bleeding brakes

Having a problem here...

I've replaced the right rear brake cylinder and bled everything including the slave cylinder. Must have went around the car about 3 times and used up about 4 cans of brake fluid.

When I depress the brakes slowly----nothing!!!!

When I pump or depress brakes quickly---have pressure.

I'm scratching my head here---what gives? I didn't have this problem before. I am using those air "compressor brake bleeders" that I've got from Moss motors...

getting to the end of my rope here...a simple brake bleed that is getting nowhere...

Tom

BTW---I've got some 2 x 4's and applied pressure to brake pedal---very tight and opened up the MC cap. Going to let it sit overnight and let the air work its way to MC...This was an old chopper trick we used to get air out of lines...hope this will have some effect.

From your description, doesn't sound like a bleeding problem. If you let it sit for a minute, and then press the pedal once quickly it should do exactly the same thing as if you let it sit for a minute and then press the pedal once slowly(air in the lines compresses the same amount whether compressed quickly or slowly). If it works differently when pressed quickly and slowly, then I would suspect the master.

If it doesn't work when pressed once(either quickly or slowly) but does work when pumped, then it could be bleeding but it could also be adjustment of the brake shoes or possibly a bad hose that is ballooning under pressure.

PS Did you change anything other than the wheel cylinder? New brake shoes can also cause it to only work when pumped if they don't match the radius of the brake drum.

Suspect Master Cylinder. Correct me if I'm wrong.

Took the car out for spin---sometimes clutch works and sometimes it doesn't work and then have to pump once or twice to get it back again.

---Same thing with brakes, sometimes have brakes then I'll have nothing---then pump once and have brakes again.

The PO rebuilt the master cylinder just before I bought the car. It looks like the "rebuilding" using a rebuild kit didn't hold up very long.

No leaks anywhere, so my guess is that I will need to replace the MC. Where is the best place to get a new MC?

Tom

Did you replace all the rubber bits? If you flooded the system with brake cleaner while the rubber was in place, and then simply filled it up again, you may have ruined the rubber cups in the MC. Pull the dust covers off the rods and look for leaks.

If this is all new rubber then that's another matter. I would definitely suspect the MC. It sounds like the primary cups are not sealing very well against the bore.

Thanks for jumping in...

Didn't flush the system, just pressed out the old "DOT 5 silicone with fresh synthetic fluid using GTLMA by castrol (It was about a gallon worth---until all colors were cleared matching the GTLMA.

Hoses are reasonably new---can tell by looking (fresh fittings, tags on hoses, etc.) PO just rebuilt M/C using kit. Was OK then...

I was told that the DOT 5 will ruin the system thus my reason for replacing with Castrol.

Up-date:

This morning I went out the garage just to be sure there was no air in system...I did the gravity bleed. All systems solid w/o air at all 4 wheels. Not too sure about the slave cylinder tho.

If pressed slowly once it feels like nothing---empty/no pressure at all (same for both clutch and brakes).

But if I were to press quickly---have pressure (again the same for both clutch and brakes).

Does this mean the M/C is suspect? It has been rebuilt once already (recently---past year). Should I attempt a rebuild or get a new one? And if so----where can I get one from?

Again---thanks for helping.

Tom

Any mention of DOT5 vs DOT4 is likely to start a religious war and there is much misinformation floating around, but the change over may be the source of your problem. There are some that say you can change by just replacing all the fluid like you did, but most people on both sides say that if you do change you should at least completely flush and clean the system of all the old fluid first and most agree that it is best to replace all the rubber in the system before the change. Since a new master is so expensive, you might want to try just cleaning and rebuilding it with new rubber seals first.

PS Lets not start another flame war and just try to help Tom out.

Thanks Jeff...

After re-reading my post and after reflecting, I might have sort of misstated the DOT deal. According to the "local" british restoration shop it is NOT whether it is a DOT 5 or DOT 4...it is about what is in the formula or the mixture that may damage rubbers---And I don't remember what it was. Told me just go with the Castrol GTLMA and be done with it. Really doesn't matter to me...I want to drive but I need the car to stop!!! Right now, after checking all systems, there are no leaks anywhere that I could find.

