Proportiong valve question

[davidmij]

Can anyone tell me (reassure me) that this picture is accurate.

[DKheld]

Hopefully this link will help....this is the unit I used. Comparing the line sizes on both units it "looks" like your drawing is correct.

http://www.mpbrakes.com/uploads/products/VL3350_Rev10_07.pdf

If that link doesn't work just scroll to the bottom of their tech support page and the combo valve guides are at the bottom.

http://www.mpbrakes.com/technical-support/installatin-guides.cfm

Eric
registry 5347

[simplyconnected]

Yep, that's my picture. It is a typical FORD combination prop valve. GM's are a little different as they require adapters from 1/2" to 3/8" IFF.

The reason for different sized fittings is, Ford didn't want the guy on the assembly line to put brake lines on backwards. They are all inverted flare fittings. - Dave

[Jimz Bird]

Here is a good 2 pg tech note I ran across yesterday that does a good quick job of explaining Brake Valves. (Proportional, Residual, Combination).

http://www.thebrakeman.com/valvetechi

Interesting Note:
"Some or most OE disc/drum combination valves have a small delay circuit in the front system. The purpose of this delay is to allow the rear brake cylinders time to move the shoes the much larger distance than the disc pads need to travel. IF the pads were not delayed then potentially the rear brakes will come on late and produce excessive nose dive combined with a 'loose' feeling at the rear. Some folks experience this and others do not. I've no idea what the differences might be.

No proportioning valve that I'm familiar with, particularly those made by my former employer Wilwood (R&D Engineer), have any "metering" in them. They do proportion the outlet pressure to a certain percentage of the inlet pressure when the input pressure reaches a set point. That set point is called the "Knee Point" because it is the point where the outlet pressure diverges from the inlet pressure. I can see how that might be thought of as "metering", but it really isn't affecting flow, just pressure. The knob does not adjust the outlet pressure. That is what a regulator does, supply a fixed outlet pressure regardless of inlet pressure so long as the inlet pressure exceeds the outlet setting. Prop. valves are not regulators. They "Proportion" the inlet pressure.

To summarize; with a proportioning valve the outlet pressure is equal to the inlet pressure below the knee point, and is a fixed percentage of the inlet pressure when above the knee point. What you are changing when you turn the knob of an adjustable prop. valve is where that knee point is, i.e. at what pressure the outlet pressure starts to diverge from the inlet pressure."

From here:

http://classicbroncos.com/forums/showthread.php?t=154116

Some other good links on that page also.

And this from Summit which looks like the "combination" valve that many sell for a lot more. Before buying this one I would check to make sure it is a combo valve with "proportioning and/or metering".

http://www.summitracing.com/parts/RSD-PVK71/

Even less at Jegs:

http://www.jegs.com/i/Right-Stuff/965/PV71/10002/-1?parentProductId=1502558

HTH

[davidmij]

Thx gents! Lots of good info.
Dave, I had saved that picture from a thread somewhere and couldn't remember who posted it. I appreciate you letting me know it was you, and that it is correct. I was wondering why Ford had different size nuts for the same size tubing - that seemed weird. Now it makes perfect sense though.
The brake job is coming along great - everything fits perfect except one side of the Scarebird brakets needed a touch of grinding to get it to sit flat. I'm also switching out my brake pedal for a brake clutch pedal for down the road when I get a 4 speed. I'm working this weekend, and a grad party for my son next weekend, so it'll be sitting there for a another couple of weeks before I finish up. I'll keep you posted and post progress pix when I get done.
regards, Dave Jones

[simplyconnected]

DJ, I am pleased to hear your brake system is coming along well.

...everything fits perfect except one side of the Scarebird brakets needed a touch of grinding to get it to sit flat...

Are you sure? The bracket fits against the spindle with flat steel. I can believe the brake hose hole in your caliper may need a little
'casting grinding', but not the caliper bracket (not at all). If this is really true, I would seriously contact Mark at Scarebird.

Jim, thanks for the extensive technical research and report. You went into depth and we appreciate your time and efforts.
There are a couple things to note. The 'knob' type of 'adjustable proportioning valves' is not what most think. It is simply a needle and seat, which makes it a "Flow Control". Flow controls slow the rate of flow but once flow stops (when all the shoes and pads are tight on the castings) the pressures equalize giving far too much to the rear shoes. It's like pounding your brake line down with a hammer (I'm serious). These valves are not plumbed to the front system so they do not 'proportion' anything.

A "combination proportioning valve" is what the OEM's use on disk/drum brake systems. It meters, proportions, and also shuts off the leaking side (if you blow a hose) so no more fluid is lost. When the 'healthy PSI' side shoves the internal piston to the leaky side, the electrical connection grounds (turning on your warning light) and the spool closes off the 'zero PSI' side. Once the leak is fixed, pressing hard on the brake pedal should reset the spool to the middle.

