Has anyone used silicone brake fluid in a street/track car? I am going to be doing the brakes on my Miata (90, non-ABS) in a few weeks or so and was curious about its advantages/disadvantages to DOT3/4 fluid.
I used it in my MG Midget a few years ago but never really drove the car enough to notice anything.
We use silicone fluid as a spring element in some suspensions...it's surprisingly compressible. One of the disadvantages is that it doesn't absorb moisture, which means water "pools" in areas. I'm not sure if all the seals are compatible with it, which would be a major concern.
Right off, this info is a bit dated, but, FWIW, I would not mix it with an existing brake system. 100% new--seals that have never, ever touched any brake fluid, ditto lines--maybe then. There have been mucho problems with compatibility, and horror stories about bleeding silicone brake fluid.
I'm a bit surprised you didn't have problems with the MG, but then you drive it much.
IMO, stick with DOT 4, especially since it's a dual purpose car. Straight race car. then, yeah, it can be superior, for it's higher boiling point. But, quality of "silicone" fluid varies--therefore affecting it's ability to have the advantage of a higher boiling point. Proceed with caution.
Silicone DOT 5 is going away. I think there is a DOT 5.1 coming that is ok with DOT 3 and 4.
I don't think there is a legitimate reason to use Silicone brake fluid.
here is a rather long winded but excellent read on brake fluid
http://www.stoptech.com/tech_info/wp_brakefluid_1a.shtml
DOT 5.1 has been out for quite a while, it's another Glycol fluid with higher boiling points than DOT 4.
I'll never use silicone brake fluid again.
I'm putting DoT 5 in all my hydraulic clutch systems as they come up for servicing. For the brakes, I'm sticking with DoT 4, except in my bikes, which came with DoT 5 from the factory. Some people have reported issues with DoT 5 on the track in cars. The extreme heat or something causes problems not seen in a bike brake system.
DoT 5.1 is not compatible with DoT 5.
You can get DoT 5 on eBay for cheap, like $30/gallon or so, Mil Spec. M1 Abrams tanks use it.
I could see it working well on clutch systems.. the sponginess would help with shock loads
I've used it in my MGA since I rebuilt the brake system 20 years ago. I had to replace the worn out seals in the MC recently-- the bores were pristine.
I also use it in my MG Midget vintage racer, again after a full rebuild. Has worked great.
Two main advantages-- it doesn't eat paint and won't absorb moisture. I haven't had any trouble with "pooling". I think that may tend to happen more when mixing fluids.
I think some of the bleeding/sponginess problems people report are due to too much air in the fluid. You have to let it sit for a long time to let the air settle out of it. Don't gurgle it when you pour and don't dump it in your system immediately after getting home from the parts store with the bottle rolling around on the floorboards.
I'm just at the end of a very painful learning process on silicone brake fluid with my MGA. the PO that restored the car used it and I have now had a brand new master cylinder be replaced, new brake hoses, rebuilt front calipers. The previous master was leaking so I had it replaced at my local shop and they refilled the system with silicone. It didn't take long to realize the fronts were not releasing. After several tries with replacing other parts and flushing the system the new master they put in is being replaced under warrantee. They failed to see on the box that it says"use of silicone voids warrantee". After lot's of reading online I'll never use silicone brake fluid again. It just seems to create havoc with the rubber and you don't know which rubber parts it will work with and not.
I think the lesson learned is, do not mix DOT 3/4 with DOT 5(silicon).
I believe tech has improved where the advantages of DOT 5 are almost completely gone.
DOT 5 does have one HUGE advantage. It works wonders as a rubber black compound.
Don't do that with 3/4
When I restored my TR6, I replaced the entire clutch and braking systems (including stainless hard lines). Since none of the parts had ever touched fluid, I used silicone. This saved paint damage later when some leaks developed, particularly around the clutch master cylinder. The pedal feel is a bit spongier, but not horrible. I bleed the brakes every year to avoid water build up, so that hasn't been an issue. The boiling point and possibility of water in the system would worry me with any kind of performance driving, however.
I would never try to mix silicone with DOT 4 fluid. If it wasn't for this, I'd switch over to using DOT 4.
DOT 5 in all my brit cars for the last 20 years. Never had a problem. It has save the paint on freshly restored cars since all british brakes seem to leak at some point and to various degrees...quite common to see recently rstored MGs with the paint off the firewall around the pedal box.
As to the track, well, I have used it on track days and had no issues. That said, if I were racing, I would want as much advantage as I could get and stick with the racing fluids. NOT Silicone. They have a higher boiling point.
As to the sponginess of silicone, all I can say is I suspect internet hearsay at work rather than first hand experience. Never an issue and in fact I find it easier to bleed than the previous stuff.
I have to wonder about this damage to rubber components. Why do I not have the problem?
All the hyrdraulics were restored on this car when he did it and I don't know the make of the master cylinder that he put in. It lasted for a few years, but obviously they're not all the same as the one I had put in a couple of weeks ago died right away and the manufacturer is protecting itself by not waranteeing them when silicone is used. The longtime tech who works in this shop's parts sales told the service manager and me to get that silicone stuff out of my car! He says he's had and read many examples of it wreaking havoc with Brit hydraulics. So who knows? In a Miata it might be a different story. I'd love to have the paint protection, but I want reliable brakes more.
NOHOME wrote: DOT 5 in all my brit cars for the last 20 years. Never had a problem. It has save the paint on freshly restored cars since all british brakes seem to leak at some point and to various degrees...quite common to see recently rstored MGs with the paint off the firewall around the pedal box. As to the track, well, I have used it on track days and had no issues. That said, if I were racing, I would want as much advantage as I could get and stick with the racing fluids. NOT Silicone. They have a higher boiling point. As to the sponginess of silicone, all I can say is I suspect internet hearsay at work rather than first hand experience. Never an issue and in fact I find it easier to bleed than the previous stuff. I have to wonder about this damage to rubber components. Why do I not have the problem?
All I'm saying is, Silicone is compressible enough to use as a vehicle suspension medium. I "believe" it's also used as the spring element in certain anti-recoil mechanisms
Sounds like it would be best for me to just stick with DOT3/4 then. Thanks for the information.
njansenv wrote:NOHOME wrote: DOT 5 in all my brit cars for the last 20 years. Never had a problem. It has save the paint on freshly restored cars since all british brakes seem to leak at some point and to various degrees...quite common to see recently rstored MGs with the paint off the firewall around the pedal box. As to the track, well, I have used it on track days and had no issues. That said, if I were racing, I would want as much advantage as I could get and stick with the racing fluids. NOT Silicone. They have a higher boiling point. As to the sponginess of silicone, all I can say is I suspect internet hearsay at work rather than first hand experience. Never an issue and in fact I find it easier to bleed than the previous stuff. I have to wonder about this damage to rubber components. Why do I not have the problem?All I'm saying is, Silicone is compressible enough to use as a vehicle suspension medium. I "believe" it's also used as the spring element in certain anti-recoil mechanisms
I, too, ran my GTV autocrosser/track car for many years with DOT5. I've heard the "compressible" reason many times, but never actually found it to be true in my application. Brakes didn't feel spongy at all. Didn't even notice the fear of air being more entrained in the fluid....
After a boched rebuild on my part, I did go back to DOT4, and discovered the reason it's not good- part of the bad caliper rebuild was a partially pinched seal, which casued the front to over-retract, and that pushed fluid back into the main, and right out the vent at the top. So my hood got stripped of paint thanks to the fluid and heat. oops.
Loved the DOT5 fluid.
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