Trying to diagnose my brake issue

I am trying to figure out a problem that I am having with the brakes on my Coupe that I picked up over the winter. When driving at any speeds above 5mph the brakes seem to work correctly. When traveling at 5 mph or so it seems that it takes A LOT of pressure on the pedal to get the car to come to a complete stop. Also, to hold the car stopped at a red light or stop sign requires me to stand pretty heavy on the pedal. Other that the slow speed issues the brakes feel pretty good. I bled them out and didnt get any air out of any of the bleeders. The dual reservior master cylinder is new (as per the previous owner). The front brakes are 46 Ford drums. The rear drums are out of a 70's Ford Maverick. The master cylinder is mounted under the dash at 90 degrees to the pedal.

Any ideas, or suggestions on what is happening and where to start troubleshooting? Thanks.

 

Sounds like EITHER the pedal ratio (GOOD should be a ratio between 5:1 and 6:1) is TOO low, or that the master cylinder bore is too large, as compared to the wheel cylinder bores, and possibly a combination of BOTH symptoms. DD

 

try swapping the lines on the M/C. The wife falcon was like that and switching the lines cured it.

 

The lines going to the rear are a smaller diameter than the ones going to the front. I can swap them at the master cylinder without an issue since the appropriate reducer is already on the line. Swapping the lines gives me a chance to re-bench bleed the master. We'll see.

 

Different diameter lines won't make a difference...pressure is pressure! Different size master cylinder BORES (front/rear) could make a difference. DD

 

Thanks guys for your tips. I have no idea what master cylinder was put in prior to me getting this car so I don't anything about the bore sizes. If I am understanding each of you, swapping the lines is a good place to start? Also, how do I determine the pedal ratio?

 

http://www.mpbrakes.com/uploads/documents/pedalratiopdf.pdf
brake pedal ratio...................

 

The usual m/cy used these days is a Corvette type.... Use the smaller bore, for non power setups.

4TTRUK

 

IF using '47 brakes on the front you may have to readjust them. It's a bit tricky, not like newer style self energizing. But I'd go towards M/C size. Also are you sure front and rears are both actually operating?