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Brake Fluid

Brake Fluid
(to go silicone or not, you will have to read all available information and make your own decision)

HI All, I am in the process of overhauling the brakes on my XK150. A friend who knows a lot about cars, but know nothing about Jaguars, recommends that I use a silicone-based brake fluid. Does anyone concur with this advice? What experiences have you had with silicone brake fluids (or any other brake fluids) that might be useful to a novice mechanic? - Paul Patek

YARRRGGH!!!,,,The dreaded brake fluid thread!! RUN EVERYBODY!!

;-) Well Paul, it's like this...everything has it's advantages and disadvantages, opinions are common to everyone, (we'll avoid the usual crude reference here), and free advice is worth every penny.

I use the off the shelf Girling LMA and have no unusual problems, and few of the usual problems because I think about changing it every year or ten.

You should know though my MGB is sitting waiting for the engine/gearbox to be reinstalled, the Spitfire-6 is just now being completed by my 15 year old and the 140 is waiting patiently for the Spit project to be done so "she" can get a little TLC as well.

The German cars also use the Girling and they get thrashed regularly but they of course don't have the finicky hydraulic rubbers usually found in the British machines.

FWIW. - Ken Boetzer

If you've got 4 wheel disc brakes..... don't do it! You'll find that unless you're using brand new, completely uncontaminated rubber and machined metal surfaces, you'll have corrosion and seal growth problems after even short periods of storage, I had to rebuild my former XKE brakes twice because of the mistakes I made by going the route you're thinking about but not de-contaminating the surfaces of the cyinders. I thought I was the only person that'd had trouble with this but I was surprised to find it's a common problem, stick with the regular fluid and bleed off your brakes once or twice a year if humidity is a problem out there, it's less frustrating. - John Morgan

I unreservably recommend you DO use Silicone Brake fluid. I have had it in my E-type for over 10 years with zero maintenance attention and zero problems. I also have put it in my Mark 2 more recently, only about 6 years ago - again no problems. I did pay diligent attention to replacing all seals and flushing out old fluid with methylated spirits, to ensure no contamination of the silicone fluid, as recommended. However, try as I might I could not successfully use it in my XK140, because I could not stop leaks 100% - silicone will find leak paths normal brake fluid dosn't, and with XK140 drum brakes, all brake fittings use coarse threads which do not seal as well or provide the clamping forces you get with fine threaded joints, and apart from use of invisible modern sealants, etc., I didn't want to physically modify visible componentry, so I remain at the corrosion and maintenance mercy of non-silicone brake fluid. - Roger Payne

Paul, Lots of pros and cons about silicon brake fluid. I have been using it in all my cars and all my customers cars that require brake and/or clutch hydralic work I have not experienced any of the cons and love it. It has two pluses right out of the can. It is not hygroscopic and it does not impact painted surfaces. My cars: 1953 XK-120M FHC 1960 3.8 Mk 2 1960 VW Bug, Porsche brakes 1962 E-Type FHC 1965 E-Type FHC FISA Replica 1968 MGB OTS 1988 Saab 900S - George Badger

Paul, I vintage race a TR3A and own a number of other old British cars, including a '53 FHC. I have heard nothing but bad stories about silicon brake fluid. Stick to good old Castrol LMA4, you won't be sorry. - Jeff Snook

I was told by Welsh Motors that silicone was OK to use and the expansion was a 'good' thing. I know to be very careful here since I destroyed clutch and brake seals with regular brake fluid. - Jeff Koch


just a quick reply - would definitely not recommend using Silicon brake fluid. This fluid can cause seals to swell in both the master cylinder and wheel cylinders - in one case the master cylinder seized completely !.

I use high quality mineral based fluid and have had no problems - just watch for spills on your paintwork !. - Dave Roche

I stayed out of this as long as I could.

Since each "new" generation of subscribers invariably brings up the subject, why not add it to the subject list.

My experience with silicone brake fluid: no problems in one of my 150 roadsters but it ruined 2 master cylinder kits (Lockheed original kits) in my green 120 roadster. As a guess, the rubber composition in the older kits, as I installed in my 120, apparently was not compatible with silicone.

On the 150 FHC I am completing, it will receive no silicone brake fluid. I had my S3 E-Type master cylinder reconditioned and it will receive no silicone brake fluid once I reinstall it. I have faired OK on one vehicle but I'm not taking any chances on the others.

Periodically replenshing the standard fluid is not a problem for me. These cars require a tinker's touch and this task is simply another routine maintenance item.

