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Disc Brake Conversion on 71 521


MK4A80

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Hi guys,

 

 

Im the original person that started this thread. So im having issues with my disc brake set up and was wondering if somebody has an idea of what im doing wrong.

 

So i went with the beebani kit and got all the other parts from my local o'reillys. I originally bought the wilwood proportional valve p#: 260-11179.

So everything at first work great, but a couple months later, the rear wheels start to lock up. So i check and found everything okay. So i decided to replace

the proportional valve with a different one and see if it would make a difference. So i bought the SSBC P#: A0730 valve. I installed and it started to work again.

Now again the brake are locking up, but this time the all four wheels lock up. Any one have any idea of what im doing wrong and is it possible to run disc brakes without the

proportional valve? I think im not adjusting the valve properly, but if you guys have any ideas please let me know.

 

 

 

Thank you,

 

 

Fredy.

 

 

 

   
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31 minutes ago, MK4A80 said:

Hi guys,

 

 

Im the original person that started this thread. So im having issues with my disc brake set up and was wondering if somebody has an idea of what im doing wrong.

 

So i went with the beebani kit and got all the other parts from my local o'reillys. I originally bought the wilwood proportional valve p#: 260-11179.

So everything at first work great, but a couple months later, the rear wheels start to lock up. So i check and found everything okay. So i decided to replace

the proportional valve with a different one and see if it would make a difference. So i bought the SSBC P#: A0730 valve. I installed and it started to work again.

Now again the brake are locking up, but this time the all four wheels lock up. Any one have any idea of what im doing wrong and is it possible to run disc brakes without the

proportional valve? I think im not adjusting the valve properly, but if you guys have any ideas please let me know.

 

 

 

Thank you,

 

 

Fredy.

 

 

 

   

What master cylinder are you using?

 

I replaced my master with a dual setup for front disk rear drum....

I'm currently upgrading to rear disk also ... so in order to use my master I have to remove the residual valve from the master... drums have a 10lb residual valve.... and I'm adding this inline externally in place of an adjustable one.... 

I'm not even sure why I currently have an adjustable one....

 

 

Screenshot_20210126-131606_Chrome.jpg

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34 minutes ago, MK4A80 said:

Hi guys,

 

Im the original person that started this thread. So im having issues with my disc brake set up and was wondering if somebody has an idea of what im doing wrong.

So i went with the beebani kit and got all the other parts from my local o'reillys. I originally bought the wilwood proportional valve p#: 260-11179.

So everything at first work great, but a couple months later, the rear wheels start to lock up. So i check and found everything okay. So i decided to replace

the proportional valve with a different one and see if it would make a difference. So i bought the SSBC P#: A0730 valve. I installed and it started to work again.

Now again the brake are locking up, but this time the all four wheels lock up. Any one have any idea of what im doing wrong and is it possible to run disc brakes without the

proportional valve? I think im not adjusting the valve properly, but if you guys have any ideas please let me know.

 

Thank you,

Fredy.

   

 

I run beebani disc brakes without a proportioning valve and have for years.  Its not needed AFAIK and if all four are locking up wouldn't that mean their is constant pressure from the master forcing fluid to them and thus engaging the pads and drums? 

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12 minutes ago, Crashtd420 said:

What master cylinder are you using?

 

I replaced my master with a dual setup for front disk rear drum....

I'm currently upgrading to rear disk also ... so in order to use my master I have to remove the residual valve from the master... drums have a 10lb residual valve.... and I'm adding this inline externally in place of an adjustable one.... 

I'm not even sure why I currently have an adjustable one....

 

 

Screenshot_20210126-131606_Chrome.jpg

 

 

 

 

Im running a 1970's 280z master cylinder. I cant recall the year, but according to beebani instructions any year works.

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21 minutes ago, d.p said:

 

I run beebani disc brakes without a proportioning valve and have for years.  Its not needed AFAIK and if all four are locking up wouldn't that mean their is constant pressure from the master forcing fluid to them and thus engaging the pads and drums? 

 

 

Im on disc all four wheels. What master cylinder you ran, to not need the proportional valve?

