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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - SILICONE BRAKE FLUID

I rebuilt my MGTD 3 years ago,as I completly overhauled the brake system,and reading that silicone fluid had many advantages I then used it. everythig seemed fine and peace of mind thinking no water absorbtion so no rusting of internal parts and pipes. However I now find that the master rubber seals semm to have expanded so restricting the fluids return to the resevior allowing pressure to build up in the system so making the stay on with no movment in the pedal.I beleive the answer to this common problem is to reduce the length of the piston by a small amount, does anyone know by how much and which end.somone mentioned looking in the archives i'm not familier with that.Thanks in anticipation, Adrian Wells
TA WELLS

You might first check the little tiny relief valve (its a tiny hole) in the m/c
Looking down through the top you will see two holes.... the front one has a tiny (pin sized) hole in the center of it...
Use a needle or Mig Welding tip file to clean it out... had to do mine and had the exact same symptoms.
Check that there isn't an extra rubber washer inside the mc... i had two (the old one was left in when rebuilt).
gordon lawson - TD 27667

So is the consensus that Silicone fluid is the way to go?

On the Jaguar XJ sedan the owners seem to be getting away from silicone but I don't recall why. I've just bled mine with Blue fluid Dot3 or 4 I think. Then in a couple of years I'll use their orange or brown fluid alternating to see when all the old is purged. I forget the name of the maker but it's from Germany and most of the race cars use it.
D Clark

I put it in after replacing all the lines and rebuilding the cylinders....
gordon lawson - TD 27667

I've just returned from a 3-day tour by the Montréal MG Car Club, of the Green Mountains of Vermont, where day-time temperatures were in the 30º to 32º range (in the shade), and some of the climbs through the high passes and gaps, caused the old TF to maintain over 100º on the gauge (using water, not antifreeze).

Of course going down the other side of these mountains, the brakes got a good work-out. I experience absolutely NO braking problems.

I've always used DOT 3 for the entire 51 years of ownership. I once tried silicone, and had many problems, especially when hot. It seems that silicone will find even the tiniest of fissures or untightened fitting and leak, whereas generally, this is less true of non-silicone brake fluids.

Gord Clark
Rockburn, Qué.
Gordon A. Clark

It may be that some seals are not suitable for use with silicone fluid. On a visit to the MG Restoration Show some 3 yrs ago I recall seeing a notice on a vendors stand stating that 'these seals are not suitable for use with silicone brake fluid'.

I have used silicone fluid for many years in my TD without a problem. However I have a issue with my E Type Jaguar where I have used silicone again for many years in both brake and clutch systems but have a problem with the clutch master /slave cylinder. I suspect that the silicone fluid has reacted with the seals. Sometimes the clutch will not release fully causing difficulty in engaging reverse.

In the very near future I plan to replace the seals in both the master and slave cylinders which hopefully will solve the problem. When I order new seals I will request that they be suitable for use with silicone fluid.

David Tinker. Wales UK
David Tinker

I guess the debate continues and the answer is "whatever works best for you". I put silicon fluid in my TD in 1985 and have not touched the brake system since. No leaks, No fading, no sticking cylinders after getting the car out of winter storage.

I am rebuilding the brakes on my 67 BGT right now and plan to use silicon in it for both the braking and clutch systems.
Bruce Cunha

David - I found your comments about the problem you had with the Jag clutch when using silicone fluid to be interesting. I had the exact same experience with our MGB clutch. I noticed that the problem was most prevelant when I was using the clutch rapidly, such as when backing in tight quarters or such. I have attributed it to cavitation of the fluid from the rapid on and off of the clutch pedal. I do know that modern vehicles with ABS brake systems and proportioning vlaves with very small orfices warn against using silicon fluid for that same reason. You are the first person who has admitted to having the problem with the clutch when using silicon fluid. I have since gone back to DOT 4 for the clutch (I still use silicone for the brakes though). Cheers - Dave
David DuBois

I can add from vintage racing experience, that when hot, we have seen several cars come in from race or practice sessions with the rear brakes locked up, or nearly locked up, becuase the silicone fluid expands to the point where that small breather hole in the master cylinder is then blocked by the valve.

