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Author Topic: Brake fluid & grease used in assembly of brake system  (Read 457 times)
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chriswgawne
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« on: 25 April, 2019, 08:17:05 AM »

I have just come across a small problem which I think is self inflicted.

For the last 50 years when working on the braking systems on our various cars, I have used Dot 4 fluid and the red rubber grease during assembly with the occasion smear of general purpose HMP grease on the exposed i.e non fluid side of wheel cylinders and master cylinders to try to reduce corrosion in these areas to a minimum.
About 2 years, someone whose opinion I greatly respect told me that silicone grease was much better that conventional grease in these exposed areas as it was waterproof. So, since then I have used a smear of silicone grease on re-assembly ( and stopped using the red rubber grease as well).

I have 3 sealed cans of brake fluid on my shelf - one is 100% unused, one is used and discoloured and when that can is full I dispose of it straight away.
The 3rd can contains fluid that I have used in the bleeding process and when put into the can was (apparently) clear, clean with no discolouration and basically indistinguishable from new.
I have come to do some brake work today on our Landcruiser and this 3rd can seems to have clusters of growth in it like a sort of mould (which it isn't) and I can only assume its something to do with using silicone on re-assembly on the fluid side of various components, not the airside. Its a little lumpy and I have no intention of using it.
So I will be going back to using the red rubber grease on re-assembly and only using the silicone grease where it wont come into contact with Dot 4 brake fluid.
I expect that some forum members use silicone brake fluid these days so this problem presumably wouldn't occur?. For me with the number of cars we have, I couldn't easily cope with more than one type of brake fluid so I stick to Dot 4.

Any thoughts from forum members?
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Chris Gawne
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Brian Long
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« Reply #1 on: 28 May, 2019, 06:50:52 AM »

Hi Chris,
I'd be wary of contaminating the 'wet side' of your braking system with anything (except rubber grease). Brake fluid seems to soak up anything e.g. water and react with other materials e.g.paint!
Silicone fluid was all the rage a good while ago because of its perceived benefits including immunity from water contamination however it had drawbacks when used in systems not deigned for it. As I recall its higher viscosity was the main problem along with contamination by any residual conventional brake fluid.
I'd stick with DOT4 and change it biennially.
As a tip, I have fitted a small electriclal wiring grommet (available from electronic hobby stores) to the stem of the brake fluid reservoir plunger on my B12. It is a tight sliding fit on the stem and acts as a seal to prevent the ingress of water, moist air etc into the reservoir.
Hope foregoing is of interest/help.
Brian.
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chriswgawne
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« Reply #2 on: 28 May, 2019, 08:04:20 AM »

Yes, I think you are absolutely correct Brian.
I use only Dot 4 brake fluid and will continue to do so.

I have just completely rebuilt the drive shafts, pot joints and rear brakes on Jacky's B24S Convertible as there was slight fluid leakage on the rear left. I last did her rear brakes about 20 years ago but of course the car doesn't do a huge mileage and the rear brakes are so massive that the shoe movement is very slight.
The rear wheel cylinders are steel so having cleaned them up carefully including honing, I used red rubber grease on the 'wet' side of the new rubber seals and a smear of silicone grease on the dry side hoping that this would keep any further corrosion to a minimum.
I am hopeful that this maintenance will last another 20 years!

And a couple of weeks ago I had a slight fluid weep on the front RH outer cylinder of our Fulvia GT so I used the same combination of greases upon re-assembly.
This problem was actually caused by a build up of sludge on the wet side of the outer front RH wheel cylinder which ended up getting between the rubber seal and the wall of the wheel cylinder. There was no corrosion evident as the cylinder had been S/S sleeved so I can only think that this sludge was in the brake system when we bought the car where it had been standing in Portugal for around 20 years without brake fluid in the system. When I put the car back on the road last summer, I bled the front RH brake first and the bleed nipple is on the top of the  inner wheel cylinder so any sludge would have accumulated (and stayed) in the bottom of the outer wheel cylinder. Another small lesson learned..

Chris
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Chris Gawne
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Brian Long
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« Reply #3 on: 29 May, 2019, 12:33:12 AM »

Chris,
Re the Fulvia calipers. What you describe sounds feasible. As you know, the Dunlop caliper pistons are prone to building up corrosion on the external surface of the piston. Then, when you fit new pads, this corroded section wrecks the seals when the pistons are retracted.
Seeing as yours had been resleeved, your observation that internally deposited corrosion products caused the leakage is probably correct.
Regards
Brian
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