4wheel disk

[GRAMSCAR]

I did a disk brake conversion, all 4, and my pedal is extremely hard. I can barely press it and get no movement, barely stops the car. I have gone through three master cylinder’s and two, three if you count the original, boosters with no change. I have bled m/c and calipers numerous times with no change. Help!! Been fighting this way to long.

 

[Aron Gleason]

What's the bore size of the Mc? Power or manual brakes. Manual uses a 15/16 bore.

 

[33 IMP]

Dump the power booster, get the right size manual master. (At least, that's what I would do. )

 

[j-c-c-62]

On a related note for those on the sidelines, 4 wheel disc conversions are needed IMO only in these applications:

1. You are converting to 4 wheel ABS
2, You are racing, and only in some applications
3. you want to impress clueless friends
4. You want to spend money

Front Disc conversions are not included in this list.

 

[Kern Dog]

Dump the power booster, get the right size manual master. (At least, that's what I would do. )

Good luck with that....
I went with rear discs for appearances. Seeing a 10" drum through the rear spokes wasn't what I wanted. A front disc/rear drum system is an excellent setup but a 4 wheel disc system is better for achieving balance in the system.
I've tried manual master cylinders in my car and it was crap. Even with a 15/16" MC, the pedal effort was high and the braking force was inadequate. To make the pedal effort lighter, I'd have to step down in bore size which would have the effect of longer pedal travel.
The OP needs to determine if the boosters he has tried are actually able to hold vacuum and are adjusted correctly. The pushrod inside the booster that contacts the master cylinder does need some slight free play but not too much:

 

[33 IMP]

My manual four wheel disc's in my Tina was a complete mixboxil mess, and it stopped great from 135.
In the eighth, it stopped two hundred feet shorter from 108, than my 62 did from 95, (with four wheel drums, I admit).
Manual four wheel disc's in my Opel too.
Of course, neither car with disc's has any room for any kind of booster, even if I wanted one.

 

[fourgearsavoy]

I did a disk brake conversion, all 4, and my pedal is extremely hard. I can barely press it and get no movement, barely stops the car. I have gone through three master cylinder’s and two, three if you count the original, boosters with no change. I have bled m/c and calipers numerous times with no change. Help!! Been fighting this way to long.

Do you have enough vacuum to pull the diaphragm? Have you changed the check valve with the boosters? These are the usual suspects for a hard pedal with power brakes.
Gus

 

[fourgearsavoy]

On a related note for those on the sidelines, 4 wheel disc conversions are needed IMO only in these applications:

1. You are converting to 4 wheel ABS
2, You are racing, and only in some applications
3. you want to impress clueless friends
4. You want to spend money

Front Disc conversions are not included in this list.

I guess that is your opinion and that's fine.
I put Wilwood brakes on front and rear of my Savoy the brakes have never been better.
Lost almost 80 pounds of weight.
Less rolling resistance
Pulls the car down from 125 at the strip with very little pedal effort. I can use the first turn off where I used to need the second or final turn with drum/disc setups.
Just better in every aspect in my particular case.
Gus

 

[j-c-c-62]

You changed it appears many factors in your brake swap, making it not an apples-to-apples comparison.
I don't dispute what you changed, nor the end result you shared above, my opinion differs mainly in the why.
One fact usually overlooked, the rear brakes in a hard stop only provide approx 30% of the stopping force, meaning if the front brakes were effectively a 1 to 1 swap (which I seriously doubt), your original rears must have been in really poor condition to see the improvement (besides pedal effort, which is mainly a design issue) you share.

 

[Kern Dog]

The stiffer the suspension, the less brake dive you will see.
Cars built for handling will have stiffer suspensions.
Apples and watermelons but this truck:

...wore out the rear pads at 119,000 and the fronts at 126,000. Yeah, the rears went first. I only hauled my work tools which added up to maybe 300 - 400 lbs.
Andy Finkbeiner states that a 4 wheel disc system needs to have an approximate 2 to 1 brake ratio. To get there, you'd need caliper sizes and rotor sizes that get you there. For example, if you have the same size rotors up front as out back AND your caliper piston surface areas are twice as much up front as out back, you're in the right place.

 

[j-c-c-62]

A perfect brake set-up is when in 101+% braking application, all four tires lock up at the same time, anything else is not ideal. the beauty of that ideal test, it is of the entire system, tire pressure, tire grip, alignment, aero, weight balance, brake balance, pad temp and pad reaction time, etc , etc. In the real world the goals are different.
Brake dive really does not significantly effect braking performance, ie weight transfer to any significant degree straight-line unless there is an aero DF component effecting body rake, or the amount of dive is gross. Depending on COG, it might move at the most 1/2"? forward. ignoring fuel slosh.
Brake Dive does effect handling because its effectively moving a mass that takes time, has momentum and achieves little that is desired. Weight transfer forces occur in braking regardless of the amount of visual dive observed.
This maybe getting into the weeds, but it all has merit while we chase the dragon.