So, I do not think I know of anyone who uses silicone brake fluid in their vintage racing TD.

I only mention this because, under really extended and severe braking situations, like descending a long grade, I suppose that the fluid gets as hot as it would under race braking conditions, and therefore it could happen to a "street" TD too.

Jeff
Jeff

Do any 2005 (that is NEW) cars use silicone?? My experience has been that it is better suited for "limited use" vehicles, altho for the 4yrs my Rover 3500s was a daily driver I had no problems and from sitting mostly unused from 1988 to 1999 the brakes were fine including the famous for trouble inboard rear discs.
Greg & Grimm
G.J. Cenzer

Hi Dave, Interesting comments about your MGB clutch. When trying to sort out the clutch problem on the E Type I drained off the silicone fluid and replaced it with regular fluid. It was a little better but I still get the symptoms you describe when forward/reversing in tight corners. I fact I can depress and release the clutch pedal quickly and get no drive for several minutes!! A clutch operating system overhaul is on the agenda but the weather is too nice to have the car off the road!!

Rgds

David
David Tinker

I have used silicone brake fluid in all my British cars for the past 15 years with no brake or clutch problems. I agree with an earlier thread that when vintage racing my MGA with silicone fluid, my rear brakes locked up due to heavy use at Road Atlanta, but that is the only problem I have ever experienced.

However, the brake light switches quit working in all my British cars every 4-5 years. Luckily they all use the same switch so I buy 2-3 at a time. I have tried 3 different suppliers, but the switches continue to last only a short time. I was told that this may be due to using silicone fluid. I don't understand how a pressure activated switch could be affected by silcone.
Any thoughts??
keith anderson

Go with a "relay"... Dave Dubois on the list sells a really nice little set up... wire it in and forget about it....
gordon lawson - TD 27667

To Kieth Anderson----- Try a brake light switch from Ron Francis Wire Works their part No. SW-32 It specifically states that it is compatable with silicon brake fluid. They are a bit pricey but if they last they are worth it. I have used this swirch in both my LBC's for several years now and have had no problems.
Keep 'em on the road! Bob
R. K. (Bob) Jeffers

I would not recommend using racing type brake fluid in a street MG. The reason it is used in race cars is that it has a higher boiling point than standard DOT 3 or DOT4. The down side of the racing brake fluid is that it is much more hydroscopic, meaning it absorbs water at a much higher rate.

This is fine if you want to change brake fluid every week or so, but in a street car it can lead to early brake failure.

Cheers,
Lew Palmer
Lew Palmer

Keith - Eithe use the Ron Francis switch as Bob suggests, or, if yow can get it a NOS Lucas switch or install a relay between the switch and the cheap replacement switch. Information on making and installing a relay and arc suppression circuit can be found at http://www.omgtr.ca/technical/brakelightrelay/brakelightrelay.htm

I have always been told that silicone fluid should not be used in racing situations. I am sure that the higher expansion rate when it is hot, plus the fact that silicone fluid will airate very easily are the reason.

Greg - No, silicone fluid is not used in any modern cars, in fact you will find that it specifically states in the owner's manual that silicone fluid is not to be used. When I asked the service manager of our local Audi dealer why that was stated in the manual, he gave me the song and dance about German cars using pure rubber seals, yada, yada, yada... When I called him on that, telling him that that was a tired old excuse that has been used on British cars for the past 4 decades, on various types of fluids, he admitted that he didn't know. I later found out that silicone fluid can't be used in modern cars because of the small orfices found in ABS systems and proportioning valves causing the fluid to cavitate and develope air bubbles in it, with all the usual problems associated with air in the brake system

Silicone fluid was developed for the military motor pools, where vehicles are left sitting for long periods of time and then needing to be put into service quickly. Silicone fluid is ideal for that situation (because it was designed for that) for the same reason it is ideal for collector cars that are not driven all year long. Some people have had spectacular success with silicone fluid (as I have for the past twenty years) and some poeple have had terrible luck with it. I think that it would be interesting to see how people (both those who have had success and those who have not) prepared the brake system prior to installing the silicone fluid. Cheers - Dave
David DuBois

