My '41 Buick has a rebuilt master cylinder, new front wheel cylinders and flexible front brake lines. Nearly 2 quarts of top grade isopropyl alcohol have been pumped through the system and bleed at each wheel. Silicon and Dot 3 brake fluids each have their own attributes, so I'm confused as to which type to fill with now. I've found no solid answers on any of the inter net forms. Any comments would be appreciated. Thanks.
I have been using Silicon since 1982 in hot rods with great success. The only down side is it takes perfect flares and EXTRA tight fittings to get little leaks stopped. Walter
Using DOT 5 brake fluid in my 48 Plymouth. Approximately 6000 miles so far and no problems whatsoever. Not original.....front disc conversion with GM metric calipers, Dodge pick-up dual master cylinder, Mopar B-body 10" drums in the rear.
I put DOT-5 in my (O/T) '68 Corvette. I spent days getting it bled correctly ("Honey, can you please come and help me AGAIN?"). Now that it's done, I love it. Since then, however, I have switched to DOT-4 and "Speed Bleeders" and am much happier; (so is the little lady).
I have had both-The Dot 5 will not hurt paint. I had trouble getting a firm pedal with dot 5 on one car-but I don't blame that entirely on the brake fluid. Dot 3 is easier to get on the road if you have a problem.
I used silicon however the pedal was never right and felt spongy. I drained the system and flushed it, installed all new seals and replaced with older style fluid which is still there today.
DOT 3 will do you just fine and as mentioned above can be purchased easily on the rad if needed. Whatever you decide to use, don't mix them.
I've had silicon in my car for over 10 years. It will not absorb water like DOT3, so no rust in the system. And as also mentioned, it won't remove paint. I have a front disc brake conversion and rear drums and I haven't had a drop leak out. Just a thought. Yes it is harder to find and more expensive than DOT3, but if you do "break down" and can't find it would it really help if you did? I mean what type of failure would require you to refill the system? I'm thinking blown wheel cylinder or hose? If that is the case, you got bigger problems than not finding DOT5.
Unless your worried about painted ch***is parts. Use DOT4. I used the DOT5 in a fenderless car with lots of painted parts open frame and such with no issue. The problem, I belive, is when people go crazy trying to "pump" bleed their system as the silicone tends to aerate a little more. I used a vacuum bleeder to fill the system, then had the helper (wife) pump the pedal once then crack the bleed screw. One pump loosen/tighten....repeat till flowing clear, move to the next wheel ect, ect. Nice firm pedal and no worry of blistering paint. Btw I was using manual brakes. Good luck.
DdoubleD has got it right, if you do what he says, you should not have any problem. When you vacuum bled, the wheel cylinders and calipers get wet and seal up better when you go to bleed. Every parts store that I go to has dot 5 these days.
There are two downsides that I've discovered with DOT5: 1. As mentioned previously, DOT5 can take a while to get a firm pedal with, as it does tend to aerate if it isn't poured in slowly, or if the pedal is pumped quickly when bleeding. This is just an issue during the initial fill and bleeding of the system, or when components are replaced. Once the air is gone from the system, it's great. 2. It isn't hygroscopic (doesn't absorb water) which means if the entire system isn't completely free of moisture, water will coalesce and lay in the low spots of the system, which are typically the calipers/brake cylinders. This can cause localized rust pits, or oxidation in aluminum components, which is not a good thing in brake systems. DOT3 absorbs the water and it just makes the fluid nasty over time, but does not result in localized rusting. Since I have a couple vehicles that do not get driven as often as they should, I use DOT3 in them, and change it every few years.
In all my years since the inception of DOT 5 I've seen and read 2 different things that can be a negative. As a synthetic I think it has a hard time keeping seals full sized and sealed. Over extended storage times this can result in a leak down, no pedal, perhaps even a rebuild with fresh rubber parts. The other thing which doesn't effect flatlanders, the boiling point changes with al***ude. I'd read a story in HOT ROD, maybe Car Craft, but someone had gone to DOT 5 and would lose their brakes while trying to head west over the mountains. It turned out that it was the boiling point change as with standard fluid, no issue. I found that pretty interesting and still recall it some 30 yrs later. Anyone else that has to top higher elevations experience that? Anyone know if the formulation changed to prevent such an occurrence?
Been using DOT5 for 14 yrs. , vacuum bleed the system[replace the fluid] every 2 years , NO problems.. dave
I have experienced the High Al***ude issues. Harley has used DOT 5 for years, mainly because of paint issues (although interestingly they use DOT 4 on the performance oriented XR1200), and have experienced everything from spongy to outright failure at high al***ude on Harley's over the years. And each time they recovered when I went back to sea level! I also experienced a VERY Soft pedal in the race car at Pikes Peak with DOT5 - not the place to have this happen. I'm not sure if it is 100% attributable to the lower boiling point, but maybe due to the fact that the Silicone has very loose molecules that allow it to absorb air (as versus Trap air) which makes the fluid compressible, and the change in air density at al***ude contributes to the soft pedal.
***uming that the vehicle is pretty much original I would stay with DOT3 or Upgrade to DOT 4 ; The DOT5 Fluid might hurt your seals ; Use DOT5.1 Brake fluid if your concern is heat/performance applications. Brake fluid should be flushed at least every couple of years.
