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

[6872n73]

Out the back into the booster?

 

[Fran Blacker]

Vacuum pump reservoir if not the booster?

 

[Kern Dog]

I have looked but will have to look closer.
As I was bleeding the system out, the rear calipers pushed clear fluid.
When I changed from the Cordoba 11.75" front brakes to the Dr Diff 13" front brakes, I switched from DOT 3 to DOT 5 fluid. DOT 5 is a purple color.
I thought that I bled the system enough to get all the DOT 3 out but apparently I didn't. There was still some DOT 3 in the rear calipers. I bled it today until all four calipers pushed clean purple fluid. The DOT 3 and DOT 5 cannot be mixed. Doing so results in a mushy pedal with greater travel.

With each step, it feels like the brakes improve a slight amount. I did several hard stops from 60 mph down to about 10-15 mph and the bite got better and better. Pedal travel is acceptable. It stops hard enough to stall the engine even with the floats set correctly.

I intend to compare the braking alongside the Wife's car. It is a 2015 Challenger R/T.
It isn't that the brakes are bad, just that they should be better.

 

[1STMP]

Hey, KD
With no visible leaks In the brake system, and both MC
reservoirs were full when you started your test drive,
the only place for the fluid to go is thru the piston
seals in the MC, or the rear wheel cylinders or brake
lines still had some air trapped.
Is the rear reservoir in the MC over full?
Also, when checking line pressures, if you have
a proportioning valve (manual or adjustable), the
manual valve should be removed or the adjustable
cranked to wide open so there's no flow restriction.

 

[Kern Dog]

I don't know if the MC was full before the drive. It was full a few months ago when I bled it last but I haven't checked it since. These aluminum master cylinders have reservoirs that are not completely separate. The divider between front and rear has a slot in it that stops about halfway from the bottom to the top, meaning that fluid moves between the front and rear until it drops below the open slot.
Today before I left, I pressed the parking brake lever 15-18 times. 1 Wild R/T Randy said that this moves the rear caliper pistons out in these Ford calipers. I thought that this may take up some of the slack in the pedal travel. Braking feel was much better until it wasn't.

 

[1STMP]

I don't know if the MC was full before the drive. It was full a few months ago when I bled it last but I haven't checked it since. These aluminum master cylinders have reservoirs that are not completely separate. The divider between front and rear has a slot in it that stops about halfway from the bottom to the top, meaning that fluid moves between the front and rear until it drops below the open slot.
Today before I left, I pressed the parking brake lever 15-18 times. 1 Wild R/T Randy said that this moves the rear caliper pistons out in these Ford calipers. I thought that this may take up some of the slack in the pedal travel. Braking feel was much better until it wasn't.

Can you shoot a pic of the fluid level
in the front reservoir vs the bottom of
the slot? (unless you've already refilled
it). In theory, the fluid levels should be
the same even if there is a fluid loss,
But the lower level in the front reservoir
seems to me that the rear circuit is
where the problem lies.
When bleeding the lines, are the
calipers rotated to where the bleeders
are at the very top?
I removed mine from the caliper
bracket, rotated the bleeders straight
up and used a piece of plywood in
place of the rotor. With the calipers
on the plywood, it allows for rotation
of the caliper to try an work out any
trapped air. Some can be stubborn.

 

[Kern Dog]

Can you shoot a pic of the fluid level
in the front reservoir vs the bottom of
the slot? (unless you've already refilled
it). In theory, the fluid levels should be
the same even if there is a fluid loss,
But the lower level in the front reservoir
seems to me that the rear circuit is
where the problem lies.
When bleeding the lines, are the
calipers rotated to where the bleeders
are at the very top?

My head was in my *** again. I had things backwards.
The front reservoir was empty, meaning the rear brakes went dry. The rear reservoir still had maybe 1/2" of fluid in it.
Maybe pressing the parking brake did pull fluid from the master cylinder because the pedal travel was a LOT shorter afterwards.

The bleeders are all aiming up at the highest point that they can. The MC is topped off now but tomorrow I can take a picture of a spare Master Cylinder to illustrate the internal slot.

 

[1STMP]

"The bleeders are all aiming up at the highest point that they can"
Is this in the installed, or in the
removed and rotated to the
highest point position during the
bleeding process?
With that much fluid disappearing from
the MC, it sounds like you've still got
a lot of air in the system, especially
if there are no visible external leaks.

 

[funknut]

Here are a few combinations that I've tried:
11" front disc 2.6" caliper, 10" rear drum. 1975 A body brake booster. Disc/drum proportioning valve.
12" front rotor, 2.6" caliper, 10" drum. 1975 A body brake booster. Disc/drum proportioning valve.
12" front rotor, 2.6" caliper, 11.7" Dr Diff rear discs with 1.5" single piston caliper. 1975 A body brake booster. Disc/drum proportioning valve.
12" front rotor, 2.75" caliper, carbon metallic pads. 11.7" rootr with 1.5" single piston caliper. 1975 A body brake booster. Disc/drum proportioning valve.
Same as above without booster but with 15/16" iron, 15/16" aluminum, 1 1/16" and 1 1/8" manual master cylinder. Disc/drum proportioning valve.
12" front rotor, 2.75" caliper, 11.7" rear rotor, 1.5" single piston caliper, drum drum distribution block, 1975 A body brake booster, modified pedal for increased leverage.
13" front rotor, twin 1.58" piston calipers, 11.7" rear rotor, single 1.5" caliper, drum-drum distribution block. Hydroboost unit with 1 1/8" master cylinder.
13" front rotor, twin 1.58" piston calipers, 11.7" rear rotor, single 1.5" caliper, drum-drum distribution block. 1 1/8" manual MC.
13" front rotor, twin 1.58" piston calipers, 11.7" rear rotor, single 1.5" caliper, drum-drum distribution block. 15/16" manual MC.
13" front rotor, twin 1.58" piston calipers, 11.7" rear rotor, single 1.5" caliper, drum-drum distribution block. 1975 A body booster, 1 1/8" MC.
13" front rotor, twin 1.58" piston calipers, 11.7" rear rotor, single 1.5" caliper, drum-drum distribution block. 1975 A body booster, 15/16" MC.
13" front rotor, twin 1.58" piston calipers, 11.7" rear rotor, single 1.5" caliper, drum-drum distribution block. 1975 A body booster, 15/16" MC, electric vacuum pump.
Now the current setup is:
13" front rotor, twin 1.58" piston calipers, 11.7" rear rotor, single 1.5" caliper, drum-drum distribution block. 1975 A body booster, 15/16" MC, electric vacuum pump and storage tank.

