WHO'S GOT THE SCOOP ON RESIDUAL VALVES?

-
CFD244

CFD244

"THE NEW OLDSMOBILES ARE IN EARLY THIS YEAR"
FABO Gold Member
Joined
Sep 7, 2017
Messages
4,652
Reaction score
6,611
Location
Northern Ontario, Canada
Hi Folks

1971 Demon with OEM 10 inch rear drums and KH discs.

I Bought 2 master cylinders for the above application. One MC came with no residual valves and one came with 2. Both mc's have the large and small brake fluid reservoirs.

The system includes original wheel cylinders and original proportioning valve. I plan on using the mc with no residual valves......Should I install the residual valve in the rear brake outlet or leave it as it came.

***On a side note, I have 2 masters from a 1993ish pick up with disks up front and drums in the rear. There are no residual valves in either port on both masters.***

What say ye?

Thanks FABO
 
I have heard that some newer wheel cylinders have built in residual valves or something that makes the valve unneeded.

If it was me I would look for a proper replacement, or see if you can get a valve and seat and install in the mc.

ALSO ..
my research shows that the 1" mc for the application has been out of production for some time. Used or NOS are the only options. Not even rebuild kits.

There are 15/16 and 1-1/32 masters available
 
Dana67Dart said:
I have heard that some newer wheel cylinders have built in residual valves or something that makes the valve unneeded.

If it was me I would look for a proper replacement, or see if you can get a valve and seat and install in the mc.

ALSO ..
my research shows that the 1" mc for the application has been out of production for some time. Used or NOS are the only options. Not even rebuild kits.

There are 15/16 and 1-1/32 masters available
Click to expand...
Manual says 1 1/32 for my master......I've seen the Dorman number posted here somewhere for the 1 inch master bore.

I was thinking of using the disk residual valve in the one mc, in the drum section of the other. Then I'll have 2 mc's with residuals in the drum sections, and nothing in the disk sections.
 
The spring in the wheel cylinder between the cups makes the residual valve in the Master cyl, redundant, not nec.
So, if the wheel cyls have a spring, you don't need the residual valve in the m/c.
 
Inertia said:
The spring in the wheel cylinder between the cups makes the residual valve in the Master cyl, redundant, not nec.
So, if the wheel cyls have a spring, you don't need the residual valve in the m/c.
Click to expand...
That makes no sense. They have ALWAYS had springs. I was taught that drums need residual, disk do not. There are sometimes exceptions, I was told depending on master cyl. location, IE older vehicles under the floor boards.
 
67Dart273 said:
That makes no sense. They have ALWAYS had springs. I was taught that drums need residual, disk do not. There are sometimes exceptions, I was told depending on master cyl. location, IE older vehicles under the floor boards.
Click to expand...

The residual pressure valve was designed to hold enuff pressure to keep the wheel cyl cup "lips" in contact with the cyl wall, to prevent fluid loss while not in use, - was what I was taught, and was in my Red Seal Manual.
Look it up .
Newer design wheel cyls came out with the spring, originally iirc with a formed cup on the ends to push the cup lips into contact, preventing fluid loss .
I just got thru doing a 67 Barracuda brakes, 9 inch drum
No springs in the wheels cyls.
 
If you look at 69 up rear backing plates, they have 2 tabs on either side of the wheel cylinder. My understanding is they are there to keep the pistons from popping out until the shoes and springs are installed.
 
Wheel cyls came with springs.....

The purpose of the RLPV was to keep the wheel cyl seals slightly pressurised. This reduced the travel that the wh cyl pistons would need to move, & kept the height higher & more constant.
Many car makers started omitting the RLPVs because they really didn't do much......except increase costs.
 
In the late sixties and early seventies Brake companies began using metal expanders on each end of the springs.
The expanders pushed the rubber cups tightly to the wheel cylinder bore which made residual valves useless.
It took a few years before, the residual valves were completely discontinued.
No harm in leaving the valve in the master cylinder but they are no longer needed unless you have some really old wheel cylinders.
Most wheel cylinder kits now come with expanders including the old cars from the forties and fifties.
 
Thanks for the replies. The kits I used from Raybestos have springs that are tapered at the ends...Raybestos literature says the shape of the springs is to omit the metal expander rings. Since I used these kits with the tapered springs, I believe that I do not have to install a residual valve in the MC (that doesn't have one) correct?
 
Some brands did not use the cup expanders. I would omit the RLPV, one less thing to fail.
 
Dana67Dart said:
If you look at 69 up rear backing plates, they have 2 tabs on either side of the wheel cylinder. My understanding is they are there to keep the pistons from popping out until the shoes and springs are installed.
Click to expand...

For flat-rate, we'd tap whichever tab (L or R) with a hammer to allow the cyl piston to come outta the bore, check, hone, replace cups/pistons/dust boot, then pry the tab back up to retain pistons.
 
Residual pressure in drum brakes is to maintain load against the return springs on the shoes. Removing it from drum brakes causes an increase in fluid needed to apply the brake. It causes spongy brakes and for front disc cars the appearance of no rear brake at all.
Under normal driving you wouldn’t miss the rears. In a panic stop you will know they aren’t there.
Original master was 1 1/32 and are available new on rock auto and other places. Guys all over FABO discuss the right master cylinder for your car in detail. Please read them. Lots of great advice. Smaller cylinder means more travel but lower pedal effort. I’ve used the 1 1/32 master on all of my manual disc brake cars and liked the feel. Currently they cost around $60.
For your safety though don’t eliminate RPV on drum brakes. It is necessary. On the other side it causes disc brakes to drag so it shouldn’t be on a disc.
 
