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TR2/3/3A Flushing Hydrulic Fluid

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  • "Do NOT use DOT-5 with seals that have already seen service with DOT-3/-4. Replace ALL the seals with new and include with that the rubber flex hoses, and the internals of things like brake servos and PDWAs."

Is this really necessary? None of the other posts in this thread mentioned this. I have been told that silicone would leak by the early Girling seals. Since I'm replacing the master cylinders with new (repros), I don't think that they will be a problem. I'm not sure about the clutch slave cylinder or the wheel cylinders. I have to believe that they are not original to the car. There seems to be a few theories on transitioning from DOT 3/4 to DOT 5. The consensus seems to be that it's not a problem.
 
It is your car and your decision about swapping old exposed rubber for new when changing from DOT-3/-4 to DOT-5. I could Google for and post links to threads and boards presenting the "new rubber" argument. However, since I would only post links supporting my argument... what's the point? You may find just as many saying it is not necessary.

My comments are based on my personal experience where seals that have lived the first part of their lives in DOT-3/-4 sluff off a black goo when the fluid was changed to DOT-5. It did not happen in an hour, a day, or even a week. However, it did happen over a couple of years. Eventually the transition to goo led to seal failure. This included seals found in new master cylinders where the supplier lubed the seals with brake fluid instead of brake rubber grease.

Again, this is my personal experience and you may certainly choose not to replace the seals in your car if you don't want to.
 
frankfast said:
  • "Do NOT use DOT-5 with seals that have already seen service with DOT-3/-4. Replace ALL the seals with new and include with that the rubber flex hoses, and the internals of things like brake servos and PDWAs."

Is this really necessary?
Click to expand...

Like I said at the top of the thread...

Geo Hahn said:
You'll get various opinions on this.
Click to expand...

Now you have them (the opinions). Replacing all the rubber bits is not a bad idea, brake fluid choice aside. It is not particularly expensive nor is it a difficult task - so if there is any doubt about the wisdom of one method or another, you may want to error on the side of caution and drive with the knowledge that these components are the best they can be (this from a guy who just dumped in the DOT5 and flushed it through).
 
Seems to me, just on my own experiences; that it depends on how long the seals have been run in DOT 3/4. If they are relatively new, they seem to usually make the transition OK.

But I've had several failures that I think were likely caused by long exposure to DOT 3/4, followed by DOT 5. The most dramatic was Stag #1, where just a few months after making the switch, the brake pedal started slowly sinking to the floor at stop lights. I had other things going on, so I drove it to a (supposedly) good LBC mechanic. On the way there, rolling down I-10 about 70 mph, the brake hydraulics quit working entirely! Mind you, this was a split system and both halves failed. Later post-mortem showed that the MC cups had gotten very soft and slippery, almost the hardness of gummy bears (tho not as sticky); and that both of them had torn through the bottom part of the cup. Very unusual failure, I've never seen it before or since.

Only time I've ever had a soft line fail, was after I didn't replace the one for the rear axle on my former TR3A. Just a few months after installing DOT 5 (and doing all the other things), the inside of the line broke and started acting like a check valve; making the rear brakes drag and overheat (literally smoke rolling out from under the car).

Not sure if it was mentioned in this thread; many people (including myself) have had troubles with the original type hydraulic brake light switch after converting to DOT 5. After too much fiddling, I converted to a mechanically operated switch, which I feel works better anyway. Others have said the switch from a Harley Davidson motorcycle will work with DOT 5; but I haven't tried that.

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So we're talking about changing front calipers, rear wheel cylinders, clutch slave cylinders and all soft lines ( master cylinders are new). The only things remaining are the copper lines and the reservoir. I'm not sure it's worth it. Since both master cylinders were leaking badly with DOT 3/4 (not sure which), can it be much worse with DOT 5? I have no idea what was replaced during the restoration about 8 years ago but the fluid I removed from the clutch slave cylinder was black and it wasn't silicone. Thanks for all your experience and I'm still not sure which way to go.
 
Yeah, it is kind of a lot (although again, I would just change the seals). And you don't have to do it now, if you don't want to.

But, that black in the clutch slave came from the seal, so you know it's already failing. Both MCs were leaking, again the seals failed. What do you think are the chances that the other seals, replaced at the same time and exposed to exactly the same fluid, are in much better shape? It seems clear to me that it's time for another overhaul of all the hydraulics.

Losing your brakes while driving is never a lot of fun; and has a tendency to be a life-changing experience. I recommend avoiding it if at all possible.
 
Turns out only the fluid in the slave cylinder was black. I vacuumed ( with a MityVac) as much of the fluid in the brake calipers and wheel cylinders as I could and blew the lines with compressed air. That fluid didn't look too bad. You're right, I probably should change the clutch slave cylinder. I'm beginning to favor using DOT4 and not changing to silicone. Still waiting for one of the master cylinders from the Roadster Factory which is back ordered. Seems everybody is out of them.
 
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