Master cylinder help (93 Cobra with 98+ plus brakes)

04-SVT

New Member
Sep 5, 2004
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Las Vegas, NV
So I upgraded my front brakes on my 93 Cobra. I have all new knuckles, hubs, 13" rotors, and the 10th aniversary 2003 COBRA calipers. I didnt change the master cylinder or brake booster. It seems to stop decently but it really requires alot more pedal effort then before and it wont seem to lock up the wheels at all. I have read the sn95brake website but I am still confused on what to use since I kinda pieced my car from various years.

Does anyone know what year master cylinder I would need to increase brake pressure? I have read that the Cobra booster should be adequate enough for the sn95 brakes, but upgrading the MC should be my first option.

The current bore of the MC is 1". Or so I have read. What years could I use that have a bigger bore and would bolt up to my current booster?

Thanks for any help
Pete
 
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I know you said you read the website but I read it about 100 times before I understood everything. I have a 4 wheels disc brake kit with the 15/16" bore MC. Brake pressure is great in mine. However, you have the 1" bore MC which is ideal for the sn95 swaps. Sounds to me like you may still have air in the lines. These brakes are VERY VERY hard to bleed. Did you bench bleed the MC prior to install? Also, my brakes didn't work properly until I went through almost 12 cans of brake fluid and bought a Motive pressure bleeder. That was the ONLY way I could get the air out.

From the SN95 site:

The stock master cylinders on the 87-93 Mustangs are marginal with just the install of larger front 73 calipers. The 3 port design is really to blame with the small 21mm bore. If you swap to rear disc, then a new MC is needed! There are 4 common MC upgrades out there for the Mustangs: the Lincoln/SVO unit, the '94-98 GT unit, the '93 Cobra unit and the '94-95 Cobra units. Each is a 2 port MC, so a conversion will be needed but they are all different bore sizes. Which one is the correct unit for you? Read on:

Here is a more specific information on the master cylinders mentioned:


'93 Cobra - (metric threads) 1.00" bore

'94-95 Cobra - (metric threads) 15/16" bore, stock plug in for low fluid sensor. Ports are reversed thread sizes from 87-95 LX/V6/GT


Low fluid sensor notes: The stock '87-93 master cylinder has a plastic reservoir with a low fluid indicator. The '93 Cobra and the '94-98 units all have this, but the SVO unit does not have this feature. You will lose the low fluid sensor if you use the SVO unit. This will not cause the dash light to stay on, just permanently off. For the E-Brake light on the dash to come on with the E-Brake, you need to make a jumper in the connection you just removed. Connect pins 2-3 (the 2 purple wires, not the black ground). Be sure to label the connection to know what it is for in the future. For the '93 Cobra and '94-98 units, it is a direct plug in.

Which Master Cylinder?:

87-93s: The 87+ mustangs all use metric threads on the master cylinders. They are 3 port units, thus you must convert to a 2 port setup to use any upgraded master cylinder.

3-2 Port Conversion Products

The SVO unit was a very popular swap until the '94-98 units came readily available. It is very inexpensive at $15 rebuilt, has a large bore, but requires adapting to SAE threads and you lose your low fluid sensor. This works BEST with the larger caddy or Lincoln rear calipers and the front SVO 73mm calipers, and is the only setup I recommend with the SVO unit! Other setups will be too stiff for most with the stock brake booster and it will not have enough pressure. The best all around unit is the '93 Cobra with the 1" bore, but it is more rare and it cost more. Its bore size is about ideal for most any brake setup out there presently.This is the unit I would recommend from most all brake swaps! The '94-98 V6/GT MCs would be good compromise for most everything with the addition of a 94+ V6 brake booster or use of the larger 99+ GT/V6 PBR front calipers. Pedal will be like stock if you use the SN95 brakes, or SVO/Lincoln front brakes with rear drums. You can find these for about $25 used at yards with the reservoir included. If you are planning on running the Cobra or Brembo brakes, then I would suggest the '93 Cobra or '94-95 Cobra 15/16" MC with the stock booster. This will give you a pedal that is not to hard. The last consideration is the cam in the engine. I make my recommendations off a stock 87-95 cam. If you are running a larger cam with less vacuum at idle, either drop a size in the master cylinder bore or set up to the larger 94-95 brake boosters to compensate. If the pedal is to firm after the master cylinder swap, then swap in the larger 94+ V6 brake boosters. Any of the 94-95s and 94+ V6 units will work. They are all larger than the stock 87-93 V8 unit, thus will give you more assist. I would not suggest trying to find the largest Sn95 booster out there as any are larger than the stock unit you are replacing.