 

[j-c-c-62]

The stiffer the suspension, the less brake dive you will see.
Cars built for handling will have stiffer suspensions.
Apples and watermelons but this truck:

View attachment 1704910

...wore out the rear pads at 119,000 and the fronts at 126,000. Yeah, the rears went first. I only hauled my work tools which added up to maybe 300 - 400 lbs.
Andy Finkbeiner states that a 4 wheel disc system needs to have an approximate 2 to 1 brake ratio. To get there, you'd need caliper sizes and rotor sizes that get you there. For example, if you have the same size rotors up front as out back AND your caliper piston surface areas are twice as much up front as out back, you're in the right place.

I have a 2004 Tacoma auto ABS bought new, that I drive in Florida, it's been known to tow 5000lb concrete blocks, it has 550,000+ miles, rear drum brakes are original. Go figure?

 

[33 IMP]

I have a 2004 Tacoma auto ABS bought new, that I drive in Florida, it's been known to tow 5000lb concrete blocks, it has 550,000+ miles, rear drum brakes are original. Go figure?

How many front pads?

 

[j-c-c-62]

How many front pads?

And rotors? Lost count.

 

[1STMP]

On a related note for those on the sidelines, 4 wheel disc conversions are needed IMO only in these applications:

1. You are converting to 4 wheel ABS
2, You are racing, and only in some applications
3. you want to impress clueless friends
4. You want to spend money

Front Disc conversions are not included in this list.

If the desired results of switching to 4 wheel disc brakes
meets the criteria below, it's well worth the effort.
Chrysler was the first domestic automaker to offer four-wheel discs, and the year was 1949. Installed on a close
to 4 ton behemouth.

Advantages to a 4 wheel disc brake system​

• Consistent Stopping Power: Disc brakes provide superior and consistent stopping power, especially in high-speed or heavy-duty applications, due to effective heat dissipation and reduced brake fade.
• Shorter Stopping Distance: Disc brakes are designed to provide shorter stopping distances, making them ideal for vehicles that require rapid deceleration, such as those used in off-road or emergency services.
• Improved Performance in Adverse Conditions: Disc brakes perform well in wet, muddy, or icy conditions, as the rotor’s surface area and the caliper’s design allow for better heat dissipation and reduced brake fade.
• Easier Maintenance and Service: Disc brakes are generally easier to service and maintain compared to drum brakes, with fewer components and simpler pad replacement procedures.
• Customization Options: As disc brakes are visible and aesthetically appealing, they offer customization options for vehicle appearance and performance enhancements.
• Better Suitability for High-Performance Vehicles: Disc brakes are commonly used in high-performance vehicles, as they provide the necessary stopping power and control for aggressive driving.
• Improved Safety: A 4-wheel disc brake system provides even braking performance across all four wheels, enhancing overall vehicle safety and stability, particularly in emergency braking situations.

This is on a custom built tube chassis where GVW is below
3100 lbs. The front calipers are from a Ford Granada, the
rears from a Jeep Wrangler. Definately not a kit.
Chassis was originally designed for the strip but
since changed course to street use. Chose the
Jeep rears due to the intrigal emergency brake.
2 lb residual check valves and a adjustable
propotioning valve to the rear. MC is from a 1985
Dodge Diplomat (1.032) bore, Chrysler Newport
dual diaphram booster. Brake fade near zero,
pedal feel is great. Flat, level, four wheel lock-up
under emergency braking.
I'll side with @Kern Dog on this one. Almost
all manufacturers have gone to 4 wheel disc
systems for reasons afforementioned.
Many have made the conversion with satisfactory
results, which you try and define as a wasted effort.

 

[1STMP]

I did a disk brake conversion, all 4, and my pedal is extremely hard. I can barely press it and get no movement, barely stops the car. I have gone through three master cylinder’s and two, three if you count the original, boosters with no change. I have bled m/c and calipers numerous times with no change. Help!! Been fighting this way to long.

Here to try and help.
When bleeding the calipers...
you may have to remove the
calipers and rotate them to
where the bleeders are at
their highest point. You can
use a piece of wood roughly
the same thickness as your
rotors for piston
engagement. If the bleeders
are lower than the top of the
calipers, some air will be
trapped in the system.
Bleed right rear first, left
rear second, passenger side
front, third, drivers side front
last.
Check brake pedal push rod
clearance to master.
Check to make sure there
are no residual check valves
in the master cylinder ports.
Without us being there, we
can only react to info
provided.
Please provide brake pedal
info as to wether or not it
includes a bellcrank that
compensates for pedal
ratio.