I have had excellent performance with silicone brake fluid in my 73 MGB GT, 62 MGB and 54 TF 1500 ( since 1984).
In all cases the system was totally rebuilt with new rubber parts and flexible lines after being flushed out with acetone (dissolves the DOT 3-4 crud that builds up in the brake lines). On filling with DOT 5, care was taken to pour in smoothly to not get air bubbles entrained.
Don Harmer

I'm at that point in my TD restoration where I have also been trying to decide whether to use silicone brake fluid or stay with the regular stuff. The main reason I was considering silicone at all is moisture absorbtion by the regular, which then leads eventually to corrosion in the brake system. But with the problems some people have with silicone, I found myself wishing for a regular brake fluid that just wasn't as hydroscopic. I'm now considering Castrol LMA... here's the specs:

Castrol GT LMA Brake Fluid
Recommended for all U.S. and foreign vehicles with DOT 3 and DOT 4 requirements, including GM, Ford and Chrysler.
Key Benefits
Exceeds DOT 3 and DOT 4 requirements.
Unique Low Moisture Activity (LMA) formulation provides maximum protection against vapor lock brake failure.
Maintains a higher boiling point than conventional brake fluids.
Superior protection against chloride and zinc corrosion of braking system parts.
Ideally suited for Audi, BMW, Jaguar, Mercedes-Benz, Porsche, Saab, Volkswagen, Volvo, Honda, Acura, and many other brake systems.
Exceeds specifications SAE 1703, SAE 1704, ISO 4925, JIS K2233 and FMVSS No. 116 DOT 3 and DOT 4.
Material Safety Data Sheet
Product Data Sheet ( pdf, 67 KB )

Any opinions on this product??

Cheers!! Jerry
J. Keller

Castrol GT LMA is what I use.
Bud Krueger

One point not discussed in favor of Silicon. If and/or when your brakes leak, it will not harm the paint on your drums, rims backing plate etc.
Bruce Cunha

Bruce - " it will not harm the paint on your drums, rims backing plate etc." Just don't try to paint over anything that has been contaminated with silicone fluid without completely cleaning it off with a good solvent or you will have more fish eyes than you can shake a stick at.

Jerry - There is nothing wrong with using Castrol or any other DOT 4 fluid. The only drawback is that it still draws moisture, just not quite as fast as DOT 3, but fast enough that you need to flush the system every other year. Cheers - Dave
David DuBois

You are very correct Dave. Problem is most of the cleaning/waxing products out there have silicon in them. I have yet to do paint work on a canand not run ito issues related to silicon.

We had a real problem with fisheye in the B on the cowel above the hood where the brake resivour is. Found out the PO had used silicon and it was either spilled of splattered up on the cowl.

Had to resort to an additive that reduces the fisheye.
Bruce Cunha

Dave and all... is it the "LMA characteristics" that make Castrol LMA DOT 4 ? What I mean is, do all DOT 4 brake fluids absorb moisture at a lower rate than DOT 3? What "DOT" is silicone fluid?

Cheers! Jerry
J. Keller

Silicone is DOT 5 fluid, it also has additives to swell the seals. These are different than in DOT 4, and this is where most of the conflicts lie in mixing 3 or 4 with 5.
seals soaked in 3 or 4 often disintigrate when exposed to DOT 5.

I have always understood that Castrol LMA meets the DOT 4 standards but is also lower in moisture absorption than other DOT 4 brands.

The will all absorb up to 10 to 11% water from the air with time, driving and heating up the braking system drives a lot of this out. But after sitting a long time it will get waterlogged and then conductive and the electrolysis induced corrosion begins. This is what DOT 5 prevents, and why it is reccomended for vehicles that are not driven for extended periods (eg in winter)
Don Harmer

Jerry - You have it almost right, it is that Castrol is DOT 4 that makes it LMA. All DOT 4 brake fluid is low moisture absorbtion by definition of the Federal Motor Vehicle Safety Standard No. 116. Cheers - Dave
David DuBois

This thread was discussed between 24/06/2005 and 18/07/2005

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.