Only thing is that somehow, somewhere I might have messed up the M/C rubbers inside due to....fluids? or too strong of a vacuum pressure when bleeding the brakes?? Thats why did the gravity bleed just to make sure all air was out...

All I have now is---slow press = nothing

quick press = pressure

pumping = more and better pressure

Tom

I agree, the changeover is most likely what caused the problem. Silicon and Glycol fluids have different swelling agents in them. I suspect that the rubber in your MC is no longer able to create a seal to the bores. When you press harder, the added fluid pressure may be forcing the cup out, and making a seal.

Without arguing what type of fluid is best (I use both types in my cars), I would say that whoever said Silicon fluid will "ruin the system" is way off base. He may be referring to reports of problems when changing from DOT3/4 to Silicon. If there is any trace of the old 3/4 fluid in there, then it is possible for clumps of goo to form and block passageways, damage rubber, etc. I have seen these effects personally and it was not the fault of the Silicon fluid, but rather a poor job on the conversion.

There are many people running happily on both types of fluid. Each has their pros and cons. At this point I would suggest choosing one, replacing all rubber components in your braking system, and re-filling. This is no place to mess around with chance, and once done you will have peace of mind for many years of happy motoring.

As far as I know, all DOT 5 is silicone based and all Dot3,DOT4,DOT5.1 are glycol based. There are different additives in each that affect the rubber parts, but most glycol based fluids can be safely mixed with each other and the same for most silicone fluids. However, many real world reports say that putting silicone in a system that has been run on glycol, or glycol in a system that has been run on silicone can cause problems with the rubber seals. Most silicone based fluid is a purple color, while glycol based fluids clear so you can tell the difference.

Using too much pressure when pressure bleeding could damage the seal on the push rod end of the cylinder, but that would only allow fluid to leak into and around the push rod boot and probably not cause the problems you are seeing. My best guess is that the bleeding was not the problem and the problem was caused by the different additives in the glycol and silicone fluids. Anyway, the first thing I would try would be cleaning and rebuilding the master.

PS I was typing when Steve was posting, but I agree with everything he said.

It appears that the conversion of fluids might've done me in...

OK...

I have a 1960 mga w/front disc brakes...

-Ordered and have M/C rebuild kit on the way

-Have the yellow stuff in the system now and will stay with this. (Castrol GTMLA)

What should I do now?

Do I have to flush system with alcohol?

Do I need to replace all hoses? including slave cylinder hose?

And what about calipers seals??

Anything else I should do??

You guys are good...Thanks!

Tom

I would do everything, right down to the seal between the two caliper halves. However many people have reported flushing the system with alcohol and filling again with brake fluid, with good results. I have re-used rubber bits in a pinch for the short term without any problems but would still be hesitant to leave it that way permanently. Since there are so many opinions on both sides of the camp, I would suggest doing some research on the web and then make a decision based on your own level of comfort. Rebuilding / cleaning the whole system and replacing all the rubber is a fairly large project so it's understandable that some people prefer to try flushing and refilling. I prefer the peace of mind that comes with doing it all "right" so that I don't have it in the back of my mind every time I hit the brakes on a canyon road.

Tom,

The first thing I would do would be to change the master cylinder seals. When you remove the pistons you may well find that the seals are visibly worn and that is the cause of your problems.

You can rebuild the master cylinder in situ by removing the pushrod clevis pins and front bolt (loosen rear bolt) and tilting backwards. That way you do not have to disconnect the pipes and fluid spills will be minimised. Now you have switched fluids remember that any fluid spilt will effectively remove paint, so cover everything up and be quick to wipe and wash over any drips!

Like Steve says, peace of mind is worth a lot. I personally would change all rubber parts; hoses and seals including calliper seals (I would not split the callipers to do the o-ring though). I did this when I bought my 1600 and replaced the rubber parts in the front suspension and steering at the same time because I knew they were over ten years old and there were visible signs of ageing. I took my time and it was a two day job to do that and a complete service. My master cylinder worked fine, but the main seal was extremely worn, so I figured that with new seals it would be good as new. However, If you are not sure about the condition of yours, brand new (TRW LUCAS) units are available for $141.70 US plus shipping (from UK).

On front calipers did you bleed bothe the bleed screw. You have to remove the front wheels to see the outside one?

