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I want to change one of my cars from DOT 3 to DOT 5. Has anyone done this sucessfully? My plan is to flush the system with alcohol then flush with DOT 5 then fill with fresh DOT 5. Good plan? Bad plan? anyone have a better plan? Thanks.......Bob.

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I changed my 40 Ford & 64 Plymouth over to Dot 4 semi-synthetic. I just flushed the system with Dot 4 until clean fluid came out, then filled & bled the system. That was over 4 years ago and have had no problems!

Merry Christmas!!!!!

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Bob,

Your going to have two camps on this one.

I'm no expert but I am a certified, trained mechanic with 10 years experience now. I prefer DOT 4. It has higher temperature properties, is more stable. DOT 5 - I would start with all new parts - no alcohol flush. I don't want anything in the dedicated brake system except brake fluid.

Those that swear by DOT 5 I'm not sure what their reasons are but the idea is that you would never have to change fluid again or worry about moisture contamination. But the swap has to be 100 per cent or else the two fluids will cross contaminate. Will you know 100 per cent for sure that your alcohol flush will accomplish that?

People say that they don't like the idea of contaminated brake fluid and the risk it may cause to safety. But it's not a bad thing to flush your DOT 3 or DOT 4 system every 2 to 3 years anyway. Brake systems should be understood, inspected and maintained just like anything. Also, brake systems in general going way back are one of the most over-engineered and well executed systems, and the fluid is just one component of many that may fail, probably won't fail though.

I have heard that some but not all that have switched to DOT 5 complain of spongy brake feel. Silicone has different compression properties, and it is possible it won't work with every brake system.

Just some thoughts. I would choose DOT 4.

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Well, I plead ignorance vis-a-vis DOT 4. Never even heard of it. Please elaborate, I might just opt for that. Personally I'm happy with DOT 5 so far. I have it in every thing but the 55 Buick. I'm not sure why I used Dot 3 in it but I want to get it out. I've had dot 5 in the Corvette, which is NOTORIOUS for leaking/corroded calipers, for near 20 years now with no leaks or corrosion that I know of.

So please elaborate on DOT 4. What are the pro's and con's.......Bob.

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Switched from DOT 3 to DOT 5 on my 71 Cuda and then did it again on the 69 Road Runner. Nothing really fancy involved. Just a matter of keeping the master cylinder filled while bleeding each of the 4 corners. When nothing but DOT 5 was coming out of the bleeder, time to button it up and move to the next corner. No hardware replacement, flushing or anything like that. Both cars were quite capable of moving up to 100 mph in short order as they were 340 W2 and 440 6 BBL engines respectively and brakes always worked great. I made the switch for cosmetic purposes. Hate it when a leaky MC wreaks havoc on my firewall paint. Brother-in-law also ran DOT 5 in his 742 hp stroked Hemi powered 68 Barracuda with no ill effects.

Rod

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As for spongey brakes... I've got DOT 5 in my Chevy II and I'll put someone through the windshield if not belted in, and I sneeze on the brake pedal. Pedal is very firm. Biggest thing is making sure you get ALL the air out of the system.

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Bob,

DOT 4 is a synthetic DOT 3, man made, so content is compacted and controlled, kind of like Mobil 1 has perfect molecules versus organic oil. It is rated at a higher temepratures for failure and has improved performance over DOT 3.

However, you have a lot fo positive personal experience with DOT 5, and virtually all of the comments after, have praised DOT 5, so maybe that is the route to go.

I still hesitate to put anything but brake fluid in my brake system and I am pretty sure I have heard that DOT 3/4 and DOT 5 are not to be mixed. I think we would have to get a pretty good sampling of users to get the "horror stories".

As a Mazda and Subaru technician, I only see the "sick" cars not the ones that are well. I have actually had a couple of kids who tried to switch to DOT 5 from an article they read in a tuner magazine and what a mess. In one case, we replaced EVERYTHING. However, these cars all have much more sophisticated circuitry due to ABS and proportioning parameters.

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I've done some further research on dot 3&4 vs dot 5. Dot 4 has a higher boiling point but other than that seems the same as dot 3. The "experts" consensus is Dot 5 sould not be used in ABS systems. They also report that if 3 and 5 are mixed it turns into a goo like Italian salad dressing. There are reports of a spongy pedal feel with dot 5 but I don't see that on the 4 cars I have it in.

I'm not really looking for a discussion of which is "better". I know which I prefer. I'm hoping to hear from people who have made the switch without replacing all the components and thier results.......Bob

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I have done a lot of these conversions. Start by dissassembling all of the wheel cylinders and the master cylinder. If they are all in good shape (rubber parts all OK, no major corrosion on the pistons or springs, cylinder bores OK, no pits or corrosion) clean all of the rubber parts with denatured alcohol and the metal parts with laquer thinner. Get everything clean. If the wheel cylinders are NOT OK, see if you can find replacements through the Raybestos or Wagner catalogue (hint: the kid at the auto part store usually will want to go the idiot book route. obtain/know all of the critical dimensions of your cylinders and look them up in the big-full line raybestos or wagner catalogue and order them that way) If you can't find the whole replacement cylinder, you can send yours out for sleeveing (I prefer stainless steel sleeves) to a new diameter that matches a newer cylinder that is available per the above method (this is very unusual, only had to do that for 1920's cars).

