Members with 4 wheel disc systems.....Can you get the tires to skid?

[Kern Dog]

Did you try a bendix dual diaphragm brake booster yet?

No, I haven't. I am considering it though.

 

[Kern Dog]

I agree it will need more pressure, a front brake hold off valve as way to get the rears on slightly ahead of the fronts to transfer weight, and once it will skid either an adjustable proportioning valve. How to get the pressure up is the hard part. I would not gut or eliminate the warning light permanently on a street driven car for legal reasons if anything ever would happen.

The warning light is pointless, in my opinion. At the point where it would light up, any intelligent person would already know due to a low pedal anyway.
I have several of those drum-drum blocks to work with anyway.

I could probably get both cars out on a road with a friend driving Jigsaw....then do a series of side by side panic stops to see how they compare.
I'm not letting someone else drive the red car this way!

 

[4406bbl]

I am saying if you crash and someone gets hurt it could be a legal issue.

 

[Kern Dog]

The exploded view of the 68 and later A body 4 wheel drum distribution block:

From the bottom…
End cap
Tension spring
Collar
Shuttle valve. Warning switch to the right.
Collar
Tension spring
To get it apart, the end cap comes off. Some are 1/2”, some are other sizes.
The warning switch is 5/8”. It comes out. The lower spring should fall right out. The lower collar needs needle nose pliers. The rest had to be pushed from above.
I used a #8 trim screw.

Threaded into the input passage at the top.

It pushed the top collar down enough to get leverage on the shuttle valve through the warning switch hole.

Now I need to soak this block in something.
Any suggestions?

I’m going to try this:

 

[4406bbl]

Muscle Car Research sells the o-ring kit for those and says to soak the parts in ammonia. He has how to articles on his site.

 

[Kern Dog]

Ammonia.
I’ll make a note of that. You don’t get put on a watch list if you buy 100 gallons of it, do you ?

The vinegar took the gunk out from what I can tell.

 

[Kern Dog]

I am saying if you crash and someone gets hurt it could be a legal issue.

Thank you.
The brakes are in no way “dangerous”, they just aren’t the best that I have felt.

 

[1 Wild R/T]

Rather than gutting the valve replace both springs with solid blocker rods... If you gut the valve you lose dual isolated systems & the switch isn't designed to handle that kind of pressure..
It'll take a little measuring with something more accurate than a carpenters tape measure but I think you got this... LOL

 

[6872n73]

If I were walking in some dog shoes...
I would check pressures on all four corners with a vacuum pump running. It would also be cool if you could check the pressure on your brake pedal with maybe a bathroom scale?
Then check all the pressures again with no vacuum pump and the booster unhooked.
Then install the gutted distribution block and check pressures again with roughly the same pressure on the brakes.

 

[Kern Dog]

Rather than gutting the valve replace both springs with solid blocker rods... If you gut the valve you lose dual isolated systems & the switch isn't designed to handle that kind of pressure..
It'll take a little measuring with something more accurate than a carpenters tape measure but I think you got this... LOL

I already gutted one. I have not swapped it in though.
The switch could be replaced with a brass plug like the one on the bottom of the block. It didn't occur to me that fluid pressure could get past it.
The other way to go is to simply plumb the system without a common "manifold" block.....MC lines directly to the front left and right and the rear line.
I'm curious what difference there would be between plumbing both MC lines to a common open on the inside distribution block versus plumbing the front and rear apart from each other.

 

[1 Wild R/T]

I already gutted one. I have not swapped it in though.
The switch could be replaced with a brass plug like the one on the bottom of the block. It didn't occur to me that fluid pressure could get past it.
The other way to go is to simply plumb the system without a common "manifold" block.....MC lines directly to the front left and right and the rear line.
I'm curious what difference there would be between plumbing both MC lines to a common open on the inside distribution block versus plumbing the front and rear apart from each other.

With the dual isolated system if you have a leak you only lose the brakes on one end of the car...
Allow a passage between them & it's 1965 all over again... And considering your comment earlier about anyone with a brain should know, well obviously you've never had a failure on an earlier car cause when there's only one system & you have a leak there's no warning, the brakes work then suddenly they don't....

 

[Kern Dog]

Yeah, I did think of that.
I figured that with todays parts, failures are far less likely.
Maybe the better route would be the totally isolated system. Front to front, rear to rear. That would truly leave one end functional if the other end has a failure.

 

[1 Wild R/T]

Yup, use a couple inverted flare couplers & see what that gets you... I think three of the four tube nuts are regular 3/16 inverted flare tube nuts & one is special maybe 1/2" I think Napa has/had a fitting to do it..

 

[Kern Dog]

I bought these just after Christmas....

The T is for the front. It has 3 fittings of the same 7/16" size. I'd have to change the MC line to put the 7/16" tube nut on it.

This union coupler is simple. The MC line can just be attached directly to the rear brake line with this.

 

[1 Wild R/T]

Is it done yet? What's the hold up?

 

[Runner 68]

The exploded view of the 68 and later A body 4 wheel drum distribution block:
View attachment 1414980
From the bottom…
End cap
Tension spring
Collar
Shuttle valve. Warning switch to the right.
Collar
Tension spring
To get it apart, the end cap comes off. Some are 1/2”, some are other sizes.
The warning switch is 5/8”. It comes out. The lower spring should fall right out. The lower collar needs needle nose pliers. The rest had to be pushed from above.
I used a #8 trim screw.

View attachment 1414981
Threaded into the input passage at the top.

View attachment 1414982
It pushed the top collar down enough to get leverage on the shuttle valve through the warning switch hole.

Now I need to soak this block in something.
Any suggestions?

I’m going to try this:

View attachment 1414984

Vinegar is the most under rated acid / solvent in our hobby. I use it on everything. Mild but give it a little time and it works wonders. Go for it.

 

[Boris7K]

Has anyone ever tried a 7/8" bore M/C with the Dr Diff 13" and 11.7" combo? I'm curious if that might make it better.

 

[68 Sport Satellite]

you mean with power brakes? I haven't, but something to keep in mind is it will make the pedal travel much lower to the floor (with less effort also).

 

[jag_mopar]

From the "glaringly obvious" department:
1. Disc brakes were originally thought by engineers to be preferable to drums because the design
inherently resists locking up better than drums.
2. Modern tire compounds, especially those of some performance brands, are formulated for maximum
grip - i.e., resistance to losing contact with the road surface.
I'd imagine the same qualities that make them so darn good at not sliding going around a corner also
makes them darn good at not sliding under braking, eh?

the wider the tire, the less prone to skidding, more grip to the road will force the rotor not to lock but come to a quick stop

 

[68 Sport Satellite]

the wider the tire, the less prone to skidding, more grip to the road will force the rotor not to lock but come to a quick stop

On dry pavement, yes. Not so in the wet or snow. Not sure if this explains KD's lack of braking power.