These notes describe what I did on my car for my personal use and are provided here for entertainment; they are not meant to be instructions for others to do maintenance on their vehicles.
This section describes how I overhauled the front brakes for my '70 TR6. As mentioned earlier, the car is completely disassembled and I was able to take the front suspension assemblies to the workshop to do the work. Everything done here could have been done with the suspension assemblies still on the car.
The book says to remove the spring clips and then slide out the pad retaining pins. Like they're going to come out that easy. Those pins seem to corrode to the caliper in 24 hours or 100 miles usage, whichever comes first. Fortunately the spring clips last a little longer --- a year or two. The problem is apparently that there are no inexpensive surface coatings that will survive the high heat the brakes generate. I used pliers to remove all of the clips I could and then used a pin punch and large hammer to drive the pins out of the caliper. This is another task that usually provides observing children an opportunity to expand their vocabulary. Once the clips are out, the old pads can be slid out and new pads slipped into position and the pins and spring clips replaced. See discussion later about anti-squeal devices. I always bleed the brakes to remove any air that might have entered the system when I opened the bleed nipple. See separate note on bleeding the brakes.
Removing the Caliper: The caliper is fastened to the caliper mounting plate of the front suspension by the two bolts noted in the left photo below. I got them loose without too much difficulty using a long breaking bar and a 4 foot length of 1 inch pipe wedged into the suspension to keep it from turning. Before removal it's a good ideal to disconnect the input pipe if the pipe is to be salvaged. In my case, the pipe was trash so I cut it off. Once the bolts are out the caliper slid off and the dust shield and hydraulic hose bracket can be removed. The bare caliper is shown on the right. I then used the process described above to remove the pads.
Removing the nipple & fittings: Sometimes the fittings and bleed nipples are hard to remove and this set proved no exception. I usually soak around the input pipefitting and bleed nipple with PB Blaster and let set overnight. I use a 6- point socket so the head isn't rounded. This time I got impatient and only waited through a long lunch. I managed to twist off the bleed nipple on one of the calipers. I ran a 21/64 drill down the hole in the center of the bleed nipple in preparation to tapping the hole 3/8-24, the original threads for this non metric caliper. When the drill passed the end of the threaded part of the nipple, the narrower part at the tip separated and started rotating --- couldn't drill any further. Turned it upside down and rapped it a couple times on the bench and the end piece fell out. I then ran the tap down the hole and it merely shoved the remaining threaded part of the nipple out of the threads in the caliper ---- cleaned up the old threads just like new.
Removing the Pistons: These calipers had been out of use for about 12 years and the pistons were stuck. I first removed the boots around the ends of the pistons (tore them off in pieces) and sprayed PB Blaster around the outside of the piston. After a short time to let the Blaster work, I shoved a steel block between the pistons and used a hammer on each side to drive the pistons into the calipers (left photo). This broke the pistons loose. I then injected compressed air into the caliper using the same adaptor as used on the master cylinder (center photo). One of the pistons moved out. I then used hammer and block to push it back in. I repeated this several times until it moved fairly easily. I then pushed it in and held it (the loose piston) with a clamp (right photo) and applied air again. This caused the other piston to come all the way out. I then tapped the grove in the loose piston a little on each side to work it out. (If you folks look very closely you'll see that these three photos are of the left caliper -- I had already disassembled the right caliper and forgot to take pictures during the process).
Caliper Variations: There were two changes in calipers during the TR250-TR6 manufacture. The first change at commission number CC29930 (early 69?) was to the front of the piston to accommodate different style boot (the later boot had a spring clip to retain it to the caliper) The photo at the lower right shows the difference in the pistons. These are new stainless steel pistons; the later style is on the far right. The type number on the casting was changed from TYPE 16P to TYPE 16BP when the piston style was changed. There was no change to the caliper castings at this time other than the number. The two style pistons are exactly the same size 2.125" (2 1/8") diameter and 1.140" depth. The 16P caliper is from my '70 TR6 commission number CC53270. The factory equipment for that commission number was the Type 16PB. My guess is that rebuilt calipers were installed at some time and with the early castings and late pistons.
Caliper variations Summary: Based on these data and checking the various catalogues I conclude the following:
With that all said, I plan to use only the later style pistons whenever I have to replace the pistons because I think the later style boot is a more effective shield. Since the pistons are the same size I see no reason why the different version of calipers can't be mixed on a car. However, it could get very confusing with different rebuild kits for each side due to different style pistons or different type bolts and fittings due to metric or non-metric. I don't think I'll mix calipers on any of my TRs.
The next step I did was to powder coat the caliper halves. One could follow the same process if painting the caliper. The rubber seals were removed from the inside of the cylinders, as was the little rubber washer seal between the two caliper halves. All the holes were plugged and old pistons were inserted into the cylinders to keep the paint out of there and the machined surfaces where the two haves mate were carefully masked. The photos below show the powder coated halves of one caliper.
