Disc brakes still mushy...prop valve?

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Disc brakes still mushy...prop valve?

November 04, 2006, 01:41:41 PM

I was wondering if there is ANYTHING else I can do to make the pedal feel less mushy.

1. 73mm front calipers (Lincoln)
2. 11" front rotors
3. Turbo Coupe rear disc conversion (SSBC Kit, including lines)
4. Big bore SVO master cylinder (including lines)
5. PF Carbon metallic pads

As far as I know, my stock 1988 Cougar prop valve could be my problem. Is there one from a Lincoln or Mustang SVO that's better? Your thoughts?

Disc brakes still mushy...prop valve?

Reply #1 – November 04, 2006, 02:27:22 PM

simple stuff first.
did you bench bleed the MC before installation?
good bleed and flush on the entire system.

if it comes down to prop valves, i would bypass the stocker and put a manually adjustable one in the rear line.

Disc brakes still mushy...prop valve?

Reply #2 – November 04, 2006, 07:14:43 PM

The stock prop valve will not cause mushy brakes with a rear disk conversion, it will cause issues with line pressure and flow to the rear brakes though.

As gumby mentioned, did you bench bleed?

Disc brakes still mushy...prop valve?

Reply #3 – November 04, 2006, 07:57:48 PM

Yeah, its been bench bled. I re-did the brakes a few months ago (new rotors/pads) and bled it again. The car stops pretty good, but I just wish there wasn't a 3-4 inches of pedal travel that doesn't do anything.

I used Valvoline Synthetic brake fluid, I think I'll go back to Ford DOT3 since it has a higher boiling point. I boiled the fluid after 120 miles of open tracking, but I only noticed it when I saw the lower half of the M/C was wet. It never felt bad otherwise.

Quote from: Chuck W;111566

The stock prop valve will not cause mushy brakes with a rear disk conversion, it will cause issues with line pressure and flow to the rear brakes though.

So is there a better prop valve for my setup?

Thank you both for your help.

Disc brakes still mushy...prop valve?

Reply #4 – November 04, 2006, 10:39:54 PM

Are you using the stock booster... I remember reading somewhere that you needed to use the 93 cobra booster with a "big bore" master cylinder... Maybe someone else more "in the know" can chime in on this.

Disc brakes still mushy...prop valve?

Reply #5 – November 04, 2006, 10:50:19 PM

One of the disk brake ones would be a better choice, but an adjustable would be ideal.

I never needed the 93 booster when I used the SVO MC...

Disc brakes still mushy...prop valve?

Reply #6 – November 05, 2006, 04:46:42 PM

Yeah I am using the stock booster. I heard that wasn't an issue either, but you could be right.

Its either the prop valve or the booster. Frankly I'm at a loss to see which one will help more. I'll cross reference the part numbers for the prop valve and start from there.

Disc brakes still mushy...prop valve?

Reply #7 – November 05, 2006, 08:14:21 PM

I thought you were supposed to use a SN95 V6 Mustang booster with a SVO large bore brake master???? , there was a site that had all this info but I can't remember if it was for just the Mustangs or if it could be used on the Fox Thunderbirds too.

Disc brakes still mushy...prop valve?

Reply #8 – November 05, 2006, 09:54:48 PM

FWIW, I'm running a stock Mustang 5.0 booster, SVO MC, 73mm calipers with stock rear disc (and the factory TC prop valve). The pedal has a little more play before it starts to firm up, and it doesn't always feel as firm as it should be, but the brakes work fine so I don't worry about it much.

Disc brakes still mushy...prop valve?

Reply #9 – November 24, 2006, 09:19:10 PM

an LSC prop valve will work fine.