Brake fluid - Dot 3 .. Dot 5

[stevenwham]

Hello .. my classic cruiser is a 53 Olds Super 88 Holiday Coupe .. this topic applies to a 72 TR6 .. assume the "technicals" are basically generic on this issue:  a year ago, I replaced Dot 3 in TR with Dot 5 .. thought I was making an "upgrade" .. just drained & refilled (no flush) .. brakes are somewhat spongy .. a year later I've learned that one must be very careful in the transition .. I wasn't .. question is:  what to do?  stick with Dot 5 & do some sort of "master flush" or even consider draining Dot 5 & going back to Dot 3 .. your comments appreciated .. 

[zeke01]

You will get as many answers as there are posters on this topic. I would give the system a good flush and refill with either one, recognizing the characteristics of the type used and service accordingly. Zeke

[Bloo]

Pick which one you are going to use, take all the cylinders apart and clean them out. Flush the brake lines with denatured alcohol. Put back together and fill with fluid of your choice. I like DOT5 and am a proponent of it, but I am not currently using it (hows that for straddling the fence?).

 

DOT5 is very difficult to bleed. Just pouring it makes bubbles and they get sucked back in if you continue bleeding too soon. Don't do anything to stir it up while you are bleeding. Use slow methodical 2-man bleeding or vacuum bleeding. When you pour more in, wait a few hours before continuing. It is fine once bled. Most people never get the air out and wind up with a spongy pedal. If you get it right, 99% of the problems with future rust damage in the cylinders just go away because DOT5 does not pull water from the air.

 

Edited August 13, 2022 by Bloo (see edit history)

[PONTIAC1953]

a word to the wise, if your 1953 Oldsmobile has the Treadle Vac power brake option, DON'T use DOT 5 brake fluid.

[auburnseeker]

Well you either get it working right with the Dot 5 as suggested, or throw everything away every 5 years and start all over with Dot 3.  I prefer once and done.  I would rather have a little spongy pedal than a rusty system and a brake failure. Since you already did it once with 5 I would definitely stick with it. Just take it apart flush and redo it as suggested above. 

Edited August 13, 2022 by auburnseeker (see edit history)

[zeke01]

See what I mean? Zeke

[Marty Roth]

DOT 5 

Done right -

Once and done !

Examples were 21 years on pour '58 Bel-air

  .....  and even longer on our '63 Impala,

   ..... same for our '66 Dart GT convertible,

several years on our '88 VW Quantum until it was wrecked

[zeke01]

And the hits just keep on coming. Z

[stevenwham]

Thanks for all your comments - helps to get broad perspective

[auburnseeker]

Dot 3 should be banned from being used in most old cars or a big warning that says "I hope you like doing your brakes over and over again.  If so select me. "

Every car that I have had in the last few years had all new brakes done and then parked for 5 -10 years.  Every one I took out all the new looking parts,  that were all rusted to crap inside but not on the outside,  then threw them away and bought all the same new parts again and put them in. Fortunately able to do that as they were nothing too rare or exotic.  $500 in parts for new cylinders and fluid once,  or $500 every 5 years.  so 2500 plus labor over the average life span or $500 plus labor and best of all, you won't have a leaky cylinder that ruins the paint on your wheel or ruin the paint on your fender or firewall with dot 3 which is corrosive and eats paint.   Pretty easy choice,  but lets here the arguments for Dot 3. 

[Paul Dobbin]

I did a 1940 Ford Pickup with Dot 5 in 1983 for th e 1984 Great American Race.    It's still in regular use today as a museum utility vehicle.. 

I did my 1981 El Camino in 2007 and it's my daily driver still today, no brake work except replacing the master cylinder this year.   It's 41 years old and I'm the third old man in a row to own it since new.

Flush the system with alcohol and go to Dot 5 and be done with it.

Edited August 15, 2022 by Paul Dobbin (see edit history)

[Bhigdog]

On 8/13/2022 at 6:55 PM, pontiac1953 said:

a word to the wise, if your 1953 Oldsmobile has the Treadle Vac power brake option, DON'T use DOT 5 brake fluid.

Why????????????....Bob

[Bhigdog]

DOT 3 and ignition points are spawn of the Devil. Yea!   Cast out the demons and lead ye a peaceful existence.............Bob

[auburnseeker]

Well Points I don't have a problem with.  Better than getting stranded with electronic,  but brake fluid is a whole different animal.  If your points go bad,  they won't ruin the entire ignition system,  where if your brake fluid does,  well,  throw it all away and start from scratch, plus instead of your car just crapping out and coasting to the side of the road or not starting,  you might lose your brakes and wreck your car. 

[Glen Andrews]

Dot 5 Silicone brake fluid aerates very easily, that's why it is not used in modern Anti-lock Systems, the pumping action of the ABS will cause bubbles in the fluid and the system won't function properly along with a spongy pedal result. I'm not sure what a Treadle Vac system is but it probably will cause air bubbles to form in the silicone fluid.