Since you can here any story you want on the subject, there is no definitive answer as to which fluid is correct/suitable/preferred/whatever... - Bob Oates

Yeah, it's a topic of contention on some lists; some people swear by it and others swear at it. Hopefully we can refrain from swearing at each other on this very pleasant list.

My vote is no, because it swelled the caliper piston seals in my XJ 12 so bad the brakes did not work at all. I had to use big prybars to get the pistons out, they were INCREDIBLY TIGHT, and when I got the seals out they looked like a section of a cone, not like a section of a straight cylinder, which is what they were when I put them in two years before.

Silicone killed two brake light switches in my 120 (leaked past the rubber seal and got on the electrical contacts). The swelled seal problem in my 120 master cylinder I described a few months ago on this list probably does not apply to 150, I don't know.

Anyway I have elected to stick with Castrol LMA and just be careful not to spill any on the paint, and change it every couple of years. - Rob Reilly

Well I think I have a understanding of the pro and cons of silicone fluid. However my question is if all the components of the break system have been freshly rebuilt can you use silicone without harm? - Skip Smith

Hi Robert Oates & all -- the secret is seals that are COMPATIBLE with DOT 5 -- Robert, if you don't KNOW the new seals are compatible (if they're NOS, probably not; check with supplier), it's best to use DOT 4. Also -- even if seals ARE compatible, flush entire system with denatured alcohol to be sure it's clean before bleeding with DOT 5. Hope this helps - Larry Martz

I rebuilt my dual master cylinder and all other brake cylinders in 1991. I did send the master cylinder to White Post (see Hemmings) for all stainless steel innards. All new lines, rubber, etc. My ace mechanic recommended silicon and I haven't had any problems whatsoever. I haven't even had to top it up yet and this is probably 10,000 miles later. Perhaps the key is all new everything. Good luck, - Gardner Howard

>From my experience, I would say that if all components are rebuilt and you have new O-rings, rubber seals, etc. -- YES, you can use Silicone brake fluid! Not that I have experience with my Jaguar yet, but my Triumph TR6 rebuild worked out fine. I initially neglected to replace an O-ring and it leaked, but once that was fixed I have been worry-free. - Carl Hanson

Thanks for your comment Larry. Just for clarification, on both my 120 and 150 cars, every component of the brake system was new or reconditioned, i.e., hoses, lines, seals, reservoirs, master and wheel cylinders etc. Additionally, no other brake fluid had been used in either system.

I used DOT 5 silicone in the 120 and DOT 4 or 5 in the 150. Unfortunately, the master cylinder on the 120 leaked fluid after about 6 months. The wheel cylinders have not leaked to date. As I mentioned earlier, I believe the rubber in the NOS Lockheed master cylinder kit was not compatible with this fluid. Apparently this silicone specification changed the rubber seals some way at least enough to cause a big puddle of fluid to leak onto the garage floor. As most of you know, accessing the master cylinder on the 120 with the engine in place is no easy task. So when I saw the fluid, needless to say, I was quite upset. I went to all the trouble to build a long-lasting system and then in a few short months a pool of silicone fluid meant that something had failed.

At any rate, the master cylinder is rebuilt and I now need to purge the rest of the system and add non-silicone fluid. Perhaps I did something wrong in the original rebuild but for this car, as I start again, I will stay with what I know will work.

My experience on the 150 with silicone brake fluid has been successful. Whether I used DOT 4 or DOT specifications, I don't know. I do believe that the rubber used in this car was compatible with the silcone fluid unlike the rubber used in the 120. So, I have a mixed bag of experience. - Bob Oates

updated 9/98...

What type of brake fluid is compatible with the new rubber parts? I have heard people say that Castrol is the one. But is it the only one? Or can you use any dot 4 brake fluid? - Dana McNair

Suggest you use sillicone brake fluid. No more rust problems and worry free driving. Be sure to flush the entire system and suggest you rebuild the wheel cylinders and use red grease inside. Good luck. - Bob Cathey xk140, markix

When I had the calaphers resleeved on my 150 recently, attached was a warning against the use of silicone fluid. I had intended to switch to the silicone fluid but was advised of the problem of leaks. - Michael P.