AbodyBB said:
Residual pressure in drum brakes is to maintain load against the return springs on the shoes. Removing it from drum brakes causes an increase in fluid needed to apply the brake. It causes spongy brakes and for front disc cars the appearance of no rear brake at all.
Under normal driving you wouldn’t miss the rears. In a panic stop you will know they aren’t there.
Original master was 1 1/32 and are available new on rock auto and other places. Guys all over FABO discuss the right master cylinder for your car in detail. Please read them. Lots of great advice. Smaller cylinder means more travel but lower pedal effort. I’ve used the 1 1/32 master on all of my manual disc brake cars and liked the feel. Currently they cost around $60.
For your safety though don’t eliminate RPV on drum brakes. It is necessary. On the other side it causes disc brakes to drag so it shouldn’t be on a disc.
Click to expand...
Thanks for the reply. I bought a brand new master for this car, and neither the front disk or rear drum portion has a residual valve. Why would that be? Do I take it apart and install a used residual valve? The wheel cyl. kits that I used for the rears has a cup expander provision built into the spring. This master has a 1 1/32 bore and is what the OEM service manual specs for my power brakes.
 
If it were mine, I'd leave the m/c alone,(warranty) install the w/cs with the expanders.
The previous post forgets the return springs returns the shoes to the "anchor", and cannot compress, or put any pressure on the hydraulics, so no delay if adjusted properly, expanders keep cup in contact with cyl walls.
jmo
 
CFD244 said:
The system includes original wheel cylinders
Click to expand...

Residual-pressure valves were used until partway through '74, then the drum brake cylinder seals were redesigned to prevent air ingress on brake retraction (which was why the RP valve had been present), so the RP valve was deleted.

You can cheaply and easily make your brake system work a whole lot better and safer, and at the same time eliminate the need for the RP valve; see here.
 
Last edited:
These are the kits I bought. Raybestos says the shape of the spring is the cup expander. They say during rebuild, not to use the metal cups if so equipped, as the spring does the job that the cups do.

BTW....The kit is the same one that is spec'd for the 75 Dart as well.

1728389843415.jpeg
 
Back in the 20th century Bendix and Wagner used the traditional expanders.
Raybestos decided to change the design of their springs so the expanders were not necessary.
Obviously either type will do the job.
The technical bulletin simply states when and why Chrysler stopped using residual valves in their master cylinders.
 
The TSB spells it out but then complicated things...

Nowadays are the rebuilt / new master cyl WITHOUT a residual valve compatible with NEW wheel cylinders for all applications?

And...

Are the wheel cylinder remanufactures / new cylinder manufacturers ALWAYS making the wheel cylinders to not need a residual valve in the master regardless of if it was called for in the past?


Sorry just had to toss that out there.
 
If you dropped your car off at my shop with the stuff in the trunk, I'd pull a w/cyl apart checking for "correct " spring expander, check size, install.
If the w/cyls are expander style then a redundant valve in m/c is of no consequence.
If old style regular poor fitting spring in w/cyls, it would be prudent to install a residual valve in the m/c, or there are many residual valve avail to go in the brake line.
But there can be no guarantee about manufacturerers, many breeds, many styles.
I'd like to note the old "rubber"seals of decades ago., prob hardened up pretty quick compared to newer rubber/composite "cups" of today.
Many vehicles I work on prob don't have residual valves at all, cept maybe "roll-control".
Let's consider worst case, minor amount fluid seeps out over long length of time. There is a sealed cap to limit volume of air to release fluid.
You regularly monitor your fluid levels, at least annually, or should, fluid loss should be noted.

jmo
 
Last edited:
Post #14 is incorrect. When you understand how the braking system works, you will see why.
Drum brakes.
The RSLP valve was not used on a lot of cars, & was deleted on many cars when it was realised it did nothing.
The wheel cyl seals are a tight fit in the wheel cyl bore. If they do not leak when the brakes are applied [ several hundred psi of pressure ], they are not going to leak with zero pressure [ brake not applied ]. When the drum brake is released, the very strong brake shoe return springs push the pistons AND seals back into the wh cyl. Ready for the next brake application. The internal wh cyl spring keeps the seal in place, but in reality, you could probably omit the spring because the friction of the seal against the wh cyl bore would keep it in place. Omitting the RSLP valve certainly does not cause a spongy brake pedal.
 
That depends on what part number you actually got. The residual valve is just behind flare fitting in the older masters.

That video shows it really well. So if you have the part number that will tell me what it is.
If it’s a new original design it will have a rear valve and no front.
 
AbodyBB said:
That depends on what part number you actually got. The residual valve is just behind flare fitting in the older masters.

That video shows it really well. So if you have the part number that will tell me what it is.
If it’s a new original design it will have a rear valve and no front.
Click to expand...

Yup, I got all that. Just trying to figure out if this new master needs one when using the wheel cylinder rebuild kits I am using. (see post 19)
 
You must log in or register to reply here.
-

Back
Top