View Full Version : Converting to DOT 5

08-07-2011, 11:06 AM
Rebuilding the hydraulics on my new (to me) TR3 and have been doing lots of reading about DOT 3/4 versus Dot 5. I think go to silicone makes sense even though I do not have a brand new paint job. I am currently planning on rebuilding both master cylinders, replacing the clutch slave cylinder, and replacing the hose to the clutch slave. The brake hoses as well as the front and rear brakes all look to me in great condition. Clearly they have all been redone at some point in the "recent" past. In order to convert to silicone do i need to replace all the brake hoses, rear wheel cylinders and rebuild the front calipers? If so, I may just go with Dot 4 so I can try and get up and running before deciding on what exactly this TR project is going to entail. Thoughts?

08-07-2011, 11:16 AM
You don't have to rebuild everything but you do need to make sure you get all of the old fluid flushed out as they will not mix. The only problem with silicone fluid is it does not absorb moisture so any that gets in the system will find the lowest spots and condence into water and sit there causing rust. Another problem is if you are on the brakes hard the water can start to boil. I would just recommend replacing it with standard fluid and flush the system out every couple years with fresh fluid.

08-07-2011, 11:33 AM
This is really an area of varied opinions. I'm a 20 year plus user and fan of DOT5. I've got an old Ford, a an old Chevrolet, and two old Triumphs using it. Way back when, I read an article in a Corvette enthusiast magazine and followed the instructions of using denatured alcohol as a "flush" followed by low pressure air blow through of the existing brake system. Then refilling and bleeding with the new DOT 5. I could honestly not tell a great difference in pedal feel in any of the vehicles. Haven't bothered to flush any of the systems. I did have to rebuild the GT6's master a few years ago because of seal leakage - but there was no disappointing paint damage.

08-07-2011, 01:47 PM
Mine is an all new system that I went to DOT5 on, including the clutch system. No problems after three years and no worries about my paint either.

Make sure you use DOT5 and not DOT5.1

Geo Hahn
08-07-2011, 02:34 PM
...In order to convert to silicone do i need to replace all the brake hoses, rear wheel cylinders and rebuild the front calipers?...

I didn't. I just introduced DOT5 into a nearly empty reservoir and bled until I got 'grape juice' out of each bleeder. In the decade or so since I have had no problem attributable to brake fluid.

I think with DOT5 you want to be a bit careful about getting little bubbles in the fluid -- I always pour very gently and let the reservoir sit overnight before I commence bleeding. No idea if that really matters, just something I heard and believed.

08-07-2011, 03:04 PM
No, you do not. Mine was only new because I did a frame rebuild at the time and the lines and hoses were part of it.

08-07-2011, 11:32 PM
If the old seals are really tired, then they may start to leak after converting to DOT 5, IMO. Ditto the hoses.

I've tried it both ways (on different cars), doing a complete flush with methanol or just bleeding until clean purple fluid. The second method is a bit odd, because the purple color will fade away over time; and you may find some black gunk in odd places (like the bottom of the rear brake cylinders). But otherwise I couldn't tell any difference in performance.

PS, while I can't prove it, I now believe that using DOT 5 may lead to rapid failure of the hydraulic brake switch. At any rate, I went through a number of original, reproduction and aftermarket switches (Ford truck as I recall) before finally converting to a mechanical switch.