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MG Midget and Sprite Technical - O rings for concentric slave cylinders

I'm want to order replacement O rings for a Concentric slave from simply bearings. They have a choice of material, Nitrile, Viton or EPDM. What is the difference? Are they all suitable for brake fluids? I'm using Silicone so which material is best?

Rob
Rob aka MG Moneypit

Viton is used in carbs as it's fuel-resistant. I don't know EPDM.
David Smith

Rob/David
Searched around and found these writeups--
Too much time on my hands--
The EPDM is the only one that mentions brake fluid where the other two appear to be for more oil based sealing - If it were my choice from this info I think I would be going EPDM
cheers
willy

Nitrile / NBR

Nitrile, chemically, is a copolymer of butadiene and acrylonitrile. Acrylonitrile content varies in commercial products from 18% to 50%. As the nitrile content increases, resistance to petroleum base oils and hydrocarbon fuels increases, but low temperature flexibility decreases.
About Nitrile / NBR:

Due to its excellent resistance to petroleum products, and its ability to be compounded for service over a temperature range of -35°C to +120°C (-30°F to +250°F), Nitrile /NBR is the most widely used elastomer in the seal industry today. Also many military rubber specifications for fuel and oil resistant O-rings require nitrile based compounds. It should be mentioned that to obtain good resistance to low temperature, it is often necessary to sacrifice some high temperature resistance. Nitrile compounds are superior to most elastomers with regard to compression set, tear, and abrasion resistance. Nitrile compounds do not possess good resistance to ozone, sunlight, or weather. They should not be stored near electric motors or other ozone generating equipment.
Nitrile / NBR usage:

They should be kept from direct sunlight. However, this can be improved through compounding. NBR is the standard material for hydraulics and pneumatics. NBR resists oil-based hydraulic fluids, fats, animal and vegetable oils, flame retardant liquids (HFA, HFB, HFC), grease, water, and air. Special low-temperature compounds are available for mineral oil-based fluids. By hydrogenation, carboxylic acid addition, or PVC blending, the nitrile polymer can meet a more specified range of physical or chemical requirements.






Viton® / FKM

Fluorocarbon O-rings should be considered for use in aircraft, automobile and other mechanical devices requiring maximum resistance to elevated temperatures and to many fluids. FKM (FPM, Viton®, Fluorel®) resist mineral oils and greases, aliphatic, aromatic and also special chlorinated hydrocarbons, petrol, diesel fuels, silicone oils and greases. It is suitable for high vacuum applications. Many fluorocarbon compounds have a higher than normal mold shrinkage rate, molds for fluorocarbon products are often different from molds for Nitrile.
About Viton ® / FKM

Fluorocarbon elastomers have grown to major importance in the seal industry. Due to its wide range of chemical compatibility, temperature range, low compression set, and excellent aging characteristics, fluorocarbon rubber is the most significant single elastomer developed in recent history. Fluorocarbon elastomers are highly fluorinated carbon-based polymers used in applications to resist harsh chemical and ozone attack.

The working temperature range is considered to be -26°C to +205°/230°C (-15°F to +400°/440°F).



EPDM

Ethylene propylene rubber is an elastomer prepared from ethylene and propylene monomers (ethylene propylene copolymer) and at times with an amount of a third (diene) monomer (ethylene propylene diene terpolymers). Ethylene propylene rubber has a temperature range of -50°C to +120°/150°C (-60°F to +250°/300°F), depending on the curing system. Special grades can even see higher temperatures.
About EPDM / ethylene propylene diene monomer

It has a great acceptance in the sealing world because of its excellent resistance to heat, water and steam, alkali, mild acidic and oxygenated solvents, ozone, and sunlight (UV). These compounds also withstand the effect of brake fluids and Skydrol" and other phosphate ester-based hydraulic fluids. EPDM compounds are not recommended for gasoline, petroleum oil and grease, and hydrocarbon environments.
William Revit

This is timely.

As I have my engine out of the Sprite, I'd like to get a new spare set of o ring seals for my Titan(Burton) concentric slave.

Burton sell them for £18.48 plus postage.

But I wonder if I could buy the same thing a lot cheaper from elsewhere? I'll get the sizes and have a look.
Lawrence Slater

Check this out.

http://simplybearings.co.uk/shop/index.php?cPath=4501_4705

Click on the --- Chemical Resistance Table "[Click Here]" selection.

I typed in Brake fluid., and I also tried Glycol ether.




Lawrence Slater

Also.
http://www.marcorubber.com/materialguide.htm

Note the NOT suitable for comment regarding Nitrile.

I can bear testimony. I have nitrile gloves. Brake fluid soon ruins them.

EPDM it is then.



Lawrence Slater

Looking at simply bearing prices, it'll cost me a little more than Burton. But I'll get 2 sets from Simply, because they only sell in packs of 2 min.

Isn't there an outlet selling concentric slave seals for Saabs?

Yes there is.
Saab 900 85'-93' Clutch Slave Cylinder Outer Seal Kit
9.99 GBP Buy It Now
http://uk.picclick.com/Saab-900-85-93-Clutch-Slave-Cylinder-Outer-Seal-281098361696.html

And here, in Euros.
http://www.skandix.de/en/spare-parts/drive-train/clutch-control/clutch-hydraulics/slave-cylinder/repair-kit-clutch-slave-cylinder/1003458/
Lawrence Slater

MUCH cheaper here on Ebay.
http://www.ebay.co.uk/itm/EPDM-O-Rings-Various-ID-1MM-C-S-UK-Supplier-/141495293347?pt=LH_DefaultDomain_3&var=&hash=item20f1c6d5a3

10 pack by 30mm, 3 quid, FREE postage.

I'll see exactly what sizes I need.
Lawrence Slater

This thread was discussed between 10/03/2015 and 15/03/2015

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