Residual Pressure Valve placement

-
Divenut

Divenut

Well-Known Member
Joined
Sep 22, 2011
Messages
3,522
Reaction score
1,799
Location
Naperville Illinois
OK brake gurus,

Finally got some time to plumb the new brake lines on the Duster. 72, Wilwood front disc/rear drum combo, new MC, Wilwood proportioning valve.

Adding a 10lbs residual pressure valve to rear drum line. Per Wilwood, it needs to be as close the MC as possible, and before the proportioning valve.

In an effort to minimize splices/conections, I'm thinking about screwing it right into the MC versus downstream. Inline. Any problem screwing it directly into the MC rear line port?

Thanks in advance,
Pat
20190721_120035.jpg
 
I put mine under the dash so I could adjust it on the fly, ran the lines through the hole for the clutch push rod there is enough room to clear the rod with no problem. Once it's set it is usually good, but I would change my torsion bars and from stiff to drag race and would have to adjust it or it would lock the rear wheels up if I stopped hard.
 
brian6pac said:
I put mine under the dash so I could adjust it on the fly, ran the lines through the hole for the clutch push rod there is enough room to clear the rod with no problem. Once it's set it is usually good, but I would change my torsion bars and from stiff to drag race and would have to adjust it or it would lock the rear wheels up if I stopped hard.
Click to expand...


Thanks Brian6pac, are you using a residual pressure valve? I'm thinking about screwing right into the MC.

Pat
 
if that's a stock style master cylinder, doesn't it already have a residual valve built in?
 
No, it shouldn't need one the wheel cyl's are make to with a metal cup behind the rubber and that keeps pressure on the cup and keeps it from leaking,

Spring and expander's in the picture
the check valve holds pressure on the cups and stops them from leaking in the earlier years

0996b43f802313f7.gif
 
Last edited:
As others have said if you have a stock MC no need to add residual pressure valve to the drum side of the system.
If the MC does not have a residual pressure valve I see no reason (as long as the threads and seats are compatible) not to mount it directly to the MC.

In regards to not needing one due to somthing in the wheel cyl. I have NEVER heard of that and with all due respect, do not think it is accurate

In regards to mounting it under the dash for easy adjustment, I suspect poster is confusing risidual pressure valve with a proportioning valve.

Residual pressure valve maintains pressure in the line to counter act the springs in the drum brake system so the shoes do not retract too far from the drum.
 
Last edited:
brian6pac said:
No, it shouldn't need one the wheel cyl's are make to with a metal cup behind the rubber and that keeps pressure on the cup and keeps it from leaking,
Spring and expander's in the picture
the check valve holds pressure on the cups and stops them from leaking in the earlier years
Click to expand...
Dana67Dart said:
In regards to not needing one due to somthing in the wheel cyl. I have NEVER heard of that and with all due respect, do not think it is accurate
Click to expand...
sometime in the early 70's they moved the valve from the MC to the wheel cylinders via the metal cups. the rebuild kits for the wheel cylinders usually come with new ones. they can also be added to older ones that didn't have them. i've done a disk/drum MC 4 wheel disk conversion by removing it from the MC, and just using an otherwise stock disk/drum MC. works fine. but an other wise stock drum/drum converting to disk/drum, it's easiest to just get a disk/drum MC
 
Dana67Dart said:
As others have said if you have a stock MC no need to add residual pressure valve to the drum side of the system.
If the MC does not have a residual pressure valve I see no reason (as long as the threads and seats are compatible) to mount it directly to the MC.

In regards to not needing one due to somthing in the wheel cyl. I have NEVER heard of that and with all due respect, do not think it is accurate

In regards to mounting it under the dash for easy adjustment, I suspect poster is confusing risidual pressure valve with a proportioning valve.

Residual pressure valve maintains pressure in the line to counter act the springs in the drum brake system so the shoes do not retract too far from the drum.
Click to expand...

As far as mounting it under the dash I was talking about the adjustable proportioning valve, why would you mount it were you have to stop get out open the hood make a adjustment and do this over and over till you get it right ?

