Which brake fluid

PostPost by: AHM » Mon Apr 23, 2012 11:11 am

Mike,

Good advice, I find fluids of all sorts don't keep either they go-off or are superceded.

I have 5 cars to do so didn't have to think much about buying 5 litres.

Simon
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PostPost by: Elan45 » Tue Apr 24, 2012 2:05 pm

I rebuilt everything in 1985 when I initially restored my Super Safety Elan, and silicon was what all the restorers were using and so did I. No problems all these years except for fade when I raced it in the first ever Columbus 500 vintage support race. I've never known if the fade was a result of silicone fluid, new, not fully bedded in pads or what. About 5 or 6 years ago, I had to rebuild the clutch slave as a result of too much heat from a long stop-go traffic situation.

So, last month putting the car back together after a body off frame rebuild, I decided to use the new bottle of silicone I'd been holding as a spare. We had some problems bleeding the system, same as I remembered from 25 years ago. Silicone isn't as lubricating as Dot 4 and it takes some time for the master cylinder to return to top of stroke until the system is free of air.

My next Elan restoration will not get silicone fluid, but rather the Girling LMA that I use in my Lotus 20/22 Formula Jr. It works well and is very stable. Race cars do get bled a bit more often than street driven cars, but that's the direction I will go. Maybe more for standardization than anything else.

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PostPost by: ardee_selby » Tue Apr 24, 2012 2:18 pm

Elan45 wrote:...About 5 or 6 years ago, I had to rebuild the clutch slave as a result of too much heat from a long stop-go traffic situation...My next Elan restoration will not get silicone fluid, but rather the Girling LMA...Roger


Roger,

Your account (on here) of having an extinguisher to hand when an Elan clutch pipe melted in traffic, and caught fire, has stuck with me!

In your view, would that be justification for using silicone fluid just in the clutch? (In addition to careful routing & using an alternative clutch pipe arrangement)

Richard
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PostPost by: 661 » Tue Apr 24, 2012 5:20 pm

Likewise, when I restored the Elan, silicon was all the rage (pre PIP scare!). I didn't change/bleed it as often as I should and I've found it's sludged in the system. Really messy and clearly not good . It was a well respected make.
flushed everything through and using super dot4 as that's what i had for the Exige. Seems to work well. (from Opie oils)
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PostPost by: mark030358 » Mon Mar 14, 2022 11:22 pm

Just a bump to an old thread.

I recently, within the last 8 months, change all the brake/clutch fluids to Castrol React Performance Dot 4 Fully Synthetic Brake Fluid.

Now when taking out my gearbox today the slave cylinder piston came out, never ever done that before, usually stays put in the cylinder. Now the seals are around 18 years old, but I was wondering if the above fluid would impact the seal. The seal was not breaking down, not gooey in any way, perhaps a little soft but hard to tell as I don’t have another to hand.

Thoughts anyone?

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PostPost by: mbell » Mon Mar 14, 2022 11:59 pm

I doubt it's a fluid issue, likely just age/wear/heat.

The seals cost very little and only take a few minutes extra compared to putting it back together as is. So unless your planning to refit the engine in next day or two you have time to order a seal set and replace them.

So the question is why wouldn't you replace them now?
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PostPost by: mark030358 » Tue Mar 15, 2022 8:52 am

Thanks…
For sure will be replaced.

Thanks
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PostPost by: JJ66 » Fri Mar 18, 2022 8:38 pm

Hello all,

Just to add to this, I have been a brake design/development engineer for 30+ years so have some experience. Silicon is great because it is not hygroscopic, hence does not absorb water/moisture. The army used to use it in all those old Bedfords and military vehicles that sat for years without being used, the silicon fluid enabled them to run without issue and without having to sort brakes out that had water damaged fluid. BUT, the down side with silicon is a) it is a bit more compressible so longer pedal travel and a bit of sponginess (But nothing a regular driver would notrice) and most importantly, b) The lubricity (is that a word?!) is not as good as vegetable brake fluid (Standard brake fluid), this is why some servo's have a sticker on them (like was shown earlier in this post) saying 'do not use silicon fluid'. Girling and Lockheed remote servo's, like those fitted to a lot of classics, need a nice slippey fluid as they tend to stick otherwise. When I was young and niaive I put silicon in my first Plus 2 (Chassis No. 60) and it had a remote M2b powerstop fitted, I had a lot of issues with sticky brakes as a result.

The key fact to highlight in all of this is for everyone who is using normal Vegetable brake fluid (that you buy from motor factors) is to change it every two years religiously (18 months is preferable). No matter how many, or how few, miles you do, it absorbs water at the same rate, and this cause much reduced boiling point and also corrodes your pistons and brake lines (if they are steel). Honestly, it sound like a pain but will save you money and hassle in the long run.

Happy Braking :-)
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PostPost by: 2cams70 » Sat Mar 19, 2022 1:23 am

Poor lubricity is the problem with silicone brake fluid. It probably doesn’t pass OEM durability standards. May be ok in a little used race car.

https://penriteoil.com.au/knowledge-cen ... -fluid/307
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PostPost by: JJ66 » Sat Mar 19, 2022 8:55 am

2cams70 wrote:Poor lubricity is the problem with silicone brake fluid. It probably doesn’t pass OEM durability standards. May be ok in a little used race car.

https://penriteoil.com.au/knowledge-cen ... -fluid/307

Yep, that’s a much better and concise summary than I gave. The durability aspect goes hand in hand with increased friction/lower lubricity.
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PostPost by: snowyelan » Sat Mar 19, 2022 2:29 pm

Hi All,

I am about to fill a completely new/rebuilt system and would like to know the current opinions on which fluid to use. I see regular DOT 4 in previous posts, as well as Girling LMA, and now synthetic DOT 4. I'm not interested in silicone fluids. I intend to bleed the system yearly as part of putting it to bed for the winter, so longevity isn't an issue for me.

Any opinions on which current fluid and why?
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PostPost by: JJ66 » Sat Mar 19, 2022 3:41 pm

The LMA is sold as a high performance fluid because of its Low Moisture Absorption capability. I don’t know much about synthetic Dot4 and if you intend to thoroughly bleed once a year, and you’re not racing your Elan, then standard Dot4 will serve you very well.
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