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MG MGA - swelling seals

Ken's response reminded me of another problem: swelling seals, not the ones basking on the boatslips in California, the ones in your master cyl.. Early on,I tried Dot 5 Silicone brake fluid in my MGA master cyl rebuild...the seals swelled so bad the brakes or clutch would not return.I used it in my XJ-6 for 10 years with no problem...probably a difference in rubber composition? I used a DOT 3 once that disintegrated the seals in the whole car! Again ,go figure. I use Castrol LMA now in the E-type and the MGA roadster. I use a German brand in the racecar with higher dry boiling point. LMA is getting hard to find here in NY for some reason. Has anyone experienced the silicone problem? I also know of people who use silicone in their MGA's with no problem...again it might depend on the source of the rubber seal..Personally, I wouldn't risk it, cause if there is a reaction, it's a pain to purge the system. It's a lot easier to bleed the system every two years or so. I had the only Brit car in the area, with no one to help with problems...now we have all of these wonderful forums...life is good.
JCoryea
John coryea

John,

This swelling of seals when using silicone fluid is common. The reason why it affects the MGA more than most other cars is because of the position of the fluid return port in the MGA master cylinder. This can usually be fixed by using double gaskets to give the internal assembly more travel.

Mick
Mick Anderson

John - Did you renew the seals in the master cylinder and clean all of the old DOT 3/4 fluid out of the system before replacing with DOT 5? I ask because I read an article on silicon fluid in which the author stated that the seals, even though rubber or neoprene, do absorb some fluid and the fluid left in the seals will interact with the new fluid and cause swelling. Whether or not this is true, I can't say, not being versed in hydraulics and/or materials, but in both cases where I changed to silicon fluid (in our TD and MGB), I completely fluched and dryed all the brake lined and replaced all the rubber components in the systems. I have never had a bit of trouble with either system. On the TD, I have had silicon fluid in the brake system for 20 years without a single leak, incident of sticking or changing the fluid. The last time I checked the fluid (about a year ago) is is still as crystal clear as the day I put it in the system (no moisture absorbtion, no corrosion). By the way, LMA fluid is still carried by most auto parts stores, just not Castrol. Just ask for DOT 4, which is by definition, LMA. Cheers - Dave
David DuBois

dave-
It was 13 years ago when I had the fluid problem, but I do recall that everything in the system was new, as I was restoring the car,so I don't recall mixing fluids as an issue..I've used LMA since with no problems..Thank's for the tip!!!
John
John Coryea

Dave & John:

I had the same problem with silicone brake fluid in a TD even though everything was new except the steel lines which were flushed. The solution was the same, go back to LMA
Bullwinkle

In the debate over silicone fluid versus LMA the main discussion points seem to be swelling seals with silicone and water absorbtion or paint damage with LMA.
After trying both I cast my vote for LMA.
I have had swelling with silicone. Spilt silicone, while it does not damage paint, is very difficult to clean up in restricted spaces (this was discussed in an earlier thread). Although water is not absorbed by silicone, this itself can be a problem, as any drops of water remain as individual drops and are more of a corrosion problem than a little water evenly mixed with LMA.
If LMA is spilt on paint it is 100% removed by simply running some water over the area, resisting the temptation to wipe off with a cloth. This can be done before damage occurs.
As regards water absorbtion, the usual method is to change the fluid every two years. However, this period can be greatly extended by fitting a cap using an air bellows, as on most modern cars. The water gets into the system when the fluid level rises and falls during use. Air containing moisture is drawn in through the cap, the hygroscopic LMA absorbs the moisture, and expels partially dried air.
The cap with the bellows prevents this, as the hole in the cap only goes into the bellows, which expands and contracts above the fluid. A drop in fluid level due to brake pad wera is also offset by the bellows.

Mick
Mick Anderson

My entire hydraulic system was new in 1997 when I filled with silicone fluid. Never had a problem with the seals since.

I had previously been told about problem of the piston blocking the fluid return hole. I recall that I machined a few thou of the face of the piston. Works fine.

I have had one brake light switch go but doubt that it had anything to do with the type of fluid. My supplier suspected a duff batch.

Steve
Steve Gyles

Just to be contrarian; I have used silicone fluid in all of my vehicles including the MGA and two vintage Triumph motorcycles for over 10 years with absolutely no problems.
Many years ago I did hear of seal problems, but at that time it was thought to be caused by using old rebuild kits or components which had older incompatible rubber.
John
John

Hi folks! I have also used silicone brake fluid in my MGA. I Have been using it for about 20 years. I have NEVER had any type of brake or clutch hydraulic problem until this year. My hydraulic fluid level has started to drop a bit, and the master cylinder is weeping fluid from both clutch and brake sides. So come spring, I will rebuild my master cylinder, replace all rubber hydraulic hoses, and replace my steel brake lines with cupro-nickel never rust brake lines. In short, I am thoroughly impressed and amazed by silicone brake fluid, and by how long my hydraulics went, wihout needing any attention. I know some people seem to have had problems with silicone brake fluid. Whether this is due to incompatible silicone fluid, or incompatible rubber brake seals, I cannot say. All I know is that silicone worked great in my MGA! As an added bonus, the stuff does not eat paint, and really does preserve rubber seals. Cheers! Glenn
Glenn

This thread was discussed between 24/01/2005 and 28/01/2005

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