Flushing brake/clutch

I need to flush DOT 5 out, should I use rubbing alcohol or boatloads of cheap DOT 3 before I put in LMA?

Which ever is most economical , However , if using alcohol be sure to select 90%.

I remember when I put DoT5 in my BJ8 I flushed the system with denatured alcohol, which is ethanol with a toxin added (maybe some of the hand 'sanitizers' being sold would suffice?). Dunno what would be best to go the other way, but if I had to do it I'd probably flush with the alcohol, then the DoT3, with lots of compressed air after both.

Gotta ask, why do you want to do this?

What is LMA first??? SYN fluid and why change to it?? Most any alcohol will flush system and then add air pressure. ( NOTE ) DOT 3 DOT 5 are alcohol base and by number 3 or 5 temp rated 5 being higher temp rated for new cars with disk all around. If you are racing OK down hill a lot mountain driving OK DOT 5 will handle all that. If you car sat for years it might be needed. I will tell you that alcohol will not freeze and in a pinch you can add water to it and easy drain when back home. I was at a class last year doing valve seats on a Jag head they cooled the seats in dry ice and rubbing alcohol. The point of boiling is quite high also
DOT 5. And last why, we would like to think about the same when working on our cars. Madflyer

Madflyer said:

What is LMA first??? SYN fluid and why change to it?? Most any alcohol will flush system and then add air pressure. ( NOTE ) DOT 3 DOT 5 are alcohol base and by number 3 or 5 temp rated 5 being higher temp rated for new cars with disk all around. If you are racing OK down hill a lot mountain driving OK DOT 5 will handle all that. If you car sat for years it might be needed. I will tell you that alcohol will not freeze and in a pinch you can add water to it and easy drain when back home. I was at a class last year doing valve seats on a Jag head they cooled the seats in dry ice and rubbing alcohol. The point of boiling is quite high also
DOT 5. And last why, we would like to think about the same when working on our cars. Madflyer

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I'm not quite sure what to make of this comment. DoT3, 4 and 5.1 are glycol-based. Chemically, a glycol is a type of alcohol, but 'alcohol,' whether ethylene or isopropyl (rubbing) would not be suitable brake fluids (their boiling points are very low; in fact, they evaporate at room temperature).

https://www.britannica.com/science/glycol

DoT5, aka silicone BF, is not an alcohol at all but is based on silicone compounds:

https://en.wikipedia.org/wiki/Brake_fluid

The people at the Jag tech session used dry ice with alcohol--alcohol freezing points are much lower than water's, and some older formulations of antifreeze used alcohols--to slightly shrink the valve seats so they'd go into the head easier (I suspect they heated the head somehow, too?). A few years ago I put new bearings and races in new hubs for my BJ8, and put the hubs in the oven and the races in dry ice. As the races warmed-up and the hubs cooled they made a most scary-sounding wail; I assume they were rubbing each other as the temps equalized (I was actually afraid something would crack).

Alcohol will dissolve glycols, as they're in the same general chemical family; I don't know what would be the best solvent for DoT5. Water is absolutely the last thing you want in your braking system (and DoT5 is not miscible with water). I've noticed the BF makers have started putting 'synthetic' on their labels, perhaps to cash in on the cachet of synthetic oil but, aside from some plants and animals that can manufacture glycols to survive freezing temps all glycols are 'synthetic.' 'LMA' is a Castrol BF, it stands for 'Low Moisture Activity' because, as I said, water in BF is undesirable.

Edit: If I was going to make this switch, I would try both ethanol and isopropyl alcohol to check for solubility/miscibility with DoT5 (note both alcohols are hygroscopic and could introduce some water into the system). Maybe something else entirely, like 'brake parts cleaner' would work better.

bdcvg said:

I need to flush DOT 5 out, should I use rubbing alcohol or boatloads of cheap DOT 3 before I put in LMA?

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That's OK, but you may have a small leak or bleeding issue that's causing you to not have a hard pedal.

Personally, I'm willing to put up with a slightly softer pedal to avoid all the paint-damage issues.

