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MG MGB Technical - Changing from silcone to reg. brake fluid

My clutch is acting like it has a hydraulic problem. It grinds going into reverse, disengages a fraction of an inch off the floor, and needs some effort to put the lever into gear. It did this earlier in the year and the hydraulics checked out ok; there was ample movement of the pushrod at the slave and the master and the slave cylinders are nearly new with a few thousand miles on them. Parts were and are Lockheed and Borg &Beck. The previous problem turned out to be a bad clutch cover.
It's acting the same way as before, but before I pull the engine, I want to bleed out the clutch to see if a bubble found its way to the slave or something. The problem is that bleeding a clutch on a B is big PIA, and gets expensive when using silicone. Silicone also does a much better job of holding the air bubbles than regular fluid, so it always seems to take more fluid/more pedal strokes than reg, again resulting in using more fluid to do the job. Of course it may turn out that my problem is not hydraulic, but if I can spend less money on brake fluid and have an easier time bleeding to find that out, that would be great.
So my question, finally - I'm thinking that I'll flush out all the silicone fluid, pump through a boatload of alcohol to rinse out the system, blow through some air to dry it out, blow through some more air to be sure its dried out, then fill and bleed with Valvoline Syn-Tec or Castrol LMA. Any thoughts?
BTW, I have silicone in my brakes also and there has been no silicone boogeyman, my only gripe is that it's expensive and a pain to work with.
Thanks in advance, Wade
Wade Keene

Hi Wadem
Any air in the system usually finds it way up to the 'U' bend in the pipe up by the master cyl. One way to get this air out is to push the slave cyl back as far as possible & the let it sink out again by itself. Doing this 2 or 3 times usually works. If the pedal - slave cyl dosn't come out by itself then the culprit is usually a blocked/perished hose.
Good luck
Garth Bagnall
Garth Bagnall

Dito to your cost of fluid concerns. However, I am a hardcore silicone convert and never plan to go back. What I do is "reverse" bleed the system. You can buy a vacum pump that has a reverse mode of operation. This pumps fluid in from the cylinder. The bubble rises as the fluid does. The clutch is easy as it is only a single line. For the brakes, I go around and pump a bit on each one. Works for me.

Pete
Pete

Garth, are you suggesting that air will sink down through the brake fluid " by itself"? Now silicon fluid had not been invented when I finished my last high school physics class, but I cannot believe it behaves any differently to any other fluid. fluids may sink, but not air- it rises. What do you mean?
Ken R
Ken Rich

Gentleman;
Another simple trick that works. hook a long piece of hose from the bleed nipple to the reservoir. Then just pump your fluid in a circle. This WILL get the air out with no fluid lost. On the down side it also pumps any dirt around in a circle as it does not float to the top of the res like the air. I work by my self and something about the mother of invention Bob/International Auto Service
Bob Thompson

Hi Ken,
Yes the air will always stay at the u bend unless pumped down through the slave but because the pipe is quite large it is difficult to pass a large volume of fluid through the system by pumping so it takes a lot to bleed the system as the fluid just goes past the air bubble. one pump of the pedal just pushes the air to the bottom of the pipe & then just rises back to the top. I have found after 25 years of repairing MGB's that once you have a slave full of fluid, pushing back the slave piston displaces enough fluid up the pipe to push the air bubble back into the master cyl - I too work by myself. If the hose & slave are OK then the fluid will gravity down & the slave piston will just come out again. Pumping fluid around in a circle as Bob does is also good if everything is clean.
Garth.
Garth Bagnall

One caveat to the pumping in a loop method: Probably not a good idea with silicone. This fluid does have a reputation for "frothing" and giving a spongy pedal. Even when doing a conventional 2 man bleed, with silicone, use slow pumps rather than a quick jabbing motion. The air absorbtion tendency is why I bought the vacum pump in the first place: sucking fluid though does not agitate the fluid. Six years and counting with silicone. No problems, and firmest pedal amongst all my LBC friends. (The braided lines are probably a big factor in this)

Pete
Pete

Thanks for the comments, but what about replacing the silicone fluid w/ "regular"? Anyone have any experience with this?
Wade Keene

Wade - I am not sure why you would want to change from silicone to regular (DOT4) fluid, but the procedure would be tha same as the other way around. Get as much of the silicone fulid out and then fill with DOT4 fluid and flush this through the system by bleeding it several times, this will get rid of 90% of the silicone fluid. All the reports are that DOT4 and silicone fluid are not compatable .All this refers to is that they don't mix, but they will coexist together without causing any problems. The big reason to get all of the DOT4 fluid when converting to silicone is that any DOT4 fluid in the system will still draw moisture and cause corrosion, the very thing advantage of silicone fluid that needs to be maximized (it doesn't draw moisture).

Pete in Canada - Got you beat, I have had silicone fluid for 15 years now and it is as clean and clear as the day I put it in. It is so clear, in fact, that when I checked the level in the master cylinder after about 6 or 7 years, I thought it was empty because I could look right through the fluid and see athe bottom of the cylinder as though there was nothing in it.

Dave
David DuBois

Wade,
Go talk to Barney ;-)
Yes, he has changed back and forth at least once. Just because the mountain was there, of course.
Ask him about 15 minutes before the gavel falls at the next club meeting so that you have time to get the info with a built-in time limit.
David "plan ahead" Lieb
David Lieb

Hi Dave,
Of course I have an expensive class on Monday nights, so I haven't been able to make any meetings since August. Your advice on how to talk to Barney is great, I'd never have thought of that. BTW, I just picked up a '71 midget for the drivetrain parts - do you need anything?

Hi David,
I initially put silicone in because I had my brakes together and would be waiting a long time until the entire car would be together and driveable so its preservative qualities were appealing. Now I'm driving the car as much as I can so that is not an issue and the disadvantages of difficulty in bleeding, expense, and softer pedal even w/o any air bubbles outweigh any silicone advantages I've heard about or experienced. I've had cars with regular and silicone brake fluid and have not had any problems like the naysayers predict, but I also don't believe it performs any better nor is it worth the extra expense and trouble now that I've compared the two types. Just my preference.
Wade Keene

This thread was discussed between 02/11/2001 and 05/11/2001

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