Dumb Brake Plumbing Question - Removing a Wilwood Residual Pressure Valve

[Duster256]

The previous owner of my 1971 10" manual drum brake car installed Wilwood drag race 4-piston disc brake kits on both front and rear, and installed an aluminum Strange Engineering drag race dual master cylinder (MC) which was stamped "STRANGE" but curiously has no part number on it and which the Strange tech support line could not positively ID for me. Strange said that their dual MCs deliver equal pressure to both front and rear ports, with volume being greater from the port closest to the push rod (rear port). The previous owner also installed Wilwood residual pressure valves (RPV) on both MC hard lines.

I just swapped out the front Wilwood kit with a Dr. Diff Stage 1 front disc brake kit and successfully bled it, needing to add brake fluid only to the rear reservoir (closest to firewall) on the Strange MC. Due to the presence of the RPV, residual line pressure is keeping the front brakes locked up and the rotors unable to turn (brake drag). Cass recommended that for his Stage 1 single-piston calipers that I remove the RPV from the front brake hard line (I presume this will allow the caliper piston to relax and avoid brake lockup when the brake pedal is released). He said that I can leave the other RPV on the rear brake hard line because I'll be replacing the rear Wilwood drag race disc brakes with 10" x 2.5" rear drum brakes.

FABO Nation - Please take a look at the diagram below showing the MC/hard line/distribution block setup on my car, and offer me your opinion on which RPV (the one for the front brakes) that I need to remove - A or B. Apologies for the dumb question but I'd rather be sure and get it right the first time whenever removing parts.

 

[Duster256]

What is confusing me on which RPV to remove is that when I was bleeding the front brakes, the MC's rear reservoir fluid went down and needed to be refilled, but the hard line to the rear MC port is plumbed to the distribution block port that is opposite of the port going out to the rear brake.

 

[MV8]

Based on the rear port going down when bleeding the front brakes, I think you've mis-identified where the master lines go on your car.

 

[4mulas]

1-MV8 is likely correct in that you may have mis-identified which lines out of the master are going to the front and rear ports on the proportioning valve/distribution block (called proportioning or pro valve moving forward)

2-Typically the reservoir and port on the master cylinder that is closest to the firewall (or driver) feed the front brake circuit, the port furthest from the firewall feeds the rear.

3-Whichever circuit you have going to the front brakes is the one that you need to remove the residual pressure valve from. In fact, you likely don’t need to have a residual pressure valve on the rear line segment either as modern day wheel cylinders have cup expanders built into them, but it won’t hurt to have and RSV on the rear brake segment so I can be left.

4-if the lines from your master cylinder are indeed going to where you have shown in the proportioning valve I would say to remove RSV labelled “A”.

5-I am not familiar with the strange master cylinder and it is possible that the internal plumbing is reversed hence leading the rear reservoir to go down when bleeding the front brakes even though it appears like the front brake line is taken from the front reservoir/port location but I doubt it, - ALL OF THIS ACCORDING TO YOUR DIAGRAM - hence which leads me to believe that MV8 is correct in that you may have misidentified which lines go where.

Action plan: carefully follow and trace which lines go where in the pro valve from you very Strange master and then report back.

 

[67Dart273]

Those ports go straight through in an obvious way, so unless the tubing is difficult to see under there, the hookup should have defined it. I don't know

 

[Duster256]

Thanks everyone who have chimed in so far. When I get home from work today, I'll crawl under my car and double-check my diagram with what's on my car - it's possible that the diagram may indeed be incorrect as to the hard line between the MC rear port and the distribution block. Dunno about the possibility of the Strange MC being crossed-plumbed internally compared to regular MCs.

In any event, because I had to add brake fluid to the MC rear reservoir during front brake bleeding, would it be safe to assume that I need to remove the RPV on the hard line that is plumbed to the MC rear port?

 

[4mulas]

Thanks everyone who have chimed in so far. When I get home from work today, I'll crawl under my car and double-check my diagram with what's on my car - it's possible that the diagram may indeed be incorrect as to the hard line between the MC rear port and the distribution block. Dunno about the possibility of the Strange MC being crossed-plumbed internally compared to regular MCs.

In any event, because I had to add brake fluid to the MC rear reservoir during front brake bleeding, would it be safe to assume that I need to remove the RPV on the hard line that is plumbed to the MC rear port?

Don’t get ahead of yourself. Confirm which lines are going where first.