While the car is up on jack stands, plug the ends of the lines and fill with denatured alcohol. Leave that in overnight, burp as much air out of the system while filling. Drain out the alcohol the next day, blow out the lines with compressed air.

VERY IMPORTANT: if you are using new cylinders (which I highly recommend) take them apart, clean off the cosmoline (anti-corrosion goo) by the method above, denatured alcohol for rubber, laquer thinner for metal. I like to paint the exposed cast iron parts black (or whatever color) to keep them from rusting.

COAT (PRE LUBRICATE)ALL OF THE WHEEL CYLINDER PARTS WITH WHATEVER FLUID YOU WILL BE RUNNING THE SYSTEM ON.

Put everything back together and bleed the system SLOWLY. The Vacuum pumps don't work as well with DOT-5 as they do with DOT-3. I just do it the old school way, put a person behind the wheel and have them do the old pump N' hold, but have them pump the pedal in S-L-O-W deliberate strokes, not the jackrabbit style we're used to. Pumping fast will induce air that will take a long time to get out. Do a re-bleed a couple of days later (after some use/driving) and again in about a week, and you will be set for decades.

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Bill,

I just spoke to Prestone (now owned by Honeywell) technical as I have been thinking about making the switch on the old vehicles. Here is what they said; Dot 3, 4 & 5 are all classified as synthetic. Dot 3 synthetic will mix with non synthetic Dot 3.

Nothing has changed in regards to product classifications, and differences between Dot 3 synthetic & Dot 5 synthetic (still apples & oranges). Dot 3 synthetic will still attract water and melt your paint and Dot 5 is just the opposite.

Would have been great though but to good to be true unfortunately.

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Just wanted to emphasize a point brought-up by Mr. Pushbutton: DOT-5 does tend to aerate (form air bubbles) very easily, so be careful when filling the MC not to "glug" the fluid or shake the bottle.

Likewise, I would avoid using a pressure-tank bleeder with DOT-5, and do the two-man technique, going nice and easy.

When I did a full-system rebuild on my '41 De Soto in 1998, the only original parts left were the drums and backing plates: all other components were new, NOS, or NORS. All rubber was brand new; all steel & rubber lines were new.

I went with DOT-5, hoping to maximize the lifespan of my pre-war Stepped=bore wheel cylinders.

I was entirely unaware of DOT-5's sensitivity to air bubbles, and went full speed ahead with my freshly cleaned-up 1950's pressure bleeder ( no diahpragm to separate the air/fluid)... when I aired-up the tank, I apparently frothed the DOT-5...

Blissfully ignorant, I went around to all four wheels with my bleeder hose & jar, and bled-out the system...

After four trips around the car, I still had air-bubbles in the fluid, and a very spongy pedal.

Afte much frustration, and finally a phone call to the fluid mfr's (Cartel) tech line, the company tech and I finally figured-out what happened ( DOT-5 frapp`e ), and his suggetsion was to leave the cap off the master cylinder ( covering it with a clean rag), and letting things stand for a day or two, then GENTLY pedal-bleeding with a helper.

This method worked, and ever since, the brakes have worked very reliably (for Lockeed fixed-anchors), with no further fluid-related issues. The pedal is quite firm, although in really cold weather, it seems like the fluid is "thick" (?).

SO, aside from my mis-handling of the DOT-5 initially, it has worked well in the one car I've used it in. I started with an absolutely clean, dry system: all parts washed-out with brake-kleen or alcohol. I have not attempted converting a system previously filled with DOT-3 or 4.

If the cost of contamination is a system full of "caesar dressing", it might be well to pull everything apart and clean and dry thoroughly.

Good luck !

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The "regular fluid" likes to change state readily, and it also likes to invite moisture to the party, which causes trouble down the line. I worked for a 150+ car collection for over 12 years and every silicone (DOT-5) car we did, or others did (correctly) prior to purchase always had good brakes, no matter how long they sat. Some of the DOT-3cars were fine after sitting, many were trouble. When we found a car with the usual DOT-3 troubles (pitted cylinders, swollen rubber parts, alloy pistons crumbling, master cylinder full of jello) we did the above listed job and never had to mess with the brakes again, except for occasional adjustments to drivers.

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You know I think I am being swayed to the DOT 5 camp. I have 3 cars under full body offs so I will be using new brake parts throughout. I will use DOT 5 with careful attention to foaming/over pumping.

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From personal experience I've used DOT 4 on many cars made for earlier stuff with no problems. It works and I have no need to try DOT 5 as it won't make the car stop faster. A mechanic told be about the DOT 4 when it 1st came into being many years ago and I used it for a couple hundred thousand miles with no ill effects in 60-70s daily driver cars or 50s ones.

Here's a pretty complete info analysis

http://www.stoptech.com/tech_info/wp_brakefluid_1a.shtml

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