so many things unknown with this swap.

It was not documented at all. Too many variables.

[devilsbullet]

I was just going off the questions of is it a disc/disc or disc/drum master. it shouldn't be a residual valve issue in the way wayno and mike were thinking as long as its a 15/16.  as to other issues with the swap...that's a whole nother bag of worms lol.

[wayno]

Let's understand what the issues are that we are talking about, this is about brakes seizing, it does not matter what the bore is, that has nothing to do with it seizing, the bore is basically how far and/or hard you have to push on the pedal to stop the vehicle.

The residual valve is what keeps the pedal at the top so one can be a little lax on keeping the drum brakes adjusted properly, you see there are springs on brake drum assemblies that pull the brake cylinders/shoes back to a resting position, the 10lb. residual valve holds the brake shoes out against the drum, otherwise if your brakes are not adjusted properly, you would have to pump the pedal to have it be at the top.

A 10lb. residual valve will cause the disc brake pads to rub against the rotor so hard that it will heat up the brake assembly, and will eventually start a fire it your able to keep the vehicle moving, that is why disc brake masters have 2lb. residual valves in the disc brake circuit, it's not rubbing hard enough to heat the assembly up.

 

Here is a little fact, if you have a front disc/rear drum brake vehicle and you have a proper dual reservoir M/C, and if your rear drum brakes do not have a properly operating residual valve in the M/C, and the rear brakes are not kept adjusted properly, but the front disc brake residual valve is working correctly, you likely are only using only your front brakes to stop the vehicle unless you pump on the brake pedal, and believe me when I say, they don't stop near as good using just the front brakes.

[datzenmike]

Take a look on the side the master, they usually say the size on them. Earlier 280z used a 7/8 diameter master through '78, look for the 280zx to be a 15/16". If it has the 15/16 then likely the residual valve is not the problem. This is easy to do and solves this part of the discussion.

[devilsbullet]

Let's understand what the issues are that we are talking about, this is about brakes seizing, it does not matter what the bore is, that has nothing to do with it seizing, the bore is basically how far and/or hard you have to push on the pedal to stop the vehicle.

The residual valve is what keeps the pedal at the top so one can be a little lax on keeping the drum brakes adjusted properly, you see there are springs on brake drum assemblies that pull the brake cylinders/shoes back to a resting position, the 10lb. residual valve holds the brake shoes out against the drum, otherwise if your brakes are not adjusted properly, you would have to pump the pedal to have it be at the top.

A 10lb. residual valve will cause the disc brake pads to rub against the rotor so hard that it will heat up the brake assembly, and will eventually start a fire it your able to keep the vehicle moving, that is why disc brake masters have 2lb. residual valves in the disc brake circuit, it's not rubbing hard enough to heat the assembly up.

 

Here is a little fact, if you have a front disc/rear drum brake vehicle and you have a proper dual reservoir M/C, and if your rear drum brakes do not have a properly operating residual valve in the M/C, and the rear brakes are not kept adjusted properly, but the front disc brake residual valve is working correctly, you likely are only using only your front brakes to stop the vehicle unless you pump on the brake pedal, and believe me when I say, they don't stop near as good using just the front brakes.

the only reason I brought up size is because a 15/16 only (to my knowledge) came on a 280zx, which is a 4 corner disc brake car. otherwise, you're right.

[flatcat19]

Bullet-it did.

Answers being received is vague and short.

Gotz to cover the bases.

[benrob]

I am using a 15/16 master.

[benrob]

so i bought/ installed 2 in line residual valves and it seems to have done the trick. still cant get the peddle as stiff as id like it but no more siezing.