The articles mention the 'spring return' on drum brakes as 'necessary' to overcome. I agree but using a residual valve is NOT the way to do it. Working self-adjusters is the way to go, or be very diligent in keeping your shoes adjusted close to the drums. Self-adjust kits are cheap and available in most auto parts stores.

After installing a combination proportioning valve, I felt the rear brakes were still hitting too heavy. So, I changed the rear brake cylinders from 7/8" to 3/4". That did it, and the system works very nicely.

When I apply my brakes, the rear shoes engage, then the fronts engage, then it's a linear torque increase as I apply more pedal pressure. The drum brakes work perfectly and I can lock up all four wheels in a severe panic stop. Very impressive braking distance for a big old Galaxie. - Dave

[davidmij]

Yup, I'm dead sure. I checked it over and over and it just wouldn't sit flat. And only on the drivers side, the passenger side was fine. I measured for parallel etc and the bracket was good. It hit the spindle just below the top bolt. If you go to my pictures at this link and look at the 2nd pic of the bracket you'll see where I ground it down just enough to sit flat. Before it would sort of teatertotter. You can make the picture larger by clicking the "+". You can't really tell but the back side is ground down more than it looks.

https://picasaweb.google.com/101492851059660555641/TBirdDiscBrakes2011?authkey=Gv1sRgCK6Gg9yhpdfGWg#

Afterwards it was great.

[simplyconnected]

My concern was for the welded-in bushing on the bracket.

If it was cocked in the welding fixture, it could be welded wrong on the bracket. I believe the spindles were machined 'true'. Maybe I'm making too much of it. After all, the bushing is a counterbored 'step' that takes care of any sideways torque from the brake. The 9/16" bolt simply holds the bushing from coming out of the counterbore.

I'm glad to see you put a big washer under the bolt head. Did you bend your brake lines yet and are you flaring? So far it looks great. - Dave

Oh... I forgot to ask; how difficult were the 'donuts' to put on the spindles?

[davidmij]

I'm pretty sure Scarebird checks each one for machined accuracy, at $150 I sure hope so. They also included a bag with the bolts, washer and even banjo bolts for the calipers. The banjo bolts were too long though. Still, I'm very pleased with the bracket. After installing it I can't see how anyone would feel comfortable with just a 2 bolt bracket.
The spacers were a perfect fit - with a little grease they went on by hand. I should have included a picture of the clean spindle and the spacer. I cleaned it up with a wire wheel and a hand drill. The old grease had kept it pretty air tight and clean.
Haven't done the brake lines yet, I'll be doing that in a few weeks. Autozone will loan me all the tools so I'll get the tubing from them.

More to come.......

[simplyconnected]

...The banjo bolts were too long though...

Remember to use TWO copper washers on each banjo bolt (one on each side of the hose end). If you do not have copper washers, bring your banjo bolts to the auto parts store and buy four. These are VERY important if you want no leaks at the calipers. You may find the banjo bolts are perfect in length.

...I should have included a picture of...

There is no such thing as too many pictures. (I always take 100.) And when you think you took enough, you will be looking for that one angle that is missing. It always happens to me. - Dave

[Rigormortor]

Can anyone tell me (reassure me) that this picture is accurate.

Hello. I did a disc brake conversion on my 59 Dodge and I did what just about no one else does, and many people think im crazy.... I tossed out the prop valve and run my brakes 50/50. I couldn't be happier. No nose diving, front wheels locking up. My car brakes evenly and smooth..... just something to consider. Why have the front doing all the braking? Dosen't make sense to me.

[davidmij]

That makes total sense to me Rigormort. It's all about handling, and if what you did makes for better handling and stopping then that's what you want. I'm gonna see how this setup handles and if I don't like it I can put in smaller rear cylinders or remove or change out the prop valve.

[Jimz Bird]

I tossed out the prop valve and run my brakes 50/50. I couldn't be happier. No nose diving, front wheels locking up. My car brakes evenly and smooth..... just something to consider. Why have the front doing all the braking? Dosen't make sense to me.

I am curious if the Dodge conversion used just a proportioning valve or the "combination" valve that had both "metering" and "proportioning".

It appears that some folks have trouble with just a "proportioning" valve (especially an adjustable one) in getting the brake pressure balanced.

The other thought would be if they used a "residual" valve on the rears to keep pressure there to prevent the nose diving.

I agree that the fronts should not do all the breaking but since there is more weight on the front wheels during breaking (especially hard breaking) that they should have more than 50% of the job to do.

Thanks for your input on the Dodge.

[simplyconnected]

I always assume the car will have the same tires all the way around. There are several ways to change your braking bias.

The goal is to prevent the rear tires from locking up long before the front tires. This is particularly important when braking around curves where the potential for fishtail and understeer is at its greatest.

Larger diameter slicks could tame rear braking a bit if the back end isn't jacked up (transferring the weight back to the front).

When you do your road test, I'm sure you will discover if your braking bias needs adjustment. Much of this is, 'personal preference'.