TR6s use hydraulics to transfer the clutch pedal motion to the clutch-operating
shaft in the front of the gearbox. The
system is nice in that it is self-adjusting and requires little maintenance
except for occasionally checking the fluid level in the master cylinder
reservoir. The sketch below
shows the basic system. (The sketches are from a TR6 Maintenance Manual.) The clutch pedal connects to a piston in the master cylinder
(on the right). When the pedal is
pressed, the piston in the master cylinder is pushed in forcing hydraulic fluid
from the master cylinder through the tube and hose to the slave cylinder (on the
left). The fluid pushes the slave cylinder piston toward the open end of the
cylinder pushing the push rod that connects to the lever on the clutch-operating
shaft that in turn releases the clutch.
The major wear components in the hydraulic system are the rubber seals in the cylinders that prevent the hydraulic fluid from escaping past the pistons as the clutch pedal is pressed. The first sign that the seals are leaking is usually a puddle of on one’s left foot or on the carpet under the clutch pedal (leaking master cylinder) or a puddle under the left rear of the engine from a leaking slave cylinder (you must be careful to differentiate a puddle of hydraulic fluid from the puddles of engine and transmission oil than are usually under a Triumph). Another sign that the seals are leaking is a reduced fluid level in the reservoir. (Hopefully you detect the failing clutch before the pedal becomes soft and fails to operate the clutch when you’re 200 miles from home in a thunderstorm.)
I’ve noticed is that the fluid in the reservoir turns black when the seals are
about to fail. After about
ten years the seals seem to dissolve in the fluid; I’ve suspected that planned
obsolesce is at work here.
following describes how to refurbish both the master and slaver cylinders on a
TR250 or TR6. The directions
probably also apply to most other models.
You’ll see that the task is well within the capability of almost anyone
possessing a little energy and a couple monkey wrenches.
experience has been that the slave cylinder fails first (probably because it is
the hardest one to get at). However, whichever has failed, it’s likely the
other is not going to last much longer. Therefore,
it is suggested that when working on the system, both cylinders be pulled and
refurbished at the same time.
Note: If the clutch is not operating properly but there
is no sign of leaking fluid, the problem is most likely not the hydraulic
might want to check out some of the suggestions at the end of the article.
Draining the system
Removing the Cylinders
the parts are cleaned. I usually
apply engine degreaser, rinse that off and then wash with hot water and hand
clearer or dishwashing detergent to get rid of the film from the degreaser.
The inside of the pipe and hose should also be flushed. Finally,
everything is rinsed off with hot water.
I bought a
junk ’76 TR6 about 20 years ago. It
had been driven in the salt for several years so holes were rusted through the
bumpers; big holes were rusted in the sills, the floorboards, and the lower part
of the rear fenders were rusted off.
My main interest was the J type overdrive and a good differential (I
hoped). The young woman from who I
purchased it said that she had had a lot of trouble with the clutch and finally
gave up on it and let it set for a couple years. I paid $200 for the car and
another $50 to have a wrecker drag it home.
checked out the slave cylinder I found that a stack of washers had been inserted
on the bolts between the slave cylinder and the mounting plate to move the
cylinder about a half an inch toward the rear of the car. The slave cylinder piston was missing and the push rod was
hanging down from the clutch shaft arm.
the gearbox was pulled, the push rod was examined more carefully and found
modified; it had been cut and a piece of tubing brazed in to lengthen it.
This rod and a standard rod are shown in the following photo.
Both these modifications suggest that the gearbox had separated from the
engine and migrated toward the rear of the car.
The actual problem was a broken clutch fork pin; the clutch wouldn’t
operate no matter how far the lever was pushed back because the fork rotated on
Slave Cylinder Overhaul
piston doesn’t come out, a little more work is required.
Spray lubricant (WD40 works fine) into the cylinder though the input port
and around the piston at the front of the cylinder.
Then, use a punch and hammer to force the piston into the cylinder a
half-inch or so. Clean the exposed
inside of the cylinder with steel wool. Often,
this area of the cylinder becomes corroded because it is beyond the point where
the hydraulic fluid flows in normal operation.
This area is especially corrosion prone if the cylinder has been out of
service and stored in a damp area. The
piston will now likely come out when compressed air is applied. Sometimes the piston will just move back to its original
position at the front of the cylinder. If
so, then it can be forced back, air applied again, etc. until it finally comes
out. Be sure to not become
lax about the target when the air is applied.
