25th_anniversary_stang90

I have a 1990 Ford mustang 5.0 With the SVE Cobra bake system from Late model restoration. 13in rotors in the front and 11.65in in the back. It has cobra master cylinder and also cobra brake booster.

Late model restoration is nice enough to actually have step by step instruction on how to do the install so it was fairly easy. But I am having problems with the brakes I don't know if I might have done something wrong hopefully you guys can help me.

Every time I want to stop very fast as to almost slamming the brakes the pedal gets really hard and the cars stops very slow. If I actually want to stop fast I actually have to slowly push in the brake and work my way through the pedal. this was never an issue with my stock brakes if i actually slammed on the brakes the brakes would lock (stock brakes). now these new cobra brakes wont and I dont want them to lock but i want them to just be at that point where they just might lock so i can stop as fast as possible. Also the master cylinder also shows signs of leakage from the cap as if i over filled the MC but its not.

I contacted late model restoration and they mention that it could possibly be the stock proportioning valve and that i probably did not gut it out but i did I removed the parts that was illustrated to do. I also installed the FRPP proportioning valve and its opened all the way Rear wheel wont lock.

I already verified that the stock proportioning valve was gutted out and that there wasnt anything in the proportioning valve (debri). I already bleed my system over 3-4 times trying to solve this problem I dont think its air in the system. i honestly think that i might have a bad MC its always showed signs of leakage from the cap which is why i Had contacted Late model Restoration either that or maybe there is some blockage in the stock proportioning valve. that forces the fluid back to the the MC and causes it to overflow.

Sorry for the long notes but just didn't want to leave any important information out. Any help is appreciated thank you

dawson1112

Hmm have you verified vacuum to the booster? Does the car idle ok? No vacuum leaks any where ?

It sounds like a booster problem to me.

25th_anniversary_stang90

Well I have checked the vacuum to the booster it's pretty strong I don't have a gauge to read the pressure but if I do disconnect it then it does idle really rough. The cars idle is a little rough during cold starts but nothing alarming I haven't been able to find a leak anywhere I've checked all the lines for holes or cracks but nothing. when I had the stock booster the pedal was always hard so I upgraded to the 93 cobra booster which makes a huge difference but I still feel the hard pedal during hard braking. Also is the master cylinder cap is showing signs of over spill as if to much fluid was added to the container or a if the cap didn't have a proper seal. It's a new MC and a new cap I've even tried using my old cap from my other MC but it still does it. What really throws me off is the leakage of the MC. I think if it was just a bad booster I think the pedal would just get hard but i don't think it would cause the brake fluid to spill through the cap. Would it? Idk I'm stumped.

yurizx6r

1. Check for vacuum leaks.
2. Did you purchase a adjustable proportioning valve? Purchase all the lines and components from Maximum Motorsports. I did, and I did not have any issues at all. You will have to do a few 30-0 stops until you get it right. You want to keep adding rear break pressure until you either start to see in increase in your 30-0 distance or until the backs lock up. Once either of those happen, back it off a little and you're good.

25th_anniversary_stang90

I will try to check for vacum leaks again on sunday im stuck at work today and tomorrow I work 12hrs shifts so its hard to make time.



This is the adjustable proportioning valve the Kit came with and it also came with the maxixum motorsport hard brake lines from the master cylinder to the stock proportioning valve. As to adjusting the proportioning valve. I adjusted the way you said a while ago the only difference i was doing 50-0mph i ended up opening the valve all the way because the rear brakes never locked.





This is the cobra MC look at how it shows signs of spill through the cap. i dont understand why the MC would leak. I think i might have gotten a bad MC

25th_anniversary_stang90

I will try to check for vacum leaks again on sunday im stuck at work today and tomorrow I work 12hrs shifts so its hard to make time.



This is the adjustable proportioning valve the Kit came with and it also came with the maxixum motorsport hard brake lines from the master cylinder to the stock proportioning valve. As to adjusting the proportioning valve. I adjusted the way you said a while ago the only difference i was doing 50-0mph i ended up opening the valve all the way because the rear brakes never locked.





This is the cobra MC look at how it shows signs of spill through the cap. i dont understand why the MC would leak. I think i might have gotten a bad MC

yurizx6r

Sorry, I overlooked where you mentioned you had a proportioning valve. Sounds like your problem is most likely the MC, but still check the vacuum to the booster. All the booster does is make it easier to push the pedal, so I doubt that's your problem. If you bled the system a few times (I'm assuming in the correct order), then there should not be a problem unless a bleeder on one of the calipers are open and air is getting into the system. When I put mine in, I found my front passenger side kept leaking brake fluid on my brand new rims. It turned out that on that side I had to turn it tight, then back of a 1/4 turn to get it to seal. It's weird, but I have not had a problem since.

Did you bench bleed the MC when you put it in? Worst case swap the MC. It's under warranty, so change it for free and rule it out. Worst case you lose 5 bucks in brake fluid and you can check it off your list. There are only so many things it can be!

25th_anniversary_stang90

Thanks yurizx6r I figured it was the master cylinder I just wanted to make sure . I will talk to late model restoration hopefully they will exchange it or at least give me a discount on a new one. I did bleed the car the right way (I think). I worked my way from the furthest wheel (rear passenger side caliper) to the master cylinder in a Z pattern. I also did bench bleed the master cylinder I remember going to napa to buy a bleeding kit because i didn't have one. I also made sure that I measured the Boosters push rod correctly. So I will try to replace the MC and look at the calipers bleeding ports too for any issues. Thanks again yurizx6r hopefully that solves my problem. Also you have a nice ride

yurizx6r

No problem at all. I remember doing this swap very well. It's totally worth the headache because no matter how much hp you have, you will ALWAYS need good brakes. Power means nothing if you cannot control it. The good thing is that there is only so many things that it can be, so you will find the problem. Just remember to do a really good bleed after you put the new master in and double check that your front brake lines are not touching the tires. I got one right, but the other was rubbing in the tire when I turned right, so I had to adjust it. You can check this by turning the wheel left in right in the drive way.

Also, late model is really good about returns, so you should not have a problem with that.