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TR250 & TR6 Brakes
Overhauling Rear Brakes
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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
rear brakes for my '70 TR6. As mentioned in other notes, the car is completely
disassembled and I was able to take the rear suspension arms to the
workshop to do the work (it's February, cold in the garage but nice and
warm in the basement workshop). Everything done here could have been
done with the suspension arms still on the car.
| Removing the drum:
The first step to get at the rear brake components is to remove
the drum. The photos at right show the right rear suspension
arm with hub on the
workbench. The drum
is retained to the hub by the two little flat head
screws. (Actually, the drum is sandwiched between the wheel
and hub and held in place by the four studs and lug
nuts. The main purpose of the little screws is to make
drum removal difficult.) If I can't get the screws out
and end up buggering up the heads I drill out the screw heads with
a 1/4 inch drill. I only drill though the head far enough so
I can knock the head off with a chisel and not so far as to damage
the threads in the hub. I later use PB Blaster on the remnants
in the hub and then a screw extractor.
The book says that once the little screws are out, you withdraw
the drum --- like it's going to slide right off. No way! That sucker holds on like a
tick to a dog. If the stuff is still on the car, I make sure that the
handbrake is released
and then push the lever where the handbrake cable connects as far
as it will go toward the brake back plate as shown in photo.
I next make sure I can turn the
drum. If not I use a brake-adjusting wrench to turn the
adjusting screw out as far as it will go out. The adjuster
screw is on the bottom of the back plate. I always use a
brake-adjusting wrench to avoid damaging the 1/4 inch square head of the adjuster
screw. Once the hub can be turned, I use a big
hammer and punch on the lip around the outside of the drum. It usually
comes off after I pound a while. (This task usually expands
the vocabulary of observing children). |
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Removing the Hub: The components with the drums removed are shown above. Yes they are filthy. All maintenance can be done
on the bakes without removing the hub. However, I wanted to
clean and paint the back plate so I pulled the hub at this point. It
also makes for better photos with the hub out of the way. (Also, to
make for better photos I removed the back plate, wheel cylinder and
adjuster, cleaned them up and then put everything back
together.) The six nuts holding the hub to the studs in
the suspension arm are accessed through the two holes in the hub using a
socket and extension as shown on the left photo below. I used a
construction pry bar to get the hub loose. The hub was then withdrawn as shown in center
photo. The handbrake cable and hydraulic pipe were then disconnected
(right photo). The pipe in this case was not worth saving so I cut
it at the wheel cylinder.
Removing the Shoes: I removed the brake shoes next. The ends of the brake shoe
hold-down pins were grasped with pliers and rotated 90 degrees to release
them from the hold-down springs, see left photo below. The trick I
use to remove the shoes is to grasp the top end of the rear shoe with
pliers as shown in the middle photo --- the pliers act like a lever ---
then lift the end of the shoe out of the slot in the cylinder and pull it in
front of the cylinder. This releases some of the tension so it
is easy to pull
the lower end of one of the shoes out of the slot in the adjuster. At
this point the springs are all loose and shoes with springs can be pulled
off leaving the plate with wheel cylinder and adjuster as shown in right photo.
| Removing Adjuster & Wheel Cylinder: I removed the two nuts
that hold the adjuster next as
shown on the right. The wheel cylinder is a little more difficult to
remove. I first drove the small locking plate to the
rear using a punch as shown in left photo
below. Next, I slipped two small screwdrivers under
the back end of the female locking plate and pried it up and out
of the two tabs on the male inner locking plate. I could then
drive the female plate to the rear as shown in the middle photo. Once the female plate was out of the way, the rubber dust
cover was removed. This left sufficient slack in the cylinder
so that it could be lifted away from the plate enough to
slip the handbrake lever out of the retaining
slots. The handbrake lever was then removed from the brake
plate. With the lever out of the way, the male retaining plate was
free to
slide toward the front allowing the wheel cylinder to be removed
(right photo). |
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The right side brake components are shown in the photo below ---
less the drum and shoes. The left side is identical (same part
numbers) except for the Brake Plate. Different pipes and rear hoses
are used on each side as discussed in the section on
pipes.
| Disassembling Adjuster & Wheel
Cylinder: The adjuster came apart pretty easy this
time. In the past however I've had trouble freeing the
adjuster screw. A shot of PB Blaster, and overnight wait and
then heating with a propane torch seems to free the steel parts
from the grasp of the aluminum castings. I usually don't
want to wait so give it a shot of PB Blaster --- get a cup
of coffee --- heat -- PB Blaster, heat again, at which point it
usually comes free.
