1970 rear brake valve

[mbarjbar]

Does anyone know how much pressure it takes to get the rear brake proportioning valve to open? I am trying to flush and clean the lines going to the rear brakes. I am using a 60cc syringe to force fluid thru but it won't go. So I'm thinking that I just cannot generate enough pressure to open the valve or its very blocked with crud. M/S is not installed as yet. Fittings on the valve are so tight I can't get them off.

Mike

[Maples71240Z]

Does anyone know how much pressure it takes to get the rear brake proportioning valve to open? I am trying to flush and clean the lines going to the rear brakes. I am using a 60cc syringe to force fluid thru but it won't go. So I'm thinking that I just cannot generate enough pressure to open the valve or its very blocked with crud. M/S is not installed as yet. Fittings on the valve are so tight I can't get them off.

Mike

If your talking about the one in the back it not a proportioning valve, its a residual pressure check valve. Its purpose to to maintain about 10 pounds of pressure to overcome the springs on the shoes and keep the shoes positioned at the point of drum contact. To flush it will take 10 or so pounds to open it.

The distribution valve under the M/C has springs in both sides under the caps that fill up with crud also.

Edited November 9, 2008 by Maples71240Z

[mbarjbar]

The distribution valve is clear and clean. Pressure check valve, got it. No way is my syringe applying that much pressure. Do you think that air pressure could be used, just to blow the crud out? Then, when the M/C is in, I could flush with fresh fluid before I attach the lines to my new wheel cylinders.

Mike

[Maples71240Z]

The distribution valve is clear and clean. Pressure check valve, got it. No way is my syringe applying that much pressure. Do you think that air pressure could be used, just to blow the crud out? Then, when the M/C is in, I could flush with fresh fluid before I attach the lines to my new wheel cylinders.

Mike

Did you try to get the nut loose on the bottom side of the valve? If it will come loose you can remove the plunger and clean it out with brake clean and just put it back together. If it is full of crud it will end up in the wheel cylinders if that is the point where you are bleeding it out of.

[mbarjbar]

Yeah, I tried that too. The sheet metal its mounted to is pretty flimsy and that nut is on there tight! As I said, the w/cylinders are not installed yet. The metal lines are disconnected at the flex hose. If air pressure doesn't work, I'll try flushing after I install the M/C.

Mike

[26th-Z]

I took mine apart just as you guys are talking about and it was full of crud. I blame it for one rear wheel locking up under heavy braking. After soaking the valve, I blew it out with air pressure. On the nuts, try using something like PB Blaster.

[Maples71240Z]

Yeah, I tried that too. The sheet metal its mounted to is pretty flimsy and that nut is on there tight! As I said, the w/cylinders are not installed yet. The metal lines are disconnected at the flex hose. If air pressure doesn't work, I'll try flushing after I install the M/C.

Mike

As a last resort if all else fails blow compressed air through the lines. Then follow that with a brake fluid flush. Since the hoses are on it, plug the end of the a rear hose with a 3/16" inverted flare plug so all the fluid is directed out other side, then swap the sides with the plug. Catch the fluid in a bottle so you can see it when it becomes clear. The flare thread of our cars is 10mm X 1.0 but a plug in that size is impossible to find. The 3/16" is slightly smaller and screws in easy by hand and will seal the hose. If the old hoses are going to be replaced then just clamp them with vice grips.

[mbarjbar]

Thanks guys, I'll let you know how it turned out.

Mike

[mbarjbar]

Well, I tried air pressure--no luck at 100 psi! Line and valve must be really plugged. So I guess I HAVE to get the lines off of the valve. I'm going to try freezing spray on the compression fittings. BTW, I just bought a Clymer 240Z manual published in 1972 and they call it a proportioning valve.

Mike

[mbarjbar]

Here is my happy update. I decided that my Autozone flair wrench was part of the problem, so I bought a new Craftsman flair wrench that has a deeper contact area. Cost about $15.00 bucks but it did the job. I got the lines off the Prop. valve, removed it and cleaned all the crud out. Yes, it was plugged up good! Now I can clear all the lines and finish the brake rehab. Lesson learned: get the best quality tools you can afford.

Mike