This is topic brake boosters 91 &93cobra any differance in forum Tech Talk at Northern California Ford Owners  .


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Posted by rokcrln (Member # 2536) on :
 
I have a 91GT with sn95 brakes and the 94GT master w/a gutted perportioning valve and an adjustable in it place. But my brakes still don't ferel right, almost like the booster is not boosting enough. So I want to know if the 93cobra (4x disk) is any different. It takes alot more foot psi to stop than it should.
 
Posted by JohnB (Member # 969) on :
 
Have you checked to make sure none of your calipers are seized/sticking? From what I can see, there's no difference in the 91GT/93 Cobras. I've got 5 Fox's here at the house to compare.. [Big Grin] they all look the same.

Oh, and I've got a cowl for ya. I'll bring it up to Sam's my next time up. [patriot]
 
Posted by rokcrln (Member # 2536) on :
 
Yeh John I have checked that and they are all working and putting heat to the rotars. I need to order some 2lbs residual psi valves to put in line to keep the pads in contact but this won't help the pedal psi problem just that anoying break squeek.
So what are you looking to get for the cawl.
 
Posted by 90LX (Member # 1487) on :
 
I have the same brake setup you have and I have the same problem. I have been told by a few shops that the stock booster is the problem and the 93 cobra booster will fix the problem? If you find one and put it on let me know how it worked.
 
Posted by rokcrln (Member # 2536) on :
 
Will do thanks for the info!
 
Posted by 93PONY (Member # 60) on :
 
My 93 Cobra's brake boost is thicker then 91PONY's GT.
 
Posted by rokcrln (Member # 2536) on :
 
yeh Auto zone is 74.95 and grand auto is 139.95 for the same part. Auto zone is out even at the hub store and grand doesent know if they can price match for it. But it seams this is the problem I am having, and the larger one should have more vacume pull than my 91.
 
Posted by mustanggt5091 (Member # 444) on :
 
There is technically a slight difference in the master cylinder itself, larger bore by 1 or 2 cm than the gt's, but not the booster's!
 
Posted by Sean90GT (Member # 33) on :
 
There is certainly a difference in the 93 Cobra booster. But, if you don't want to go through the hassle of swapping out the booster (and it IS a hassle) you can go to a 94/95 Cobra master cylinder. I believe that the bore size on those is 15/16". The smaller bore will help generate more pressure.

This is the master cylinder that Baer supplies with their Track Kit, which is basically the same as the Cobra brake kit from Ford. Baer does not supply a new booster, they just go smaller on the master cylinder. I got this info directly from Baer and was about to do this since I had the same problem you are having. But, I found a local totalled '93 Cobra and scored the booster and master cylinder (1" bore) off that and swapped them as a set. My 13" Cobra brakes now stop sweet where I could not even lock them up before.

Good luck.
Sean.
 
Posted by TOPnotch (Member # 1340) on :
 
Your booster is not the problem bro. It is your master. The stock master on your car is 7/8 of an inch. 93 cobra uses a 1 inch. And a 94-95 mustang uses a 1 1/16 bore. I have 13 inch 2 piston brakes with a 95 master and stock booster. And it stops great. The problem is that your master doesn't have enough pressure and doesn't move enough fluid to support your new brakes. 4 wheel disk requires much more fluid than drum.
 
Posted by rokcrln (Member # 2536) on :
 
I think you guys are not reading my first post real well! I have the 95 master with the 1 1/16" bore and it pushes plenty of fluid. I have a real nice firm/hard petal. Yes the stock 23mm bore was not enough and I think my 1 1/16" may be to much fluid and not enough line psi. My car stops ok just not like it should. Even with the adj perportioning valve you can not lock up ether end. I am thinking I may need to go for a cobra master to increse line psi!
Thanks for the info keep it comming.
 
Posted by 90LX (Member # 1487) on :
 
I hear you man! Like I said also, mine is exactly the same as yours with the same problem. It is for sure a booster issue. Mine new booster is on order as we speak. But I not going to put it in utill I pull my motor in a couple of months. With my car it stops fine when you slowly push the pedal but if you just stomp on it, it gets really firm and nothing really happens for a second. Is that the same thing with yours?
 
Posted by rokcrln (Member # 2536) on :
 
What happens with normal (un-fucked with brakes) is the harder you push the more stopping power you feel and if you just jamb them on you skid to a stop. With mine you jump on them and you slow fairly quickly but you can tell their should be more stopping force. When you just apply psi it slows but the more you push it doesn't seem to make a differance. I worry some times when I am in traffic if it would stop in a panic stop or roll in to the car in front of me as it is slowing down. As far as boosters when I called auto zone they show the cobra booster but it is also the same part# as the gt. So I think I am left with playing with bore size and line psi.
 
Posted by Sean90GT (Member # 33) on :
 
Actually I did read your first post well and thought I answered your question.

I know exactly what you are saying because I had the same problem. I started with 73mm SVO brakes in the front with an SVO master cylinder (1-1/8" bore). The car would stop fine under normal driving conditions but if I had to romp on them the pedal would be FIRM. I upgraded to 5 lug SN95 spindles and used the SN95 brakes and still had the same problem. I then installed 13" twin piston Cobra brakes on the front and figured I'd be able to lock them up for sure now. Nope.

The problem is that your master cylinder is just too big. You are not able to press hard enough on the pedal to generate the same pressure as a smaller master cylinder. Pushing the same amount of fluid through a smaller cylinder increased hydraulic pressure and force. SVO's even had a different brake pedal to help with leverage and increase pressure. So, either get the 15/16" 94-95 Cobra master cylinder or a 1" 93 Cobra master cylinder with a bit larger booster. If I were you, I would be trying out the 94-95 Cobra unit since that is what the tech at Baer told me is the one they use in their kit while retaining the stock GT booster. I haven't heard many people complaining that their Baer Track Kit brakes don't stop.

The parts houses now list the 93 Cobra and GT as the same pieces but the original equipment from the factory is definitely different. They may now just offer a middle of the road booster that works for both applications since Ford no longer offers that booster and cores are rare, not sure. The original 93 Cobra booster is physically larger. I know because my stock booster came out no problem but I had to wrestle the Cobra booster in when I swapped them out.

Now quit typing on the internet and fix your brakes! [Razz]
 
Posted by VenGeance (Member # 1724) on :
 
Did you make sure to "bleed" the brakes?
 
Posted by rokcrln (Member # 2536) on :
 
Sean90GT

Thanks for the info you are on the same track that I am. I will be doing the 94cobra.

VenGeance
I did not need to bleed them since no fluid leaked out when I changed them. I have more fluid but it is still full last time I checked...LOL Yes they are bleed and the pedal is nice and firm just not enough line psi from my master!
 
Posted by Sean90GT (Member # 33) on :
 
No problem.

Check the For Sale section here. Somebody is parting out a 94 Cobra. Maybe he still has the master cylinder.

Good luck

Sean.
 




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