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Expert
Posts: 2196
  
Location: Muskego, WI | I've upgraded the brakes on my 1960 Plymouth Belvedere to 4 wheel disc using a kit from AAJ. The kit uses GM calipers at all four corners (larger ones up front, smaller in rear). I have a master cylinder from a '74 Charger, which has no check/residual valves built into the ports. Brakes are manual on this car. I do have an adjustable Wilwood proportioning valve in the rear line, the only valve in the system, and it is currently wide open for bleeding. I have the system all together, no leaks anywhere, and I cannot seem to get the pedal to firm up after bleeding for just over an hour. I cannot see any air bubbles in the fluid at any corner when I bleed, only a solid stream of clean fluid.
I am no stranger to disc brake conversions or repairing stock systems, but I've never had this trouble before. Am I having a moment and missing something obvious? I do note that the rubber lines to the front calipers do arc up higher than the bleeder, could that be causing my trouble? If it would help I could take pictures of the lines vs. bleeder placement. Thanks for your help. |
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Temporarily suspended to cool off
Posts: 316
| It's likely to be a bit spongy till the pads get totally seated. Right now they aren't going to be sitting totally flush on the rotor. There is always a break in period with disc (and drums too for that matter) and you'll have an iffy peddle and decreased braking force and increased braking effort till everything is seated. Personally, what I do is get things together, get it feeling sort of good, then go out and get things good and hot without glazing the pads or getting the rotors glowing.
You could have a caliper that isn't slidding on it's pins all that well, again, just getting in it and taking it for a drive could well clear that up. |
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Board Moderator & Exner Expert 10K+
Posts: 13055
 
Location: Southern Sweden - Sturkö island | Try this;
- press the brake pedal down, slowly but firmly
- take a measure how deep down the pedal goes
- pump twice on the brake pedal
- if it's not going down to the same measure, then you could still have air in your system.
then;
- press the brake pedal down, slowly but firmly
- take a measure how deep down the pedal goes
- wait for at least 1 minute and press down the pedal again
- if it goes down to the same measure, then the problem is not air
- if it goes down below the measure, the problem might be air in your system.
The "could" and "might" depends on the area on the m/c contra the calipers and the pedal ratio..... |
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Expert 5K+
Posts: 7207
Location: Victoria, BC, on Vancouver Island, Canada | Bore diameter of the master cylinder is also a critical issue for pedal travel. Large bore diameter - less travel, more foot pressure needed to push. Smaller bore diameter, more pedal travel and less foot pressure needed. This was an issue with the conversion on my 1960 Chrysler and the master cyl. that AAJ specified had too small of a bore and too much pedal travel. Also the original push rod in the car was too short by about 1.25 inches for the new master cylinder, and I had to have a new one machined ( friend machined it for me no cost). |
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Expert 5K+
Posts: 6504
Location: Newark, Texas (Fort Worth) | You could pressure bleed it up hill to the Master cylinder. This would ensure the air is getting pushed out especially if the bleeders are lower than the calipers. The bleeders are on top of the calipers I take it. Marc. |
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Expert
Posts: 3780
Location: NorCal |
I'll probably get some disagreement on this but I've found that, with single-piston floating calipers, you'll never get a rock-hard firm pedal like you can with drums or rigid-caliper discs. |
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Expert
Posts: 3575
Location: Netherlands | You can take off the calipers and hang them higher in the wheelwell for perhaps better bleeding. (Put a piece of wood in them to keep the piston inside.)
But I don't think this is your problem. I've never felt GM-cars have a real solid pedal. It might just be the calipers.
Residual valves could firm up the pedal, but usually more with drumbrakes. |
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Temporarily suspended to cool off
Posts: 316
| I'll believe it... just too much flex in that setup. But it's cheap! |
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Expert
Posts: 2196
Location: Muskego, WI | As Ian stated, I'm short strokin' it. I was using a MC pushrod that was left over from my Imperial parts, but now have an original to the Plymouth pushrod and it's about 1/2" longer. I'll swap it out and see how that works. What did you do with your MC, did you find one that was more appropriate to your setup?
As for the other comments, yes, my bleeders are up top on all 4 calipers. BigBlockMopar, I like your idea about raising the calipers, I'll bleed one more time with the calipers up high and with my longer stroke pushrod. I'll let y'all know how it works out. |
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bleeding brakes - just want to make sure I haven't missed something
