Brake combination valve - better off without it ??!!
 

My truck, a '79 F350 dually, has been a daily driver for 15 years, and during that time, I've replaced the master cylinder, booster, front rotors and pads, rear drums, shoes, and all internals, changed the rubber hoses to braided, and replaced all hard lines.

The parts were changed at different times, not all at the same time, but any change made has never changed the 'feel' or effectiveness of the brakes.

Bleeding the brakes with 2 people, simple gravity bleeding, or vacuum bleeding, made no difference.

The truck has always stopped ok, and I would consider the brakes to be simply 'ok'.

I use new or newer cars with disc/drum brakes as a benchmark, they stop on a dime, and I can feel their brakes 'bite' consistently.

I would feel the brakes 'bite' on my truck, but it would be once in a blue moon.

If the tiny discs/calipers and drums/shoes on new/newer cars are that effective, then why aren't mine, which are huge by comparison ?

Over the years people have told me, 'It's an old truck, you can't compare the brakes', but I disagreed.

One can fit cheap crap pads or shoes, and for sure, they won't be as good as better quality pads or shoes, but I've fitted the better quality parts.

Then it occurred to me that I'd changed everything, except the combination valve (CV), so I got a new one.

Nope, no change in the feel or performance of the brakes.

The modern Range Rover is about the same weight as my truck, stops on a dime, and I can feel the brakes bite.

So I decided to convert the rear drums to discs. (Still busy with that.)

When converting disc/drum to disc/disc, the metering valve inside the CV has to be disgarded.

It then occurred to me that I won't need the CV at all, but rather a simple proportioning valve (PV) to control the rear brakes.

I was curious as to what difference no CV would make, and decided to remove it before I get to the rear disc conversion.

I removed the CV completely, fitted a PV and fitted new hard lines.

The PV was not adjusted and still allows 100% pressure to the drums.

OMG ! I have more powerful brakes. I can feel the bite, and I can feel and see the truck stopping a lot quicker.

Forest Gump is no longer the braking system, Chuck Norris is. :)

Throughout November and December, the brakes worked consistently with a nice 'bite'.

The Range Rover has four bad a$$ Brembo calipers, and it sure feels like The Terminator is controlling those brakes.

I'm hoping that the rear disc conversion replaces Chuck Norris with 'Arnie'.

Back to the CV.

The CV has a metering valve which prevents nose dives during emergency braking.

Hmm, I felt/saw no real nose dives without it.

The metering valve can prevent full power to the front discs in a certain circumstance, but I forget what that circumstance is.

The CV also has a PV, but it is non adjustable. (That's helpful ! LOL)

And lastly, the CV has a 'brake pressure differential valve' connected to a dash warning light.

Well, that warning system is crap.

Over the years I've had the brake pedal go all the way to the floor twice, and both times a drum cylinder had leaked. No warning light !

I tested the new CV when I was fitting it,and the only way to activate the light was by simulating a full leak. Useless !
(Then you have to go and 'centre' the pressure valve again.)

My replacement master cylinder is a modern one with a built in 'reed switch'.
As soon as the brake fluid level drops to half, I will know about it with the warning light coming on. Much more useful !

With or without a CV, the braking system is still split into two circuits.

I don't know if both of my CV's were faulty (no way to check!) , if the CV system is flawed, or if I'm an idiot, but with or without the rear disc conversion, I wouldn't use one again.

Some pics to finish off :

https://cimg8.ibsrv.net/gimg/www.for...97b33df815.jpg
This is the old CV. Might be OE, might not.


https://cimg9.ibsrv.net/gimg/www.for...9933520986.jpg
This is the new CV. The orange 'thing' prevents the pressure differential moving during bleeding.

https://cimg0.ibsrv.net/gimg/www.for...68f02c8fbf.jpg
The new MC with the warning wires attached (still to be tidied up 2 1/2 years later :o).

Still to be tidied up, eh? In other words, it's temporary unless it works!:D
It's how I do most stuff, but yours looks very well sorted already.

Unless they used different ones on export vehicles (unless yours was made in-country?) then both of those are aftermarket. The stock ones were always rough cast pieces that I've seen.
And unfortunately, those aftermarket blocks of brass are best used as paperweights! I've sold them for years, but usually try to talk the customer into either trying their brake modifications without one, or into using a manually adjustable proportioning valve so they can dial it in themselves.

