Chris Grayson's (of MC2Racing) Guide to a Reasonably Priced, Street Setup for Handling

Chris Grayson has been involved in Merkur XR4Ti performance for a very long time. He formed MC2Racing to provide quality performance parts t...

Monday, December 7, 2020

Throwback: David Godfrey's Rear Disc Brake Conversion with Thunderbird Rotors, Calipers

David Godfrey's XR4Ti Rear Disc Brake Conversion

David Godfrey is somewhat of a legend in the XR4Ti circles. He was one of the first to figure out a bigger front disc brake option using off the shelf discs, as well as a rear disc brake conversion. 

David no longer makes this and his site is no longer maintained, or even available. I pulled this out of the Internet archives to give it a new place to live, so people can see it, and hopefully start making them again some day. 


PS - there are better options out there today, though. Mainly in Tim Spencer's Ford Focus 280mm/11" rotor and compatible calipers. I'll get links and information out here on that as well.

Thanks for your interest in the rear disc conversion brackets I offer. In the past I have provided a copy of the instructions that were included in the Stainless Steel Brake Company's rear disc conversion kit. These instructions are sufficient if you are installing SSBC's complete kit, but more info is needed for the D.I.Y. types. Also, the parking brake cable routing and connection is a bit of a pain to work out even if the SSBC kit is used. Hopefully the info provided will be sufficient to allow for an easy and trouble free installation.

The cheapest rotors to use come from the rear end of a 87-88 Turbo Coupe. These rotors are not perfectly hubcentric on the XR hubs can be made to work just fine by carefully centering the rotor before tightening the wheel or making a .020 thick shim (using shim stock) .2" wide x 7.50" long and placing this shim between the hub and rotor. SSBC will not tell if the rotors in their kit are standard TC or specially machined TC items with a smaller hole to make it hubcentric. Not a big deal anyway.

Rear calipers from an 87-88 Ford Thunderbird Turbo Coupe or 90-92 Lincoln, Taurus, or Sable will fit the brackets that I supply. The interchange manual does not show an alternate listing for the Turbo Coupe calipers but the Lincoln, Taurus and Sable calipers are the same.

Before you buy rebuilt calipers check and make sure of what is included. The local parts stores list rebuilt rear calipers as "loaded", "unloaded" and "semi loaded". Loaded calipers refer to calipers coming with brake pads and unloaded calipers do not. I was not given a specific answer as to what "semi loaded" means. One guy said it comes with hardware but could not tell me what the hardware was.  I asked if the rebuilt caliper included the factory sliding pin mounting bracket and was told it does. When I looked at the caliper they had in stock the bracket was not included. I have run into this before on the SVT/T-bird front brake conversion. If you get rebuilt calipers make sure you ask for "rebuilt calipers, loaded, with brackets". This should ensure you get the entire caliper assembly.

Complete Brake Warehouse (800-581-2339, ask for Brian) understands the terminology and has the complete caliper assemblies in stock. Core charge for this caliper is high and typically runs around $75 each. It pays to go scrounging junkyards for either good rear caliper assemblies or cheap cores.

Brake hoses
I looked at various ways to connect the Merkur XR4Ti hard line to the T-bird calipers and settled on a pre-made stainless steel brake hose, part number 3-21-S-B, from Pegasus Racing (800-688-6946).  The hoses have crimped on ends and are pressure tested to 3K PSI. Brake line adapters, part number 3265-16 (also from Pegasus Racing), are required to go from the XR 10mm flare nut to a -3 AN male fitting.  These parts from Pegasus are cheaper than braided steel XR brake hoses. The stock XR flex hoses and the hard lines attached to the rear trailing arm are discarded. Another source for these is Transatlantic Racing  (770-889-0499, ask for Paul). A description is listed below. Transatlantic will get the hoses quickly if they do not have them in stock. Pegasus will not and will call, maybe, when/if they get them.

Note that the caliper has a unique to Ford 10mm x 1.5 thread pitch banjo bolt thread. If you get your calipers from a junkyard make sure you get the banjo bolts also. CBW has the correct banjo bolts listed under part number H9469 at a cost of $6.60 for 4 pieces.

Caliper brackets
The adapters are CNC machined from 1018 series steel and allow the T-bird caliper to be bolted to the XR swing arm.

