Can someone explain what the spring and cup seal do in the Kelsy-Hayes proportioning valve in the attached drawing and photo and why its call the proportion valve? Red arrows are only for o-ring identification.
There are numerous posts on this subject with many different opinions , try searching " brake combination valve" as well .
I think proportion because it’s shifting the proportion of the braking / pedal force. Typically people use them to have the front brakes hit harder. my guess on this particular set up is that the spring and seal stays closed until the pressure reaches a certain point and then it collapses/ opens and lets pressure go to the rear brakes
Tim, thats what I thought, but the fluid enters at the spring and goes up and out to the rear. My only guess is it holds some pressure on the rear lines. The drawing shows the path of the fluid.
Oh! I think I’ve got it. I didn’t see the drawing at first. I think it’s a combination valve. There is a proportioning valve and a metering valve aka residual valve. It’s 100% maintaining some pressure in the line so you don’t have to pump the pedal.
Is this the section of the COMBINATION VALVE you are describing? If so, that is the PROPORTIONING VALVE (fixed) section of the COMBINATION VALVE you showed. READ HERE -
Learn something new everyday. metering valve =/= residual valve A brake metering valve is used to Balance the Braking Forces. It is only found on vehicles with front disc and rear drum brakes. The metering valve holds back fluid to the front brakes until enough pressure is created to overcome the return springs inside the rear drums.
These valves showed up in 1967 with the federally-mandated split braking system/brake warning light requirement. Prior to then they didn't exist. Their main reason for being there is to allow the brake warning light IMO. But the engineers figured out by adding the 'metering' and 'proportioning' functions they could make balancing the system easier, requiring fewer brake parts combinations to achieve that. Before these came into use, balancing the brakes required careful selection of braking swept area, wheel cylinder/caliper piston sizing, tire size, front/rear weight distribution, etc, etc. Separate front/rear master cylinders with a 'balance bar' between them were sometimes used. Keep in mind that what they were trying to accomplish was preventing the rear brakes from locking first under extreme braking. When that happens, the vehicle will swap ends. The front brakes MUST lock first. So.... The pressure differential valve is only there to turn on the warning light when pressure loss in either end of the system occurs. The proportioning valve is just that. It proportionally meters pressure to prevent the rear brakes from locking prematurely. By doing this, the OEMs could be a lot sloppier about rear brake sizing as they could bring them into balance with this. The metering valve is mis-named IMO; it should be called the 'delay' valve. What this does is very slightly delay/limit the application of the front brakes to allow the rear brakes to engage first. This can actually be done in the master cylinder if a two-piece piston is used. The fly in the ointment is there are literally dozens (if not more) of 'factory' proportioning calibrations, depending on year/make/model etc, etc. If you are doing a rebuild of a factory system, no problem. But if you're re-tasking OEM bits to another vehicle, it's a crapshoot as to whether the calibration will be right, especially if mixing bits from different cars. To make matters worse, almost all of the aftermarket valves that are out there are 'generic' calibrations. As far as I can tell, they sell three versions: drum/drum, disc/drum, and disc/disc. Chances of any of these being 'correct' for your car are pretty much zero. There are no residual pressure valves in these. On a factory system, these will be installed in the outlet ports in the master cylinder for drum brakes ONLY. Disc brakes don't use them. If you have an under-floor master cylinder, they may be installed in the lines to the wheels, but here they're preventing the brake fluid from running back to the master under gravity. If the master is higher than the calipers/wheel cylinders/lines, they won't be needed.
A metering valve is not a residual valve. And metering valves are used on disc/disc systems also. The eye-opener for me was when I owned some XJS Jaguars. You didn't find any of this on those, and this was a near state-of-the-art brake system at the time. Big 4 piston front calipers and two piston rears. The 'delay' or 'metering' was handled by a two-piece master piston separated by a light spring. The rear piston moved first, giving the rear brakes a head start on engaging, and when the rear piston contacted the front one, the fronts were applied. No proportioning valve needed as Jag properly sized the brakes at both ends. There was no physical connection between the front and rear brakes after the lines left the master via their separate ports. The one issue was a pressure differential valve to operate the warning light couldn't be used. Because there was a brief difference, a light would possibly light each time the brakes were applied. Instead, Jaguar used a low brake fluid light as it's warning light. To this day I don't understand how Jag got that past the feds, but they did.
What valve(s) are you referring to? The PROPORTIONING VALVE and FRONT METERING VALVE were introduced in 1965 (describing FORD). The PRESSURE DIFFERENTIAL VALVE was introduced in 1967 by federal mandate along with the dual reservoir master cylinder. The RESIDUAL PRESSURE VALVE had already been in use (drum brake). All US manufacturers during this period (1965/1967) used the K-H designed systems, so all are basically alike.
Thanks Steve for well written explanation. So if I understand this right, the fluid for the rear brakes enters by-way of a port at mid spring, then goes upwards, through and around the spring to the seal, then out to the rear brake line, according to the drawing. Does it fill the chamber, then push down on the spring opening the port to the rear brakes? If so, it now makes since why I couldn't bleed the system, the movable valve was rusted it to the hex nut cap. This is going on an original car with all factory parts, so calibration will be correct.
If you had trouble bleeding the brakes, the PRESSURE DIFFERENTIAL VALVE (pintle) was not centered for whatever reason.
Maybe, but the proportioning valve was rusted in place after 35 years of storage. I'm still trying to understand how fluid gets out to rear line when the spring is pushing up and the fluid is going the same way.
See if this - https://www.freeasestudyguides.com/proportioning-valve-diagnosis.html - helps any. It can be confusing, mostly due to different people using different terms. A COMBINATION VALVE is a body with two or more separate valves (Metering - PDV - PPV and possibly RPV combined in one body. The mistake made is calling a PPV a COMBINATION VALVE or vice-versa. It's one are the other. https://www.ecihotrodbrakes.com/brake-facts What is your valve off of and you know it has to be rebuilt (if possible). The MC is most likely in the same shape. Get back if the above do not answer your question(s).
This is the proportioning valve, it moves byway of fluid, the spring holds pressure on the valve closing off the rear line port. Fluid is entering the chamber about mid spring, fluid wants to go to rear line. How does the fluid open the port from below? Looking at the rubber lip seal and all the little ridges, I assume the fluid is pushed past the lip to the point of compressing the spring. This is what I am asking about. Fluid does not enter from above compressing the spring. Thanks for the help so far.
See if the below helps. As brake fluid application pressure increases, the valve begins to restrict outlet fluid pressure to the rear drums/discs to hopefully alleviate brake lock-up. CLICK HERE - https://www.carparts.com/blog/brake-proportioning-valve-problems/ PPV SECTION of COMBINATION VALVE ----------------------------------
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