Technical Help with Brake Combination Valve Question

My only argument with what Steve posted is mostly semantics but proportioning valves don’t reduce pressure to the rear they slow the pressure rise in relation to the front.

In addition I’m not in anyway questioning the AMC application, I would like to see documentation.

 

Sending you a PM...

 

You have that backwards Steve. Early rear slide can cause loss of control. You want the fronts to always slide first.

 

I have worked on and taught hydraulic brake systems for many years. While there may actually be a valve setup that does block one system or the other, I've never seen one. Take a look at the diagram I've posted. Note that the failure switch is located between the front and rear inlet ports on the combination valve. The ends of the valve that operates the switch are undercut so that even when the valve moves to one side or the other, fluid flow from either inlet or outlet port is not blocked. Also this valve only moves (operating the warning switch) when there is a failure in either the front or rear brake hydraulic system. A failure means that the fluid is either leaking out or already has. The real fail safe is the fact that you have a dual master cylinder. It will still operate the system that hasn't failed.

I can also state that many cars are running around with the valve moved to one side or the other because it was never reset during a brake job. Both the front and rear brakes operate normally when this happens. I've reset many of them.

 

You are correct. I mis-wrote that.

The AMC product I worked on had an odd-ball valve, it was laid out differently for some reason. I'll admit it's the only one like that I've seen, but I did see it....

 

Crazy Steve is a good man to have on our team. Wish I could type with all 4 fingers, I would have put down much the same info. I'm just a Hunt-n-Pecker 2 finger kind of guy. Wish I could give him 4 likes for post #27. Spot on pal!

 

Some observations I made earlier today
1. With the engine off I can rotate the front wheels freely not feeling too much resistance (I'm assuming I still have 2 psi in the system from residual valve)
2. When I turn the engine on I don't notice any difference when I spin the front wheels.
3. With the engine on when I press on the brake pedal the fronts were totally locked up.
4. When I release and let the pedal come back to normal I can feel resistance on the front wheels, it didn't go away completely even after a couple minutes.
5. When I turn the engine off the resistance goes away quite slowly.
6. Leak still there right where the fitting goes in to the Wilwood 10 psi residual valve. I ordered a new one which comes with two fittings.

 

Those are way too complex, best suited for where they are designed on an OEM application. I have a CPP style distribution block on my car with a combo valve. The valve is wide open in my case, the car stops very well. Couple that with the residuals you may need and call it done.

 

I'm more interested than most in the design/implementation as I had the experience of total brake failure when the front brakes lost all fluid due to a rusted line.

Odd situation though, little Mitsubishi cabover truck. Brakes were 4 piston disk upfront (actually 4 single piston calipers), drum rear with a load sensing valve in the rears. When the line bursts I had no brakes at all! Fortunately it happened in a parking situation so no harm was done. The truck was lightly loaded and the valve wasn't depressed.

I know on that one the open port was not sealed a all of the fluid left, quickly, if the shuttle really sealed some of the fluid would still be in the reservoir.

 

Just finished fixing the leak here's an update:

1. I installed the new 10 psi residual valve for the rear drums.

2. I flushed the fluid entirely and bled the brakes.

3. I then bled the brakes twice carefully I did this carefully two entire times for each wheel going passenger rear, driver rear, passenger front, to driver front.

4. Re-checked and no more brake leaks. I went through 2 one quart Dot3 bottles to flush and bleed.

5. Adjusted the rear shoes.


With it on jackstands, and the engine on the brakes lock up.

 

The booster pin sounds kinda wrong. Are you measuring it correctly? The tool to do it looks to make it easy, otherwise its straight edges and vernier. Easy enough to do but easy enough to mess up! There shouldn't be any preload.

The rod to booster clearance is more of a feel the clearance affair, than measure.

Chris

 

Thanks yep used a straight edge and digital calipers that have an end to measure depth. Did this many times and drew the geometry on paper to do the calculations.

 

I wasted so much time trying to diagnose the issue. For one the TuffStuff booster I got from someone on ebay who listed it as new was never used but was 5 years old. I found this out later after conversations with the seller. The only reason I bought this one was in November all of the TuffStuff boosters were out of stock with estimate of being available in January.

