|
 |
TR250 & TR6 Brakes
Overhauling Pedal Assembly
|
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.
The pedal assembly is a fairy straightforward collection of steel
components. I've found three areas that usually require attention on
the pedals, the hole in the clutch pedal arm where the clutch master
cylinder pushrod connects, the bushes at the top of the pedal arms and the paint that is usually screwed up from
leaking hydraulic fluid. The other typical failure is the brake lamp switch that is mounted to the
pedal box.
The sketch at the right below was taken from a TRF catalog and then processed. The unit is disassembled by
removing
the circlip from one end of the pedal shaft and sliding out the
shaft.
|
The sketch shows bushes that are driven into the end of each side
of each pedal. I've never had a problem with these bushes and
have never replaced then. I tried to drive one of the (steel) bushes
out so I could show what it looks like. I was able to get it
one to move with considerable force but didn't go further as I was
afraid I'd ruin the bush and I didn't have any replacements on
hand. If I really wanted to replace the bushes and had as
much trouble as I had here, I'd probably slid a hacksaw blade into
the hole for the pedal in the pedal and slit one side of the
bush. That should release some of the forces allowing the bush
to come out easier. (See more on bushes below.)
The pedal shaft is 5/8 inch and the inside of the hole
in the pedal appears to be a little less than 3/4 inches meaning that the bush wall
thickness is ~1/16 inch or a little less. The TRF catalog says that the
bushes were changed at CC 50,000 ('70?) and the later bush is now
supplied for all applications. The pedal box I'm working on
here came from a '73.
The sketch shows return springs for both the clutch and brake
pedals. That is an error, only the clutch pedal has a a return
spring. If the brake pedal had a spring has shown, it would
have to pass through the brake lamp switch. |
 |
| Elongated Hole in Clutch Pedal Arm: This hole supports the
clevis pin between their pedal arm and the clutch master cylinder
pushrod. After considerable service the holes in both the push
rod and master cylinder push rod tend to elongate as shown in photo on
right. (This photo is of a different pedal, not the one
overhauled here.) The clevis pins
also wear but are easily replaced. The hole in the clutch pedal
overhauled here was worn more than that shown on the right, but the bushes showed no wear.
I've
never seen a problem with the hole and clevis pin between the brake pedal
arm and the servo pushrod. |
 |
I hate to think of how many
thousands of clutch hydraulic systems and clutches have been
replaced to fix a "hard to shift into 1st or reverse gears
problem" only to find no improvement. One thing nice
about unnecessary repairs is that it keeps the parts volume up helping to hold
down the cost of replacements when I really need them.
As far as I know neither new pedals nor new clutch master cylinder push rods are
available. One can get a new push rod with a new master
cylinder for > $100. I won't go that route because I'm not going
to replace my nice shiny powder coated MC with a crummy looking new one.
So, I repaired both.
The clevis pin is 5/16-inch diameter. The holes are usually
elongated to something like 7/16 inches. My first thought was to
just drill out the holes with a 7/16-inch drill and make a set of bushes
7/16-inch OD and 5/16-inch ID. That way the next
time I could just replace the bushes. Bad Idea! Fortunately,
this time I though before I wasted my time. The problem
with that idea is the center of the 7/16-inch holes will
be displaced from the center of the original holes because the holes
elongate in only one direction. Using those centers will result in
loss of pedal (and release bearing) motion. The solution I
used was to weld pieces of 7/16-inch rod into the holes, grind the sides
smooth and drill new holes at the location of the original
holes. The original holes were in the center (front-to-back) of
the pedal arm. If you look real close at the hole in the
photo below, the new hole appears to be to off center toward the front of
the arm (bottom of photo). In fact it is about .030 inches off
center and will give about 1/8-inch additional pedal.
Once I had the center of the holes in the approximately correct
position I could have drilled them over size and used the bushes mention
above. Another option was to drill 3/8-inch holes and use a 3/8-inch
clevis pin. I decided against all these schemes because they are non-standard. Also, this fix will last ~ 100 K miles, long beyond the
expected time to expiration of the owner.
All parts except the pedal shaft and circlips were powder
coated. The clutch return spring and brake lamp switch were missing
from his unit. I purchased a new spring and found a switch in
the junk box --- didn't powder coat the spring or switch. Before reassembly I ran a tap though all the
threaded holes to remove and sand from the blasting and any other debris.
| Reassembly: Reassembly was straightforward. I
Packed some white grease in the pedal arms between the two bushes and lightly
coated the pedal shaft before installing it. Note from the diagram
above that the double coil washers go on the center side of each pedal
arm. New clevis pins and cotter pins were then installed to
complete the reassembly. The completed unit is shown on the right.
