what proportioning valve I should use?

[socaldatsun]

So I think after searching all last night and today it is safe to finaly ask for help.

 

I am doing Beebani drumb-to-disc set up on my datsun pick up, BUT the only thing that is holding me up right now is what valve I should use?

 

I had to upgrade the master cylinder to a 280zx since im going disc on all four; however, the original propotioning valve only has one Input then from their it splits off.

 

So what can I use for a dual res m/c.

 

my set up is:

 

280zx m/c

 

nissan 300zx calipers "4ppot" front

 

Isuzu amigo calipers "single pot"

 

 

I dont want to go straight to aftermarket yet unless I really need to.

 

thanks in advance.

[rpowell25]

If a 521 is like the Datsun cars then there is no proportioning valve but a distribution block with a pressure safety light switch. The 280zx master should provide you with appropriate brake pressure to a 4 disc setup. You can run what you have or swap it out for an after market distribution block(s).

[socaldatsun]

well doesnt the 208z m/c have dual ports? I thought I had everything figured out but this kind of threw me off.

 

the way I thought it was going to be set up was

M/C runs tow lines = (one to the front to a 510 T-block then left and right calipers) then ( one going straight to the rear to the D21 T-block to the calipers)

 

am I missing something?

[rpowell25]

Someone with more intimate knowledge can answer this better but I believe the 521 had a single reservoir master and I suspect there is a junction block that is one to four. With your 280 master you should be able to run a separate front and rear line to t- blocks to the calipers.

 

Brake piping

[socaldatsun]

So was I correct? from the master straight to the t-blocks and to the calipers? no proportioning valve or anything else in between? like i said im completly lost on this now.

[burrito213]

I am doing disk front and drum rear. I was told I needed a proportioning valve but no specifics as to what I need to buy, don't recal where I need to place, and haven't quite yet gone to that point in my build. I guess outta sight,outta mind.

 

 

However, reading this thread does interest me to get the job done right. Cuz I know that project will come soon for me..

 

*suscribed.

[socaldatsun]

woops must have missed this thread, im trying to under stand it :)

 

http://community.ratsun.net/topic/35687-drum-to-disc-conversion-info/page__p__547866__hl__%2Bproportioning+%2Bvalve__fromsearch__1?do=findComment&comment=547866

[datzenmike]

Generally front brakes do much more work than the rears so there has to be some bias to the front to prevent the rears locking up. This can be done by using smaller rear brake cylinders to tune the system. I don't think the trucks have a proportioning valve. Bias is designed in at the factory and by mixing and matching front and rear brake cylinders eliminates the need for a mechanical proportioning valve.

 

If discs are added to the front they have a larger piston surface area than the drum brake cylinders so you need a larger master to provide more fluid volume for this. You have a zx master which is designed for front and rear disc brakes which might be a problem if you were running rear drums. A zx master would over power rear drums.

 

You say you have 300zx calipers on the front and Isuzu rear calipers on the back which would be somewhat similar to what was in the ZX car. There is a good chance that the system may be fine as is... certainly much better than if you still had the stock drums. No way to know without trying it out. Braking hard on dry pavement should cause front and rears to begin to lock at the same time. This can easily be tested at low speed and just looking at the tire marks. Rear lock up before the fronts is to be avoided at all costs as it will induce severe oversteer even on seemingly straight stops. Sudden braking on a corner will bring the back end around every time. If this is the case and you had rear drums you could back off the shoes so the piston in the cylinders have to travel further or even remove the residual pressure valve in the master. Rear disc brakes can't be adjusted like this so an in line adjustable proportioning valve will be needed. Wilwood makes them. I used one in my 620 because of severe rear lock up due to 16" lift. I can dial up to 60% less rear pressure and now can brake hard with confidence.

[flatcat19]

So was I correct? from the master straight to the t-blocks and to the calipers? no proportioning valve or anything else in between? like i said im completly lost on this now.

