Requirements for Brake greases

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A couple of statements in that link leave me wondering. ''PAO-based brake lubricants are also excellent for assembly work and lubricating seals and boots.'' PAO"s are still hydrocarbons and should have similar solubility parameters as the mineral oils that swell internal brake parts. ''Silcone’s normal working range is -40 degrees F to 400 degrees F. But it does not have the high temperature staying power of a high solids synthetic lubricant'' Sil-Glyde claims 600 degrees.
 
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7,742
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MI
Lots of interesting comments here. Konst: Larry Carly has an entire library of automotive topics here: http://www.aa1car.com/library.htm He talks with authority,his articles are generally good, but when it gets to the fine details, I get the impression that he often states HIS opinion, which might differ from others. His coolant articles are similar. Excellent info, but sometimes not perfect. IE, he generally recommends to use one type (silicone) grease for "rubber enclosed brake areas" (caliper pins) and another type (high solids) for metal to metal, exposed to elements areas (pad backs). Yet, Ford and many others recommend their silicone grease for both areas. Who's more correct? REF: read Ford TSBs: http://www.fcsdchemicalsandlubricants.co...ategory=Greases Labman: Regarding PAO types, all I can say is that the packaging claims compatibility with rubber brake components. Sil-glyde is a mystery product. Unlike other silicone lubes, it turns yellow exposed to light/air. It's MSDS is vague since polypropylene glycol is it's main ingredient, it appears to have castor bean oil (yellowing?), and little mention of polysiloxane? I have seen different labeling that shows 425 and 600 degrees F. IMO, it is not a true silicone lubricant like the Ford or Dow products. Ref.: http://www.agscompany.com/downloads/msds/sil-glyde_lube_compound_-_020107.pdf (MSDS) http://www.agscompany.com/products.php?line=5&category=17&subcat=97&product=212 (425 degree F) SteveS: On this rare occasion, I agree with your comment. Unless we get some real experts here, we are left with incomplete MSDSs and anecdotal stories. Much the same with oil, filters, etc., etc., etc.. It's tough for OCD types seeking truth over opinion when the "experts cannot agree". It really becomes a biased, personal decision based on incomplete information.
 

MolaKule

Staff member
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Quote:
PAO"s are still hydrocarbons and should have similar solubility parameters as the mineral oils that swell internal brake parts.
Not all hydrocarbons possess the same characteristics. PAO's and GroupIII oils have poor solubility and poor seal swell for example, but Group I, II oils have good solubility. Ester are hydrocarbons yet posess good solubility and excellent seal swell.
 

MolaKule

Staff member
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Iowegia - USA
Quote:
The primary lubrication points in rear drum brakes include the raised pads on the backing plates that support the shoes, the star adjuster mechanisms, hinge points for self-adjusters or the parking brake linkage, and the parking brake cables. One place you never, ever want to get any grease on is the friction surface of a brake lining - which is another reason for not using low-temperature or petroleum-based lubricants which can melt, run off and foul the linings. Grease contaminated shoes or pads will be grabby and usually cause a brake pull to one side. The only cure is to replace the fouled linings with new ones. Cleaning is out of the question because solvents and cleaners can adversely affect the linings, too. For lubricating hydraulic components, such as the piston seals inside calipers and wheel cylinders, you can use a silicone-based brake lubricant or ordinary brake fluid. This type of lubricant will help assure smooth movement of the seals in their bores, and will help prevent these parts from sticking or corroding.
 
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8,711
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Originally Posted By: MolaKule
Quote:
PAO"s are still hydrocarbons and should have similar solubility parameters as the mineral oils that swell internal brake parts.
Not all hydrocarbons possess the same characteristics. PAO's and GroupIII oils have poor solubility and poor seal swell for example, but Group I, II oils have good solubility. Ester are hydrocarbons yet posess good solubility and excellent seal swell.
It doesn't take much solubility to swell brake parts. Plain old mineral oil will do fine, as well as poly alpha olefins that are still just alkanes, certainly not the highly polar material safe for brake parts such as polyglycols.
 
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southeast US
Originally Posted By: MolaKule
Not all hydrocarbons possess the same characteristics. PAO's and GroupIII oils have poor solubility and poor seal swell for example, but Group I, II oils have good solubility. Ester are hydrocarbons yet posess good solubility and excellent seal swell.
Esters contain oxygen and thus are not hydrocarbons by definition.
 
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8,711
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I once thought I was wrong, but I wasn't. That is why in my 12 October post I used the more technical term alkanes. I think MolaKule and I both forgot the definition of hydrocarbons. They are purely compounds of carbon and hydrogen with no oxygen, nitrogen, etc. They do include the aromatics, benzine and other compounds with its ring structure. As such they are still hydrocarbons, but will swell/destroy a wider range of elastomers. Unkind people will say they stink. I have no idea of their lubricating properties. Were they much good I doubt the oil companies would go to all the work of breaking down the naphthenic crudes and reassembling them into either straight chain alkanes or branched ones. Alkanes include straight chain, branched, and cyclic hydrocarbons as long as they are saturated. Olefins are unsaturated, but once polymerized, become saturated, PAO.
 
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9,448
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USA
If we are talking about lubing the pins in slider set up's on cheap disc brake designs it doesnot take much to get the job done. Even though I have been told not to do this 8 out of 10 mechanics still use Nickle based antis sieze. In spite of what we have been told it with stands wash out better then any moly ep grease Ihave used for this and better then silicone like Slyn-Slide or whater it is called.I have not had it attack boots at all, Now for the pistons seals I use what ever grease I have on hand becuase you are just putting the thinest film on them. I mean I use more chapstick on my lips then I do any grease for the seal of pistons. You never put it inside just on the outside. A silicone based product if you had it would work well for this but I seldom do. I have even use Diletric grease before and had good results. really any hydrocarbon you put on a rubber and carbon black based seal is going to in some way affect it. So one has to decide if you even want to lube it. If it is a high end seal like Teflon or Viton then you really have no need to lube it and very little is going to react with it. I seldom lube the piston seals at all and have had no issues with the seals ever failing even on vechile over 17 years old. It is always a mechanical failure.
 

Kestas

Staff member
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The Motor City
John, though you've never had problems with your practises, for the sake of others I must advise against the practise of buttering the seals with regular grease. The grease is incompatible with the seal and can swell it. You probably have no problems because it washes away quickly in service. I also advise everyone get a tube of silicone grease for their toolbox for brake jobs and other uses. It'll last a long time.
 
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8,711
Location
Nothern USA
I put Sil-Glyde on everything but the friction surfaces, seals, bushings, boots, bolts, backing plate, backing plates, bleed screw threads, and likely some places I can't think of.
 
Messages
8,711
Location
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Originally Posted By: labman
I put Sil-Glyde on everything but the friction surfaces, seals, bushings, boots, bolts, backing plate, backing plates, bleed screw threads, and likely some places I can't think of.
Hummmmmmmmmm! Rereading that it could be taken to mean I don't put it on any of them. I meant everything but the friction surfaces. Note, I wouldn't risk a conventional lithium grease on internal brake parts. I think the external rubber parts are formulated to resist them. Just make sure it is a high temperature one.
 
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