Nothing wrong with silicone used it for years.

Just to change the direction here . Have you double checked the copper sealing washers are sealing properly on the rear brake cylinders , we had a small scratch on one that was passing fluid and not visible as the fluid was running down the wheel and pooling around the tyre . are you loosing any fluid overnight when it just sitting ?

Paul...

Yes. But I could also tell fluid was coming from under the rubber boot. Anyways---pulled it out and put in a new one. Opened up the old cylinder--it has 2 large 25 cent size pit inside of the cylinder. Glad I didn't bother rebuilding that one. But yes...it happened exactly as you described it!!! BTW---I've replaced and used new copper washers with this new cylinder.

Tom

Did some research and can't find information about "removing" silicon based fluids from brake system. It appears that it is easy for alcohol to remove DOT 3/4 but not so for removing silicon based fluids. What do I need to use to remove DOT 5 fluids from system?

Once I am able to do that---will tear open all parts for cleaning. But need to know what I can do to remove silicon from brake lines first before opening...

Tom

Silicone best brakes I ever had.

Pulled the M/C afternoon and open her up---All black fluid floating and lining the M/C. This indicates rubber break down. Pulled all apart and soaked everything in gasoline because it is the only known solvent that can cut through silicone.

Now...I need to decide and I'm getting all confused here.

The car had silicone before switching back to glycol and as of now---there is no known solution that I know of in removing silicone from system. My take is rather than throwing out the hard line and whole braking system---just go back to silicone. Flush system with denatured alcohol to remove the glycol stuff (light colored castrol fluid) and blow dry with air. Flush possible remaining glycol and alcohol out with purple silicone fluid. Does this make sense?

Or just leave it alone (leave the glycol in system) I've pushed out all the purple silicone with about a gallon worth of glycol (light colored castrol GTLMA) in pass couple of weeks. Just mount M/C and fill with Castrol and bleed. The nagging thing is that since silicone is very difficult material to remove, I would have to expect some remaining silicone in the system even after flushing out the silicone with glycol.

I'm ready to finish up tomorrow and I'm not sure which is the best way to go...

Tom

I've flushed thoroughly with brake spray cleaner and refilled with both types of fluid, and had good results. I suspect that if you have trace amounts of silicon, it won't do any real harm. That's just gut instinct however, no data to back it up. If refilling with silicon, be extra diligent in cleaning out all Glycol. Then bleed the system again after a spell, and check the drained fluid and MC reservoir for "goo". If none is found then you're probably fine. I've recently converted brake fluid in three systems, going both ways. No problems so far on those cars. Hope this helps your decision.

Thanks a million Steve....!

Just what I need to know/understand. Perfect...

Many thanks to all of you for jumping in...I know what I want, what I need to know and know what to look for, etc.

Tom

Tom, Steve,

I changed to silicon in my Midget in 1991 and MGB in 1993. I replaced hoses and seals then just filled with silicon using an Eezibleed letting it run through until clear. No problems with either car up they were sold a few years ago. I changed my MGA to silicon three years ago the same way and again no problems whatsoever.

I didn't clean out the system at all except by running through a bit of extra fluid. Following some posts on here, this summer, I ran some more fluid through the system; bleed screws (again with Eezibleed) in each corner to check for discolouration, contamination, rubber, water etc. The fluid was perfectly clear.

Ditto Neil on my my cars since silicone first hit the market

Neil,

Thanks for sharing your experience---that confirms or shall I say, the confidence that my work won't be in vain!!!

Got the M/C rebuilt and put back. Took only an evening to pull, soak, clean and rebuild and have it back in the car!!! Really not all that bad at all! The bitch was getting it bled! Took 3 trips around the car/wheel before I finally got most of the air out. As a final touch---did the gravity bleed at the end to assure that all air was out. Drove the sucker yesterday and all of today---in the rain and it was good to rip the car around the wet pavements and winding it out at high rpms!!! It was a total blast.

Thanks for all of the input---this made a difference in the confidence of what was needed to be done...

And---I do have other issues that need to be addressed but will give you blokes a couple of days rest before my next dilemma! Smile...

Tom

I have been very happy with Silicone fluid in my car for the past 15,000 miles. No problems and NO paint damage.