Changing from DOT 5 to DOT 3 fluid

R

Royal Ryser

Well-known member
After replacing all cylinders and lines, I filled my system with DOT 5 brake fluid. Now I have a leak that I have been unable to stop. It is in a T fitting where three lines come together, one of them being a flex line to a wheel cylinder. The new brake line ends were double formed and the nuts were new. I tightened the nuts until I rounded over the corners. Still leaks.
Any suggestions about what more to do, using DOT 5? Or should I go back to DOT 3 which is not so prone to leaking?
Is there any problem in changing back to DOT 3? Any special way to flush out the DOT 5?
Comments?
 
You are using DOT 5 which is silicone if I'm not mistaken or unsober, redo the thing and use a little sealant, take it from the plumber, a leak does not know why or how or that you were tired or got a phone call or whats inside of it that is leaking, it's not prone, it's Murphy's Law, take it apart and fix it and chase Murphy back to the tavern.
 
Loosen the leaking fitting just barely and then move the joint around a bit. This will knock off any minute burrs and help the fittings get together.
clem
 
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It won't cost that much to redo it with new parts, get proper fitting wrenches, my guess it's the double flairs,I bought a new Eastwood double flaring ( 200.00) tool and ended my problems, Dave
 
If you DO change from one type to the other, take everything apart- all the rubber from wheel cyls, master- and clean it perfectly clean... I learned the hard way, four calipers seized up, no fun... Karl
 
Richard at EV8 Ford showed me a trick when forming the double flairs. Instead of torquing the final flair down hard only compress until the flair forms itself with moderate resistance. This technique will leave a slight cushion in the flair which helps seat the nipple when tightening the nut. I'm using DOT 3 and have had no leaks/seepage since setting up my system. Before switching to DOT 3 I would try reflaring new lines and stick with DOT 5.
 
I have been reading about the different "DOT's", they say that the DOT 5 is very resilient and almost impossible to get out of a system once it is in, and if you go back to DOT 3 or 4 it will jell up and be a big problem.

"They" say once you go DOT 5 you pretty much have to stick with it.

Yea I know, who is "they"..... :D
 
9 times out of ten, if you have a leak at a joint it is beacause the double flair was not made exact. Re do the flair at the leak and everything should be OK. NEVER shake the DOT 5 can of fluid! That inserts miner air bubbles into the fluid stdhat can take months to settle out. Many complain of spongy pedal and it is because of the air abubbles.
 
Try some Hydraulic Sealant. Comes in little bottles, same as threadlockers. Loctite and Devcon/Permatex have it. Dot 5 is slippery stuff!
 
I've seen the three way fittings crack and leak on casting seams. This happens more with aluminum than brass types and also more prevalent on the national pipe types. If it is set up for internal flare, then the flare has to seat well with the seat. Any scratches on the seat or, as mentioned earlier, problems with a cracked or scratched flare will cause it to leak.

Dot 5 is less suseptible to moisture absorbtion so it is an acceptable fluid where you don't want cast iron cylinders rusting up. As far as whether it leaks easier or not I don't have a clue. I use both and have had same luck with both. Both seem to deteriorate equally so I can't say either one is better than the other with the exception of the moisture thing.

Kerby
 
I had two used brass blocks with very minute cracks in them. I bought a new one and all was fixed. This was the one that bolted to the master cylinder with a banjo bolt on a 49. It took a lot of assembly and reassembly before it was closely inspected and the crack was found.
 
I use the silicone for one reason, it does not cut into your paint, I use orange citrus spray to clean it off, I used dot 3 on my last car and I'm a slob, or some thing, it wasn't pretty.
 
It is a plus that DOT 5 silicone will shine paint not remove it but I use it because it must not absorb moisture or be a victim of it or something. I have better winter storage now then I use to for old cars but for years I fought problems every spring startup with conventional brake fluid especially in a cement block garage,moisture,rust with temperature fluctuations and quick thaws= stuck pistons in wheel cylinders. If you have a temperature controlled garage or live in better climates not as important.
 
Amen Coupe, I cannot afford to heat that garage all winter, for some reason dot 5 resists moisture a lot better, I also recommend using stainless lines with it, moisture can pass through the steel lines with oxygen, not so with SS brake lines.
 
I had a '57 Ford That required frequent wheel cylinders with DOT 3. I finally changed them all out, flushed the lines, rebuilt the master cylinder, and installed DOT 5. I never had any more problems with it in 15 years. With that pleasant experience, I put DOT 5 in the '40 when I built it and have had a soft pedal ever since. I can bleed most of the air out and it returns after a little use. My theory is that the master cylinder under the floor is more prone to aerate the fluid.
 
Re-do your double flare and when your doing the final flaring don't over do it. This will allow the two surfaces to mesh and form a seal. Also you could have a fine crack in the flare. Just finished doing my brake lines and a leak at the tee. Replaced the tee and still had the leak. Re flared the line and solved the problem. If you had a poor flare and damaged the tee you'll still have to replace the tee after repairing the flare. As they say a leak is a leak just like a wife is a wife.
 
My 1991 Harley-Davidson came with dot 5 and it has been in there since, with not the first problem. I am completely satisfied !
Like one fellow said, fix the problem. It is not the fluid's fault.
MIKE :)
 
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