Brake fluid question

[jpane]

I recently had my master cylinder rebuilt by White Post. After my mechanic reinstalled it, he said the pedal would slowly go to the floor. (By the way, this is a system that no longer has the boosters.) I sent it back to White Post and just had a conversation with their rebuilder. He said the seals had swollen. He had asked what kind of fluid, and said not to use DOT 5, only 3or 4. My shop says they used 4, definitely not 5.
White Post said to make sure it is a fresh container. Any ideas what could be the problem?
Any suggestions?
Thanks, as always,
John

[Rainer]

DOT 3 DOT 4 and DOT 5.1 standard glykol-ether brake fluid.
DOT 5 is silicon brake fluid.
you should never not mix these.
But i have customers who use silicon brake fluid for years, only in complete rebuild systems of course, and we have never encountered a single problem.

The only time i have seen swollen seals, is when people used mineral oil based brake fluid in DOT systems or the other way around. old Citroen's are prone to this.

Regards
Rainer

[jpane]

Thanks, Rainer. Since it was definitely DOT 4 not a mineral oil base, I think bad/contaminated fluid is a possibility. From my conversation with White Post, I gather that "old" fluid that may have absorbed water could be the cause.
What is the fluid capacity of the entire brake system. I want to bring sealed containers of fresh fluid to the shop, and have them thoroughly flush it. (I would assume that was already done, but will ask.)
Thanks,
 John

[BDA]

That's somewhat worrying that your shop may have introduced water into your brake system. That is an obvious no-no.

I can't say I remember for sure how much fluid you'll need. I would get 3 pint (or 500ml bottles). That should be enough with some left over, especially since you don't have boosters. I've had good luck with Motul 5.1 brake fluid. IIRC, it has a similar whet and dry boiling point to DOT (and thus higher than DOT 3 and 4) 5 but it is glycol based so compatible with DOT 3 and 4. It should cost in the neighborhood of $10/bottle.

[jbcollier]

Water, in no matter how much quantity, is not going to cause your brake seals to swell.  You can soak them in water all day from now until kingdom come, and the seals will be fine.  Water, or water contaminated brake fluid, will cause your brake metal parts to corrode.  Down long hills, the water in the fluid may boil and cause a complete brake system failure.

Seals swell when they are exposed to the wrong fluid, period.  If the seals were new, then, somehow, they were exposed to an oil product of some sort.  I have seen people put a lot of different things in their brake reservoirs: engine oil, transmission oil, automatic transmission oil, WD40, 3n1 oil, etc.  All with unfortunate results.

What happened here?  And, who's responsible?  Hard to say.  Could have been the rebuilder, your mechanic, or even yourself -- you did have a look at it after all, maybe polished it with something?  Not accusing anyone, least of all yourself.  Just pointing out, it's easily done.

[EuropaTC]

Water, in no matter how much quantity, is not going to cause your brake seals to swell.  You can soak them in water all day from now until kingdom come, and the seals will be fine. 

John's right, water isn't the culprit here. Technically, if you leave a soft rubber in contact with water it will absorb some over a very long period but it's minute, you'll need a chemical balance to determine the percentage it's so small.  Some seals will swell with normal brake fluid if you leave them long enough, but we're talking years now and even then it's not enough to cause failure.

The other key is the time involved.  Rubber will absorb, swell and soften but unless it is a very aggressive chemical then we're usually talking weeks/months/years depending on chemical or temperature.  If you've fitted this cylinder, filled up with fluid and it's not worked from the start then I just don't get it. (and that's with my ex-Materials Engineer hat on - I've tested lots of elastomers with chemicals in the past)

The other thing that puzzles me is that if the pedal went down that makes me think the seals weren't holding pressure. But if they'd swollen, wouldn't they have jammed in the bore ? The only way I could see a swollen seal losing pressure would be if it was swollen/softened so much that it had rubbed away on the bore or it was just so soft that it collapsed. Both options would need either an aggressive chemical/solvent or a far longer time than you've had.