[Bhigdog]

1 hour ago, auburnseeker said:

Well Points I don't have a problem with.  Better than getting stranded with electronic,  but brake fluid is a whole different animal.  If your points go bad,  they won't ruin the entire ignition system,  where if your brake fluid does,  well,  throw it all away and start from scratch, plus instead of your car just crapping out and coasting to the side of the road or not starting,  you might lose your brakes and wreck your car. 

I,m guessing here but every car made in the last, what? 40 years has had electronic ignition. Ergo.... no points burning, adjusting, replacement, caps going bad, dwell meters, point files, losing tiny nuts down into the distributor while laying on your belly. My oldest pertronix is 23 years now. Zero poblems.

Don,t know where my dwell meter is. Used my timing lite first time in ten years last week.....

Points?  We don,t need no stinkin points......bob

 

[auburnseeker]

A friend that fixes vintage cars for people has had to replace a few of them.  Just going off what I have seen or been told.  Seems new cars (modern) have a much lower (huge percentage difference)  failure rate than the conversions.  

[Bloo]

I suspect the concern with "treadle vac" is the same as it would be with a few other power brake systems, namely that if the system leaks then brake fluid could get into the power brake's vacuum supply and make it's way into the engine where it would get burned. Internet wisdom suggests that when the SILICONE burns a by-product is SILICA, and the engine would essentially be getting abrasive sand in it's cylinders. I am no chemist, and I have no idea if that is true, but a bunch of people on the Internet think it is . There are probably several among our ranks on the forum who have chemistry knowledge and who could answer that question definitively, but I am not one of them. 

 

I used DOT5 silicone fluid in several power brake cars in the 80s and 90s. Ignorance is bliss I guess.. or not.

 

Edited August 16, 2022 by Bloo (see edit history)

[Bhigdog]

23 minutes ago, auburnseeker said:

A friend that fixes vintage cars for people has had to replace a few of them.  Just going off what I have seen or been told.  Seems new cars (modern) have a much lower (huge percentage difference)  failure rate than the conversions.  

I can only relate my anecdotal positive experiance and that i haven,t had to lay across an engine, trying not to dent a radiator tank, hoping not to drop teeny little bits and wrenches in twenty plus years. For the record though i do keep my aaa policy up to date......bob

[PONTIAC1953]

3 hours ago, Bhigdog said:

Why????????????....Bob

according to several Treadle Vac rebuilding business, it doesn't work well. 

[auburnseeker]

12 hours ago, Bhigdog said:

I can only relate my anecdotal positive experiance and that i haven,t had to lay across an engine, trying not to dent a radiator tank, hoping not to drop teeny little bits and wrenches in twenty plus years. For the record though i do keep my aaa policy up to date......bob

I guess it might depend on the car as well.  A flat 6 Chrysler product for sure,  points are no big deal.  Now an early Ford V8 with the front distributor,  I might agree.  Did the points on my 40 Ford and that was a nightmare. 

[Bhigdog]

Agree.....

Dist on my 39 JC pick up is at the side looking right up at you. Easy Peasy.  Buicks and Olds are at the back hard against the fire wall. Vette also in back covered with noise suppression hardware. ARRRGH!  At any rate everything is Pertronix with no failures so far (here crossing fingers)........Bob

[Frank DuVal]

Keep them crossed*! When diagnosing issues with old engines the first thing is to replace the Pertronix with points/condenser and see if the problem goes away. Or, replace it with a new known good Pertronix, less hardware to find. And of course buy the right Pertronix to start with. "My engine will not idle right" well, you have the wrong Pertronix for that engine with an automatic transmission, idle speed too low to work right. Crane XR system much more reliable in the Corvair world, where people actually drive their cars more than a few hundred miles a year. I'm still speaking of relatively few failures of Pertronix. If they failed as often as us naysayers say, they would be out of business!😲

 

Every year I take the front distributor off the Ford 8N to clean the points (and whatever insects have taken up residence), maybe that would be a good Pertronix candidate in my world.😁

 

*and carry a spare or the populated point plate in the glove box, better than crossing fingers, never will need them 99.9% of the time. A sort of insurance.👍

[Bhigdog]

56 minutes ago, Frank DuVal said:

Keep them crossed*! When diagnosing issues with old engines the first thing is to replace the Pertronix with points/condenser and see if the problem goes away. Or, replace it with a new known good Pertronix, less hardware to find. And of course buy the right Pertronix to start with. "My engine will not idle right" well, you have the wrong Pertronix for that engine with an automatic transmission, idle speed too low to work right. Crane XR system much more reliable in the Corvair world, where people actually drive their cars more than a few hundred miles a year. I'm still speaking of relatively few failures of Pertronix. If they failed as often as us naysayers say, they would be out of business!😲

 

Every year I take the front distributor off the Ford 8N to clean the points (and whatever insects have taken up residence), maybe that would be a good Pertronix candidate in my world.😁

 

*and carry a spare or the populated point plate in the glove box, better than crossing fingers, never will need them 99.9% of the time. A sort of insurance.👍

I've kept a spare point/con. set for the 39 JC in the glove box for the last 20 some years because the dist is so accessable. They are right under the phone # for AAA. As for the other 4 cars the chances of finding me on the side of the road, laying across a hot engine with a flash light in my mouth, trying to install/adjust a set of points is somewhere between nil and zero.................Bob