Manual Brake Conversion

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Manual Brake Conversion

March 11, 2007, 10:32:57 PM

I just finished the 4-wheel disk brake conversion on my '87 Cougar, but now my brakes are REALLY mushy (even more than before!) I can even stand on the brake pedal and the car just takes it's good ole' time to stop. It has brand new brake lines and master cylinder, so all I can figure is that either I don't have enough vacuum (I've got an aftermarket cam) or my booster just went kapooie. It seems like the easiest fix would be a conversion to manual brakes (the Cobra boosters are hard to find, and even then you don't have a guarantee with a used booster.) Has anybody tried this conversion? Should this fix my brake problem?? Thanks

Jason

Manual Brake Conversion

Reply #1 – March 12, 2007, 06:55:35 AM

A Cobra specific booster is not needed. Sounds like you need to bleed your brakes (some more)... and possibly an M/C upgrade. Did you install an adjustable proportioning valve? What did you change when you upgraded?

If you want a taste of manual brakes disconnect your booster vacuum line. :) If your booster was failing the pedal should get harder to press down.

Manual Brake Conversion

Reply #2 – March 12, 2007, 09:06:34 AM

Yeah, I put in a new proportioning valve, new lines to the rear brakes, and a new mastercylinder. I had a mechanic do most of the work, including bleeding the brakes, so maybe I should start there first. Thanks for the help!

Manual Brake Conversion

Reply #3 – March 12, 2007, 10:42:24 AM

Just disconnecting the booster won't give a true taste of manual brakes. Although the manual brakes do require more "Driver Input", you tend to get more feel of the brakes than if you have a booster. Depends on what you're going to do with the car. If you only going to drive it on the street, then stay away from the manual conversion for comfort reasons. If you'll be autocrossing/open tracking w/limited street use, I'd think about using the manual brakes. Don't know much about the strip though as I don't particularly care for straightline runs. I personally am changing to manual brakes in my car as It'll be used alot for autoxing/opentrack and alot of street use. But that's my preference to use manual brakes.
Like the others have said, bleed your brakes again and go from there.
Good luck and have fun :D

Manual Brake Conversion

Reply #4 – March 12, 2007, 11:04:16 AM

What M/C did you use?

What specific "4-wheel disk" convsersion did you do?

Manual Brake Conversion

Reply #5 – March 12, 2007, 12:12:27 PM

Thx 1BadBird, that helps alot. I'm only gonna be drivin it on the street, but it's mainly only driven for pleasure, do you think I could get away with doing the conversion under those cirspoogestances?? My clutch is already crazy heavy, so maybe that way I could even out how my calf-muscles look, lol. It's got a brand new factory OEM M/C, and I installed an entire rear end out of a turbo coupe with it's disk brakes, running new lines back to them.

Manual Brake Conversion

Reply #6 – March 12, 2007, 03:41:47 PM

if you used the OEM proportioning valve, and master cylinder. Thats your problem. The rear disk brakes need more fluid and pressure to operate, and the factory master cylinder and proportioning valve dont allow for that. Most guys run a 93 Cobra Master cylinder, a gutted prop valve, and adjustable prop valve ,and it works well.

Manual Brake Conversion

Reply #7 – March 12, 2007, 04:19:33 PM

Thx T-Bird, that helps bigtime. Does everybody agree with his diagnosis?? I'm sick of messin with the brakes, wanna git 'r done!! - oh, and would it be possible to just run a 93 cobra M/C without messing with the proportioning valves?? I don't know much about "gutting" them, and don't wanna be stuck without brakes! Thx
Jason

Manual Brake Conversion

Reply #8 – March 12, 2007, 04:43:04 PM

You absolutely HAVE to mess with the proportioning valve. The proportioning valve is what limits the fluid to the rear brakes. You need the Cobra M/C to push the volume of fluid, and you need the proportioning valve to allow the proper amount of fluid to the rear.

http://mjbobbitt.home.comcast.net/

That has a lot of information on the brake setups. The stuff isnt exactly the same as our cars, but its more than close enough to figure it all out. Line routing is the main difference.

Manual Brake Conversion

Reply #9 – March 12, 2007, 10:09:34 PM

Alternatively, if you can get your hands on a turbo coupe proportioning valve, you could just use that.

Manual Brake Conversion

Reply #10 – March 12, 2007, 11:12:25 PM

I'm using the SVO M/C and a booster from an 85 bird, my brakes are working fine

Manual Brake Conversion

Reply #11 – March 13, 2007, 08:30:38 AM

Quote from: Tbird232ci;134053

You absolutely HAVE to mess with the proportioning valve. The proportioning valve is what limits the fluid to the rear brakes. You need the Cobra M/C to push the volume of fluid, and you need the proportioning valve to allow the proper amount of fluid to the rear.

I totally agree with Tbird 232ci. You need the 93 cobra m/c but the biggest area of concern is the proportioning valve.

On my conversions, I gut the P/V and use an inline adjustable valve to the rear brakes. The correct master cylinder really helps. That has been my experience.

Manual Brake Conversion

Reply #12 – March 13, 2007, 09:33:37 AM

Thanx guys, wonderful info. HOWEVER, I just got that new M/C!! Would that mastercylinder work if I just put the new proportioning valves on it?? (I would think this would work, if not, how did the stock Turboo Coupe's brakes work??) thx!
Jason

Manual Brake Conversion

Reply #13 – March 13, 2007, 04:05:28 PM

It would "work", but you would still have a squishy pedal.

In your situation, the master cylinder is whats causing the mushy pedal, and the proportioning valve is killing your brake bias.

Turbo Coupes use a 100% unique system compaired to the rest of them, thats how they work.

TC Proportioning Block

Reply #14 – March 16, 2007, 07:26:58 PM

Thanks for everything guys, it all helps bigtime. Got 2 more q's for ya, most of the mustang MC's are 2 brake lines instead of three, right? How hard is that conversion?? Also, could I use a TC proportioning block instead of an aftermarket proportioning valve, or would the valve work better?? THANKS!!

Jason:cougarsmily: