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Veteran
Posts: 177
 
Location: Omaha, NE | Did a total brake rebuild: Rebuilt master cylinder, all new wheel cylinders and hoses. Now it's time to put fluid in. I'm debating using synthetic. Opinions, experiences?
Thanks! |
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Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!
Posts: 19146
 
Location: bishop, ca | Doug, on your total brake rebuild, did you have Just Suspension create/install Carbon Metallic brake linings
onto your car's brake shoes?
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Expert 5K+
Posts: 8948
 
Location: WHEELING,WV.>>>HOME OF WWVA | you can use either but some like one over the other . but you can't top off synthetic with the old style in a pinch . it'll reduce the effectiveness of the synthetic . you can though , top off the old
style with synthetic . ------------------------------------------------later |
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Board Moderator & Exner Expert 10K+
Posts: 13055
Location: Southern Sweden - Sturkö island | There's a couple of negative things about synthetic;
1 the brake light hydraulic contact will leak and must be replaced with a mechanical one.
2 the brakes will feel more "spoungy"
3 you need to bleed out half a coffe cup at least once a year due to that synthetic is not hygroscopic.
4 its very expensive in comparison
The positive thing is that the synthetic;
1 will never ever freeze, because it don't mix with water
2 will not damage your paint
3 will not effect your rubber parts negativly.
I have thought of changing from dot 3 to synhetic many times, but I'm old school and change my brake fluid once every year or two and bleed the brakes in between. For me it would be more expensive and like to do the maintenance on my car.
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Location: Under the X in Texas | Just my opinion and many don't share it, however, I feel that because our Mopars seem to have fairly low brake pedals (even when fully properly adjusted) that I prefer regular high quality Dot 3, glycol based brake fluid. The reason is that synthetic fluid actually has some small percentage of compression whereas glycol fluid has none. When I have had synthetic in two cars, the pedal feel was even lower than factory and I really REALLY don't like a low brake pedal. And as mentioned above, I didn't like having my brake light switches fail over and over, keeping a spare in the glove box and changing them in a park lot when other drivers told me I had no brake lights! |
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Expert
Posts: 3780
Location: NorCal |
Don't confuse silicone with synthetic. Although silicone is synthetic, it is always DOT 5; there is synthetic DOT 3 and DOT 4.
The OP specified "synthetic". |
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Expert
Posts: 3577
Location: Blythewood, SC | I have used all three. I currently use Dot 4 in my cars. It's a little higher boiling than Dot 3, but it does not aerate. I had a soft pedal problem for a long time in my Lil Red Express from Dot 5.
In the end, you can use any of the three. Dot 5 will be hardest to get bled without aerating the fluid. Dot 3 is the cheapest. |
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Regular
Posts: 62
| Years ago, I had a discussion about DOT 5 brake fluid with a chemical engineer. He told me to further investigate the matter with one of the original manufacturers of the product. I ended up speaking with a PhD research scientist at was then called Wacker Chemical Corporation. She would not speak on the record due to legal liability issues, but here is what everyone should keep in mind about this product: DOT 5 silicone brake fluid was never engineered as a direct replacement for DOTs 3 and 4 brake fluids, especially when a motor vehicle has a hydraulically actuated brake switch. DOT 5 brake fluid can leak past the switch, and in a best case scenario, cause the switch to fail. However, DOT 5 brake fluid is a DIELECTRIC COMPOUND, and in a worst case scenario, will cause a dead short, and then the car burns down to the rims. Remember, only DOTs 3 and 4 Polyglycol brake fluids were engineered specifically for use in motor vehicles, while people started using DOT 5 silicone brake fluid in classic cars because of certain, supposed advantages. Not a good idea. |
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Expert
Posts: 3780
Location: NorCal | 300XMAN - 2015-02-22 12:47 PM
However, DOT 5 brake fluid is a DIELECTRIC COMPOUND, and in a worst case scenario, will cause a dead short,
Uhhh, "dielectric" means it's a very poor conductor of electric current aka an insulator. |
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Regular
Posts: 62
| Dielectric compounds are touted for providing moisture barriers and having corrosion resistance properties, but they still conduct electricity. Even "a very poor conductor" is still a conductor of electricity. Personally, I would not want to risk a dead short and catastrophic fire due to the type of fluid in my braking system. DOT 5 was never engineered to be installed in older vehicles. Period. |