 

Yes.

Already explained in your other thread.

Don't listen to your boss.

[socaldatsun]

Generally front brakes do much more work than the rears so there has to be some bias to the front to prevent the rears locking up. This can be done by using smaller rear brake cylinders to tune the system. I don't think the trucks have a proportioning valve. Bias is designed in at the factory and by mixing and matching front and rear brake cylinders eliminates the need for a mechanical proportioning valve.

 

If discs are added to the front they have a larger piston surface area than the drum brake cylinders so you need a larger master to provide more fluid volume for this. You have a zx master which is designed for front and rear disc brakes which might be a problem if you were running rear drums. A zx master would over power rear drums.

 

You say you have 300zx calipers on the front and Isuzu rear calipers on the back which would be somewhat similar to what was in the ZX car. There is a good chance that the system may be fine as is... certainly much better than if you still had the stock drums. No way to know without trying it out. Braking hard on dry pavement should cause front and rears to begin to lock at the same time. This can easily be tested at low speed and just looking at the tire marks. Rear lock up before the fronts is to be avoided at all costs as it will induce severe oversteer even on seemingly straight stops. Sudden braking on a corner will bring the back end around every time. If this is the case and you had rear drums you could back off the shoes so the piston in the cylinders have to travel further or even remove the residual pressure valve in the master. Rear disc brakes can't be adjusted like this so an in line adjustable proportioning valve will be needed. Wilwood makes them. I used one in my 620 because of severe rear lock up due to 16" lift. I can dial up to 60% less rear pressure and now can brake hard with confidence.

 

thanks that helped you alot, i was alreaady looking at a wilwood PV.

[socaldatsun]

Yes.

Already explained in your other thread.

Don't listen to your boss.

 

 

So sorry! it will never happen again sensai! lol

well i got a little confused, I had you telling me go straight lines from mc and i had some one else tell me that every brake system needed a PV. just a little confusion but its all set now (;

going to pick up a pv off the isuzu just in case.

well fellas! this should be schedual next week if parts come in. time to take a cruise with the family to the mountains :D

[datzenmike]

Some Datsuns may have a proportioning valve, I can't think of one that does but don't want to say none do. There are two things in a Datsun braking system that are often mistaken for a proportioning valve though. One is the pressure differential system on a dual master cylinder set up. This is just a switch with a front and back brake line on either side. If there is a leak and a pressure drop on one side the switch is closed by the unequal pressure from the other and the red BRAKE warning light comes on. The other is usually on the trucks, maybe the wagons and is the load sensing valve. This adds more braking to the rear tires in response to suspension sag due to increased cargo weight.

[emj322]

Some Datsuns may have a proportioning valve, I can't think of one that does but don't want to say none do. There are two things in a Datsun braking system that are often mistaken for a proportioning valve though. One is the pressure differential system on a dual master cylinder set up. This is just a switch with a front and back brake line on either side. If there is a leak and a pressure drop on one side the switch is closed by the unequal pressure from the other and the red BRAKE warning light comes on. The other is usually on the trucks, maybe the wagons and is the load sensing valve. This adds more braking to the rear tires in response to suspension sag due to increased cargo weight.

 

Now if my load sensing valve was bad, would that cause my back breaks to lock up before my fronts? This has been my problem since I bought my 79 620, and I am trying to figure out how to fix it. 

[datzenmike]

Raising the vehicle will cause this. Is it at stock height or raised?

 

Is the front nose down and the rear higher? This will affect the NLSV (Nissan load sensing valve)

 

 

Willwood has a $50 adjustable proportioning valve that can be plumbed into the hydraulic brake line to the rear. It will reduce the rear pressure up to about 60%. These are technically illegal for use on the street but rear lock up on a curve is worse. You could dial it back till the front and rears lock together.

[scooter]

If your rears are locking make sure your seals aren't leaking. Gear oil and brake fluid will make your rear brakes grab. Opposite to normal thinking.