The most common failure point is the delay valve under that rubber boot leaking brake fluid. The newer and nicer the paint, of course the more likely they are to leak.
Looks like the new one has a centering tool locking out the shuttle valve? Good idea.

One odd thing about your old one though, that makes me think it might actually be an original of some kind, is that it's using the original 2-wire switch. Whereas all the new ones are using a 1-wire switch that makes you re-wire your old connector by twisting the three wires (two on the harness side, one on the switch side) together to make the lamp work.
Does your lamp illuminate momentarily when you turn the key to START? It's supposed to, at least on some vehicles, as a test each time you start the engine.
Doesn't really matter now. Good on you for upgrading to newer, more modern stuff that you can use to better effect it sounds like. Glad your brakes are waking up.

My '79 had great brakes I thought. Until I realized that the fronts were not doing anything and the rears were doing it all. Unfortunately I realized that when the road was very wet and I could hardly stop without locking up the rears!
Not a great way to find out your brakes are not up-to-snuff.

Anyway, I didn't think the proportioning/combination valve would do such a thing, but have found out since then that they can cause all sorts of ills. I'm glad my company is finally pushing the adjustable prop valves more and more now too. I'm already on that bandwagon.
So yes, if you can gut yours and use it strictly as a convenient distribution block so you don't have to re-make any tubes, so much the better.

Great looking truck!

Paul

I can't offer any help with the CV question, but I can say that these old trucks, or at least some of them, can stop pretty well. My '77 F100 came with disk/drum manual brakes. I swapped in a power brake booster/mc/pedal assembly, but kept everything else the same. I don't know if the CV is different from manual brake trucks to power brake trucks like the mc's are, but my truck stops awesomely. I'm also comparing to more modern cars/trucks that I've driven and it does just as well. Everything in the system is new though, minus the hard lines and the CV.

My '78 Bronco on the other hand doesn't stop nearly as well at my F100. Like yours, I'd say it stops "ok". I'm eventually going to go through it's complete brake system and give it a similar treatment like I did to the F100 and see what that nets me. I know a lot of guys do the F350 brake booster upgrade, but if I can get the Bronco's brakes to work like my F100 then I don't see the need for it. I know the Bronco is noticeably heavier than my F100, but I don't feel that "bite" as you describe like I do on my F100.

Good morning Gents,

My motivation for this thread was to illicit thoughts/questions/answers from/to whoever is questioning why his/her brakes are merely 'ok'.

Your posts do that ! :-X22

@ 1Ton,

Yes, they still need to be tidied. My Doctor told me that I must regularly feed my OCD ! LOL

I can't comment on the 'old' CV, but my new one was USA made which I got via Summit racing, and it's definitely aftermarket.

It feels like I don't need the PV at present, although I ran out of time to do some thorough testing.

I expect it will be needed for the rear discs though.

I bought the centering tool and one wire connector, both aftermarket, to go with the CV.

Hmmm, my truck has an F600 chrome dash face, and originally it had the one piece clock setup with a circuit board.

I have since replaced all gauges and wiring, but no, the brake warning light would not come on just before startup. (I know what you mean.)

Mind you, there was never a wire connected to the CV. P.O.s huh !

I don't like your method of brake testing !! LOL

That's exactly the sort of sh$t brakes I had when I first got my truck, not as bad as yours, but bad all the same. :-arrgh

I bought a $200+ flaring tool for the brake lines. Fantastic tool !

The savings on labour if I had to pay someone has paid for the tool, and I can do brake lines at my leisure in the comfort of my own garage.

@ 75BB

I agree with you, these trucks should stop pretty well.

I imagine all trucks left the factory with good brakes.

'Theory' tells me that the manual brake setup with a 6 : 1 pedal ratio should feel similar to a power brake setup with a 4 : 1 pedal ratio.

Did your brakes feel/work any better after the booster etc swap ? (Just curious.)

I'd imagine the disc/drum CV to be the same on a manual or booster setup, but I also don't know for sure.

It's good that you have the F100 as a benchmark for the Bronco.
I've seen several F350 booster conversion threads, but I agree that your Bronco setup should work better than 'ok' without a conversion.
That said, I haven't got hands on experience with Bronco brakes so I'll shut up.

If you ever do 'fix' the bronco brakes and obtain the 'bite', and it turns out to be something silly like a CV, I for one will enjoy reading your thread if you do one.