If compressed air isn't available, one can try to force the piston out with a small steel rod inserted though one of the two threaded holes in the closed end of the cylinder. This should be done carefully so that the spring is not damaged.
cylinder components are shown in the following photo.
Some older cylinders have a different type of piston that looks nothing
like the one in the photo. The
piston with rubber seal and the rubber boot are discarded --- the repair kit
contains new replacements.
step is to inspect the inside of the cylinder for corrosion, pits and other
imperfections. The area of concern is from a depth of about ¾ inches to about 2
inches – the area where the rubber seal travels in normal operation.
The last ¾ inch nearest the open end is prone to rust but not a major
concern. This area can be cleaned
with steel wool enough so the piston (with the rubber seal removed) passes
freely. If the cylinder
further in is smooth and shiny, as is likely if the cylinder has been in use
recently, then no further work is required.
cylinder surface is not smooth and shiny, then a cylinder hone should be used.
A hone is a tool with two or three small abrasive stones on spring-loaded
arms that press against the inside of the cylinder.
The hone is rotated with a drill to smooth the cylinder.
Suitable small cylinder hones can be obtained at most auto parts stores.
The following photos show a small hone and the hone in use.
One should not be too concerned about the hone enlarging the diameter of
the cylinder--- You can run it for hours without having much effect on the steel
cylinder. If the hone is not able
to eliminate all imperfections in a few minutes, one can try wrapping ~ 100 grit emery cloth around the end of the hone and
rotating the emery cloth for a few minutes.
If this doesn’t clean up the cylinder, throw it out and buy a new one.
If the emery cloth is successful, then the hone without the emery cloth
should be used to remove the scratches caused by the 100-grit cloth.
Next, the bleed nipple is removed and cleaned as required. A wire or small drill bit can be used to clean dirt out of the center of the nipple. Engine degreaser should then be sprayed into the cylinder and a cloth forced into the cylinder and pushed around with a screwdriver to clean the rear of the cylinder. The two ports at the rear of the cylinder should also be checked to make sure they are clear. The parts should then be washed thoroughly and blown dry with compressed air (or a hair dryer if air is not available).
Once the cylinder is known to be good the rebuild kit can be purchased.
I use The Roadster Factory (TRF) part number LDSSB629 usually purchased
during the winter parts sale for about $10.
I also purchase a tube of Girling rubber grease, part number GISP 1230.
One tube will probably last a lifetime if you don’t misplace it. (There
is a small packet of grease supplied with the master cylinder rebuild kit.
There is sufficient grease in that packet for both the master and slave
Next, the inside of the cylinder is thoroughly lubricated with fresh brake
fluid. The small end of the spring
is slid over the small end of the piston, the seal lubricated with rubber grease
and then the spring followed by the piston slid into the cylinder.
The piston should then be forced in and the last ½ inch of the inside of
the cylinder should then be coated with rubber grease.
This is the area that is corrosion prone because it is not lubricated by
the hydraulic fluid. Installing
the bleeder screw, putting the new rubber boot on the end of the cylinder and
then inserting the push rod through the boot completes the rebuild. The completed cylinder is shown in the next photo.
Oh, one more thing, the flexible hose and still connected pipe should be
attached to the cylinder.
Master Cylinder Overhaul
The master cylinder overhaul starts with using small pliers to remove the
circlip retaining the pushrod. These
parts are shown in the next photo. The
next step is to remove the piston. If
it can’t be shaken out then air is used in the same way described earlier for
the slave cylinder. There is one
difference; the air inserted into the output port goes to both the cylinder and
the reservoir. The reservoir cap
must be in place to allow pressure to build up in the cylinder.
Unfortunately, pressure also builds in the reservoir.
If the piston doesn’t let go, the cap may blow off so we have a
double-barreled missile launcher here. (The
voice of experience speaking; fortunately, the cap has little mass so no damage
was done when the cap hit the side of my head).
Eye protection and care in the direction both barrels are pointed are in
order. The removed piston
assembly is shown in the subsequent photo.
The cylinder inside surface is inspected to make sure it is clean and
smooth. There is usually some
corrosion near the open end of the cylinder.