As far as the brake shoes returning, they always return to the post on the backing plate, the adjuster at the bottom of the shoes keeps them close to the drum. Just a FYI
 
Thanks as always folks. Did some research but wasn't able find a definitive answer. Does anyone know if the Rabestos #MC36406 has an integrated residual pressure valve? If so, I'll skip the Wilwood piece.

Thanks again!
Pat
 
Wow, He ask a question about the residual valve, did he not?
Photos show a proportioning valve.
The reply's are getting crazy.
The most of ya are correct when you say the "residual valve is in the master cylinder"
I have been a ASE master tech for over 35 years and never heard tell of a residual check valve in a wheel cylinder. What would happen if you only changed one rear wheel cylinder?
 
Divenut said:
OK brake gurus,

Finally got some time to plumb the new brake lines on the Duster. 72, Wilwood front disc/rear drum combo, new MC, Wilwood proportioning valve.

Adding a 10lbs residual pressure valve to rear drum line. Per Wilwood, it needs to be as close the MC as possible, and before the proportioning valve.

In an effort to minimize splices/conections, I'm thinking about screwing it right into the MC versus downstream. Inline. Any problem screwing it directly into the MC rear line port?

Thanks in advance,
Pat
View attachment 1715373342
Click to expand...

Divenut said:
Thanks as always folks. Did some research but wasn't able find a definitive answer. Does anyone know if the Rabestos #MC36406 has an integrated residual pressure valve? If so, I'll skip the Wilwood piece.

Thanks again!
Pat
Click to expand...

The type of master you have is already a disc/drum master and should already have a residual valve in the front port. (That's what that type master is made for)
Screwing a residual valve direct into the master wont work without an adapter setup, and even then it could get snapped off pretty easy from sticking out so much.

Again, you don't need a residual valve for the rears with that master cylinder.
 
Quick "hillbilly" way to check.
Put a small amount of brake fluid (silicone brake fluid) in the front (small) reservoir. If it does not leak out on its own it has a check valve in it.
As I said "shade tree" test, but it works.
You can not have a residual valve on disc brakes cause they would not release.
No return springs, just the square cut seal.

For a rule of thumb, if a master cylinder has two small reservoirs it is a drum-drum.
If it has one large and one small it is a disc-drum cylinder. Large for disc.
I really did not want to post this but I will.
 
Donnie514 said:
Wow, He ask a question about the residual valve, did he not?
Photos show a proportioning valve.
The reply's are getting crazy.
The most of ya are correct when you say the "residual valve is in the master cylinder"
I have been a ASE master tech for over 35 years and never heard tell of a residual check valve in a wheel cylinder. What would happen if you only changed one rear wheel cylinder?
Click to expand...

It's not a residual check valve in the wheel cyl, they just added the expander that goes in the cup of the wheel cyl. Pryor to the 70's the wheel cyls would leak fluid because there was no pressure on the cup to hold it tight in the bore when the car sat for a while. The addition of the expander would keep the cup tight at all times so there was no need for a check valve.
 
Appreciate all the replies fellas. Thanks again.

TrailBeast - Thanks for the clarification on the MC/RPV question for my specific MC! That makes perfect sense. I'll proceed without adding the rpv I bought. One less thing to do!

Be well all and thanks again for all of your individual replies and insight.
Pat
 
brian6pac said:
It's not a residual check valve in the wheel cyl, they just added the expander that goes in the cup of the wheel cyl. Pryor to the 70's the wheel cyls would leak fluid because there was no pressure on the cup to hold it tight in the bore when the car sat for a while. The addition of the expander would keep the cup tight at all times so there was no need for a check valve.
Click to expand...
Well now we are talking bout something that happened about 50 years ago.
 
crap like this was a lot easier before the internet. you asked a buddy that knew someone who had maybe done it before, and just copy what they thought they remembered doing
 
You must log in or register to reply here.
-

Back
Top