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SN95 5-lug conversion

Under the Hood    -    Rear Brakes    -    Front Brakes

At this point you are ready to get started with the disassembly process. Before you begin, I would like to share a few tips that may make your life easier. First, I cannot stress how important flare wrenches are to this project. You will be turning quite a bit of brake line fittings, so it is a good idea to go to the hardware store and buy a set of standard and metric flare wrenches. The last thing you need is to strip one of these fittings and then have to either get new brake lines and fittings, or have to cut and re-flare your existing lines. Next, be aware that brake fluid will eat up your paint, so avoid spilling or dripping this fluid on your fender or any other part of your car that is painted.

Begin by removing the two brake lines that run from the stock master cylinder to the combination valve. Make sure to put a towel or some fluid absorbing material under these lines to soak up the brake fluid that will run out. Save these lines as they will be reused. Do not remove the brake lines below the combination valve since they will remain there.

Next remove the third brake line from the stock master cylinder and remove the MC by loosening the two nuts that attach it to the booster. *Please note that I bent my third brake line down before I realized I was going to go with the Maximum Motorsports 3-2 kit. If you will be using this kit, DO NOT bend your third brake line in any way. Just let it point straight up until it is time to do the 3-2 conversion.

At this point you are staring at the brake booster. A question that many people ask when doing a 5-lug conversion with rear disks is, "Can I keep my stock booster?" The answer is you could if you are comfortable with a pedal that feels like you are stepping on a brick! The stock 87-93 booster is extremely small compared to the SN95 booster and holds far less vacuum which results in little power brake assist. Here you can see the sheer difference in size between the two boosters. The length is close to identical.

I recommend using a 93 Cobra booster because it has the same vacuum capacity as the 94-98 booster, but the studs are in exactly the same position as the stock 87-93 booster, and thus no elongating of the firewall holes is necessary. I went with the '94-95 GT/V6 booster because that is what was available to me. Make sure you do not use a 96-98 booster because they have an "eyelid" on the booster arm is not curved like the stock 87-93 and the 94-95 boosters are. There are many people using '96-98 boosters (straight eyelid) with success, but I have heard of rare instances of pedal binding problems being associated with these boosters on a foxbody because of the angle at which the pedal shaft pushes the booster arm in. Here is an illustration of the eyelid differences (courtesy of Juan Rodriguez):

 

In order to begin removing the booster, disconnect the vacuum hose that runs to the booster from the vacuum tree. Next, ask yourself, "Am I a double jointed contortionist?" If you answered "no," then go and remove the drivers side front seat. The booster nuts are not easy to get to so any extra room you can provide yourself will keep you from cursing and throwing things. There are four bolts on the seat rails that hold the seat to the floor. After you remove the seat, position yourself under the dash and remove the red clip that holds the booster arm eyelid and brake switch on the brake pedal shaft. Also pay attention to where the white spacer is on the pedal shaft so you know what order to install these things when you get the new booster on. The four nuts that hold the stock booster are not readily accessible, so it is easiest to use a combination of rachet/socket/extensions, as well as a normal wrench. Get creative and use whatever works.

After you pull the stock booster off, you will see the four holes in the firewall that are used for mounting purposes. The sn95 booster bolts are a bit thinner and have different spacing. It is best to make a template by overlaying some cardboard on the bolts of the new booster, making marks on it with a sharpie and drilling holes in it. This way, you could place the template against the firewall and know exactly how much material to take off. *Note: Do not just remove the outer portion of the firewall. You will have to grind/drill deeper than this surface since a non-metallic material is also present directly behind the metal surface but isn't necessarily visible right away. If you are careful, you shouldn't have to hammer the strut tower in any way. Tie all the wiring out of the way and if you have a 5-speed, it is a good idea to remove the clutch cable. Be patient, and elongate the necessary holes little by little until the booster finally slips in. I won't tell you which holes need to be elongated because everyone seems to have their own theories. I have read tech articles where someone was able to get it in with only elongating one or two holes. Personally, I enlarged all four slightly. After it slides in, install and tighten the four nuts that hold the booster to the firewall and position the booster eyelid, brake switch and spacer in the same order as they originally were on the pedal shaft. Reconnect the red clip as well as the vacuum hose and the booster job is finished. I should point out that this was the biggest headache of the entire swap, so it is nice to get it over with.

The next order of business is to get a 2 port master cylinder from any '94-98 GT/V6. The 87-93 MC has a 3rd port which must be addressed by using a 3-2 conversion kit in parallel with the 2-port MC. After spending quite a bit of time researching the fittings I would need for the conversion, I ended up giving up and ordering my kit from Maximum Motorsports. It is extremely overpriced for what it is, but it will prevent a headache. The problem stems from these lines/ports requiring a standard to metric hydraulic fitting adapter. Walk into any autoparts or hardware store and tell them that, and see how they look at you. You can re-use all your stock brake lines. Here is an illustration of what needs to be done:

   

Towards the front of the combination valve you will notice there is a plug that needs to be removed in order for the combination valve to be gutted. When you remove this plug, you will see a spring, rod, and a sleeve. Remove these items and discard them. Transfer the rubber O-ring to the FMS plug that you ordered, and connect this new plug to the combination valve.

The next thing to do is remove the factory front/rear bias valve. This item is designed to be used with stock brakes. As soon as you change anything in the braking system, this item no longer functions as it was intended. Remove it and in its place install the Wilwood knob style front/rear proportioning valve. Attach the two inlet/outlet NPT fittings that come with the valve. Turning it all the way in (clockwise) allows for max rear braking bias, while turning it all the way out, reduces rear brake power by 57%.

 

*Remember, when you bleed the brakes, make sure the knob is turned all the way in. When you are done bleeding the brakes, you want to adjust the system so the front brakes lock up just before the rears under hard braking... But this will be done at the very end.

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