Which Master Cylinder to use on fox3 ('87-93) cars with SN95 brake parts:
Well since you are using the Sn95 parts, you should use a SN95 master cylinder as they are designed together from the factory. The '94-98 V6 master cylinder will bolt directly into the PV to MC fittings that you have! You just need to convert the stock 3 port setup to a 2 port one . You can do this with fittings under the proportioning valve to keep things clean! The low fluid sensor is even a direct plug in!

If you use the '94-95 Cobra master cylinder for a softer pedal feel, you will need to get 2 fittings to swap the lines on the master cylinder. The cobra has fittings that are the opposite of the v6/GTs so they did not get mixed up on the assembly line.

Now you need to convert the stock 3 port MC to the newer 2 port MC design. You can either purchase a 93 Cobra combination valve from Ford for about $60, or use a 3-2 port conversion kit. The 3-2 kits is a T fitting that screws into the bottom of the PV and has an adapter for the 3rd port! It will work with the the '94-98 V6/GT MC, the '99 V6 units, the '94-98 Cobra, and '93 Cobra MCs! This is very neat looking at I am selling them at $25.00+ shiping! No Cut, No Flare! 3-2 Port Conversion Products

The other option is to use the parts from a '94-present NON-ABS mustang or '79-86 Mustang. They have a large fitting and special nut that will screw into the back of the stock combination valve. You will have to cut your stock 3rd port line and double flare the brake line there. Be sure to not remove any of the shuttle valve parts in the rear of the combination valve if you go this route.

Master Cylinder Notes:
1. If you install a new MC or upgrade the calipers, you will need to adjust out the brake rod booster to take out the slack in the pedal; this is of course after being sure there is no air in the system. There will be about 1-2" of travel in the pedal that does not push on the MC bore. This is when you need to adjust out the booster. Adjust the brake booster rod out 1-1.5 turns. Click here for a diagram
2. If you plan to go to rear disc brakes, then the 2 port MC will be required along with the FMS M-2450-A plug and an adjustable proportioning valve.
3. For the 93 Cobra Mustang, you can keep the stock master cylinder and proportioning valve; just adjust out the brake booster rod 1.5 turns with the larger 73mm calipers. It will work great with the SN95 parts, adjust the booster as needed.
4. The '96 and newer V8 Mustangs use a Hydroboosted master cylinder. The mounting flanges are vertical vs. the horizontal flanges required on the vacuum boosted units. Thus they are not compatible with vacuum boosters in the ealier mustangs!
 
tunedin302 said:
3. For the 93 Cobra Mustang, you can keep the stock master cylinder and proportioning valve; just adjust out the brake booster rod 1.5 turns with the larger 73mm calipers. It will work great with the SN95 parts, adjust the booster as needed. QUOTE]

Ok, well first off, I gravity bleed the brakes, and the pedal seemed to be right on, with no leaks in sight. I could mash the pedal and it wouldnt go to the floor, stays about half way out.
Secondly, where would I find the booster rod? I will try that too, see if that helps any.
 