The wheel cylinders are usually not so easy. The
piston can be pulled out with pliers. The problem is the
bleed nipple and the pipefitting. I've had good luck with
the PB Blaster & heat cycle described above for the
adjuster. I use a 7/16 inch 6 point socket and try not to
twist them off. If I twist one off -- all is not lost.
Both the fitting and bleed nipple have holes in the center so they
can usually be drilled out 21/64" and then tapped
3/8-24. Usually the old threads from the steel parts come
out when the tap is started. Note that the drill should not
go all the way into the hole as it might damage the end part where
the fitting and nipple seal. The end of the nipple and
the end of the fitting aren't threaded and should come out after the top threaded
part is drilled out.
The rubber parts were discarded and everything else was
sandblasted and the castings were then powder coated aluminum
color at the same time as the master cylinder. The powder
coating should keep everything looking nice longer. |
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I decided to purchase the following new parts:
I decided not to pay $2 each for the shoe hold-down
springs. I already had a new set of brake shoes and was also
considering reusing the old ones, so I didn't order those either. Replacement of both the springs and
wheel cylinder fitting kits is probably overkill. I'm keeping all the
used parts -- maybe I'll blast and powder coat them for some future project.
Before starting the reassembly I blasted and powder coated
the backing plates, and shoe hold-down springs gloss
black. The wheel cylinders, adjusters and park brake lever
were all powder coated in aluminum.
Reassembling the Adjuster: I ran a tap into the casting threads and a die down the
adjuster screw threads. I then put some wheel bearing grease
inside the casting and screwed the adjuster screw all the way in. I then
coated the tappets with grease and slid them into position. The
adjuster was then mounted to the freshly painted back plate as shown on the
right using stainless steel internal lock washers and nuts. I have two
wrenches for the 1/4" square adjuster screw heads, a ratcheting type that
can stand little torque and a longer box end, both shown in photo on
right. The handle on the box end wrench is at an angle to the end
to give some clearance for the wheel and tire. I recently had a
bout with the 5/16" square head taper bolts used to secure shifting forks
in the gearbox and was on the lookout for a couple 4-point sockets. I
found that McMaster-Carr carries 8 point sockets and that's probably the
best I'll be able to do.
Reassembling the Wheel Cylinder: The first step
in the reassemble process was to hone the cylinder (to remove any glaze as
well as any imperfections. I use a little brake fluid for
lubricant when honing. The hone is shown in action in the left photo
below.) These cylinders were pretty crummy looking when we started on them but
are now better than new with the nice powder coat. I then ran a 3/8-24 tap
into the two ports to clean out the threads. I then washed them
thoroughly in detergent, rinsed and dried with air. The pistons were
then polished on a wire wheel, coated with red rubber grease. The piston
with a new seal installed is as shown in center photo. The inside of the
cylinder was coated with brake fluid, the piston inserted and the area around
the end of the piston and cylinder coated with grease as shown in the right
photo. The piston orientation is off about 90degrees in that
last photo. It was easily rotated with a pair of pliers.
| The next step was to install the dust cover and dust
cover retainer as shown on right. The final step
was to coat the threads on the bleed nipple with the red rubber
grease, install the nipple and then the bleed nipple
cap. It'll be at least a year before these see service so
it's import to close the input port. I temporarily used silicone
plug from my powder coating masking kit. After everything is
installed I plan to plug the hole with a short 3/8-24
bolt. |
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| Installing the Wheel Cylinder: I
bought a new wheel cylinder fitting mounting kit containing rubber dust
covers and the three wheel cylinder locking plates for two cylinders.
