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Are people having good luck and not having seal trouble with silicone fluid in these cars?
I usually go silicone for my garage queens, just thought I’d ask before I fill my reproduction wheel cylinders and master with Silicone brake fluid.
Thanks!
I’ve read here of people who have had XK brake seals destroyed by silicone - yes, I know, I thought it was pretty benign stuff too! From personal experience, I used to have an Iso Grifo on which I used silicone for the brakes and never had a problem in 25 years. But, when I used it in the clutch it swelled up the O-rings in my fancy-dancy McLeod co-axial slave cylinder (which fitted around the gearbox input shaft and pushed directly on the clutch release bearing. That was an engine-out job to get to it inside the bellhousing!
Hi Catman,
In my XK 140 is silicone.
Replace all rubbers, flushed brakes with alcohol/spiritus spirits (The composition of fire spirits is usually: 85% ethanol, 10% water, 3% methanol, 1% acetone and 1% pyridine (a fragrance) plus a blue colorant) Alcohol is good, spiritus also but cheaper. All pipes blown dry with compressed air, let 1 day dry and filled with silicone. I did the same before with my Healey MKIII, and drove 12 years (K/year) without any problems. Never change the brake fluid in the Healey. The 140 now for 2 years with 1 problem: Brake switch (normal brake switch is not silicone compatilble) ordered this one: https://www.ronfrancis.com/prodinfo.asp?number=SW-32
Stories on the internet are different about use of silicone in old cars. This is my info/experience
Suc6
Regards,
Teun
My only experience with silicone was many years ago when I replaced slave cylinders on my 63 Corvair. At that time, the stuff was inert and did nothing to the seals. That was the problem. My seals failed to seal–and others had the same experience. They subsequently included a seal-swelling additive. I haven’t kept up, but perhaps there is more than one type of additive out there, or perhaps a particular additive affects seals of different compositions differently.
Either of these possibilities could yield a variety of results among users–which currently seems to be the case. I don’t intend to find out. Just rebuilt calipers/cleaned system on my 72 Alfa and refilled with DOT 5.1 glycol-based. IMHO.
Reference Plate L16 in the Service Manual, in my XK120 single system with all new seals and silicone Dot 5, the seal F swelled in the length and it was just enough to block off the relief port X. The pressure failed to relieve, such that the car was stuck, 3 men could not push it. After about an hour it would release the pressure. Flushed out all the silicone, new seals all around, refilled with Castrol Dot 4 and its been fine ever since.
In my '74 XJ12, all new seals and Dot 5 silicone, the seals swelled and gripped the pistons in the calipers so hard that I had no brakes. I had to disassemble the calipers and pry out the pistons with crow bars. The seals, originally cylindrical, were distorted like a truncated cone. I put the seals to soak in a jar of Castrol DOT 4 for a week and they shrunk back to a cylindrical shape. Flushed out all the silicone, put the seals back in with Castrol Dot 4, brakes have been fine ever since.
My modern S-Type and Volvo specify to use only DOT 4.
Silicone will never enter my garage again.
I’ve never figured out how the seals actually work. At least in some calipers, they are supposed to not only seal but to “rock” as the piston moves–they deform into something like you describe (truncated cone) within their rectangular grooves, when brakes are applied and then elastically return to their original (round or square) shape when pressure is removed, withdrawing the pistons just a bit. It’s easy to see how just the proper amount of swelling is necessary to get these to work as designed. IMHO.
I tried DOT5 silicone about 20 years ago in two Healey s. In the first car I had the pedal go to the floor after a spirited drive, nothing wild - left the car to cool and it sort-of came back, changed the fluid when I got home. About a year later the second car lost its brakes coming down Porlock Hill, following a 300SL Gullwing. I had decided to hit the dry stone wall instead of the Gullwing, for cheapness’ sake, when enough pedal returned to stop the car, with the aid of the handbrake and switching the motor off in gear. Again, after cooling the brakes came back after a fashion. Got home, changed the fluid and threw all my bottles of silicone fluid away. I use ATE blue or gold DOT4 now and will not use anything else.
They’ve actually stopped doing the blue colour, which is a shame - it was easy to tell when you’d flushed all the old fluid through at the bi-annual fluid change by alternating colours, not so easy to tell now.