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I am disc front drum rear and I don't remember which one I got it was so long ago but I think it was from a 620?  

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6 minutes ago, MK4A80 said:

 

 

 

 

Im running a 1970's 280z master cylinder. I cant recall the year, but according to beebani instructions any year works.

Well if its designed for 4 wheel disk get rid of the proportioning valve and you should be good....

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27 minutes ago, MK4A80 said:

 

Im running a 1970's 280z master cylinder. I cant recall the year, but according to beebani instructions any year works.

I actually wonder if this is some of your issue..... looking up a 76 280z it looks to me like they are front disk rear drum vehicles.... 

Oh 1970 is a 240z....

Edited by Crashtd420
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A proportioning valve provides less braking to the rears as they will lock up first because of the lack of weight on the rear tires and weight transfer to the fronts when braking. n some Nissans there is no proportioning valve as the rear wheel cylinders are simply made smaller. My 620 was raised 16" on 33" tires and the weight shift was enormous. It would lock up coming to a stop light. I put an adjustable Wilwood proportioning valve in and cranked it till all tires locked at the same time. If the rears are allowed to lock first the rear end will try to come around.

 

A residual valve is in the outlet of the master cylinder and on drum brake vehicles retains about 10-12 PSI to keep the shoes out slightly against the return springs so they have less distance to travel. On disc brakes this pressure is only 2 or 3 PSI as the pads are already against the rotors.

 

 

A single master cylinder has the disadvantage of total brake failure if there is a leak anywhere in the system. I would definitely make damn sure my e brake was fully adjusted and functional.

 

If you have a dual master cylinder from a car it's likely disc front and drum rear. If switching to read disc as well get a residual valve (disc) from another master and replace the drum one.

 

 

Rear brakes locking up after some use is classic drum residual valve on a disc brake set up. It's meant to be 2 pounds not 12.

 

All wheels locking could also be not enough pedal play. The piston in the master is not returning fully allowing brake fluid back into the reservoir and some pressure is trapped in the system. As you use it more and more pressure is trapped. Push down on the brake pedal with thumb and there should be about 1/8" of slack before firm resistance is felt.

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I had this happen to me on my 521.

all 4 would build up pressure everytime I hit the brakes. I would get my wrench and relieve the pressure on the rear brake bleed screw.

 

Since a 521 is a single resivoir its obvious that its the Master cylinder. I swapped it out and was ok.

 

only other thing is make sure your master is all the way out on the firewall under the pedal. A lot of time the new Master the threaded rod is actually longer than the stock one and when one bolts it up the pedal arms is already pushing on the pedal when one goes to bolt the master on the firewall. Meaning bolt to long!!!! 

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i'm running disc on front and drums on rear with dual master cylinder on my 1970  521 but i plan on putting rear disc brakes from silvermine motors will i need to change my master cylinder as well or add a proportioning valve?

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6 hours ago, gene knight said:

i'm running disc on front and drums on rear with dual master cylinder on my 1970  521 but i plan on putting rear disc brakes from silvermine motors will i need to change my master cylinder as well or add a proportioning valve!

 

You can either get a master that's setup for front and rear disk or change out the residual valve in the master if you have some spare parts....

Or You can just remove the rear residual valve from the master cylinder and install an inline one like I posted from willwood.....

Dont get the adjustable type proportioning valve.....

Edited by Crashtd420
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On the adjustable proportioning valve....

 

It's intended to BE adjustable so you can tune out the locking of the rear tires first. This is especially true if converting to disc rear brakes or altering the system from what Nissan engineers designed to work for you. Also true if lowering you vehicle. A lowered vehicle has less weight transfer to the fronts, off the rears and you may actually be abe to add some rear bias. Obviously you can't just go out an buy a proportioning valve to suit your custom set up. BTW.... adjustable proportioning valves are illegal.... but improved stopping trumps this.

 

Mount out under the hood. I say this because if accessible, you'll fiddle with it for dry, wet and snow conditions. I drove down hard gravel road and applied brakes till they appeared to lock equally by their marks. Once set, resist the urge to mess with this. Get comfortable with it.

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