As with the slave cylinder, this area is beyond the travel area of the
seal and can be readily cleaned with steel wool. I’ve never seen a damaged
master cylinder so in most cases no honing is required. If honing is required, a small hone with light spring
pressure should be used. Unlike the
steel slave cylinder, the master cylinder is made of relatively soft aluminum
and is easily scored with course abrasives.
If the cylinder can’t be made smooth then a replacement must be
purchased. This hurts a bit. The new master cylinder costs about $120 whereas the slave
cylinder costs about $45. If
cylinder is to be reused, the inside of both the cylinder and the reservoir
should be thoroughly cleaned and dried.
The piston assembly is taken apart next.
A small screwdriver is used to pry up the tab on the spring thimble to
separate the thimble from the piston as shown in the next photo.
Some of the parts are under tension and subject to flying everywhere when
the pressure is released so eye protection should be worn.
It’s also wise to work in a relatively clean and confined area so the
parts can be retrieved easily. The
disassembled piston is shown in the subsequent photo.
There are two types of master cylinder used on the TR250s –TR6s.
The earlier one through 1969 has a 0.75-inch diameter piston and the
later has a 0.7-inch diameter piston. The
repair kits from TRF (early – part number GISP1967, later – GISP2102) cost
about $10 during the winter parts sale.
The kits contain the gland seal (11), valve seal (9), wavy washer
(between 7 & 8), circlip, boot and a small amount of rubber grease.
Next, the new valve seal (9) is slid on the valve stem (7).
The new wavy washer is slid on the valve stem followed by the plastic
spacer (8) and spring. The valve stem is then fed through the spring and hooked into
the end of the thimble (6). The
final step is to push the thimble onto the piston far enough for the tab to
catch on the lip. It may be
necessary to use the small screwdriver to bend the tab in a bit.
Lubricate the cylinder with fresh
hydraulic fluid and the gland seal with a
small amount or rubber grease. The
piston assembly is then inserted into the cylinder, pushed in slightly and the
end of the inside of the cylinder coated with a small amount of the rubber
grease. The end of the pushrod and
the washer are greased and a new boot is then installed on the pushrod.
Some grease is squeezed on the cupped end of the piston and then the push
rod is inserted into the cylinder and secured with the circlip. Finally, the
boot is slid over the end of the cylinder completing the master cylinder
This is a good time to talk about hydraulic fluid.
A purest might use the Girling LMA fluid available from TRF or Moss.
In the past I preferred to use regular high quality brake fluid available
at grocery and auto parts stores. Both
these are mineral based fluids.
Another option is silicone brake fluid. The good point with the silicone fluid is that is a less effective paint remover. The bad point is that it costs more than good quality whiskey. I’m having my ’76 TR6 repainted at the present time. I just cleaned up the mess on the brake servo unit caused by a leaking brake MC and on the pedal assembly caused by a leaking clutch MC. One thing you can be sure of --- all Triumph hydraulic cylinders will leak sooner or later ---- more likely sooner, especially those near observable paint. So ---- I’m going to use only silicone fluid on my TRs from now on.
The reassembly process is the reverse of disassembly.
The master cylinder is mounted with the two bolts and then the clevis pin
connecting the push rod to the pedal assembly is installed and secured with a
washer and cotter pin.
The pipe and hose are fed through the hole in the slave cylinder mounting
plate followed by the slave cylinder that is then secured with two bolts.
Be sure to mount the cylinder such that the bleed nipple is at the top
and the hose is at the bottom. The clevis is then inserted through the push rod
and clutch-operating lever and secured with a washer and cotter pin. The last
thing is to screw the steel pipe fitting into the master cylinder output port.
Bleeding the System
The final task is to fill the system with hydraulic fluid and then bleed
the air from the system. Connect
the hose and bottle used for draining the system to the bleed nipple, put enough
fluid in the bottle to cover the end of the hose, and then open the nipple about
1/2 turn. Fill the reservoir with fluid and screw on the cap (to prevent the
fluid from splashing out). .
Pump the pedal several times until some fluid exits the tube into the
bottle. Refill the reservoir as
required. One can use this
method to completely bleed the system – just pump the pedal until no more air
exits the end of the hose and then close the bleed nipple while the pedal is
still depressed -- use a stick to hold the pedal down.
I’ve always had trouble getting that last bit of air out by this method
and the clutch will not operate properly if there is air in the system.
I prefer to call on the significant other for help here.
her in the driver’s seat and then jack up the left side (of the car) so you
can crawl under it (remove the keys so she doesn’t get any ideas about life
insurance). I also secure the frame with jack stands as a backup. Get a 7/16-inch wrench and crawl under the car.
