Hot Rods Any experience using Dot 5 brake fluid?

Hey y’all. I need some feedback from those who have experience with Dot 5 brake fluid. Background is that I was using Dot 3 and found myself changing/rebuilding leaky wheel cylinders every 3-4 years. I got tired of that and decided to change the fluid to Dot 5. This is in a 1934 Ford with 39-48 drum brakes.
So I changed the fluid out and now I cannot get a hard pedal. Even pumping them up doesn’t seem to give me the rock hard pedal I used to have when I mashed the brake pedal.
I have bled the system using a pressure booster, so all the air is gone, but pedal firmness is just not there.
I’m asking if others have used Dot 5 and what their experience has been, before I go back to Dot 3. (maybe should have done this before I changed it in the first place, huh?)

Thanks in advance for any input.

 

The system should be flushed out with denatured alcohol and when bleeding you have to be gentle so you do not aerate the fluid, slow single strokes of the pedal and do not pump it up before cracking the bleeder screw. I have had DOT 5 in my pick up since 2016 and the pedal feels the same as when it had DOT 3, even after moving from the coast to 1 mile up.

 

Same here with my old caddy,i put Dot 5 in it back in 2007. It was whole new system with a rebuilt MC and new lines and wheel cylinders,pedal has been rock hard since day one and never ever gave any trouble.Let your MC sit with the cover off for a day or so,maybe some air bubbles are in it and need to get out?.Possible it was agitated and absorbed some air?. harvey

 

My truck has had Dot 5 since 1999, I've had no issues with it.

 

I put dot 5 in my 32 cabriolet and had gremlins getting a hard pedal for years. It was seeping thru the brake light switch and then the proportioning valve . It would also have to be bleed if she sat for 6 months. I understand it has its benefits but I went back to dot 3 as it had no benefits for my applications

 

DOT5, as I understand, does have a tendency to keep tiny air bubbles in suspension longer than other type of brake fluids. The suggestions above about not doing anything to agitate DOT5 are good advice, along with the suggestion on thoroughly flushing the system. DOT5 doesn't play well with other fluids.

I have DOT5 in 2 hot rods and a front engine dragster and have been very happy with my choice.

Lynn

 

The fluid flush with alcohol is normally done to help clean and push any contamination in the system out. Once dry, the fluid should be good to go once bleed. I have done alot of DOT 5 back years ago on performance cars. Never had any issues with soft pedal. Only time you get soft pedal is air trapped, sounds like either air trapped in master itself or proportioning valve. I assume you still have master under the floor also? When you think you are done on those, bleed em again, manually. All those handy dandy things for bleeding brakes these days just do ok, the old school method of push, hold, crack, close and repeat fixes issues galore.

I guess the thing I am worried about is you keep popping wheel cylinder issues. Sounds like the bores are too large, or improperly honed. I would suggest trying to find either new tooling, and go through and Micrometer all aspects of such wheel cylinders. There is something not right with that problem happening that frequently.

I just think it would be a better use of time to address the wheel cylinders and those issues there before chasing fluid issues. It's not a fluid issue causing the leaking cylinders.

 

Don’t !!!

 

My 65 Plymouth has Dot 5, no issues with air or performance. All new brake system when I built it.

 

One thing to consider is there is Dot 5 & 5.1, Dot 5 is silicone based unlike your 3, 4, and 5.1. When you switched to a Dot 5, did you get all existing fluid out and do a flush? As it isn't compatible with the others.

 

Only issues with dot5 is the fact that any moisture has nowhere to go and settles at the bottom. No amount of bleeding will get it out so it sit there and corrodes brake cylinders and pistons.

Moisture can get in through condensation in the master cylinder and by osmosis through rubber hoses.

It's a proven issue with harley davidson bikes that used dot 5 as standard 20 years ago.

 

I have used DOT5 for 30 years, maybe more with Great results. I learned that hydraulic switches dont work with DOT5 so I use mechanical brake light switches. I learned about the awful corrosion that forms with DOT3 back in the 1960s and was happy to learn about DOT5. DOT3 absorbs moisture from the air and one of the ingredients from that moisture is acid. It turns to sludge and eats pits in the metal. I have many old cars and the corrosion on the cylinders turns them into junk. For my 1950 Crestliner I went to the u pull it and from a jeep, got the brake pedal with mount, the booster, the master cylinder, proportioning valve and lines, poured out the DOT3 and filled the system with DOT5. Notice I did not clean the old brake fluid out with alcohol or anything else, just poured it out and filled it with 5. Its been about 10 years since on that car and the brakes work superbly. I recently had a wheel cylinder leak on my 59 Ford and suspect its chinesium, its very rare for any problem on my cars and motorcycles with DOT5, never had a soft pedal on any of my cars. New cars use DOT3 because the manufacturers are cheap. DOT5 is so good that DOT3 should be outlawed. There are people claiming that mixing 3 and 5 will cause the mixture to gel. I put a cup of half and half on the shelf and watched it for more than a year. I accidentally knocked it over, end of test but the two liquids never mixed or gelled. I could clearly see 2 different liquids. I believe the guys who have trouble with 5 but have never had any of the problems people talk about.

 

Silicone brake fluid in my 55 Tbird/w manual brakes. No problems.

 

Fellas. this is exactly what I was looking for- thank you!!
Yes,,I bled the DOT3 out of the system before I loaded DOT5; however, I am guilty of pumping the brake pedal while trying to get a firmer pedal.
Keep the comments coming. I am adding this info to my knowledge base.

 

Paint will never stick to anything that Dot5 fluid has touched while Dot3 fluid will eat away at existing paint, especially if it's not catalyzed.