 

[67Dart273]

Yes

 

[Duster256]

I put a sliding tag on each hard line at each MC port, marked "F" for front and "R' for rear, and slid each tag down the line all the way to the distribution block - see photos 1 and 2 below. Turns out that my diagram was correct.

I put sliding tags on both front brake hard lines, marked "L" for left and "R" for right, and slid them down the line all the way back to the distribution block - see photos 3, 4 and 5 below. Turns out that my diagram was correct.

1. Because I had to add brake fluid only to the rear MC reservoir when I was bleeding my new front brakes, this doesn't make sense at all.
2. What do I do now to determine which RPV is for the front brakes?
3. Has anyone here ever rebuilt a Strange master cylinder?

 

[Bewy]

The RPVs are often in the outlet port of the m/c. While the drawing shows them as being stand alone, that is probably just for convenience.

Contact Strange to find out where they install their RPVs.

Another way to tell: remove the brake line at the m/c; get a paper clip & poke it into the hole in the brass ferrule. If no RPV, it should go all the way to the m/c bore. If there is a RPV, there will be an obstruction about 3/8" in.

 

[4mulas]

1- Just remove the residual pressure valve coming off your brake line labelled F. It is the ones that go to the distribution block and then goes to the front brakes. Regardless of which resovoir gets drained. The only segment you’d potentially want an RSV on is the rear.

I can’t say why the rear resovoir is emptying when it appears the line to the front is a coming off the opposite resovoir.

The strange master cylinder appears outwardly to be a later model mopar two post master.. but who knows what they have going on at Strange.

Here are the instructions for the strange master cylinder.

https://static.summitracing.com/global/images/instructions/str-b3360.pdf

It tells you how to plumb it and which port should be used for the segment that requires the most fluid.

I’d just change it out with a doctor diff master and redo the lines in the proper mopar manner. Also just put A one piece proportioning valve on it and do away with the rsv’s.

 

[Duster256]

Thanks 4mulas - your advice is sound and I'll try it this weekend and let everyone know how it goes.

My plan has been that when I install factory 10x 2.5 drum brakes in the rear next month, to swap out the Strange MC with a disc/drum '73+ cast iron MC (residual valve in the front port for the rear drums) and also install the Dr. Diff 1-piece proportioning valve. I already have all the parts ready to go.

Thanks to all who offered their advice. Dave

 

[4mulas]

Good luck

 

[MV8]

You can try plumbing the old (original?) prop brake warn sw to the right ports and keep the rear 2psi RPV, but I think the prop piston seals are bad and probably some corrosion going on in there. Options are to replace, try to rebuild if you can get the seals, replace with an easier to find universal from speedwaymotors for about $40, gut and plug the rear ports of the prop to run separate with a adjustable valve or tee the front lines and go without a light.

 

[Duster256]

Just to reconfirm my problem of brake lockup and only the rear MC reservoir fluid level going down during bleeding (even though the rear MC port is plumbed to the distribution block port that is across from the rear brake port), I just bled both front brakes again.

Bleeding the front left side, now BOTH front AND rear MC reservoir fluid levels went down! I refilled both reservoirs and then bled the front right side - same thing, now BOTH front AND rear MC reservoir fluid levels went down! And, now the rotors can be barely turned by hand (some brake dragging), whereas before they wouldn't budge at all.

Based on these new symptoms, I now suspect that MV8's opinion above is on the right track - that the problem is inside the distribution block. I plan to replace the distribution block and hopefully that will remedy the problem. Your opinions on this are welcome.

BTW, the installation instructions for Strange MCs provided by 4mulas, might provide us with a clue as to the reason for my unusual MC plumbing - front brakes to front MC port and rear brakes to rear MC port. The instructions recommend that for a drag race car (which I understand my car was at some point in the past), the higher-volume MC rear port should be plumbed to the rear disc brakes. And for a street car, they recommend that the MC rear port should be plumbed to the front disc brakes (as is normally the case).

 

[MV8]

Strange's instructions are not as clear as they could be. The larger master reservoir should go to the end of the car with the largest caliper pistons so there is more reserve volume available to cope with pad wear that will require more fluid. Rotor size is not a factor.

They also say 10 lb RPV for drums but with it installed between the master and prop, I don't know if that will trip the brake light on when the pedal is released (differential at the brake switch piston of 10#r/0#f) or what the original master integral RPV lb rating is. The existing 2 lb RPV is a safer bet.

FWIW, I prefer drums on the rear. Usually less trouble/maintenance (corroded sliders and leaks around the park lever shaft seal are common) and a better holding parking brake.