Oh and I forgot to mention that I have not replaced the MC or booster. its stock that came with the car.
Basically everything else has been replaced though, calipers, rotors, pads, brackets, hubs, spindles, axles, knuckles, etc... (front and rear)
Oh and I have v6/GT rear disc brakes
 
04-SVT said:
Ok, well first off, I gravity bleed the brakes, and the pedal seemed to be right on, with no leaks in sight. I could mash the pedal and it wouldnt go to the floor, stays about half way out.
Secondly, where would I find the booster rod? I will try that too, see if that helps any.

I would pressure bleed the brakes before I adjusted the booster rod. When you pressure bleed them, get it up to 15psi and loosen the fitting that go into the top of the stock prop valve until fluid begins to come out. I found that I had air trapped in the stock PV. Not sure how the lines run on the 93 cobra. If you had to modify the stock PV, are you using the M-2450-A plug on the front of the stock PV? Looks like this:
View attachment 501281

To adjust the prop rod (ONLY do this after you bleed the brakes about two more times) ... pull the driver front wheel, undo the bolt in the fenderwell that holds the stock PV to the fenderwall. Next, undo the nuts that hold the MC in place. Carefully, pull the MC from the booster with the lines still in tact. You will see a acorn nut on the end of the booster rod. Mark this nut with white out so you know where the starting point was located. You will have to use some vice grips or pliers to hold the booster rod while you turn the acorn nut counter-clockwise about 1 full turn. Reinstall the MC and PV. Be forewarned, if you do this procedure prior to getting all the air out of the lines then the pressure will swell and cause your brakes to become locked after they heat up. You will then have to loosen the nuts on the MC in an emergency situation (essentially disengaging the booster rod from the mc) so you can drive home.
 
cpurtellII said:
Upgrade to the sn 95 booster and mc I belive that is your probelm

I don't believe this is the problem. Would hate to see him do a change over and still have the same problem. He has a 1" bore MC already and it is very common to run the fox booster with the sn95 brakes.
 
Garden Sprayer Pressure Bake Bleeder

1 each pump type garden sprayer, 1 - 1 ½ gallon capacity (size doesn’t matter much, it just has to be cheap and small enough to be easy to work with)
6-10 feet 3/8” clear plastic tubing
1 each ¼” brass pipe tee
1 each ¼” pipe to 3/8: hose adapter
1 each pressure gauge 0-60 PSI or so – all you’ll ever need is 5- 10 PSI, so the gauge range doesn’t have to be high.
1 each large rubber stopper – this is the hard part to find. It may take some searching to find one that is a snug push fit to the inside of the filler port on the master cylinder. You can use silicone rubber to seal a brass fitting to an old master cylinder cap, but they tend to leak too much.
Home Depot or Lowes has some ¼” brass pipe stock that is continuously threaded in the electric lamp repair department, along with the brass nuts that go with it. This is better than a pipe nipple, since the nuts can be used to secure the pipe in the cap or stopper.
OR if you can’t find the threaded pipe stock,
1 each ¼” nipple, 1 ½”- 2” long

The rubber stopper needs a hole drilled in it for the ¼” pipe nipple or threaded pipe stock. After you drill the hole, use some silicone gasket sealer to seal the pipe nipple as you push it into the rubber stopper. If you used the threaded pipe stock, use the nuts to secure the stock into the stopper.

If you can’t find a suitable rubber stopper, an old master cylinder cap can be used. Drill a ½” hole in the center for the pipe fitting. Cut the brass pipe stock to about 1”- 1 ½” long, the exact length isn’t too important. Push it through the hole in the master cylinder cap and thread one nut on top of the pipe stock where it sticks though the cap. Put another nut on the other side of the cap to lock the pipe stock in place. Apply some silicone rubber gasket sealer to both sides and when it is dry, screw the ¼” pipe that sticks out of the top of the cap into the tee.

Remove the sprayer hose and wand from the garden sprayer. You may find it easier just to cut the sprayer hose off short and connect it to the 3/8” plastic tubing. The idea is that the 3/8” tubing connects to the pickup tube inside the sprayer in a reliable, leak proof fashion. Another alternative is to remove the spray nozzle from the end of the spray wand and connect the 3/8” tubing to the wand. This leaves the hand valve in place and may be useful to start/stop the flow of brake fluid.