The next thing I did was run a tap though all threaded passages and then blow out all passages. I then covered the cylinder with a light coat of brake fluid. It is very important that no petroleum based grease or oil get into the brake system so only brake fluid and the Girling or Lockheed Rubber grease were used on the parts.
I then inserted a new seal (Moss part # 583-820) in the passage between the two halves of the caliper and bolted the two halves together. I found the little seals listed in the moss TR2, 3 & 4A catalogue. On the same page as the seal was the following caliper tip: Girling "split" calipers should not be separated for any reason. They were not designed for separation and reassembly and proper torque specifications are not known, other than the inner and out bolts are torqued differently. The inside bolts are 7/16" diameter and the outside bolts are 3/8" diameter. I torqued the outside 3/8" bolts to 40 ft-lbs and the inside 7/16" bolts to 70 ft-lbs. I then coated the bleed nipple threads with rubber grease, screwed it into position and covered the end with a new cap from the rebuild kit.
Rotors: There is always a question as to whether the rotors should be resurfaced. I don't have the rotors resurfaced unless they have been gouged (pads wore through) or the rotors are not running true. I removed the rotors from the hubs on the first TR I rebuilt. After I reassembled everything I found that the rotors didn't run true and kicked the pads back so that the pedal went to the floor each time I applied the brakes. If I pumped the brakes quickly I could get the pads against the rotors and the brakes would function. I must have reassembled the rotors to different hubs or got the orientation different. Resurfacing fixed this. I have an old Haynes manual that says to be sure to make a locating mark on each piece if separating the rotor from the hub. (Should have read that before I took the rotors off the hub.) They also list the maximum run out at .002 inches. Neither the Factory TR6 manual nor the Bentley manual mention resurfacing the rotors or list any specifications as to the minimum thickness. I polled the 6-PACK e-mail list and Dick Taylor passed on that the new rotors are about 1/2 inch thick and several others pointed out that some rotors have markings on the inside that say the the minimum thickness is 0.45 inches. I had two sets on rotors in the workshop, one set was unmarked and the other set had the 0.45 minimum thickness cast into the rotor.
The rotors I decided to use for his project originally came off a '76 and were later used on a '73. They have a thickness of 0.50 inches indicating they have never be resurfaced. The rotor surfaces were heavily pitted from corrosion. I degreased and basted the hubs along with the the brake dust shield and the hose bracket. These components are shown in next photo below. If you look closely you can see the pits in the rotor surface. This was before I had them resurfaced.
Recall that the rotors were 0.50 inches thick before resurfacing. After resurfacing they measured ???? (I'll fill this in when I actually get them resurfaced)
The sketch below is from the TRF TR250 catalog and then processed to show the points I wanted. Note there is a shim shown by the dust cover. I've taken apart many front suspensions and never seen one of these shims. The shim goes between the dust cover and caliper and serves to move the dust cover away from the rotor. I have seen cases where the dust cover was too close to the rotor and rubbed against it. I've always been able to deal with that problem by bending the offending part of the dust cover away from the rotor.
Replacement Pads & Shims: The pads removed from the calipers had plenty of life remaining. However, both the pads and shims are heavily corroded. The concern I had was that the corrosion might have weakened the bond between the pad and the steel backing so I purchased new pads. I've always used the standard pads from TRF and have encountered no problems. Some suppliers sell higher priced pads and well as cross-drilled rotors, etc. I've never felt a need to use anything but the standard OEM product. However, if I were racing or had encountered brakes problems due to unusual usage I would investigate those products.
I have encountered front brake squealing on most my TRs from time to time. At the moment my '76TR6 doesn't squeal and my TR250 does. The '76 doesn't have the anti-squeal shims. I'm not sure whether the TR250 has the shims. However, I do remember some of the worst squealers had the shims installed. The squealing is caused by vibrations between the pad and piston. In the past the anti-squeal shim kit from TRF contained a little packet of grease. This time it didn't so I bought a tube of brake grease from the Auto Works.
I found I had a new pad retaining pin kit so I used it rather than cleaning up the old pins. The pads, anti-squeal shims come in sets that do both sides. The components for one side are shown in the left photo below. The assembled rotors are shown in the right photo. Assembly is straightforward with the caution that the shims must be oriented such that the arrow points in the direction of rotor rotation (when going forward). Apparently the anti-squeal kit doesn't help much when braking while traveling backwards. I applied the brake grease to both sides of the anti-squeal shims.
Finished Photo: I'll add a photo here of the front suspension with brakes installed after I get the suspension cleaned up, pained and reassembled.