Technical Help with Brake Combination Valve Question

If you do consider removing the booster to go just manual, make sure you check and have the correct pedal ratio or you'll another can of worms to sort out. Brake pressure gauges or a single gauge can do more fore sorting brake problems than guessing.
https://www.markwilliams.com/brake-... pressure, the,pressure right where it counts.

 

If you look @ the cutaway at the front of the combination valve, the metering valve has two outlet ports, both controlled by the actual metering valve. It needs two outlet ports to provide enough pressure/volume to a larger size caliper pistons/bores.

 

Thanks, I was hoping to get another 7" dual diaphragm booster and M/C kit...

 

Ummm…no. Pressure is determined by the master cylinder and is equal and undiminished in all directions. That is a law of hydraulics, non negotiable. When the system is bled of air there is less than a teaspoon of “flow” under normal brake applications. Hydraulic brakes are a hydrostatic system not hydrodynamic.

plug one of those front ports on the combination valve and tee the remaining one to the front brakes somewhere else, they will work just the same.

 

Umm... (excuse me ... one more m)

Pressure and volume is determined by the MC bore size and length of stroke. The reason for two outlet ports AFTER THE ACTUAL METERING VALVE for a DISC setup (combination valve) is to supply both the needed pressure and volume (dictated by caliper piston/bore size) (in other words, the MC design must be able to supply the caliper design). DISC needs much more line pressure and volume. Splitting the outlet (as done on the old drum systems) on a disc system may give the correct line pressure but not volume, especially if a KIT MAKER passes through GM METRIC low drag calipers without a matching quick take-up MC and not informing the buyer ...

Another reason to have power assist on a DISC setup, more line pressure is needed over a self energizing drum system drum system.

No need for college book learning here as formulas are readily available to help build any needed system. Just study OEM setups hows and whys and you will learn a lot.

And we won't get into the general misunderstanding of the PPV here ...

 

Well you can test and see if the booster is causing the problem. Apply the brakes to the point where there is drag on the front wheels with the pedal released. Crack a bleeder on a caliper and see if they move freely. If they do, something is holding pressure on the caliper. If it doesn't make any difference, it is normal.

 

Well considering Lots of people run manual discs that theory is out the window, you are sort of correct that discs require more output force which is dictated by pressure and area of the out put piston, pressure is dictated by the master cylinder like I said, input force and master piston area. The metering valve is only to delay front brake application, has nothing to do with suppling more flow or pressure. Try it sometime and see what the results are, block one and tee off the second, I bet you find they work the same, just like we run one line to the rear brakes although no metering valve but somehow they still get enough volume, hmmm…But hey, if you want then I’m wrong you are right. Yay!



It’s well explained here…
https://www.jalopyjournal.com/forum/threads/tech-week-57-fargos-brakes-101.1229211/

 

Thanks I played around with this quite some time and found it drags then slowly releases..… I noticed the difference on the bench between the old and tuffstuff booster when pressing in by hand and got me thinking the tuffstuff is maybe slow because of the rubber and seals being in a static position for 5 years.

 

I never said a thing about the METERING VALVE PURPOSE or operation other than referring to another poster implying both front lines are not needed. I fully understand the purpose and need of a METERING VALVE on a FRONT DISC DESIGN.

The OP has come here seeking advice and not one swinging chicken here has been able to help. Actually they are causing more confusion as most do not fully understand how a braking system works. It is not rocket science.

I fully understand MANUAL FRONT DISC. It was popular in the day for a hot street car with a large cam. Yes it does require more leg pressure than a power assist. It all depends on the weight of the car, how fast it goes and the type of brakes on the rear axle.

No, you do not need a METERING VALVE until the rear brakes begin to lock and the rear gets squirrely. DO NOT worry about how long those rear shoes take to move outwards and grab the drums. And don't even consider the accelerated wear on the front pads and loss of vehicle brake bias balance.

It's as simple as this, whoever issued that kit has no idea of how to retrofit an early vehicle. That COMBINATION VALVE has no business being in that system. There is no need for the PDV, it will not block-off a failed circuit. It was never intended to. The PPV section is not calibrated for that vehicle. Get into a panic stop situation on a slick surface and see how much seat cover you can inhale.

"... just like we run one line to the rear brakes although no metering valve but somehow they still get enough volume ..."

Rear drum brakes or disc brakes do not require the same pressure/volume as the rear wheel cylinders/rear calipers have smaller pistons and hopefully if drum, they are self-energizing.