About 2 years ago I spent a lot of time tidying up the area under the carbs/master cylinders on my rhd FHC E Type (which has regular brake fluid). Painted a part of the firewall and some of the frame. Plated and polished a lot of parts on the carbs/linkages etc.One of the harder preparation and masking jobs I’ve ever done. Was very pleased with the results.
When I looked at it about a month later the fresh paint was bubbling in places. No visible brake fluid leaks. I swear my surface prep was perfect - I do know how to get that stuff right.
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So I’ve just finished a Healey 100 restoration and I will go through hell and back not to use that paint destroying mineral/ glycol whatever crap. Have only done a few miles in it so far - just to get it sorted. But the brakes bled up well and seem to work normally. And I’m not worried about the paint.
A hydraulic fluid reservoir should never be filled to the top - often releasing the pedal quickly will produce an upward jet of fluid and if the reservoir is integral with the cylinder this can encourage fluid to find its way over the lip and out.
I did use silicone originally entirely because I was concerned about the paint around the cylinders. My cars do quite a high mileage for historics, though - and these days I’m far more concerned about the effectiveness of the brakes than the paint on the bulkhead. In view of my experiences, and Erica’s post above, I’m happy to stick with DOT4.
About 10K miles with Dot5 in my E so far. No brake issues but the clutch slave seal failed at 9K miles or so. Not sure if the fluid is implicated though. I went to silicone after damaging the paint with Dot3, no other reason. I haven’t charged the 120’s brake hydraulics yet - was leaning toward Dot 5 till reading Rob’s comments, now having second thoughts.
As I understand it, one may flush a system originally charged with Dot5 and safely refill it with glycol based fluid but not the other way round.
Anecdotal evidence seems to be all there is, so I’ll add mine.
I ‘converted’ three British cars (TR3, TR4 and the E-Type) to DOT5 by simply emptying the reservoir, filling it with the purple stuff and bleeding until it came out the other end.
Cringe worthy but effective.
That was 20 years ago for the TRs and 7 years & 38,000 miles for the E.
I’ve had no brake issues I can attribute to the fluid in use. I did have a servo leaking into the booster but when I emptied the pint of fluid that was in there it separated into two layers (lower one was reddish brown) that clearly showed that the problem existed long before the move to DOT5.
A tough choice with benefits and risks each way and precious little data to consider.
For what it is worth, I have for over a 10 or longer year period used Dot 5 usually supplied by Bill Hirsch in the 4 XK120s and 2 Alfa Romeos that are still in my garage. The only problem I have encountered is seepage at the new copper washers which I find annealing cures. I have never swapped from Dot 4 without replacing all the rubber components with new ones.
Thanks for all the great replies. The only reason I even asked is because of the horror stories, not personal experience. The 120 has the most complicated drum brake set up I ever dealt with and the most expensive, got me to worrying, probably about nothing.
I suppose the real question is, are all seals made equal?
Here’s what Moss Motors said in
Brake fluids are classified by their chemical type and boiling points. The different chemical bases currently used are polyalkylene glycol ether (commonly called glycol), silicone, and mineral oil. (Of these, mineral oil doesn’t concern us, as it is used in very few cars, none of which Moss Motors deals with.) D.O.T. 3 and D.O.T. 4 brake fluids are glycol-based, while silicone-based fluids are classified as D.O.T. 5. To further confuse matters, there is now a D.O.T. 5.1 brake fluid which has a diethylene glycol-ester base, with properties similar to D.O.T. 4, but with enhanced performance characteristics. These D.O.T. (Department of Transportation) specifications also indicate minimum boiling points. It is important to note that these D.O.T. specifications are performance specifications, not material specifications; for example, D.O.T. 5 sold in Europe is not silicone-based, as it is in the USA.
In the good old days, little good could be said of brake systems. Warnings such as, “as the cups in the master cylinder are pure rubber; it is imperative to use only the recommended fluid. Any other fluid may be dangerous” were common. Such strong concerns were very valid in the s, much less so now, even for ’s vintage cars. The reasons for this lessened worry about our hydraulic systems “turning to goo” if the wrong fluid is used is that: 1.) pure rubber hydraulic seals are no longer made for our cars, and 2.) D.O.T. 3, 4, and 5 brake fluids are safe to mix, and are compatible with the seals now available. While these brake fluids are safe to mix, mixing them is not recommended.
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