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 V6 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:
'84-86 SVO - (SAE
Threads) 1 1/8" bore, old style aluminum reservoir unit. no low
fluid sensor. This is the same as the 84-90 Lincoln Mark 7. The
difference is usually the SVO is aluminum, and the Lincoln can be a
cast iron unit. The aluminum is what you want to keep the weight
'85 Towncar - (SAE Threads)
1" bore, old style aluminum reservoir unit. no low fluid sensor.
'93 Cobra -
(metric threads) 1.00" bore
'94-95 GT/V6 -
(metric threads) 1 1/16" bore, stock plug in for the low fluid
'94-98 V6 -
(metric threads) 1 1/16" bore, stock plug in for the low fluid
'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
'99 V6 -
(metric threads) 1.000" and 1.006" bore. Can be converted to work
for the low fluid sensor on the fox3 cars
96+ V8 Units -
These are hydroboosted and the mounted flange is vertically vs
horizontal required for a vacuum booster. They will NOT work
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
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. Do NOT use this unit
unless you have the SVO front 73mm brakes and rear SVO brakes
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. 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 vaccum 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
available since they are all larger than the stock unit you are
replacing - but finding the most cost effective unit.
Since you already have a 2 port SAE threaded MC, you can swap one
from a different car. The '85 Lincoln Towncar with a 1" bore is
about the best unit for most all brake upgrades.
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.
Either the 1" 93 Cobra unit or 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 '94-95 GT/V6, '94-98 V6 MC, the '99 V6 units, the
'94-95 Cobra, and '93 Cobra MCs!
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
Master Cylinder Notes:
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 earlier mustangs!
Once you have the larger master cylinder on
your Mustang, you may find that it takes more pressure on the pedal
to lock up the brakes then you would like. First, check all the
vacuum lines for dry rot, cracks or holes. Replace all hoses that
look skeptical. This will restore the vacuum for the booster to work
If that still does not help, then you can
consider two options. The first being to change to a smaller master
cylinder. The second it to upgrade the brake booster. 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. If you have heard
about the Cobra brake booster, the same unit in the Ford M2300K
brake kit (same as 1994-1998 Mustang Cobra and 1993 & 1995 Cobra R),
you probably have heard horror stories about installing the unit.
You do NOT need to beat the strut tower to install this unit for
most all 87-93 installations. Remove the old unit and the lower hole
in the firewall you need to elongate down about 1". This will allow
the unit to slide right in!
Cost $100-200 depending on if it is reman
or new. You may be able to find one from a person selling it from
their M2300K kit for cheaper.