As for your TECH ARTICLE, please allow me to review it at my leisure.

This is how people lose nice cars and hurt either themselves or someone else. If I were a STATE INSPECTOR and looked under that car, it would get a bright red sticker.

BTW - What is a 'coaster piston area'?

FOR YOUR VIEWING PLEASURE -
https://www.reddit.com/r/cars/commen...brake_failure/

 

Coaster was a mistype, should have been master, It was me that said both lines aren’t needed. So explain to me where we get more pressure to the front when the bore on both circuits in the master is the same? Pressure not output force…as well as a difference in volume between the two. Because believe it or not some of us do actually understand. Maybe we are misunderstanding each other…

 

One or two lines to front brakes? Every FACTORY master I've worked on had one port and one line attached. That includes the 70s mopar that I'm adapting to my 56PU. Some have a combo valve instead of a tee fitting. I really doubt that there is enough restriction in the Combo valve front section that it needs more than one outlet to pass the input flow. Probably there only to make the valve fit in a more universal way, i.e. replace the tee fitting.

 

Not everything had a combination valve either. Some had the three valves separate, some Chevy trucks had the metering valve under the rad, one line from the master to metering valve then split to the front wheels but what do I know.

 

I think that is the main problem, a failure to communicate. Just read all of the suggestions made just on this one thread and you can see the problem(s)...

No, you are correct. Just for example, FORD did not use a true COMBINATION valve until the 1972 model run although they began front disc brakes in 1965.

Design has progressed, aftermarket vendors have not.

I ain't trying to bust anyone's a$$ (too damn old for that anyways) but try and help a young fellow build a safe ride.

IMO, most of these so-called disc conversion kits are junk (and mostly CHI-COM) and the seller has no more idea of how to install than the novice that has bought one. They should be regulated or at the minimum ASE CERTIFIED.

I could not imagine having something beautiful and proud of and a simple no fit MICKEY MOUSE part takes it away from you.

 

MOONRNR,
You come on this forum as a newbe with a bit of an attitude, without really knowing the knowledge base and experience of some "swinging chickens" you so kindly refer to. First thing you need to do is learn more about brakes systems yourself before you "cause more confusion". Your statement below clearly shows you have no idea how metering works.

"No, you do not need a METERING VALVE until the rear brakes begin to lock and the rear gets squirrely. DO NOT worry about how long those rear shoes take to move outwards and grab the drums. And don't even consider the accelerated wear on the front pads and loss of vehicle brake bias balance."

Loose the attitude, bone up on brake system components, and we'll get along just fine.

 

You are missing the point. You are working with old tech but there is nothing wrong with that. I would think you would want to bring it up to modern current standards.

Flow restriction is not the subject. Delivering the proper volume to the caliper piston is. Size does matter here. Do you want to stop at a casual pace or bring the thing down?

How late of a system have you ever worked on? 1970 TECH was how many years ago? Some are hanging HI-TECH CALIPERS/ROTORS and you think a 1970's MC/BOOSTER COMB is going to operate it properly?

Personally, I love the older 60's KELSEY-HAYES four piston calipers but there is a lot of tech now that allows making them work even better than the old days.

OK, I am retaining water and need a MIDOL.

 

'YOH!?!'

I am not here 'to just get along fine'. I am posting only to show how someone can ask a very valid question and be given "I CAN NAME THAT PROBLEM IN 100 POSTS' and never help the OP. He is now worse off than if he never posted.

He is now going to point a parts cannon at the car and still be in the same predicament, most likely worse.

BTW - Who is we? You have a tape-worm?

You don't know who this is? Think real hard ...

 

You have to have someone there to work the pedal for proper diagnosis. You are chasing your tail.

 

You mean apply the brake pedal and release then see if the wheel turns freely (taking into consideration normal pad drag - design of system). If the wheel is hard to turn, crack the bleeder screw and then if the wheel turns easily there is a defect in the system that will not allow fluid pressure release (bad hose - mis-adjusted/defective MC for example).

 

Why do you think the MC and booster are defective? You should be able to hook a test gage to the system and check to see if its working properly before opting to spend money replacing it. Be a good learning experience and a nice tool to have for future cars.