The 3/8” plastic tubing connects to the pipe tee using a push on hose barb type adapter. The pipe tee has one port for the gauge, one for the 3/8” hose and the other to connect to the rubber stopper or master cylinder cap that you modified.

Fill the pump sprayer with a quart of brake fluid. Set the garden sprayer on the ground and screw the pump handle down tight, and pump until brake fluid fills the plastic tubing. Then put the modified stopper or master cylinder cap on the master cylinder and pump slowly to make sure that nothing leaks or pops loose. No leaks, continue pumping until you get 5-10 PSI. Put a 6”-12” length of clear plastic tubing on the bleeder ports. Then open the bleeder ports on the wheel cylinders one at a time and bleed until the bubbles are gone. I use a 2 liter soda bottle with a coat hanger to catch the fluid . DO NOT REUSE THE OLD BRAKE FLUID. Repeat the process until you have finished all 4 wheels. You will have to pump the sprayer several times to maintain the 5-10 PSI needed to do the job. When finished bleeding, loosen the pump handle to relieve the pressure, remove the stopper/modified master cylinder cap and test the pedal.
 
tunedin302 said:
I don't believe this is the problem. Would hate to see him do a change over and still have the same problem. He has a 1" bore MC already and it is very common to run the fox booster with the sn95 brakes.

The 93 Cobra Booster is much larger than the stock fox Boosters!
 
tunedin302 said:
To adjust the prop rod (ONLY do this after you bleed the brakes about two more times) ... pull the driver front wheel, undo the bolt in the fenderwell that holds the stock PV to the fenderwall. Next, undo the nuts that hold the MC in place. Carefully, pull the MC from the booster with the lines still in tact. You will see a acorn nut on the end of the booster rod. Mark this nut with white out so you know where the starting point was located. You will have to use some vice grips or pliers to hold the booster rod while you turn the acorn nut counter-clockwise about 1 full turn. Reinstall the MC and PV. Be forewarned, if you do this procedure prior to getting all the air out of the lines then the pressure will swell and cause your brakes to become locked after they heat up. You will then have to loosen the nuts on the MC in an emergency situation (essentially disengaging the booster rod from the mc) so you can drive home.

That confused the shyt out of me. I never knew that and if that is true then I will have to remember that when I do my conversion..
 
Shakerhood said:
The 93 Cobra Booster is much larger than the stock fox Boosters!

I'm talking about the MC ... the 93 cobra has a 1" bore on the MC. However, it seems that if the booster on the 93 cobras are larger than the fox then there is no need to upgrade to the sn95 booster. :shrug:
 
oh no problem, after I read it a few times I figured it out. I only have a few pieces to get for my conversion (the biggest thing being tires, so expensive for 17's) and the mc and booster is one of them. Everyone seems to want a lot for them.
 
tunedin302 said:
I'm talking about the MC ... the 93 cobra has a 1" bore on the MC. However, it seems that if the booster on the 93 cobras are larger than the fox then there is no need to upgrade to the sn95 booster. :shrug:


Well the M-2300-K Kit comes with a 93 Cobra M/C and a 93 Cobra Brake Booster, so they are designed to run Cobra discs all the way around.
 
Shakerhood said:
Well the M-2300-K Kit comes with a 93 Cobra M/C and a 93 Cobra Brake Booster, so they are designed to run Cobra discs all the way around.

Hey Shaker ... sorry but I don't understand what you're trying to say. If he already has the 93 cobra MC and booster then there is no need for an upgrade. :shrug:
 
tunedin302 said:
Hey Shaker ... sorry but I don't understand what you're trying to say. If he already has the 93 cobra MC and booster then there is no need for an upgrade. :shrug:

That has been my point from the beginning, I have been saying he has the correct M/C and Booster for the brakes he is running!