Do I need a bigger master cylinder

[Jason72Bronco]

All,
Thanks to all the help from this forum, I've completed the front disc conversion. Though the process I ended up replacing the master (twice) and all the lines.

I have a firm pedal, and I'm stopping nice and straight. However, the pedal travel to firmness is less than desirable, and the "stopping power" is not exactly confidence inspiring. I had expected better with the front discs.

I have a booster, and my master cylinder is 7/8 inch bore. During my install ordeal, some posters here commented that size bore might be a bit undersized for my application. I do have a proportioning valve.

Question: would going up to a 1" bore or larger make that much difference in stopping power? I suppose its logical that pushing more fluid earlier would also lesson the pedal travel to firmness?

Thanks, Jason

 

[bronconut73]

All,
Thanks to all the help from this forum, I've completed the front disc conversion. Though the process I ended up replacing the master (twice) and all the lines.

I have a firm pedal, and I'm stopping nice and straight. However, the pedal travel to firmness is less than desirable, and the "stopping power" is not exactly confidence inspiring. I had expected better with the front discs.

I have a booster, and my master cylinder is 7/8 inch bore. During my install ordeal, some posters here commented that size bore might be a bit undersized for my application. I do have a proportioning valve.

Question: would going up to a 1" bore or larger make that much difference in stopping power? I suppose its logical that pushing more fluid earlier would also lesson the pedal travel to firmness?

Thanks, Jason

Smaller bore will produce more pressure. That should feel strongest.

The larger bore moves more fluid but with less pressure. I like the bigger bore. It gave me a more confidence inspiring pedal feel.

Think of your water hose sprayer. When you decrease the size of the orifice it sprays further even though less water is coming out.

The best power will come from hydroboost. Many threads here on it. Most use Astrovan units.

 

[SteveL]

Are the front and rear lines correct on the mc? What size tire you trying to stop? Could be the pushrod adjustment from the bracket to the mc. I was never real happy with my power brakes even with 4 wheel disc. I finally swapped to hydroboost. . Stops the 35s on a dime

 

[sykanr0ng]

What size are your tires?

Vacuum power boosters work okay below 35" tires, above that most find hydroboost to be better.

That is a small master cylinder.

 

[Broncobowsher]

Is the booster even working?

As pointed out above, going to a larger master cylinder will reduce travel and make the pedal even firmer.

What are the rest of the brakes? Still all drums, disk/drum?

 

[Jason72Bronco]

I'm running 31X10.5 15, tires. 75% street use. New disc front, stock rear drums.
The comments from Broncbowsher and Bronconut73 are contradictory.
I'm not a hydraulic physicist, but brake fluid as a hydraulic does not act the same as water, in a physical compression sense.
IMO, the brake pressure of a properly functioning hydraulic system should not differ based on bore size of the MC. The bore would just change how much of the fluid is going to the lines/brakes for each fraction of an inch push on the MC.
Someone smarter than me tell me!

 

[nvrstuk]

Easiest explanation I've seen in a while... bore size makes all the difference

http://www.snaponindustrialbrands.c...-Hydraulic-Principles-and-Troubleshooting.pdf

Make sure you read page 4

 

[Apogee]

Your "problems" have opposite cures. If you want more brake torque, then you want a higher output pressure from the MC, so go with a smaller bore. If you want a higher, firmer pedal (less pedal travel), then you would want to increase the bore size.

Given your MC bore size, which is about 23% smaller than a 1" bore unit (Factory Ford disc/drum setup), I would expect 23% more pressure and 23% less pedal travel. Most wouldn't run a 7/8" unit even for manual brakes, and you're running it with vacuum assisted power brakes (and complaining of low brake torque), so per Bronocbowsher, is your booster working like it should? Have you tested it?

FWIW, bBrake fluid does act just like any other virtually incompressible fluid such as water in a hydraulic system, it just doesn't make a good brake fluid because of its relatively low boiling point and terrible corrosion inhibitor properties.

 

[Jason72Bronco]

Thanks for all of the advice. Upon review, I think I will go with a new booster/MC setup. (Heck, I've changed out everything else in the brake system, why not.) I see several of the sponsor vendors offers booster/MC setups. Anyone have a preference? I'm leaning toward either the TBP or BCbronco setup.

(In case you are wondering why don't I just get a new booster, get a 1" bore MC, etc., I'm tired of dealing with the setup I have, which is a "custom" job by a previous owner, consisting of a booster and MC from a 1980 Monza. I can't even find a booster in stock. I'd rather just drop the bucks on a Bronco-proven install.)

Jason

 

[Justafordguy]

I think getting a complete system from one of our vendors that is made for the later Disk/Drum EB is a good idea.