Video says you need to insert a stop in the combo valve in order to bleed the system .
www.youtube.com/watch?v=qPLaPv8DITE

www.youtube.com/watch?v=3aAORYNLrzU

www.amazon.com/Speedway-Motors-Single-Brake-Pressure/dp/B075G3977P/ref=sr_1_7?adgrpid=1339205727262824&hvadid=83700680661848&hvbmt=be&hvdev=c&hvlocphy=88414&hvnetw=o&hvqmt=e&hvtargid=kwd-83700705129892%3Aloc-190&hydadcr=7498_13249747&keywords=brake+pressure+gauge+kit&qid=1703975150&sr=8-7

 

Flow restriction is exactly the subject. Volume delivered is a result of flow! Volume delivered is simply a function of master cylinder volume, stroke and delivery 'piping'. Basic hydraulics. Caliper volume need, master volume delivery is and the clamping force not high tech, it's simple math. As long as the path from the master to calipers is capable of delivering the desired volume at the speed of pedal travel things will work.

As to late systems, only old stuff this year, 56, 97, 2011, 2013, 2014 so nothing really late.

Actually most really good newer stuff exerts more control over braking with the sensors, computers, pumps and electrically controlled valves than the mundane parts we have on our old stuff.

 

All of you guys need to get it through your heads that flow is irrelevant for the most part, the whole premise is the fluid acts as a solid, there is almost zero flow, that’s a fact. Like it or not. Also disregarding abs modern brake systems operate exactly the same as old ones, similar bores, similar reservoir capacity etc. one thing I agree on is none of it is rocket science…

 

^^^^^ EXACTLY ^^^^^

 

It is flow, maybe not so much with drum wheel cylinders or rear calipers, but the front calipers requires volume. especially as the pads wear. The MC is going to require frequent top-offs.

You need to study the basics of hydraulic braking not some college book description of flow. How much fluid do you think a caliper (and there are many sizes) needs to move that piston?

I would quote some of these so-called kit vendors but most of their offered info is either incomplete or totally wrong.

As for late, I hope I never have to see how you guys would service an ABS SYSTEM.

The OP is going about the diagnosis all wrong. That is where he needs help.

I am really looking forward to reading your TECH ARTICLE ...

 

The way you are going about this is all wrong. You need to bleed the system, make sure the booster to MC push-rod is correctly adjusted and go from there. The rear shoes have to be adjusted correctly to ensure a high pedal. Front DISC takes a minimum of 1200PSI to actuate (one good reason to have power assist, especially on a heavy car).

Set the car down, put it in gear, let her roll slightly on level pavement and apply the brake pedal. She either stops or she don't. At a roll she should stop with just the handbrake (MT or AT?) IF THE BRAKES FAIL

Don't worry about the COMBO VALVE at this point. There is no adjustment.

What was the car doing that you felt it needed a replacement booster?

 

Uhhh ...

While the dual reservoir is an advance for safety, if there is an internal failure or if there is a catastrophic fluid loss in either circuit, that MC ain't gonna help you.

The reason for the PDV LAMP is to warn the driver if it sees a pressure imbalance from circuit to circuit. That informs the driver to slow down and drive it slowly to get it off the road.

The PDV PINTLE does not stop flow. It may interrupt it slightly but when opened will allow fluid from the sound side to transfer to the bad side. The pintle can also move when bleeding. There is a special service tool to prevent that.

 

READ THIS TECH ARTICLE - https://www.brakes-shop.com/brakepedia/general/brake-proportioning-valves

Are you a true TECH or just a hobbyist?

 

The divider in the master cyl reservoir leaves plenty of fluid for the "good" side of the system to still work.

The warning light switch does not permit fluid to transfer from one side to the other. Seals on both ends of the spool prevent that.

 

If the fronts lock and slide you will lose steering control and if the rears are still turning, the rear can come around (the rears still have traction whereas the front won't), especially on wet pavement. If the rears lock only, the rear can also come around.

The reason(s) for a METERING VALVE and a true PPV. An adjustable so-called PPV is not a PPV. Somewhere in the parts listing it will state not for a street driven car (is illegal), competition only.

That relieves them of liability if someone busts their a$$ and tries to sue them. Same for a true combination valve from who knows what application. It somewhat relieves the kit vendors liability if someone busts their a$$.

Remember, when you kit a car, you are not making a service repair, you are modifying the vehicle. Different states, different rules.

If it comes in a white cardboard box and there is a fortune cookie inside, leave it alone.

 

If the piston seals are not overcome or damaged. GIGGLE it. It is a safety feature not a fail-safe.

What seals?

 

The spring(s) in the MC are compressed on brake application and it/they return the piston(s) to rest if the system is installed/adjusted and functioning correctly.

You know, we had this same argument maybe one or two years ago. It's like Deja' Vue' all over again.