This is crazy, I took my roadster (has DOT 5) to the Hot Rod Hill Climb last year, and at 11,000 feet I had barley any brakes. Pedal was nearly to the floor before it would start to stop. I adjusted them and all was good. I thought maybe they had just gone out of adjustment...no one there said al***ude would have any role in a spongy pedal. Now it makes sense. I thought it was just a coincidence....
Thanks guys for all the replies. My '41 Buick has stock shoe style brakes. I don't believe the metal brake lines have ever been replaced. Ch***is is not show, so if the brake fluid drips on it there is no big deal. The only anticipated brake mod is to install a double chamber brake master cylinder. right now I don't know of a master cylinder that would fit and/or what mods would be required to install one.
From my experience, since the development of "Speed-Bleeders", DOT-5 is unnecessary and a pain in the ****. I have a brake fluid tester that will tell you the moisture content in your system. From experience, I find it takes about 10 years for conventional fluid to absorb enough moisture to be concerned about. I have tested all of my cars, and when the moisture reaches a certain level. I install a set of "Speed-Bleeders" and flush the system. The "Speed-Bleeders" make the flushing a quick, one person job. Ebbsspeed makes two very good points against using DOT-5 that have merit. In Minnesota, I don't have al***ude concerns, but it's still something to think about. I don't think any major car company that uses DOT-5 from the factory. That also tells me something. For me, checking and flushing is an infrequent maintenance exercise that should be performed by anyone who has a "special" vehicle.
So, if you want to change from DOT 3/4 to DOT 5...or vise-versa, what is the best procedure to completely flush your system?
DOT 3 & DOT 4 ARE compatible. Both are glycol ether based DOT 5 IS NOT. You would have to flush the system in its entirety, seal damage could occur.
I had a friend called me from colorado lost his brakes in 66 corvette replaced dot 5 with 3 0r 4 drove the rest of the way to mich,
@ 34toddster No you did not dream this up. When the Original Equipment Manufacturer (OEM) Delivered the vehicle to be sold the public; it applied a DOT (Department Of Transportation) approved fluid designation to the brake system; usually affixed to The Master Cylinder Cap.
We run Dot 5 in everything. I first used it in my 27 over 25 years ago, and when I redid that car about 8 years ago, I drained out the original 17 year ish old fluid, and it was as clean as a whistle and the internals of the brake system were spotless and rustfree. I mainly use it so my paint won't get ruined, but it has other benefits too. Don
Been running DOT-5 in my Bug for 22+ years; I converted when I built a new floorpan for the car, complete with new hoses, lines, calipers, and master cylinder, so no fluid compatibility issues. I did recently replace the master cylinder, but I attribute that to age and lack of use while in storage.
Very interesting feedback on the high al***ude thing. I only indicated boiling point because that's what the answer was to the tech letter. It may very well be air getting in, maybe a simple viscosity change at high al***ude. The boiling point thing made sense, also molecular structure was mentioned as to why. I'd be less than candid to say I recall the whole deal, it's just that the al***ude thing stuck with me. I experienced severe brake fade once. A GTO with drum brakes all around, did some silly freeway racing against a Buick GN, around the bend traffic dead stopped. My brakes lasted about 5 seconds and then done. Stopping a 2 ton car from 110 with drum brakes? Not this guy ever again. DOT 3 fluid, just a different scenario. Boiled in a hurry and damn near gave me a "2 shorts" day... Quick edit, I was handling the GN quite well. He couldn't p*** me.
I've used the silicone fluid in one of my hot rods for over 13 years. Yes, when spilled on your paint, it wont hurt it. Yes, it's miserable to bleed. Yes, you must have perfect seats and flares in your line and fittings. It will leak past anything that's not completely perfect. One very odd thing I have encountered is in damp (rainy) weather at the same time while traveling in high al***udes the brakes act like severe brake fade. Almost serious loss of most braking. I have power disc / drums, all GM components with a dual diaphragm booster. No logical explanation except maybe a quirk with DOT 5.
Flush the system thoroughly with iso-propal alcohol-(available by the gallon at farm supply stores) I have used a big syringe(again available at the farm supply store) and some clear hose and back flushed from the bleeder screws. Then let the system stay open and empty-the alcohol will evaporate-then refill and flush some clean fluid through before you bleed the system
In the mid 70 or a bit earlier I started using DOT-5. Started with farm tractors and trucks and then circle track cars and, finally, street cars when it became abundantly clear DOT-5 is outstanding stuff. At first it couldn't be purchased at the local NAPA for instance. Have one comment directed at the original question in the first post that asked for good advice: As your system is stock with drum brakes rebuild by using some silicon paste on the cup, then on the slug and then a goodly amount under the rubber protective boot that the rods go through. Otherwise there's a chance the aluminum slug will not get lubrication and will freeze up by corrosion. With 'regular' brake fluid there is a tiny amount of 'seepage' of fluid past the cup lip which generally suffices. Simply coating, at ***embly, the above mentioned parts in DOT-5 will work but with the paste you'll be 100% OK.
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