Old master cylinders had vented caps, which allow moisture to enter. Newer master cylinders have a rubber diaphragm on the top which keeps moisture out. Keep this in mind, no matter which fluid you use.

As mentioned, with Dot3 the moisture gets absorbed into the fluid (which is water soluble), and with Dot5 the moisture collects in the bottom (it's not water soluble).

none of this is a condemnation of either fluid, just things to be aware of. I live in a dry area, I do fine with 3.

 

I had DOT-5 in a '68 Corvette 20 years ago. It worked well in the end, but was so difficult to get bled correctly that I never used it again.

One thing that may have helped. When I got the DOT-5 fluid, it had a note to heat it up almost to boiling to drive out the air bubbles. I bought a cheap teapot for this and it seemed to work. Just make sure you don't let it boil.

These days I have meter to check the moisture content in DOT-3,4. When it gets to a certain level, I replace the fluid.

 

10 years with DOT 5 in the '57. New system at the time. No issues at all.

 

Why?

 

Dot 5 and Nicopp brake lines for the win…trust me!

 

Like @tubman mentioned about heating it up. SSBC's pdf recommends you pour their DOT5 into a pot and heat it on the stove until it quits bubbling to get all the retained air out.
https://static.summitracing.com/global/images/instructions/ssb-silicone_brake_fluid.pdf

 

Been running DOT 5 for almost 30 years in my Chevelle, and 4 years in the '50 coupe. Never had an issue with soft pedal. Disc/Drum setup on both cars. Chevelle has vacuum power brake. '50 had manual.
I will tell you this though... You use stainless steel double flare lines and DOT 5 fluid, you have to tighten the crap out of your fittings to get them to not leak!

 

Dot 5 and single flare stainless lines with AN fittings since 1984 in my 3W. No leaks and hard pedal. That was the first time I used stainless lines and the last, very labor intensive. I gave the flaring tools to a friend so I wouldn't be tempted to use it a second time.

 

New system , 2002 , dot 5 ,been flushed & refilled twice, no troubles .

 

I've never had a rig that I put dot 5 in but I don't have fancy rigs that I would think needed it.
With a good number of years of doing brakes daily as my job and 13 years of teaching high school vocational auto mechanics and having a lot of different helpers pump the pedal over the years there is a correct way to pump the pedal and lots of wrong ones.
The correct way is to tell your helper to pump the pedal SLOWLY and then hold the pedal down until you actually tell them to let up on it. It has to be pumped slowly so the fluid has time to flow from the reservoir to the bore of the cylinder.
The two things that you have to put in a helpers head are the slow part and the hold the pedal down until I damned well tell you to pump it again or let it up thing.
You have to check and keep track of the reservoir level and make sure that the fluid doesn't get too low. That usually revolves around the "I can bleed it X times between filling it back up" concept.
As far as who ever has the bleeder wrench in hand. Bleeder screw closed except when you are actually letting fluid or air out. It does no frigging good to try to pump a pedal with the bleeder screw open no matter what the guys at the spit and whittle club say. That especially includes closing the bleeder screw before telling them to pump it again or let the pedal up and check the fluid.

40 years ago I never had trouble with a flare on a brake line unless I just flat screwed up.. lately I have had some that just would not seal before I bought my new flair tool. On the OT van I had a line that I couldn't get to seal and finally robbed a line off a donor rig to get it to work. That one would work fine but after about two days if that had a mushy pedal because it was letting air seep in even though it didn't show brake fluid leaking.

 

On a new system, its a great option. Doesn't eat paint if you spill. Only issues i had were it is more challenging to bleed as the air bubbles are harder to work out. Lots of tapping of the lines and making sure the lines had no "high" spots for the bubbles to get trapped in. After bleeding properly, i've had no issues whatsoever. I used a hydraulic brake switch with no issues.

 

35 years using it, zero issues. There is a learning curve to the bleeding process. I now use a pressure pot to bleed my systems and make it a one man job.

 

I have been using Dot5 silicone fluidin my avatar roadster since 2009 without any major problems. At first, I was going through hydraulic brake light switches quickly. That was until I found out that Harley uses a hydraulic brake light switch made for silicone fluid. I put one on and it fit perfectly with only having to change the terminals to match the Harley switch. Once that was done, no more problems at all. I did this with a brand new system and parts.

 

Dot5 and high altitudes don't play well. It boils easier in those conditions. Learned that over 20yrs ago when I was researching using it. Leaky cylinders, the new soft parts don't swell and seal from the fluids like the good ol stuff. To get things to finally stay I had to do a high speed wet 400 grit hone until it was damn near chrome looking. And even with that (funny as this seems) regular use keeps em tight and sealed. I don't like 5. Maybe because I'm a finisher at heart and it's a real enemy to a paint shop area.

I've had to go through brakes in wallflower cars that sit a lot. "...and I used Dot5 so this wouldn't happen!" was exclaimed a time or 3. Final advice, if you find NOS wheel cyl kits that are still fresh and new, they're head and antlers above the new synthetic rubber parts. Old is good. Wait we already know that, sorry...

 

Do yourself a favor and beg, borrow, or steal a pressure pot like the Motive shown above. I have a Motive and it makes bleeding brakes a simple procedure. Easy to bleed the lines and keep ahead of any moisture issues no matter what type fluid you use. When my truck was finished I used Dot5 in the all new brake system. I didn't like it, seeping joints and it was hard on the brake light pressure switches, even the Harley Davidson switches failed. Flushed the system and used Dot3 after I installed new brakes up front and have not had any issues since.

 

Don’t bother with hydraulic brake light switches! Trust me.
Seeping joints, sounds like a joint problem.