If I was doing this conversion, I'd rebuild the entire system with all new rubber and flush the lines with brake cleaner and compressed air before reassembling. This is what I did a few years ago when I converted from DOT 4 to DOT 5. DOT 5 is not compatible with the other DOTs.

Why not use 5.1? It has a higher boiling point and you can probably get it in quarts or liters. LMA in its small containers is unnecessarily expensive - just my 2 pence.

Well here is My dilemma. I topped off My reservoir with DOT 4 LMA and then I found out My restorer used DOT 5. I pulled some out with a syringe and sure enough it's purple (car quest DOT 5) and had a few small globs from the DOT 4 suspended in it. I only put a few teaspoons in probably so maybe keep the DOT 5 suck the res as empty as I can and flush a bunch more though the system?

bdcvg said:

Well here is My dilemma. I topped off My reservoir with DOT 4 LMA and then I found out My restorer used DOT 5. I pulled some out with a syringe and sure enough it's purple (car quest DOT 5) and had a few small globs from the DOT 4 suspended in it. I only put a few teaspoons in probably so maybe keep the DOT 5 suck the res as empty as I can and flush a bunch more though the system?

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That's what I'd probably do. Get every drop out of the reservoir, fill with DoT5 and bleed it all out. I'd probably use a full quart of DoT5, and pressure bleed (which is what I usually do anyway). Examine the fluid that gets bled out, and keep repeating until you get a complete reservoir's worth with no DoT4.

bdcvg said:

Well here is My dilemma. I topped off My reservoir with DOT 4 LMA and then I found out My restorer used DOT 5. I pulled some out with a syringe and sure enough it's purple (car quest DOT 5) and had a few small globs from the DOT 4 suspended in it. I only put a few teaspoons in probably so maybe keep the DOT 5 suck the res as empty as I can and flush a bunch more though the system?

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I would keep the DOT 5, especially if you've got a decently hard pedal. After you get beyond this issue you won't be sorry.

I'd siphon all the fluid out of the reservoir and fill it up with DOT 5. Your judgement call, but personally, I probably would not flush the system. Flushing can introduce bubbles that soften the pedal. DOT 5s main problem is little bubbles get in suspension and don't float out as easily as the other DOTs. There's a lot of info online about techniques for avoiding introducing these bubbles.

Your restorer should have put a DOT 5 label near or on the reservoir:

Yeah that sounds like a good plan, there can't be much DOT 4 in the res. My restorer probably told Me and I forgot, after so many LBC's I just defaulted to Castrol DOT 4 .

I always chuckle about paint problems with brake fluid. I have been using dot 4 in various British cars since 1970 and never had any paint problems. If a drop gets on paint I just wipe it off within a few minutes. No problem. I do cover everything just in case and use a funnel when pouring into the reservoir. I recall a few years ago that the military switched back from dot 5 but I have forgotten the reason. Maybe the cost.

Hey TH :

U So lucky--LOL

Thank you I stand corrected as to brake fluid base. I am sorry . And yes they heated the head to a high temp and installed a guide in valve hole and for setting tool to set seat quick work. Madflyer

If you only “topped off the reservoir” then chances are the Dot 4 has not made it out into the piping system .
suck out all the fluid in the reservoir . Stuff paper towels into the reservoir and suck up all the residue . Refill with Dot 5 purple stuff , if you have a firm pedal drive and enjoy .

Yep that's the new plan. Thanks for Everybody's help I was gonna over think this one into the ground.

Looks like I got lucky, I had removed an OZ. or 2 with a syringe and observed the gelatinous DOT 4 last week. Today I went out to remove the rest of the fluid in the reservoir but took a look with a very bright flashlight into the fluid. There was nothing, no blobs or discoloration dirt or anything but purple so I'm not touching it.

Apparently, DoT4 has a lower specific gravity--i.e. it's lighter--than DoT5 (which I didn't know; SG and viscosity aren't usually mentioned in BF discussions). If you poured the 4 in carefully it would have just sat on top of the 5 (and eventually 'floated' to the top anyway).