snakeman56

I was checking the master cylinder and was wondering about the color of the fluid. Thanks for your help.

yellow 72

purple..

snakeman56

Okay so what color does it turn after being in the master cylindar a while? and is it normal to look kind of cloudy towards the bottom of the well?

Thanks

Double Aught

I recently installed a master cylinder in my 67 Impala and bled the brakes. The color of that stuff was a dirty brown, not the appropriate color. It is supposed to be clear to a very light tint. I will be pressure bleeding the entire system this Saturday.

yellow 72

Dirty purple...seriously,unless it's real nasty it should still have a discernible purple tint. I flushed my entire system with denatured alcohol when I switched to silicon 13 years ago and it's still translucent purple

memLT-1

did you have to change out any seals or anything?

Tom454

The color apparently depends on the source and how long it is in the system. I believe it all starts out with a purple tint. I converted my C2 to DOT 5 around 1976... or when the DOT first came out. I have not changed the fluid... just re-used the original & topped it off after doing seals. It still has a purple tint to it, and is very clear. However... I converted my C3 to DOT 5 about 2 years ago, and this past week had to rebuild a caliper (because of non-use)... the fluid in the master cylinder had lost it's tint, although it was strill very clear. In fact it was so clear, I had to do a double take... thought maybe I forgot to convert it to DOT 5.

I have purchased DOT 5 from SS Brakes Corp, MidAmerica, and Zip.

I believe the C3 got the MA version, which was less tinted than the SSBC which I have in my C2.

So... you can't always tell by the color.

UKPaul

That you can't. I've run DOT5 silicon fluid in my bike for many years. The master cylinder is a translucent plastic & the fluid was originally purple. It's now perfectly clear. My wife's bike has a metal master cylinder & after about 6 years the fluid is still purple, so I'm wondering if the dye is like the dye used in anodising, in that it gets bleached by UV light?
For those thinking of converting to silicon Dot5 fluid, here's a word of warning:
---------------
Brake system contamination:

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil, etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some owners change to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. Brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

British Cycle Supply Company does not recommend use of DOT 5 silicone brake fluid on British motorcycles equipped with any AP Lockeed disc brake components.

---------------

Both bikes I used it in (fitted with AP Lockheed disc brakes ) had new brake lines, new seals & scrupulously clean master cylinders & callipers prior to filling. Wifes bike hasn't had any problem (but 6 years probably isn't enough time to find any?) & mine has been using the silicon fluid for about 20 years. It has iron callipers (much like the stock C3 ones, except they don't leak!) & I've not noticed any problems with water collecting at the lowest point (in the calliper) & causing corrosion. As the master cylinder is exposed to the elements, & has a breather hole in the cap, it used to be excellent at grabbing water from the atmosphere & messing up DOT3/4 fluid. Not seen any hint of this with DOT5.
Thought I'd get in first before the usual debate for/against Dot5 kicked off I've never noticed any problems with DOT5 in use & the brakes used to get a good workout, at one point both discs (rotors!) were bright blue after a "spirited" ride through mountains in high ambient temps. I never got any brake fade or other problems, & with 500' vertical drops next to the roadside on hairpin bends those brakes were getting a major workout!
Even though I've not had any problems with silicon fluid, I've got no intention of using it in the Vette, partly because of the warning above about sludge, partly because the system would have to be scrupulously clean & partly because I can't see any advantage over a quality Dot 4 fluid. The only reason I use it in the bikes is that the master cylinder is above the gas tank & I didn't want any risk of spilling DOT3/4 fluid over an expensive paintjob. Spill it in an engine bay & it's not the end of the world. Spilling it on a $500 paintjob is a different matter!

Rodbuster

I am changing my master cylinder and I was told it had dot 5 in the car when I got it.Than I found out the brakes were done at Firestone.So I call the them to make sure thats what in it and they say it should be dot 3. If dot 5 has a purple tint to it mine is clear.Guess I will just blow all the lines out and start new.

yellow 72

When I switched to silicon I also rebopped the calipers with o-ringed pistons and replaced the master cylinder, so the only thing to flush were the lines...and I agree with not mixing petroleum and brake parts.

Tom454

And I will add...

All forms of fluid DOT 3,4,5 will form "goop".
All OEM type seals will take on "flat spots" if the car is not driven, and will leak.... regardless of fluid type.

DOT 3 is more goop subsceptible because it absorbs water, but goop will form regardless... as said above.... by the gradual deteriation of the non-metallic components.

DOT 5 is not a cure-all. But it sure cuts down on maintenance.

When I convert a Vette over to DOT 5, I absolutely will not do the job unless I am allowed to disassemble the entire system (including the brake switch) and either replace or rebuild the master cylinder. There is no method of "flushing" in existence that will remove the built up sludge from the interior of the various brake system components. It simply cannot be done without disassembly. This is based on my experince as a mechanic, both working for other people and in my own 7 bay machine/repair shop.

I had DOT 5 in my C2 for 20 years before I tore the system down... absolutely no corrosion or rust. The fluid was clear except for some "particles" which I filtered out. I re-used the fluid... with absolutely no problems or issues. That is one advantage of using DOT 5.

If you bleed your brakes completely every few years (how many of us do this?) then you will reduce (not eliminate) corrosion caused by absorbed water in DOT3/4 fluid.