Parking brake
In the installation instructions below is a description of how to route the parking brake using the stock XR brake cables.

This is a bolt on installation and the parts install just as easily as the standard XR brakes.

Loosen the wheel flange retaining nut before jacking the car up. Note that the driver's side retaining nut comes off turning clockwise. Then remove the wheel, brake drum, and wheel flange and disconnect the brake line.  Remove the 4 bolts that hold the bearing hub to the trailing arm and then remove the hub and backing plate. Squeeze the 3 prongs on the parking brake cable where it protrudes through the backing plate and remove the cable.

Install the conversion brackets with the caliper mounting holes at the 11 o-clock position on the passenger's side and the 1 o-clock position on the driver's side. Re-install the bearing hub using the stock bolts. Place the wheel flange on the splines and sung down the retaining bolt. At this time you can install the rotor and caliper. Note that the RH caliper is used on the LH side of your XR and the LH caliper is used on the RH side. When installed the parking brake lever should be facing slightly up and forward. The calipers bolt to the brackets with 12mm x 1.75  x  25mm long bolts (now supplied).

The Merkur XR4Ti brake cable can be modified to work with the Turbo Coupe type calipers without using additional brackets.
The brake cable is routed through a hole and grommet on the rear subframe and then secured with a fold over clip on the trailing arm close to the wheel. Remove the cable from the clip and then from the grommet Route the cable back toward the caliper but this time run it between the subframe and body.  After making sure the parking brake handle is in the down position cut the passenger side inner cable wire about 5" in front of the cable mounting clip on the inside of the drive shaft tunnel. Pull the inner cable from the housing and remove the spring from the end of the cable. Re-insert the inner cable in the housing. Remove the driver's side cable and then the spring. Re-insert the cable in the housing and then route it between the sub frame and the body and then around the anchor on the parking brake handle. Position the cable adjuster about 3" from the end of the cable.

Insert the caliper end of the cable through the anchor on the caliper and connect the inner cable to the parking brake lever.  Pull all the slack from the cables and let the ends overlap. Cut the end of the driver's side cable (the end running to the rear) so there is about 3" of overlap. Strip 3" of the plastic covering from the end of each inner wire and splice the together using at least 2 wire rope clips for 1/8" cable. These clips consist of a small U-bolt and saddle and are designed to splice cable together. They can be bought at home supply stores. Tighten the snot out of the clips and then pull hard on the parking brake handle to make sure they do not slip.

An alternative way to make the cables work without cutting is to work the springs from the ends of the cable and make up the length difference by forming the cable in a loop and then securing the loop with the wire rope clamps.


Parking Brake Cable U-bolt Splice

Parking Brake Cable View

Parking Brake Cable, Brake Hose, Bracket, & Caliper

Remove the brake flex hose that goes from the body to the trailing arm as well as the hard line that went to the wheel cylinder. Install the brake adapter fitting on the end brake line on the body. Connect the brake line to the adapter and the banjo end of the line to the caliper using the correct banjo bolts and copper sealing washers.

Rear Brake Hose Routing

Remove the stock proportioning valve and replace it with a length of tubing connecting the master cylinder port directly to the rear brake line. The fittings on the hose are kinda odd so it might be hard to match up. Some have used an after market proportioning valve with success. Perhaps the easiest thing to do is pull the guts from the stock proportioning valve. This is easy to do and works well.  Use the dust shields if you want, but I left them off.

Finished Rear Brake Conversion

Required parts
Item                                              Part Number/Application            Quantity        Source
rear brake adapter brackets                                                                   2                      me!

Turbo Coupe rotor                        87-88     Turbo Coupe                     2

rear caliper                                    87-88 Turbo coupe, 90-92              2                     varies
                                                        Lincoln, Taurus & Sable

Banjo bolt                                       stock Ford or CBW #H9469           2                    varies

brake hose                                     3-21-S-B                                           2            Pegasus Racing
                                                        18" long, -3 AN to 10mm (3.8) banjo         Transatlantic Racing

hose adapter                                  3265-16                                            2             Pegasus Racing
                                                          -3AN to 10mm male                                   Transatlantic Racing

copper crush washers                   3241-3/8                                           4             Pegasus Racing

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