Finally, I'm not sure about their comments on Dot5. I know it's a silicone fluid and has pros & cons for use but I didn't think you had to fit different materials for seals with it. Considering it's often used by collectors who infrequently use their cars I'm surprised that it's not compatible with conventional seal materials.  I know folks usually fit new seals when going to Dot5 but I thought that was to remove any residual absorption in the old seals because you shouldn't mix Dot5 with Dot3/4/5.1 ?

Brian

[Pfreen]

I have used silicone brake fluid for 25 years in my tcs.

I have nothing but good things to say about it. I do not remember any change in braking performance.

I have not had to rebuild the brake seals in all that time. I did rebuild everything and flushed the lines with alcohol when I made the change. 

[jpane]

It sounds like I need to talk to both White Post and my mechanic some more to figure this out.
I should explain that the pedal went down to the floor slowly, under hard pressure, if that helps understand this.
Thanks to all,
John

[jbcollier]

That is a pretty standard master cylinder failure.  The seal(s) are allowing some fluid to escape (called "bypassing").  This is a common problem with rebuilt cylinders. 

Some reasons it can happen:
- corrosion in the bore
- oversize bore
- worn piston
- seal(s) "nicked" on installation

It happens so often that I no longer fit overhauled masters.  I only fit new.  In 35 years of pulling wrenches I have had many, many faulty "rebuilt" masters and exactly zero (0) faulty new ones.  In that time, I have installed 100s of cylinders.

I also agree that seal swelling sounds iffy to me.  DOT 5 (silicone) fluid is not something a shop would have readily to hand.  They are also very unlikely to have used some other incorrect fluid.  My money is either worn piston or damaged seal on assembly.

It is also correct that DOT5 doesn't cause seals to swell.  It's the reaction of DOT5 to DOT3/4 impregnated seals (or vice-versa) that causes the problem.

[mike alain]

Well,  I asked the same question,  but my fear was different,  I was taught to use ONLY the girling brake fluid in these cars, not dot3 for some reason,  after I purchased rebuilt units
I asked the same question,  seems most of the folks here say use dot-3- now,  I wonder why owners manuals said girling only. Oh Well.   Mike.

[BDA]

Any quality brake fluid will work fine. The choice is really between silicone and glycol based fluids. If you choose a silicone fluid, it requires a complete flush because it is not compatible with glycol fluids. If you choose a glycol fluid, I think it makes sense to choose the fluid with the highest DOT specification since it gives the highest boiling point but when these cars were new, DOT 3 was the best that was available and it worked fine. Back in the day, Castro’s LMA was the trick stuff.

To be honest, I didn’t realize that Girling made brake fluid!  I found this Girling fluid on fleabay: https://www.ebay.com/itm/152385080668?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=152385080668&targetid=4580702889855929&device=c&mktype=&googleloc=&poi=&campaignid=410488079&mkgroupid=1233652272632056&rlsatarget=pla-4580702889855929&abcId=9300488&merchantid=51291&msclkid=c75f60dc9d0118fd63ff009edf00715a

It says it’s for MGs. It’s a DOT 5.1 fluid. It’s all pretty expensive and as I noted earlier, I’ve had no problems with Motul DOT 5.1 fluid for approximately $10/bottle.

[jbcollier]

Just a slight correction, the higher number (3 - 4 - 5.1) does not mean the higher the boiling point.  Generally, a generic DOT3 will have a lower boiling point than a generic DOT4 but not always.  The formulation of DOT 4 and 5.1 involves more than just boiling point, there's changes to facilitate rapidly cycling valves, etc.  There are racing DOT3 fluids with very high boiling points.  One fluid is not "better" than another.  They are formulated to perform specific tasks.  Choose a fluid based of the requirements of your system and operating environment.

[Richard48Y]

Anyone else here remember when you bought your Girling brake fluid to the manufacturers recommended COLOR?
Jags and TR's or MG's might use red or green.
Back then the wrong fluid ruined the seals immediately as they were natural rubber.
There may still be some very old rebuild kits around that will not work with modern fluids.