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MG MGA - Silicone Brake Fluid

Guys I'm about to redo my brake system and I want to use a silicone brake fluid.

But to be honest I'm a little confused by the different types of brake fluid available.

I've seen Dot 3, Dot 4, and Dot 5

is there a silicone version of each of these?

or is only one of these silicone?

Which do I need to get?

Thanks,

Tysen
Tysen

DOT 5 is silicone; DOT 3, 4, and 5.1 are all glycol-based. DOT 3, 4 and 5.1 can all be freely mixed with each other whilst DOT 5 cannot be mixed with any of the others....

HTH!
Rob Edwards

Tysen,
Search the archives on this subject. It's very important to purge ALL of the old fluid and residue for this transition to succeed. I started mine by having Apple Rubber sleeve my M.C. in stainless steel. If you hone or sleeve pitted bores, understand that a better finish is needed to avoid leakage. Apple tried to discourage using silicone for this reason. This said, I'm pleased with the results, but everything was new save for the master cylinder, banjos and unions. At that I still chased down leaks due to surface finishes at the banjo unions and some of the brakeline flares in the unions.
BOL,
Doug
D Sjostrom

Tysen - Rob's comment that DOT 5 “cannot be mixed with any of the others” gives you a hint of what needs to be done when switching to DOT 5 silicone brake fluid. The brake system has to be completely cleaned of any of the old brake fluid. This includes all new software (rubber seals, etc.) in each of the wheel cylinders as well as the master cylinder and each of the brake lines nave to be flushed out with something like CRC Brake-clean and then blown out with dry air to get them completely cleaned and dry. I have also changed out each of the flex lines before I changed fluids in our TD and MGB. The results is that in both cars I have experienced trouble free operation of the brakes in both cars. The TD was switched to silicone fluid over twenty years ago and the fluid has never been changed or flushed in all that time, yet it is as clear as the day I installed it. The best part is that I have never suffered from a gummy or seized wheel cylinder since making the switch. Good luck - Dave
David DuBois

Tysen

I'd echo the comments above. It's well worth the effort, but everything has to be in good condition otherwise it will leak. Having said that, if it is it in good condition it will stay that way with Si fluid. I have been using it for 17 years and although I have had to change the rubber seals and the flex hoses once (which is pretty good in my opinion), all the cylinders are like new, even on the outside!

Dominic
dominic clancy

Thank's guys

I'm doing a complete brake rebuild all the way around as part of the switch over.

I have all the rubber parts on my shop bench even as we speak.

The last part was to figure out specifics about fluid so I could get some to act as lube as I rebuilt all the various cylinders.

Next project,

King pin rebuild

after that

rear hub oil seal.

I got a busy winter ahead of me.

tysen

I agree that to get the full effect of silicone fluid you must flush the system but I don't think it is as critical as you make out. I've used Automec fluid certainly on new systems but it does point this out on the tin. It seems that if you bleed the system through until clear silicone flows then all will be well. I've gone this route on other cars and 10 years have passed with their brakes still being in good condition
Iain MacKintosh

Tysen, I have silicon fluid in my B and don't recommend it to anyone. The brake pedal feels considerably softer. You are better off using a cheap Dot 3. Having the paint not peel when it leaks is great, but not worth the loss of a solid pedal.
Jeff Schlemmer

Hi Jeff. If your pedal feels spongy or soft, it is not the fault of the brake fluid, silicone or otherwise. Hydraulic fluid does not compress, therefore there must be air in your braking system that is making the brake pedal feel soft or spongy. I will admit that silicone brake fluid can sometimes be more difficult to purge air bubbles out of. However with some effort, all the air bubbles can be bled out, and your brake pedal will be as firm as with any other type of brake fluid. I have used silicone brake fluid exclusively for about 20 years now in all my vehicles. In my opinion, the significant advantages of silicone fluid far outweigh the disadvantages. Of course this is just my humble opinion, and you are certainly entitled to disagree. Cheers! GLenn
Glenn

Silicone fluid is slightly compressible because it will entrain air into itself. This air is impossible to remove. That said, I use silicone fluid in my B and have no problem with a spongy pedal. It may be slightly softer than before the silicone fluid, but the difference is slight enough that I don't even notice.

As for DOT 3/DOT 4, I won't use it. The DPO of my C let one of the boosters leak. It of course ate the paint, and because of it's hygroscopic nature, it aggressively drew moisture to the bare metal with predictable results. Now I've got lots of cutting and welding to do in very awkward locations....
Rob Edwards

I know most of the arguments, pro and con, for silicon brake fluid. Still, isn't it interesting that most new cars still use Dot 3 or 4, as do most racers? Yes, regarding the auto industry, there is the cost issue. But if it was really superior don't you think they would have gone with it "across the board"?

