[jdog0799]

Hey guys! So I'm having serious braking problems.

If I give my brakes any more than light, even pressure, the rear wheels lock up. From what I can find this usually means proportioning valve issues, and when I looked at my valve, it's condition seems to support this theory.

My problem is I can't find any parts or relevant material for this specific valve. It's like it doesn't exist. All other valves are "load sensing" and connect to the rear axle whereas mine is only bolted to the frame without a spring.

If any of y'all have some advice or can help me identify this part I'd appreciate it.

 

[jdog0799]

Well update (sort of)
I found a diagram with my part listed as "Brake Power Regulator" or just "Valve Assembly".
Though all websites have it listed as not available or want a ridiculous amount.
Part number appears to be 46400C7910 or 46400C7911

 

[geeyoutoo]

I don't know much about them, but I often here this place named by OS members.

PartSouq Auto Parts Around the World

We present to your attention our wide range of quality auto parts for many brands of cars. Our genuine parts catalogs and search by part number will help you!

partsouq.com

 

[4200delta]

Load sensing or brake proportioning valve is the same thing

 

[geeyoutoo]

Load sensing or brake proportioning valve is the same thing

Maybe so, but, what he has operates on a totally different system that is why he is asking us the question.

 

[james008]

To my understanding, its not really a load sensing valve in the sense that it adjusts front vs rear brake bias with increasing/decreasing load, it just regulates front vs rear brake line pressure. Early MQ without them had a habit of locking rear brakes when unladen and heavy braking.

I suspect that dark staining on yours is slight weep, which will reduce effective pressure in the part of the valve that regulates rear brake pressure, allowing more fluid to pass, hence the locking.

I've never pulled one apart, but there will be a gasket or O ring or something that holds the front and rear sections together, you could try replacing that for a quick fix, or just replace the whole thing with an aftermarket adjustable proportioning valve.

Here is a diagram of how it works. I suspect the weep is likely somewhere around the chamber the springs act in.

 

[james008]

Also if you have recently replaced your wheel cylinders or master cylinder, ensure it is the same as what came off.
At least in AU, where we didn't have that valve on early cars, there were 2 different master cylinder and wheel cylinder bore sizes.

Early cars, without that valve, 23.8mm bore master cyl and 19.05mm wheel cyl.
Later cars, with the valve, 25.4mm bore master and 22.22mm wheel cyl.
Front caliper size didn't change, so a mismatch in master/wheel cyl will affect rear more than front.

 

[Swero]

I don’t have much info on the valve but it isn’t the same as in the manual James mentioned. The number of connected lines is different.

Try to purge the brake circuit or take it apart. But for safety issues, perhaps it´s better to replace it.

 

[Slo4x4]

jdog0799, from what I see is one piece in stock at Amayama. But it's not cheap. (Nissan 46400-C7910 (46400C7910) VALVE ASSEMBLY)
I would, as james008 and Swero mentioned, try to fix yours. Or find another. However, these types of valves are only to find on k160 and k260 Patrols, Gq and further on they already had a lever and spring to the axle.

 

[Karsten]

This reacts on the retardation of the car.the steelball in the rear ov the valve reduce or open for brake fluid. I had/or have the same problem. Tok it apart and cleaned it, changed some o-rings. Put it back together. Worked perfekt. I think the today's brake fluids is not compatible with these old cars and systems.