WELL... My F150 that is deceased will soon be dismantled as soon as the weather gets better here, so I don't have to do it in rain or snow. I'm going to keep what I'd like and then send it on its way and in light of this conversation I'll probably snag the CV off of it, so that I might swap it in to the Bronco if other changes to the braking system don't work out and see if it makes any difference. I'll have to make a "shopping list" of stuff to keep when I get around to picking it apart.

I honestly can't tell you how the brakes were before the swap to the booster or should I say how well new manual brakes would have been prior to the swap. The brakes were in terrible shape and barely worked. I basically bled all the fluid and put in nice clean fluid, swapped the mc/booster from my F150 and swapped the pedal assembly from the F150 as well. It worked pretty well, but I could tell the old booster from my F150 was on its way out, it would audibly wheeze when you'd hit the pedal. I know just going from the old booster to a "new" re-manufactured booster made a world of difference as far as how much effort was needed to make a stop. That's when I just had everything done front to back and was really surprised with how well they worked with all new components.

I know it's difficult to put into words how the brakes feel, but with the brake booster push rod set properly so it doesn't take a long pedal throw for the brakes to actually start working, I can literally rest my foot against the brake pedal and the weight of my foot alone will bring the truck to a nice smooth stop. If I give it a nice firm push it'll put your passenger's forehead into the dash if they're not expecting a hard stop. With my Bronco you really have to push the pedal to get it to stop with urgency. Again, one is 2wd and the other is 4wd and weighs a bit more. I haven't been in an "oh ****" situation with the Bronco yet as it's more of a toy and sits a lot while I daily drive my F100, but I'd imagine if I wanted to get the most out of it's brakes in an emergency I'd have to put both feet on the pedal. There is definitely room for improvement!

I hope you get a solution. It really increases the joy of driving these trucks when you don't have to worry about their performance, especially when you need it most.

Totally agree on the brake thing. To me my truck brakes are also just "ok". I cant feel anything! They just feel....numb. best description. Not like my wifes car where i can feel the bite like you said

Thank you, but I got the solution already.

Simply removing the CV and putting it in the bin gave me the Chuck Norris bite. :)

However, I want the 'Arnie' bite, and I hope the rear disc conversion gives me that.

If it doesn't improve on Chuck Norris, I don't mind at all, as long as it's not Forest Gump again ! LOL

Good point about 2wd versus 4wd.

The Range Rover is 4wd, albeit with discs all round, but I reckon the Bronco should stop like the F100, or close enough.

I understand what you mean about replacing boosters etc, and setting the booster push rod correctly.

My truck has a 5.7 : 1 pedal ratio which creates a noticeable, but not too bad, 'long pedal throw', but I can live with that.

I totally agree with your fun comment.

Over the years I've replaced steering, suspension, etc, etc, and boy is it fun to drive.

Now that the brakes have a decent bite, I'll be staying a lot closer to cars during 'dances'. }>

I wish you and niko20 luck on getting the Chuck Norris bite.

If you want the brakes to REALLY bite, go for a hydroboost upgrade. It's not the cheapest, but it's a relatively simple upgrade that gives a lot of "bite" for your buck ;)

Ford trucks with a GVW of less than 6900# used a cast iron Kelsey-Hayes brake valve. During the brake bleeding process on the front brakes, the pin on the cast iron Kelsey-Hayes brake valve is pulled outwards.

On models with a GVW of 6900# or greater, a brass Weatherhead brake valve was used. Highly probable the brake valve shown is an original Ford brake valve. During the bleeding of the front brakes with the brass Weatherhead brake valve, the pin is pushed inwards.

I've heard that too Steve. But my '79 F350 came with the usual cast pieced that looked similar to, but not exactly like the ones I was used to.
As far as I know too, it is original.

I remember reading about the push vs pull thing, but don't remember which direction mine had to be done. Pretty sure it was a pull though, which caught me off guard having expected the push type.
Interesting about the factory using the brass type. I'm glad to hear it. And I will not completely rule out the possibility that at some point mine was changed. Just not very likely as I bought it from the second owner (first owner only had it a few months and sold it to his neighbor, who I bought it from) with about 88k miles on it.
So while that's not proof of originality, it seems less likely to have been changed at such a low mileage.
But you never know. Could have been a warranty issue. Now I'm curious and going to have to look at other trucks of my type to see what they're sporting.

Thanks for the extra info.

Paul

I meant to add too, that having this type of valve from the factory would explain why FMJ's looks original and has the proper thread for the old style switch as well.
That was what brought the question about those having been used into my mine in the first place. Just never seen one myself.

Paul