Close the bleed nipple. Have
her pump the clutch several times and then hold the pedal down (be sure to
calmly tell her that the clutch is the left pedal).
(If you hear a pedal moving but see no movement of the slave cylinder,
you might calmly suggest she try the other left pedal.) While she’s still
holding the pedal down, unscrew the bleed nipple and let the air escape thought
the still connected tube to the bottle. Tighten the nipple again before she
releases the pedal. Repeat this
process until no air escapes when the bleeder nipple is opened.
When finished, check and refill the reservoir as required.
Why doesn’t the cap blow off?
the compressed air injected into the master cylinder can blow the reservoir cap
off. One might ask: “Why
doesn’t the cap blow off when the pedal is pressed?”
There is a
small hole at the back of the master cylinder that connects to the reservoir.
When the pedal is out, fluid is free to flow from the reservoir though
this hole into the cylinder and then thorough the output port and pipe/tube to
the slave cylinder. When the pedal is pressed the small valve seal (part 9 in a
previous sketch) is pressed against the little hole at the back of the cylinder
closing the access to the reservoir. All
fluid pushed by the piston as the pedal is pressed further must escape through
the output port and then via the pipe and hose to the slave cylinder where it
pushes the slave cylinder piston. Thus,
the valve seal prevents pressure buildup in the reservoir.
much should the operating arm move?
While under the car bleeding the system you might notice that the clutch
operating arm doesn’t move very far while the pedal moves a large distance from full out
to full in. What is going on?
This subject is addressed in the accompanying Clutch Calculation note.
For a 0.75 inch master cylinder (TR250 & early TR6) one can expect the clevis
pin in the center hole of the clutch operating arm to move about 0.6 inches when
the pedal is pushed all the way in. This is for a system with relatively
little wear. A system with substantial wear around the clevis pin between
the pedal and master cylinder push will probably loose 10% or more of this
motion. Air in the system will also degrade the system motion.
For a 0.70 inch master cylinder (later TR6) one can expect the clevis
pin in the center hole of the clutch operating arm to move about 0.55 inches
when the pedal is pushed all the way in. This will degrade due to wear and
air in the system in the same way as described for the 0.75 master
does one adjust the clutch?
should be adjusted so that the front of the release bearing is just about in
contact with the clutch pressure plate when there is no pressure applied to the
pedal. In mechanical systems there
are adjustments on the levers or cables that must be changed from time to time
as the clutch components wear. The
Triumph hydraulic system adjusts itself each time it is used.
After the pedal is released, the force from the clutch pressure plate
springs push the release bearing back which in turn rotates the clutch-operating
shaft and via the operating lever and push rod pushes the slave cylinder piston
into the cylinder. The piston
is held against the push rod by the spring behind the slave cylinder piston.
Hence, there is no slack in the system after each use – completely self
hydraulic fluid should the clutch use?
hydraulic fluid should the clutch use?
should consume very little fluid. Some
small amount might be lost as a film is left on the side of the cylinders when
the pistons move. If the system
looses more than ¼ of the reservoir in a summer, then you probably have a leak
and the system is in the process of failing.
Best get to work on it right away.
A typical clutch problem with TR6s is that it is difficult or impossible
to shift into first or reverse gears.
This is an indication that the clutch is not releasing when the clutch
pedal is pressed. The system
is more tolerant when shifting into the higher gears so the problem shows up
initially with first and reverse.
This problem is nearly always the result of insufficient movement of the
slave cylinder pushrod. Note
that the self-adjusting feature described previously compensates for any slack
between the slave cylinder and the clutch.
Therefore, the problem is most likely between the clutch pedal and the
slave cylinder. The first
thing to do is to measure the travel of the clevis pin connecting the push rod
to the clutch operating shaft arm --- it should be at least ½ inch. If the travel
is 1/2 inch, then the problem is in the clutch components or the operating shaft
or clutch fork.
If the clevis pin travel is
less than 1/2 inch, then the following
should be checked:
If none of the above fixes the problem, one can remove the stop tab on the clutch pedal arm. This will give a little more pedal. Another alternative is to fasten the slave cylinder push rod to the upper rather than the middle hole in the clutch operating shaft arm. If none of these works, consider selling the piece of crap to your brother-in-law.