The mounting hardware for one cylinder and the rear wheel cylinder lever
assembly are shown on the right. The new locking plates were
black with no corrosion protection so I powder coated them when I did
the lever. The fitting kit also contained a small packet of green
mechanical grease. I was going to use a light lithium grease if
there was no grease in the fitting kit. |
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| The first step in installing the cylinder is to coat the
under side of the cylinder when it fits against the back plate with
grease, coat both sides of the male locking plate with grease and mount
the cylinder and secure with the locking plate with the tabs away from
the cylinder as shown on the right., |
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| The lever assembly was then inserted from the front side
and the pivot rods on the lever slipped into the mating recesses in the
cylinder. The rubber dust cover was then slipped over the end of
the lever and positioned around the male locking plate. |
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| The female locking plate was then slipped into position
over the male locking plate with the tabs on the male plate sliding into
the slots on the female plate as shown on the right. (This almost
sounds like sex education.) |
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| The last step was to install the small outer locking
late. All the other plates slide into position easily by
hand. This plate is a force fit. I used a hammer and small
punch to drive the plate into position. The cylinder was
then checked to make sure it would slide back and forth in the slot on
the back plate. |
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Shoes: My old Haynes manual says the shoes must be
replaced when the shoe linings are worn down to 0.06 inches at the thinnest
point. My shoes were much thicker than that but the linings had cracked in a
few places so I decided to install new shoes. The old shoes are
shown in left photo below. Note that the front (right) shoe has a
rectangular hole at the top end for the lever and the rear shoe doesn't have a
rectangular hole. Excepting that rectangular hole, the shoes are
identical. Note that the lining is closer to the bottom end of the
front shoe and closer to the top end of the rear shoe. The shoes are
mounted with the opposite ends at the top. Note the hole for
the shoe retaining pin is above the midpoint on the rear shoe and below
the midpoint on the front shoe. When the holes are in this position they
line up with the holes in the back plate. So, you know you have the shoes
oriented correctly the retaining pin holes line up with the hoes in the back
plate. The new shoes are shown in the right photo. Note that
there is no difference between the front and rear shoes. (And yes, the other
two shoes look just like these two.) These shoes were purchased in 1989
so for at least 13 years some manufactured have been providing identical shoes
in the new sets of four shoes. About three weeks after installing
these shoes I found another box of new shoes purchased in 1999. The rear
shoes in that set don't have the square hole.
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Springs: When I open the package of new springs I found them a
little shorter than the old ones as shown in the left photo below (new springs
are black). That should be expected as springs stretch with age.
The upper spring was much shorter than expected however, upon further
inspection I found the new spring attaches with a hook rather than the loop of
the old spring. The right photo shows how the old style connects
to the brake shoe. The new style upper spring is the same as both the
old and new lower springs and attach the only way I can see possible, hook
in the hole.
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| Installing the Shoes: The first thing I do
to install the shoes is to fit the rectangular hole in the front shoe
over the lever and slide the edge of the shoe into the slot in the wheel
cylinder piston. I then fit the bottom of the front shoe
into the slot in the adjuster. I next attach the bottom spring to
the holes in the two shoes, place the bottom of the rear shoe into
the back of the adjuster and pull the top of the shoe toward the
rear (right photo) and temporarily set the top of the rear shoe in
the slot in the rear of the wheel cylinder. |
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| I next hook one end of the top spring
into the top hole in the front shoe and then grasp the top of the rear
shoe with pliers as shown on the right. The rear shoe is
lifted off the wheel cylinder and brought to the front far enough to
hook the back of the top spring into the top hole
in the rear shoe. The pliers are then used to gain extra leverage
to push the top of the rear shoe to the rear far enough so that it
can be positioned in the back of the wheel cylinder. |
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| The last step is to push the shoe retaining pins in from the
rear and secure with the shoe hold down springs. I chose not
to order new hold down springs because the cost~ $2 each. Instead, I
blasted four old springs and powder coated them. (I must share this
tale of economy with the wife who seems to think I spend too much money
on car parts.) The
assembled brake unit is shown on the right. |
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| The next thing I did was to blast the drums and powder coat them
using the high temperature silver I use on exhaust manifolds.
This should solve the problem of paint coming off after a few short
trips. I decided not to turn the drums. I look at
two things before deciding to turn the drums. The first is to
determine if the surface is rough --- in my case it was not.
The other thing I look for is a ridge just to the outside of the
area where the shoes rub against the drum. As the drums wear,
this small section near the edge of the drum doesn't wear and forms
the ridge. If this ridge gets very high then it may be even
more difficult
to slide the hubs over the shoes. There was a very small ridge
on these drums but not enough to expend the effort to turn the
drums. Also, one should avoid turning the drums if not
necessary because there is a maximum safe inner diameter. One
of the drums here had "9.04 INS MAXIMUM DRUM DIA WITH NOT
LESS THAN .06 INS LINING THICKNESS" cast into the
front surface. The assembled unit is shown on the right. |
Photo of rear suspension goes here --- after I get it
all cleaned up. |
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