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Discussion Starter #1
Here is the setup:
- 1990 Mustang
- SVO 73mm front calipers
- Matt90GT style 54mm Cadillac rear calipers
- 1995 GT Mustang master cylinder (1 1/16" bore i think)
- adjustable prop valve

The Problem:
Soft pedal that goes to the floor on hard stops. Pedal gets nice and firm if the brake pedal is pumped a few times.

Is this a sure sign that there is still air in the system?

If I had let my master cylinder resevoir accidently get too low during bleeding, do I have to remove the master cylinder and bench bleed it to get the air out?

Is my Master cylinder big enough for these large front and rear calipers? It was perfect with front 73mm calipers and rear drums.
 

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You can install the front calipers backwards with the SVo and stockers from the 87-93 cars. Make sure the bleeder is kind of facing up towards the rear of the car.



Other than that, you will need to take the rear calipers off the bracket, put like a socket between the pads and point the bleeder straight up. The way they get mounted traps air in the caliper. I have not found a better way to bleed them yet.

And yes, if you get air in the MC, most of the time you need to bench bleed that again.
 

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For brake bleeding, I've used a MityVac vacuum pump with the brake bleeding accessory kit. Allows you to bleed brakes by yourself. You put the tube on the bleeder screw then pump up the pressure on the pump. With a wrench already mounted on the bleeder screw, loosen it and the pump sucks out the air in the system into the resovoir. Repeat a few times and viola!

I highly recommend it.
 

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Discussion Starter #4
Thanks guys.

Just to confirm... So when you need to pump the pedal to make it firm does that mean that there is air in the system for sure? it couldn't be some other problem?
 

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Those 73mm's do make the pedal feel more vague then the stockers. One other thing that I do, is use a C clamp or something to totally compress the piston on the caliper before you start bleeding. If the air pocket is in that, it will never come out and you can suck all the fluid out you want. I did this on my bike and my car and it really made a difference. I really dislike bleeding my brakes, it just doesnt ever work 100% as good as I think it should. I have a mighty vac and it helps, but I dont feel like it is the greatest tool in the world or anything. Now, I better run see if I installed mine backwards!
 

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Discussion Starter #6
I just installed the rear discs. Before the rear discs I was running the 73mm calipers with the SN95 MC and the pedal was really firm. I'm thinking the air is stuck in either the master cylinder or the gutted stock prop valve, or even the rear calipers (which i did bleed off the car).

I just want to confirm that the problem is air in the system and not that my 1995 GT MC is too small for this 73mm/54mm caliper combo....or that i need to adjust out the booster rod or something else.
 

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if you have to pump the pedal that is a sure sign there is air in the system.

You will have to bleed the rear calipers by pulling them off like I mentioned.
 

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Discussion Starter #8
Thanks... grrrrrrrrrrrrr.
 

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The problem I've found with the rear disc conversion is that the vacuum booster is not larger enough for the rear disc. I had the same problem and when I changed to the FRPP M-2005-K booster all my slushy, spongy, low pedal feeling went away. You will need to message the shock tower to make this booster fit. I cut it with a cutting wheel, then messaged it with a hammer. Then I rewelded it closed after I was finished. I did this from the wheelwell side. After grinding down the weld slightly and painting it looks fairly decent.
 

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7-UP BILL said:
The problem I've found with the rear disc conversion is that the vacuum booster is not larger enough for the rear disc. I had the same problem and when I changed to the FRPP M-2005-K booster all my slushy, spongy, low pedal feeling went away. You will need to message the shock tower to make this booster fit. I cut it with a cutting wheel, then messaged it with a hammer. Then I rewelded it closed after I was finished. I did this from the wheelwell side. After grinding down the weld slightly and painting it looks fairly decent.
WHile a hard pedal would indicate a need for a larger booster, it will not cure having air in the braking system. Using a MC with a larger bore will cure a soft pedal.

Pumping the pedal is a sure sign there is air in the system. Then with the way the rear calipers mount, they easily trap air unless you remove them from the car.
 

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i have a similar thread in here too. i have the same problem, but i used a complete 93 cobra m/c and no adjustable prop valve. but i have the same problem so i could be having air in the rears is what you are saying matt???:joy:
 

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That is the most likely place to have air in the system. I assume you bench bleed the MC also.
 

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Discussion Starter #13
Just out of curiosity, why does bench bleeding work better then bleeding on the car?
 

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cause you can tip the master cylinder at different angles to get the air out the ports.

See in the mustang, the front of the MC (side towards the front of the car) is angled upwards slightly. so air will get trapped at the highest point in the unit.
 
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