TR4/4A Clutch Fluid Very Dark After One Year

[RJS]

Say,

I fully bled my clutch and brake fluid last year. Now, one year later the fluid in the clutch master cylinder is very dark. However, the fluid in the brake master is crystal clear. What's up with that?

I'm thinking the rubber clutch hose to the slave may be on its way out. It's easily 14 years old.

Bob
PS: I just re-inspected and would add that there is a fair bit of dark sediment in the bottom of the clutch master cylinder. Again, I bled it just last year and was perfectly clear.

 

[HerronScott]

Bob,

When were the hydraulics rebuilt/replaced (ie are they also 14 years old)? Also, the clutch hose is plastic on our TR4A's and not rubber isn't it so I'm not sure how much it would contribute to fluid contamination as it gets older (less than rubber I would assume).

I've always noted the clutch fluid seems to get darker on any car that we've owned with a hydraulic clutch (Mazda's and Triumphs) when compared to the brake fluid which I assumed was due to the greater exposure in the slave cylinder area even with the boot.

Scott

 

[RJS]

Ah, good point, the hose is plastic. The slave is also 14 years old. The clutch master is 7 years old.

One other thought, most of last season, I ran it with the clutch slave rod mounted in the bottom hole of the arm on the clutch shaft (not the middle hole as recommended). I wonder if that put the slave rod at an angle and caused more wear inside the slave? I was attempting to see if that would help with the heavy clutch pedal but, I have since moved it back to the middle hole.

Speaking of the slave, it is 14 years old with 10K miles on it. It may be suffering from old seals or wear. I am thinking of replacing it for that, and because I suspect the slave bore is 7/8" and one of the Big Three sells one with a 1" slave bore (which is advertised as original). Perhaps that slight increase in slave bore will reduce clutch pedal effort??

Bob

 

[TR4A_IRS]

My guess is one, or more, of your seals is deteriorating. I battled this same problem for a while. It too me several master and slave reseals to correct it. I suspect there was a bad batch of rubber seals running around for awhile.

 

[Got_All_4]

Here is a paragraph from a tread I was just reading about the differences in pressure plates. May explain your problem and something potentially happening in your system. Also if you have had DOT4 fluid in there for a long time it will absorb moisture from the air and turn dark too. In the article they were talking about using a aftermarket Borg & Beck pressure plate and all of the problems it was causing in TR6s. Very informative.
4. Seal failure in the master and slave cylinders.
Seals are designed for specific operating pressures by varying the thickness and fit of the seal support.
The higher the pressure the more solid the seal support. Also, smaller clearances between the piston and
cylinder are required to prevent the seal from being squeezed into the clearance. If the operating
pressure is doubled or more and the seal is not designed for it, it will fail.
Also, the length of the piston must be considered in higher pressure applications, since high side loads
will increase piston to cylinder bearing stresses. If the bearing stresses reach the yield strength of the
piston and cylinder, excessive and rapid wear will occur. This is the cause of the brake fluid turning
black when

 

[RJS]

Good point about the pressure plates. I'll keep that in mind. Since I bleed the fluid just last summer, I am pretty certain it is the seals on the 14 year old slave cylinder. New slave cylinder going in today. After that, I would certainly hope I can get two years between bleeding the fluid.

Bob