I took the booster out and compared it to my old one. With the old one when I press in on the pedal side it comes right back out instantly. With the TuffStuff one when I press in its a bit slow to come out. I suspect it sitting for the 5 years is the cause of this behavior.

 

The pedal needs it's own return spring to fully return. Do not rely on the booster, or master cylinder in a manual system, to properly return the pedal.

 

yep! I have a return spring that brings the pedal back but isn’t strong enough to make the booster come back to resting state quicker… it’s still coming back slow from resistance caused by the booster. my old booster returns instantly.. the replacement tuffstuff booster I bought on eBay is very slow to respond…

 

Found my paperwork from Masterpower Brakes if it's any help to anyone

 

The correct identification of that picture is a combination valve, that includes a proportioning valve, front metering and pressure differential. Typical of some brake suppliers that sell stuff they really don't know much about.

 

Do you have someone locally that rebuilds masters and or boosters? I have one close to me I have used on hard-to-find boosters, like om my '68 Mustang with the Kelsey Hayes discs up front.

I have seen many a post on brake issues with "corvette style" masters. I use a Ford dual master on my car, I can get a replacement anywhere and I know it will work.

 

hmmm so I may be better off buying a new tuffstuff booster and getting a ford master that hopefully adapts to it?

 

These brake guys near SD get good reviews:
https://m.facebook.com/people/Bush-Power-Brake-Inc/100027228866906/

https://m.yelp.com/biz/bush-power-brake-inc-national-city

 

Abs brakes in Orange, ca, rebuild boosters and masters as well as supplying everything for brakes including custom applications / conversions. Worth checking out. Not too far from you! They used to be ever present at the Long Beach swap, but it's been a while since I was there.

Chris

 

This only begs the question is the original booster (unknown brand... could be chinese junk) and the master (unknown brand could also be chinese junk) worth having rebuilt? I thought about just getting a CPP kit that has both. hmmm.

 

You could have the suggested shop look at it, give their opinion on if it can be saved. I only use OEM type masters from parts places.

 

IF you stay with a booster, move to a dual 7" or 8" and ditch the single pos 7 as I previously stated. The big question I have is, do you really need a booster?
My '40 is disc/drum, weighs about 3400 lbs empty and stops great with no assist. The roadster tops around 3000 lbs loaded with two people, again with manual disc/drum. The '51, in the same weight range, will stay manual when converted to disc/drum.
There were many mid sized disc/drum vehicles in the late '60s/'70s that ran manual brakes (with boost optional) and performed very well.

 

thanks mine is a dual 7”. That is a good point about maybe not needing a booster.

 

Don't remember seeing this addressed. It would seem to me that the two ports for the front brakes have the valve to prevent application of one front while the other has failed. You would not want one front brake to apply if the other wasn't working as it would cause a loss of control when applied very hard.

Your setup where you are using one port would seem to want to cause that same thing to happen, because there is little or no resistance available in the second port.

If the statement I just made is incorrect, and the front brakes work fine using one port and one front brake line that later splits into two lines.........then it would seem that you would be no worse off than if one side failed when both ports are used. If one side leaked fluid and began not working the other side would not have pressure either............

Now thats all supposition on my part.......but it seems to make sense (IMHO) but I been wrong before.

Maybe this diagram for a 32 will help decide.

 

No valve separating the front two ports, if one side leaks the other won’t apply anyways, silly Pascals law!

since the combination valve is typically up front it’s a convenient place to tee the front lines.

 

Thanks.. I'm going to leave as is, unless someone tells me I have a dangerous situation (which I doubt). I didn't build this car and I don't know who did. I will change the booster M/C with something else... probably a CPP kit (still thinking about it)

 

Disc brakes do not have a retraction mechanism. During normal driving slight movement of the rotor pushes the brake piston back. What you are describing sound to be normal operation.

 

Hmmm, right but when on the bench comparing my old booster to the "new" TuffStuff booster I got on ebay, the old one returns fast when pushed in. The new one is noticeably slower to return. The TuffStuff booster sat for 5 years according to the previous seller which makes me wonder if its any good and maybe the internal rubber got stiff in that time causing it to return slow.