Brake Proportioning Valve

[Pop N Wood]

Globe valve. Yes and no. A globe valve would reduce pressure ONLY if there was flow. Once the flow stops (the pads reach the end of their travel) the globe valve does nothing. This would be more akin to a METERING valve or a restrictor. I think that a brake proportioning valveis more or less like an air pressure regulator on a compressor. Those regulate PRESSURE whether or not there is flow through them unlike a normal flow control valve. I have never had one of those apart to understand how they work nor have I taken apart a proportioning valve so it is difficult to grasp how they work.

 

Sorry to side track the discussion (although looks like Tony got the answer he needed), but this is someone interesting to me because I have always wondered how a prop valve works.

 

The flow restrictor idea cygnusx1 says is spot on. If it is a restrictor, then it can only slow the onset of full rear brake pressure. But a regulator cannot be 100% correct either, or it would only allow one pressure to the brakes. You would lose all modulation. Maybe something inbetween?

[tonycharger72]

Cygnusx1,

 

Thats a great setup mate, but for rego purposes i cant mount my BPV inside the cabin - its a shame because i think what you have done is the best place to mount the adjustable BPV,

 

Dave,

 

"The valve up front on a 240Z with a wire attached to it

is a self centering pressure differential switch that turns

the brake warning light on. The valve in the back is a

residual pressure check valve because of the rear drum

brakes. With drum brakes a ten pound valve is used to

compensate for return spring tension in the drums. With

a rear disk conversion it would have to be removed or

disabled or you will have rear disk brake drag",

 

I have managed to get my hands on a service manual and it says for 260z models i have a (in order of closest to the master cylinder),

1 - Dual Circuit pressure differential switch,

2 - Pressure regulating valve (Brake prop valve),

Both are mounted inside the engine bay,

 

On 240z models,

1 - Dual Circuit pressure differential switch

2 - Pressure regulating valve (which is located next to the diff - NOT IN THE ENGINE BAY, like on the 260z models),

 

So basically both models of zed have the same thing, just one has the stock BPV mounted next to the diff while the other has it in the engine bay,

 

What im curious about now is should i remove them both??? or just the Stock Brake Prop Valve? and keep the Dual Circuit pressure differential switch in my braking system???

 

I have only spoken to a 1600 bloke and he said get rid of them both, and when i read the explanation in the service manual of what the DCPDS does i thought it would be a good idea aswell - but from what i can gather no ones eles has bothered to remove it when they have installed the adjustable BPV's, they just gut the stock BPV and plumb in the new adjustable one,

 

This is the manual's explanation of the Dual Circuit Pressure Differential Switch,

 

"The switch is essentially a piston which is kept in balance when the pressure in the front and rear hydraulic circuits is equal, Should a leak occur in either circuit then the piston is displaced by the greater pressure existing in the non-leaking circuit and makes an electrical contact to illuminate a warning lamp on the vechicle facia"

 

Might be reading this wrong, but by using an adjustable prop valve you would be changing this "equal" balance which would mean the little bugger would be constanly activating the brake warning lamp, so it would make sense then to remove it from the braking system.............maybe???

[JMortensen]

The line pressure up to the prop valve will be the same regardless, so adjusting the prop valve won't trip the switch. All the switch does is light up the BRAKE light on the dash. I guess it is another set of fittings and those fittings could cause a leak, so if you're just trying to plumb things in a way that reduces the possibility of leaks then remove it.

[Nigel]

On 240z models' date='

1 - Dual Circuit pressure differential switch

2 - Pressure regulating valve (which is located next to the diff - NOT IN THE ENGINE BAY, like on the 260z models),

[/quote']

 

Be careful here... Changes to the braking system began with 1973 240Z's (which I have). My 240 has the "Pressure Regulating Valve" in the engine bay (and the larger brake booster and revised master cylinder, but earlier style rear drums).

 

Nigel

'73 240ZT

[tonycharger72]

jmortensen,

 

Just because the 2jz conversion the exhaust is going to be on the drivers side (passenger for ths USA folks) and the prop valve will literally be less than 1/2" inch away from the exhaust i was thinking of relocating it entirely, but to do this it would just be simplier to completely re-plumb the front brake lines and if not ditch, atleast move the BPV and the Pressure differential switch, but knowing that i dont need the PDS to make my brake system function correctly is good ,

 

Nigel,

 

My info was picked up from a Haynes service manual, Datsun zeds 1970-78, models 240z-260z, im assuming this information is probably only good for Aussie zeds, as there is no mention of the 280z, im sure there are little differences all over the world with this car

[Nigel]

The Haynes manual I have (covers 240Z to 280Z) also indicates that the brake system was the same on all 240's. But obviously , that's not the case (to '73 240Z owners at least). There are also differences in the wiring, which are not reflected in that manual either. I just want everybody to be aware of this, so that '73 Z owners don't get led astray

 

Nigel

'73 240ZT

[tonycharger72]

Yeah i have found Haynes manuals in the past to be not the best - Max Ellery, now they make a good service manual ,