No rear brakes after Cobra swap

[NIKwoaC]

Here is the rundown: As some of you know, I recently installed a modified 03-04 Cobra brake system, using a Lincoln Towncar MC and SN-95 booster. I also installed an SSBC brake proportioning valve, and gutted the original. After bleeding the system twice, the rear brakes still don't seem to want to bite very well, even after playing with the BPV full open and full close. When moving the BPV to more pressure, the pedal feels stiff and I can easily lock up the front brakes. When I move the BPV to less pressure, the pedal gets soft and I can't get any of the brakes to lock up. Here are my questions-

1. Do I need to bleed the system again? How strong do you have to press the brake pedal to get an accurate bleed? I've been having my 110lb fiancee do the pedal while I open the valves, I worry that shes not pushing hard enough to move a lot of fluid through the system.

2. Does the e-brake use fluid pressure to operate? When I pull the e-brake, I can't get the rear wheels to lock, and even really pulling hard on it, the car only barely shows signs of slowing. Because of this, I worry there is something mechanically wrong with the rear calipers themselves. The calipers and pads are new.

 

[90lxcoupe]

The e-brake is cable operated, it would take alot of muscle to get the rears to lock up from that.

Also, you still have the stock prop valve installed? When i put my SSBC one in it just bolted in place of the stock one and i threw the stocker in the trash.

 

[NIKwoaC]

The e-brake is cable operated, it would take alot of muscle to get the rears to lock up from that.

I've locked up the rear tires on other disc brake cars before. I just feel like the car should at least slow down pretty well if I'm really pulling on it, but it doesn't.

Also, you still have the stock prop valve installed? When i put my SSBC one in it just bolted in place of the stock one and i threw the stocker in the trash.

I gutted the stocker and the adj PV went in the junction on the passenger side firewall, per the unit's instructions.

 

[Shaolin Crane]

try pulling the handle a few times to get the rear brakes adjusted, or it could be you're running the wrong MC

 

[Mustang5L5]

I've locked up the rear tires on other disc brake cars before. I just feel like the car should at least slow down pretty well if I'm really pulling on it, but it doesn't.

Mine doesn't. It will hold the car on a steep hill, but barely makes a dent while driving.

I'd suspect the rear calipers. Put the rear up on jackstands, drive up to 20 or 30MPH and apply the brakes. Do they stop?

 

[Mustang5L5]

or it could be you're running the wrong MC

It's a 1" bore 2-port MC.

No different than 93 cobra...but it bolts into the pre-87 cars easily.


Nic, when you crack a bleeder screw on the rears, does it piss out fluid with each pump? It should be harder to fluid fluid to the rear than the fronts, but still should come out pretty easy

 

[NIKwoaC]

It's a 1" bore 2-port MC.

No different than 93 cobra...but it bolts into the pre-87 cars easily.


Nic, when you crack a bleeder screw on the rears, does it piss out fluid with each pump? It should be harder to fluid fluid to the rear than the fronts, but still should come out pretty easy

That is the thing, it does move fluid. Thus why I'm concerned that there is still a bubble somewhere in the system that just compresses when the rear system in under pressure, and doesn't allow the rear calipers to generate a lot of stopping force.

Is it common to have a stubborn bubble that doesn't want to work its way out with bleeding? If I bleed this car again, it will be only the 3rd time in my whole life bleeding brakes, so I'm not particularly experienced with it.

 

[ID89GT]

What order are you bleeding the brakes in? You usually go from the farthest one first and work your way to the closest one.

 

[NIKwoaC]

What order are you bleeding the brakes in? You usually go from the farthest one first and work your way to the closest one.

Check.

 

[Mustang5L5]

With the car off, pump the pedal. Does it get hard as a rock? If so, then it's a good bet all the air is out.

Do the rotors look like the pads are pressing against them? Toss some water on the rotors, let it rust and go for a ride. Does it scrape off after the first press of the pedal?


The rear SN95 calipers can be tricky to bleed. I suggest tapping them with a rubber hammer if you bleed again.