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Discussion Starter · #1 ·
My 64’ is running Granada front spindles with a conversion to 4 wheel disc-brakes. When dad and I did the conversion, we used a Geo Metro master cylinder, new lines etc. I believe we had to modify the stock brake pedal a bit but after doing this about 10 years ago I truthfully don’t recall.

Here is the problem; the brakes seem to lose pressure and the pedal travel is about 13 miles long before the brakes engage (slight exaggeration). I have to almost “pump-up” the brakes before they work and when they engage, the pedal is almost to the floor as if the travel is too long. Geometrically speaking, it seems the pedal, pivot etc. all seem to be right which leads me to believe this is a pressure issue. I have bled the brakes a few times with no difference in results. I was thinking that I maybe need a residual pressure valve in the line that supplies the rear brakes; does this sound right? Wondering if anyone here had similar issues and what they did to resolve this. Thanks.
 

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were they better before? or have they always been this way ? I would be looking at the master cylinder if this just started happening.

residual pressure valves are more of a rear drum brake thing..


p.s. are all your bleeders facing up ? Ive seen alot of calipers put on backwards. How are you bleeding them ? you might need to preasure bleed them .
 

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Discussion Starter · #3 ·
were they better before? or have they always been this way ? I would be looking at the master cylinder if this just started happening.

residual pressure valves are more of a rear drum brake thing..


p.s. are all your bleeders facing up ? Ive seen alot of calipers put on backwards. How are you bleeding them ? you might need to preasure bleed them .
This was the same from day one. I'm not sure about the bleeders; will look and see.
 

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I drove an early Mustang with the Geo PB unit, Granada front discs and stock rear drums. I actually liked the feel and travel, though they were a bit over-powered with the small MC bore. It was easy to apply too much brake until you got used to it. I could feel it begin braking at about 1/4 pedal, and lock the brakes up around 1/2 to 3/4 pedal. This means everything from light stopping to skidding happened in about 1/4 to 3/8 pedal or so.

I describe all this as a comparison for yours. How does yours act differently? With rear discs, your pedal throw should be about the same or a bit shorter to lock them up. Yes, the pedal throw is relatively long, but compared to other systems (like classic GM) you get more feedback rather than pressing harder or softer on a rock - if you see what I mean.

David
 

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Discussion Starter · #5 ·
I drove an early Mustang with the Geo PB unit, Granada front discs and stock rear drums. I actually liked the feel and travel, though they were a bit over-powered with the small MC bore. It was easy to apply too much brake until you got used to it. I could feel it begin braking at about 1/4 pedal, and lock the brakes up around 1/2 to 3/4 pedal. This means everything from light stopping to skidding happened in about 1/4 to 3/8 pedal or so.

I describe all this as a comparison for yours. How does yours act differently? With rear discs, your pedal throw should be about the same or a bit shorter to lock them up. Yes, the pedal throw is relatively long, but compared to other systems (like classic GM) you get more feedback rather than pressing harder or softer on a rock - if you see what I mean.

David
When the brakes are engaged (about 3/4 pedal travel before the floor) they work quite well. So far no lock-up issues but then again I have never really stood on them.
 

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Then, you have:

  • improper pedal ratio or
  • air in the system or
  • parts absorbing movement or
  • all of the above.
The first task would be to determine why it will not begin braking before 3/4 pedal. Where is all the pedal travel going? It could be absorbed by firewall flex, pedal rod length, booster rod length, brake hose swelling, air intrusion at cracks or fittings, trapped air, entrained air (from pedal pumping), front or rear system failed, excessive caliper piston retraction, caliper bracket flex, caliper misalignment, etc. Every part of the system should be examined for any contribution to pedal travel beyond normal.

The comment about bleed fitting placement is a very good one, and is a common problem. Some setups even require the calipers be removed from their brackets, and a block inserted (replacing the rotor width between the pads) and then rotated around various angles by hand to get all the bubbles up to the bleeder and out. Don't give-up. The answer is in there somewhere. If you can't find the culprit(s) fairly easily, then diagnosis with brake pressure gauges is in order.

David
 

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Discussion Starter · #7 ·
Then, you have:

  • improper pedal ratio or
  • air in the system or
  • parts absorbing movement or
  • all of the above.
The first task would be to determine why it will not begin braking before 3/4 pedal. Where is all the pedal travel going? It could be absorbed by firewall flex, pedal rod length, booster rod length, brake hose swelling, air intrusion at cracks or fittings, trapped air, entrained air (from pedal pumping), front or rear system failed, excessive caliper piston retraction, caliper bracket flex, caliper misalignment, etc. Every part of the system should be examined for any contribution to pedal travel beyond normal.

The comment about bleed fitting placement is a very good one, and is a common problem. Some setups even require the calipers be removed from their brackets, and a block inserted (replacing the rotor width between the pads) and then rotated around various angles by hand to get all the bubbles up to the bleeder and out. Don't give-up. The answer is in there somewhere. If you can't find the culprit(s) fairly easily, then diagnosis with brake pressure gauges is in order.

David
Sound advice for sure. I will have to go over every inch of the braking system to try and find this problem. I guess I didn't even think about caliper rotational placement I think they are at the 9 o'clock position but I am not sure about the bleeder. It's been a while but I want to say they are at the 10 o'clock position maybe? I need to look at it. Car is still in storage, waiting for the stupid weather here to change! Thanks!
 

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When positioning for bleeder function, keep in-mind that the bleeder location is not as important as the point the bleeder passage intersects the cylinder bore. This is why many Ford (and other brand) calipers are mistakenly installed on the wrong side, because (for example in one design) mounting the bleeder "up" traps air. When looking at your calipers, try to visualize the bore intersection point. HTH

David

 
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