GTF
G T Foster

Not if they can save a few cents a car. Plus, silicone doesn't work well with ABS (it tends to foam) which most cars have....
Rob Edwards

Hi folks I use silicone brake fluid mainly because it makes hydraulic parts and rubber seals last MUCH longer. Since silicone fluid doesnt absorb moisture like regular fluid, brake cylinder bores (aluminum and cast iron) remain unpitted and/or unrusted. Because silicone preserves rubber, the hydraulic seals often last 20 years or so! The financial benefits and reduced maintenence of the hydraulic system is unbeatable in my opinion. The fact that silicone fluid doesnt damage paint is extra icing on the cake! I have never found silicone brake fluid that much more difficult than regular brake fluid in terms of purging out air bubbles. Sometimes it might be necessary to let the car sit for 20 minutes or so between bleedings, but that is about the extent of the difficulty. The brake pedal on my MGA is not spongy at all with silicone fluid, and in fact is rock hard after the brake pedal free play is taken up. Cheers! Glenn
Glenn

I've been running Dot-5 for 15 years with no spongy brakes, and my orient red paint looks great despite little accidents with the MC. A friend painted his engine bay and had a Dot-3 spill within a month. Ouch!
Tyler
tyler

I use silicone fluid, and have a good firm pedal. When I bought my 1500, every brake cylinder was corroded, and all the brake lines were corroded from the inside out, and were paper thin. That was enough to convince me of the evils of glycol brake fluid. The fact that glycol eats paint, is just another reason not to use it. If you choose to use glycol based fluid, make sure you change it often.

Professional racers may use glycol, but they have professional mechanics who change the brake fluid every race.

Like was already said, silicone is not recommended for ABS, because the pumps cause foaming. Just because new car manufacturers dont use it, is no reason for me. Harley Davidsons are more akin to our MGAs than Detroit boatmobiles are, and Harley uses silicone in all its bikes.

Jeff





Jeff Schultz

I'll agree with Jeff and Glenn. My 58 which had sat for many years was full of sludge(brown goo) in the M/C and wheel cylinders.. I replaced with new wheel cylinders, hard lines and hoses.. sent the m/c to Joe Curto and had it sleeved because of a pitting problem.
Taking into consideration where the m/c sits on the shelve and knowing I was going to have the car painted orient red I opted to use silicone. As far as brake pedal being spongy I have not experenced that at all.. Mine are rock solid and the stopping distance is great as I experenced, when a car went thru a stop sign and I had to brake from 55 to 0... my .02 cents
Mike
mike

It really is a paint thing for me. With the location of our master cyl I couldn't bear to put any thing else in. I still recommend flushing the system every 2 years in any car with any fluid.
R J Brown

Harley went to silicon fluid in the early 80's because the heat in the brakes was boiling DOT3.
John H

Hi RJ. I have used silicone brake fluid for about 20 years, and have NEVER flushed the brake system, not even once. The brake system is still operating flawlessly, even with extended yearly Canadian winter storage. I am however, going to completely overhaul my brake/clutch hydraulic system in the spring. Although the rubber brake hoses still look perfect, and there is no sign of leakage, from hoses or cylinder seals, these are 20 year old brake parts, and any failure could be catastrophic given the single hydraulic setup. I will also replace my steel brake lines with cupro nickel ones that cannot rust, even though the steel lines look perfect and have no external rust. When I installed the steel brake lines 25 years ago, I coated the exterior of each brake line with grease. This has kept the brake line exteriors in pristine condition. When I remove the steel lines, I will check for rust inside them, although I suspect that because of the silicone brake fluid, there will be no rust. Cheers! Glenn
Glenn

Glenn, I can assure you there is little or no air left in my all new brake system. I bled it every other day, leaving it undistrurbed in between for a week and a half. I even went so far as to install Speed Bleeders, thinking that I DID still have air in the system. The pedal is just softer than it was with my old system and the "stock" fluid, even with stainless flex lines added. The brakes work great, don't get me wrong, but the pedal isn't as firm.
Jeff Schlemmer

Yet another vote for silicone: I've had it in my car for 20 years now, with no problems at all. Slightly (very slightly) softer pedal, but I stopped noticing it long ago. And the paint issue makes DOT3/4 a non-starter.

What's funny is this argument never seems to end. I can remember participating in it back in 1986 or so, in the early days of the SOL british-cars email list.
Mark Lambert

Hi Jeff. What brand of silicone fluid are you using? I am wondering if there is a quality difference between brands? Somehow I dont think so. The specs for DOT5 should be the same for all brands, I would think. Cheers! Glenn. PS, I have a dumb question: if your brakes work well, then why are you seemingly dissatisfied with silicone fluid?
Glenn

This thread was discussed between 12/11/2005 and 19/11/2005

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