What exactly was the wording of this warning? I rebuilt my 150's brakes about 19 years ago and although there was some pitting in the cylinders I decided to carefully hone them out and not resleeve them. I used all new rebuilding kits, flushed the system several times and replaced the castrol with dot 5 silicon brake fluid. Now 19 years later and about 12K added to the odometer, the brakes still work perfectly and I can messure the amount of brake fluid added to the system over this period with a table spoon! I did the same with my 67 E-type nine years and 10K miles ago with similar successful results. If this warning was to not mix fluids, carefully flush out the system and use new rebuilding kits before using silicon brake fluids, I agree. - coinman1

I missed any earlier correspondence on the subject of synthetic fluid so forgive me if I am repeating what someone else has already said. I completely agree with Coinman. All my cars with hydraulic stoppers now run with synthetic, (except track car). On two occasions I have lost the brakes in very tricky down hill situations doing a bit of mildly competitive driving. The problem was caused by the hydroscopic nature of ordinary fluid (absorbs water). On both occasions I could have avoided the problem by flushing and changing the fluid regularly but I didn't and got into trouble, (once seriously). Since using synthetic I've had no problems and the brakes are virtually maintenance free. If you ever strip old brakes that haven't been flushed for a while you invariably find a horrible, rusty, gungy mess in at least one of the wheel cylinders and at the bottom of the resevoir but not when synthetic has been used. Don't mix the two types. Although I have successfully converted to synthetic by first thoroughly flushingand not changing all the rubbers, people frequently report problems with swollen rubbers if they have been in contact with normal fluid first. I guess it's safest to replace all the rubber in the system when changing over. Btw: Synthetic is not suitable for track racing applications where high boiling point, racing fluids are required. - Roger Learmonth

Castrol has a new brake fluid which is DOT 3 and 4 compatable. It is supposed "to work with new and old rubber and fluid without needing to flush the system" - Larry J, 660636

No, I'm not starting the silicone thread again! Any of you in the States that can tell me what the differences are between DOT 3 and DOT 4 brake fluid? Are the differences worth worrying about? I'm having a hard time finding Castrol at any auto shops within a 50 mile radius and am about to look at other brand names. Alternate suggestions? - Jim Voorhies, 140 FHC

Jim, One difference is the boiling point. DOT4 is higher than DOT3. Unless you're racing I wouldn't worry about that. There's bound to be some other differences. Back when I owned an MGB I was told that DOT3 would eat pure rubber parts and DOT4 wouldn't. But that could have been urban lore or just the guy trying to get me to pay extra for Castrol DOT4. Hopefully someone else can provide some definitive answers. - Regards, Dick White, '64 3.8S, '58 150 FHC

I'm not so sure these are not old wife's tales... Maybe early 50's stuff. The stock car guys swear by FORD brand Dot 4 because it's boiling point is the highest. The boiling point is lowered by the absorbtion of water..brake fluid is naturally hyroscopic. - john shuck, westport/beijing

According to the Girling container, it is DOT 3 and 4 are compatable, and as Dick said DOT 4 has a higher heat rating. I know nobody will believe this, but my single master cylinder has not been rebuilt in 25 years, and all I have used, that I can remember is Girling. I still have an old can of Girling Crimson. Now I just hope I haven't jinxed my master cylinder. - Larry 660636

Just keeping bleeding it periodically. another hint. buy your brake fluid in small cans...use a little, then throw it away. Don't use brake fluid from half empty cans. single master cylinders mean you only get one chance..see that stone wall ahead... john shuck westport/beijing

A dual master cylinder thats only half working is still only one chance --Grab the hand brake! one vote for the list as is. - Vic

I just reread this--Whoops, I meant to say "I used to use Girling Crimson" I do still have the original can, but I have been using Castrol Brake fluid for years. You bring up a good point John, but I buy brake fluid by the quart and fill the smaller cans, that I keep in my 6 different cars. I know that you do not want to keep the lids open because of the hydroscopic aspect of hydraulic fluid, but all the old master cylinders do have air vents in the lids so they all have air exposure. Our climate is very dry, except when it rains, so I think that has helped extend the life of my braking systems. - Larry J, 51 OTS Redding, CA

Say Larry, that's just like our climate! - regards Jon Garde Canberra, AU

Jim - I found Castrol at a local Advance Auto. Surely you can find it at one of your local auto stores. Don't forget K-Mart and the like. And, you know, I don't see why STP, Prestone, or another similar brand meeting DOT 3 or 4 specs wouldn't work in our cars as well. Is brake fluid meeting the same national specifications different between brands? I don't stay with the same brand of gas. Oh well....Bob Oates

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