Guest Doctor Dirt Posted April 18, 2013 Posted April 18, 2013 Hello all, getting ready to check all fluids on a 49 Dodge coupe my only question on all the fluids is the brake fluid. Obviously the "moPar " fluid used isn't around anymore so my best guess would be DOT 3 or 4. I will look to make sure the fluid in the car looks to be healthy and not compromised if it is I'll dump whats in it!! Does anyone have a brand name or weither synthetics is good or bad for the system. Having a tuff time getting info on the net on this subject, thanx Doc
platt-deutsch Posted April 18, 2013 Posted April 18, 2013 I use DOT #5 in everything . Its universal and backwards compatible to #4 and #3. Its synthetic and wont absorb water like the Menthonol Alcohol based fluids. It also boils above 500 deg F. But its a bit costly..
ply33 Posted April 18, 2013 Posted April 18, 2013 I'm sure a little search will turn up lots of comments and recommendations. In my opinion there are pros and cons to both the DOT3/4 and DOT5. My short list, probably not definitive and may not reflect the true facts, is as follows:DOT3/4 Pros:Cheap.Basically what came from the factory.DOT3/4 Cons:Destroys painted surfaces.Absorbs water from the air leading to internal corrosion of brake parts (can be mitigated by flushing brake system periodically, say every year or so).DOT5 Pros:Does not destroy existing paint.Does not absorb water from the air so brake system does not degrade with long periods of storage.DOT5 Cons:Expensive.May contaminate surfaces you wish to paint later with silicon making painting difficult.Entrains air bubbles more easily leading to a more difficult time bleeding the brakes.Some evidence that hydraulic type brake light switches fail earlier with DOT5 fluids.Mixing and matching: Most of the failures I've heard of when switching to DOT5 from DOT3/4 seem to be when the switch has been made on an existing, filled, system. DOT5 is less dense than DOT3/4 and will float on top in the wheel cylinders so you will never get all the old fluid out without disassembling everything. And apparently having a mix of the two fluids in the cylinders can cause an issue.I have DOT5 in my '33 but don't bother with it in my new cars. Not sure I'd go the DOT5 route again if I were to do it over but it does work and my brakes have have had only one hydraulic issue in 15 years.
nearchoclatetown Posted April 18, 2013 Posted April 18, 2013 Good call there Pky33 on the DO NOT MIX. Silicone fluid will cause major problems if mixed in an existing system., like peddle going straight to the floor. There was a mess that looked like an afterbirth in the master cylinder in a truck I ttried to drive that someone that wasn't paying attention mixed 3/4 and 5.
Guest Doctor Dirt Posted April 18, 2013 Posted April 18, 2013 OK I appreciate the opinions. I'm going to go with 3 if it needs topping off. This car was restored however it was cosmetic and plenty of the mechanics were left alone. Some good some bad!!! Wouldn't it be nice of there was a different tint to the fluid options so we'd know what the hell is in a car we have no history on? To easy!!! HA! Doc
Guest DodgeKCL Posted April 18, 2013 Posted April 18, 2013 I've used DOT 3 for more years than I care to remember and have had no issues. I buy the very best I can. No cheap off brand stuff. Every 3 or 4 years I change the fluid and it does come out looking like tea. It of course goes in looking like maybe honey. As of this Spring the brakes are still 'hard' and there is no evidence of leakage anywhere. I highly recommend what an old mechanic told me to do with these old cars and trucks when they are in any kind of long term storage like Winter. You should open the driver's door and push the brake pedal a couple of times to 'wet' the cylinders,master and wheels, to keep the bores from drying out and the rubber cups from tearing when first used after the storage. I think we forget that the designers of our brake systems expected the brakes to be used at least several times a week and never considered what would happen during storage. I charge my batteries on the same day of the month through the Winter (I get 10 to 12 years out of them that way) and push the brake pedal a couple of times.
ply33 Posted April 18, 2013 Posted April 18, 2013 (edited) OK I appreciate the opinions. I'm going to go with 3 if it needs topping off. This car was restored however it was cosmetic and plenty of the mechanics were left alone. Some good some bad!!! Wouldn't it be nice of there was a different tint to the fluid options so we'd know what the hell is in a car we have no history on? To easy!!! HA! DocThe odds are that you have DOT3 in there but. . .DOT3 (don't know about DOT4) smells different than DOT5.Also DOT5 has a purple dye added but the dye may degrade in time. After 15 years I had to get in to the hydraulic system on my car recently and the first fluid out the wheel cylinders when I was bleeding them was still purple so I don't know how long or under what conditions the purple dye degrades.I guess you could take a little fluid from the master cylinder and put it on a painted surface that you don't care about. Let it sit for a few minutes and see if the paint is softened. If it softens then the fluid is not DOT5.PS to my post on pros and cons: It is my understanding that brake component manufacturers only certify their parts are good if used with factory fill and factory fill is always DOT3 or DOT4. So premature failure of a part in a system filled with DOT5 may not be backed up by the part manufacturer's warranty. Edited April 18, 2013 by ply33 (see edit history)
nearchoclatetown Posted April 18, 2013 Posted April 18, 2013 DR. Dirt, you probably have a problem somewhere. Seldom can a system be low on fluid without haveing a leak. Hope it works out for you. Do your own google on silicone brake fluid, not sure why anyone would say it can be mixed with DOT 3 or 4? Everything I've ever read says no way. IF you can get a decent peddle just by adding fluid you should flush the system if the car sat for a long time. 3 and 4 absorb water, never leave the cap off a can while playing with your system.
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