Another- already mentioned- DOT 5 doesn't eat paint. So if you spend time & money making your Vette "prissy" (like I do) this is a big plus.

Marv

Get a small, clear vial with a cap and put a sample of your brake fluid in it. Then add an equal amount of water and shake it up vigorously. Let it set. If the two fluids re-separate it is silicone - if not it is glycol based. Good luck

Tom454

Finally someone answers the original question....

I think I'll try that simple test myself tonight just for grins.

68/70Vette

I just read your post about how you install the silicon brake fluid:

http://www.corvettefaq.com/c3/bleedingsilicon.mht

Anything special about using the gravity bleeding method you describe. For gravity bleeding, I guess you just let the brake flluid leak out the caliper bleed screw, bleeding one caliper at a time? Anything special to avoid air bubbles in the calipers?


Thanks




Thanks

Tom454

I use gravity and the "two person" method when necessary.

Power Bleeders & vacuum bleeders & one-man-bleeders all work fine as long as you know how to use them. For example, a mityvac is good as long as you don't over-do the sucking & draw air in past the seals and/or bleeder threads. Air past the seals just sets you back to square one. Air past the threads fools you into believing that there is more air in the system then there really is.

The brake switch (AKA proportioning valve) will give you problems if it is in fact working correctly... most are not. When I bleed a system with a correct functioning p-valve, it shuts off the circuit I am trying to bleed if I use pedal pressure. In that case, I bleed one front and one rear caliper at the same time. This keeps the valve centered and allows fluid to flow instead of being blocked. If the valve is sticky or bound up, you can do one caliper at a time.

I typically use a pedal pressure to get the fluid going, and then let gravity take over. If I'm in a hurry, I use the bleeder cups you see at the auto parts store.

DOT 3,4,5 all bleed the same from my experience. DOT 5 "suspends" bubbles longer than DOT 3,4... but if you do the job right (and with patience), you won't have tons of bubbles to get rid of.

I've also done several tests on bleeding order... and found no difference based on order. I believe the order was based on factory production line requirements. The "correct" oder is specified by GM, but I can bleed anybody's brakes, in any order, and achieve excactly the same results. The typical prescribed order is farthest caliper from Master Cylinder to nearest caliper to the Master Cylinder. RR, LR, RF, LF (left hand drive cars).

If you're going into production.... then a power bleeder is a must. If you have time... the $10 bleeder cups at AutoZOne or Advance Auto etc work fine. You'll need 2 (one front, one back) if your proportioning valve/switch is working properly and you use pedal pressure to bleed.

Run about 1 pint of fluid through each caliper bleeder... if your system is clean, you can re-use the DOT 5 no problem. You will find small particles in the bled fluid... just don't pour those back into the master cylinder.

First- bench bleed the M/C.... you can do it on the car... tubes from the ports run back into the M/C. You can make your own if they were not included with the M/C. Pump the M/C SLOWLY until there are no bubbles anywhere... including the tiny orifices in the bottom of the chamber(s).

Reconnect the lines to the ports and begin bleeding the lines/calipers.

As a test, before I reconnect the lines, I put special blanks on the M/C output ports to seal them off tight... and then press the pedal. If it's mushy, then the M/C is bad, or there is still air in the chambers. If it's hard, I connect the lines and start bleeding the rest of the system.

If after all this the pedal is still mushy (but M/C by itself was hard), there is air in one or more calipers and you need to bleed them again.

68/70Vette

Thanks very much. I especially liked the tip about testing out the MC before going on the connecting the lines. I'll give the DOT 5 a go!!!

UKPaul

If you bleed the system by having somebody work the brake pedal then get them to depress it VERY slowly. Doing it quickly will aerate(sp?) the silicon brake fluid. The air bubbles formed from pumping quickly are a pita. I was at a show once & somebody was demonstrating DOT5 silicon fluid by pouring it all over paintwork (gives it a nice gloss!) & also had a brake system set up to show how to bleed it properly (obviously a lot of people have problems when bleeding the system). He had clear hoses in the system so you could watch what happens in the line from the master cylinder to the calliper. By pumping slowly you'd see large bubbles go down the line & then rise back to the master cylinder quite quicky when the lever was released. Pumping quickly caused the large bubbles to break up & the fluid turned into a froth. This took an age to rise back up the line, if at all, & if normal bleeding continued then this frothy fluid would get pushed all the way down into the calliper, adding more air to it. Slow but sure is the way to do it.
Something not connected with Vettes is the way both our bikes bleed their front brakes with silicon fluid in them. Whenever I've had to drain the system (eg. pulling the forks off to grease the steering head bearings) I just fill the master cylinder up afterwards & give the lever a few slow pumps. Then wait a couple of mins & do it again. Eventually the lever is rock solid, so the system is bleeding itself ie. all the air is raising to the top on its own. Being on the front forks most of the lines are positioned so that air can raise all the way up, but other bikes the same that I've changed brake fluid on (& there are many) which are using DOT 3 or 4 don't do this, I have to bleed it properly with a pipe on the calliper nipple, etc. Why this is I haven't a clue, but if you've got silicon fluid in a Vette then it could be worth lifting the front of the car up & letting the bubbles work their way up. You won't get all the air out (far from it) but it all helps. Crazy? Maybe, but if years ago somebody had told me that DOT5 silicon fluid would bleed itself in my bike then I'd have laughed at them.