I had a few questions about flushing out a master cylinder from dot3 fluid over to dot5 fluid. I read to use denatured alcohol to flush it with. Would I need to bench bleed it with the alcohol?

The reason why I'm doing this is because everything on my brake system is new, except for my master cylinder. It was in good working order and a fairly new replacement part, so I'd like to save the $ by reusing it. I want DOT 5 mainly for its non paint stripping qualities, and I have plenty of it.

NO alcohol. Suck as much DOT 3 out of the MC as you can. Fill with DOT 5. Bleed til you see purple at each wheel. Done.

The master is out of the car and more less empty. All of the lines, cylinder, and calipers are new and have not had any fluid in them yet.

Should I just use some brakekleen on the master and then bench bleed with dot 5, dump, and repeat?

That should work fine.

Don't use brake-clean it's not intended for rubber parts... Denatured alcohol is the accepted flush solvent for rubber brake parts but if the master is off the car personally I'd pop it apart & clean it throughly then lube the parts with DOT 5 before reassembling it...

I guess I thought he was going to spray out the mc reservoir with brake cleaner. Looking at the vague wording again, I can see where maybe he means he intended to use it as a flush. In that case, no, I wouldn't do that. Not sure it would have the dire consequences that you imply, but I wouldn't personally do it. Similarily, I wouldn't flush your "accepted" (by whom?) alcohol through a brake system, either. I don't think it's good to have any very-low-boiling-point liquid floating around in a brake system.

Quote:

---

What is you background? Do you actually work in the trade?

---

I was trained in and previously worked in auto repair, but have sinced changed trades. To what address should I send my resume for your review, to determine my eligibility to post on this board?

i have converted hundreds of cars over to DOT 5 brake fluid.

DO NOT USE ALOCHOL. it compresses at a different rate than brake fluid so it can give you a mushy brake petal.
DOT3 and DOT5 will intermix without problems, after mixing they will separate but will have no ill effects in performance. when mixing fluids you won't improve lower level fluid by adding higher level fluid. you will just lower the higher level fluid to the lower levels performance.

DOT 5 brake fluid retains air like DOT3 does water. this is why it isn't recommended in anti lock breaking systems.
the correct cure for this is to place the DOT5 in a pot of very hot water for about 15 min. this will boil the air out of the fluid. you can actually see air bubbles in the fluid as the air is forced out.
i usually place the bottle of DOT 5 in the sun for a few hours. this usually will force the air out of the fluid. most DOT 5 is in black bottles for this reason.

when i convert a system over to DOT 5 i just suck out as much DOT3 out of the master cylinder. then add DOT 5 and bleed as normal. when you see the DOT 5 squirt out of the bleeders you are done.

one thing to keep in mind is water can get into the brake fluid and settle in the lower areas in your brake lines and make them rust out from the inside. because of this you should change your brake fluid every few years like regular fluid.

i have used dentured alcohol on 2 cars without any problems.