One of the most misunderstood subjects in brake related posts is residual valves. (proportioning would be a real close second ) I have been involved in several of these discussions over the years, as many of you know. Early on, I found much of the incorrect information posted on this and other forums was taken almost word for word from some very well known brake supplier's "tech support" on their web sites. However, over the years most of the suppliers have corrected their descriptions of brake valves, including residuals, possibly due to our discussions here. Drum brake residuals have been around since the early days of hydraulic brakes, and began to disappear in the early '70s. They sometimes were referred to as a "check valve" and were normally located at the end of the single system master cylinder bore, but some were installed inline to the brakes. Most dual (tandem) masters had the valves located behind the tube seats. What residuals DO NOT do: Keep the shoes from fully returning to their anchors, to prevent the full return of the wheel cylinder cups because of some possible damage, or allow the shoes to "float" by preventing them from returning to their anchors. First, the small residual pressure is far below the amount to provide enough force overcome the strong shoe return springs. Second, why the heck would you want the shoes to "float around inside the drum"? Normal individual shoe to drum clearance should be around .015", not a whole lotta room to "float around", even if it was intended. Below is an explanation of residuals from a brake service manual and the 4 major vehicle application's from '68 to near the end of their residual usage. Hopefully, no more mystery and myths....about residuals. View attachment 3807991 View attachment 3807993 View attachment 3807995 Using a residual on later drum brakes may not be needed, but will help 'tighten" the pedal and causes no problems. Modern disc brakes (no return springs) never used residuals because their usage began after master cylinders were commonly mounted high on firewalls. The 2# residual is strictly aftermarket and should ONLY be used with discs when the master cylinder is below floor mounted, or lower than the calipers. Disregard the stuff below.
When I buy complete wheel cylinders nowadays, I always find there are no cup expanders or springs inside the cylinder. Should a residual valve be used on this circuit then?
Lots of new ones have the end of the spring wound to act as the cup expander but I don’t understand the no spring as well Sent from my iPhone using H.A.M.B.
Any chance you'll expand on proportioning valves? I didn't install one on my Impala when I converted the front to disc. The very first time driving it, I think it was actually to get exhaust installed, I had an oh-$hit moment when traffic came to a sudden stop and I went all-in on the brakes. The boat stopped fine and surprisingly well! I'm wondering if I even need it....
That last set of cylinders I bought was for a 48 Ford. They came from Macs (that might be the problem right there) and they had no expanders or springs in them. When I installed them I found the shoes pushed the cups too far in and made the fluid leak past the cup, getting all over the guts. I had to preadjust the shoes and then take apart the cylinders to make sure the cups were outside the fluid feed hole before I could bleed those brakes. Some internal springs would have prevented all this trouble.
I remember this being addressed by Dick Spadaro several years ago. The problem was the fluid port not being drilled in the correct location, causing the fluid leak you had. I would try and buy new wheel cylinders from someone who is aware of this issue.
I'm telling the first person who asks.... I converted my drum brakes over to Granada discs in front on my Fairlane and all I did was connect it to the same (dual)master cylinder to see if I needed any other modifications. It worked fine just as it was. Just a bolt on.
I did a thread on this issues a couple of years ago. I found that finding/making the metal discs that go behind the rubber cups cured the issues I had.
There are sooo many variables when building, converting a car/hot rod that, in my opinion, one would have to be well trained engineer to accurately determine the need for a proportioning valve on a given application. Vehicle weight distribution, tire sizes and tread compound, brake diameter, wheel cylinder/caliper dimensions....just to name a few are all components that affect brake performance. About ten years ago I built up a ‘47 Ford Coupe and used a Speedway front disc kit (12” F150 rotors/big GM calipers) and an 8” Ford rear end with 10” drums and a late ‘60s Mustang M/C, no booster. Front tires were 205...rear 235. I reasoned it was unlikely that with the size of the front discs and tires vs the rears, that the rears would NOT lock up before the fronts. And, they did not. I had a great pedal feel, very linear in application and couldn’t have been more pleased. A different combination of factors could have yielded a very different outcome. Ray
^^^^ And this is why I have gotten away from those generic "combination valves" that most kit suppliers use and just install a simple SSBC Prop valve in the rear feed line. Adjust it per SSBC instructions and no problem, you can make the brakes react the way you like them on almost any vehicle.
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