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Extreme Veteran
Posts: 594
Location: Melbourne, Australia | I'M very happy with the Dot 5 fluid in my Plymouth... approaching 10 years now.... Master cyl switch was replaced with pedal box switch as old style gave little warning to following cars. (and it did fail quickly as well after Dot 5) Pedal is very acceptable in feel and height. Didn't shake the bottle before use and had no problems bleeding brakes on first attempt. Colin |
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Expert 5K+
Posts: 8948
Location: WHEELING,WV.>>>HOME OF WWVA | so , all the manufacturers that supply dielectric grease for their do it yourself plugs wires for easier removal are wrong to do so ? -------------------------------------------------later |
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Expert
Posts: 2290
Location: Eastern Iowa | Near 30 years now in our F w/silicone fluid. Other that the brake light switch that I converted to mechanical, no problems. M/C and wheel cyls still look like new inside. Other than the location of the M/C for serviceing, I'm a happy camper! |
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Regular
Posts: 62
| My father has been using dielectric silicone grease inside the spark plug boots of cars for several decades. The grease is applied to help lubricate the rubber, but its main function is to act as a moisture barrier and provide corrosion resistance. Just make certain that you do not get any of the grease on the metal clips inside the boots and there will be no problem.
There is a different product that has insulating characteristics, and 57 Chizler referred to it in his latest post. Dielectric potting compounds are classified in the following manner: Compound type (electrical insulation), form/function (encapsulant), and they are non conductive. The purpose of dielectric potting compounds are to protect (encapsulate) electrical connections from contaminants.
My recent research about the use of DOT 5 silicone brake fluid brought to light the issue of hydrolytic stability. As indicated in the link http://www.machinerylubrication.com/Read/29397/understanding-hydrol... the top two contaminants are particles and water. The process of degradation to the lubricant, in this case DOT 5 brake fluid, is called hydrolysis. "As a lubricant is contaminated with water, the question then becomes how stable is the fluid in relation to the water. The ability of a lubricant and its additives to resist chemical decomposition in the presence of water is known as the lubricant's hydrolytic stability." Even though DOT 5 brake fluid is non-hygroscopic (does not absorb moisture out of the air), it is still susceptible to the introduction/presence of contaminants--especially water, which can then pool and either freeze or boil. Polyglycol brake fluids are a type of hydraulic fluid and are hygroscopic. |
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Expert
Posts: 3780
Location: NorCal | 300XMAN - 2015-02-22 3:34 PM
Personally, I would not want to risk a dead short and catastrophic fire due to the type of fluid in my braking system. .
"Dead short" is defined as no resistance to electrical flow; "dead" being the operative word. If there is any resistance in the circuit it's not a dead short.
Even insulators have a limit to their capabilities; an insulator that won't pass current at one voltage will pass current if the voltage is high enough. We're only talking 15 volts here. |
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Expert
Posts: 2290
Location: Eastern Iowa | I have used this grease on all the electrical connections on my over the road trucks ever since it became available. Tail lamps, brake lamps, clearance marker lamps everything. Ya gotta keep the water and especially the salt brine and crap they all use on the highways these days outta this stuff.. Ya smear everything with the stuff, fill the cavities in junction boxes, stuff the female sockets full and cram 'em together. Great stuff. All the new seal beam lights already have a gob of the stuff stuck on 'em.
And for Pete's sake don't go pokin' holes in yer wire insulation w/a tester all this road salt & crap will eat 'em alive
Now I know I'm never gonna subject my beloved MoPars to these harsh conditions but I'm just relating my past 40+ years of OTR experience here.
Your results may vary!! 
I think you guys are making a mountain out of a mole hill.
Edited by finsruskw 2015-02-23 7:07 PM
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Expert
Posts: 2312
Location: Arizona | Found this http://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm
and it seems to be based on real world experience. One of the big things I saw in it that surprised me was that dielectric grease should not be used on switches that carry enough current to arc. The arcs turn the silicon into an abrasive. |
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Brake fluid question - 1956 Dodge