Blake Lamp Switch Adjustment: The position of the
brake lamp can be adjusted by bending the mounting tab. I deferred this adjustment until the pedal assembly is
mounted in the car because the released position of the brake pedal is controlled
by the pushrod in the servo. Once that pedal assembly and servo are
mounted and the pedal connected to the pushrod with the clevis pin, I will adjust
the switch so that it is off when the pedal is released and operated when
the pedal footpad is pushed in about 1/2 inch. Caution: if the
brake pedal is not connected to the servo it is easy to pull the
pedal against the switch hard enough to force some of the later design
switches apart.
Since there is a spring inside, the parts fly everywhere (been there,
done that). |
 |
Rubber Pads: The final step was to install new rubber
pedal pads.
More on Bushes: A couple
days after finishing the pedal assembly above (originally from a '73) I
pulled the pedal assembly from my '70 to give to a friend who had bad bushes
in his '70. I was surprised to find that the bushes were bad in
the unit from the '70. More interesting still was the fact that the
hole for the clevis pin in the clutch pedal showed no wear. Strange
--- all the other units I have had no bush problem but worn clutch clevis
pin holes. When I took the assembly apart I found only one bush,
the other three were gone. The remaining bush was made of plastic or
nylon and heavily worn. From this I concluded that the early bushes
were plastic and the later steel. However, the TRF Blue Catalog
says the bushes were changed at CC50000 and my '70 is CC53270.
| Hmmm, all kinds
of possibilities --- maybe all my late pedal assemblies have been
re-bushed. Or --- the '70 may have had the pedal assembly
replaced at some time. TRF now only supplies the the later
bush but I don't know whether it's the steel one or the plastic
one. (If someone has purchased a new set of bushes, please let
me know what type you received and from where.)
The workshop was full of my brake stuff
and suspension stuff and the neighbor's gearbox and OD
so I wanted to get this pedal assembly finished and out of the
way. Decided to fabricate new bushes from
brass. The original plastic ones were ~ 0.4"
long. I made these 0.5" long with 0.718" OD and
0.625" ID. The new bushes are shown in upper right
photo. The lower photos show the bushes installed in the
pedals. They worked great.
|
 |
 |
 |
At least now I understand why so many of
my friends have replaced the bushes. I was just lucky up to this point
to have only the steel bushes.
| John Denson of Sweden sent following on April 22,
2002.
I've just finished an overhaul of the pedal box of my 1970 TR6 and
found your article on the Buckeye Triumphs site after I had completed
it. This job needed doing to replace the bushes which had vanished
completely on the clutch pedal and to make good paintwork both inside
the car and in the engine bay. Your web page looks reasonably new so
maybe its worth a couple of comments.
- I did elect to bush the worn clutch clevis pin hole. My car is the
PI
version and
has a VERY heavy clutch. Given the known problems with misspecified
clutch>
rates etc. I decided that the idea of providing a replaceable bush
with
better wear
properties seemed attractive. I compensated for the wear by filing
opposite
'wear' - an old clockmakers trick for rebushing worn holes (not
especially
accurate
I agree). I then drilled (reaming would have been better) to accept a
bronze
bush
made from a bronze TR6 exhaust valve guide. These are nominally 1/2 in
OD>
and
5/16 in ID i.e. just right! An expensive way to make a bush but I've
got
lots more left.........
- As stated above the clutch pedal bushes had vanished (lots of lost
motion....)
so I ordered a pair from Rimmer Bros in the UK. The replacements are
steel
backed
'white metal' and were reasonably cheap. I had inspected the greasy
bore of
the
brake pedal and assumed from the appearance that they had been
replaced with
steel bushes but a quick poke with a screw diver and they fell out -
plastic.
Thus I
had to order a second set from a company in Sweden who use Moss Europe
as
suppliers (not quite so cheap another middleman).
This job at least takes care of the gear changes but I'd still like to
know
what clutch
has been installed.............
Hope this info helps.
Regards
John Denson
Thanks John. Neat trick for centering the pushrod
bushes. Now I wish I'd have used bushes. I just looked up
"Bronze Bearings" at the McMaster-Carr
website and found 5/16" ID bronze bearings with 3/8",
7/16" and 1/2" OD and various lengths --- for less than
$1. I haven't installed that pedal box yet ... maybe
I'll redo it.
Also, thanks for the good news on the replacement pedal shaft
bushes -- they're steel backed, at least those supplied in
Europe.
|
|