Yeah....I have tried LOTS of combinations.

I just started digging into this thread, so apologies if I miss a few things.

I had a 1-1/8" MC with hydroboost, had issues with the HB booster, removed it and went to a 7/8" bore to use for manual brakes. Braking performance is still not what I would call inspiring, but it is acceptable for now. I plan to rebuild the HB soon and hopefully get back to better brake performance.

I'm not sure how much smaller bore MCs can be had, but the research I've done says 1200 PSI at the caliper is on the low end of 'good' and the top end is 1800-2000 PSI. I never measured the PSI when the hydroboost was working, but I have the testing kit now and will do a before/after when I swap it back in.

You have quite the mystery with the fluid disappearing. Good luck!

 

[68 Sport Satellite]

I've also heard that DOT 5 fluid is much more difficult to bleed than DOT 3 due to the viscosity.
I wonder if you might have an easier time if you install Russel Speed Bleeders.

 

[Fran Blacker]

I've also heard that DOT 5 fluid is much more difficult to bleed than DOT 3 due to the viscosity.
I wonder if you might have an easier time if you install Russel Speed Bleeders.

Put them on the rear of my Satellite worked well. Had my helper push and release brake pedal slowly. Seemed like a good idea but may not be necessary. I watched for bubbles in the clear tubing on bleeder, after a few pumps no bubbles.

 

[68 Sport Satellite]

Put them on the rear of my Satellite worked well. Had my helper push and release brake pedal slowly. Seemed like a good idea but may not be necessary. I watched for bubbles in the clear tubing on bleeder, after a few pumps no bubbles.

I installed speed bleeders on my car front and rear and the instructions say it's a one-man operation - place catch hose/container over bleeder port, crack open the bleeder, jump in the driver seat and pump the brake pedal 5 times, jump out and close bleeder, move to next one.

 

[Kern Dog]

For the past 8-12 years, During bleeding, I have placed a clear surgical hose over the bleeder nipples. This keeps the floor clean and allows me to observe the flow.

 

[Fran Blacker]

I installed speed bleeders on my car front and rear and the instructions say it's a one-man operation - place catch hose/container over bleeder port, crack open the bleeder, jump in the driver seat and pump the brake pedal 5 times, jump out and close bleeder, move to next one.

Agree one man job but first time I used them. Had rear diff out.

 

[70ChargerRT]

For the past 8-12 years, During bleeding, I have placed a clear surgical hose over the bleeder nipples. This keeps the floor clean and allows me to observe the flow.

I feel so stupid. All my life I’ve been squirting brake fluid everywhere when bleeding my brakes and then Baer puts a bleeder hose in their brake kits just for this.

 

[68 Sport Satellite]

I feel so stupid. All my life I’ve been squirting brake fluid everywhere when bleeding my brakes and then Baer puts a bleeder hose in their brake kits just for this.

I made my own with a 2 gallon plastic jug. Drilled 2 holes into the top cap and inserted 2 clear pieces of vinyl tubing all the way to the bottom with about 18 inches above the cap for each piece of tubing so the jug can sit on the ground. This allows hook up of both of the two top bleeders on my front disc calipers to bleed at the same time.

 

[Kern Dog]

FINALLY I made the order through Dr Diff.....
1966-70 B body dual diaphragm brake booster, firewall stiffening plate and under-dash linkage.

This will sit down lower than the A body unit I have on the car now which means new brake lines to the distribution block.
I am unsure of which master cylinder that I'll use. I have a 15/16" in the car now. Pedal travel with smaller bore master cylinders is always a bit longer but supposedly the pressure is higher. I have other size master cylinders including the new 1 1/8" unit I bought for use with the hydroboost unit that I never was able to get working.

 

[Mackman]

FINALLY I made the order through Dr Diff.....
1966-70 B body dual diaphragm brake booster, firewall stiffening plate and under-dash linkage.

View attachment 1503338

This will sit down lower than the A body unit I have on the car now which means new brake lines to the distribution block.
I am unsure of which master cylinder that I'll use. I have a 15/16" in the car now. Pedal travel with smaller bore master cylinders is always a bit longer but supposedly the pressure is higher. I have other size master cylinders including the new 1 1/8" unit I bought for use with the hydroboost unit that I never was able to get working.

Hope it works out.

 

[Kern Dog]

I started on the booster swap today.
The A body stuff came out easy enough.

 

[1STMP]

Cool. Curious as to the outcome.
I know you've tried many combos.
Please keep us posted.