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Brake Fluid

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Martinld123

Martinld123

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My problem was left rear brake locking up. Went to replace wheel cylinder and noticed dark fluid in reservoir. So I believe my only option is to replace all of the brake fluid. So how crazy should this get?

Replace all new wheel cylinders or just some kind some kind of fluid flush? I replaced cylinders and fluid 8 years ago. All I remember is I hate doing it, lol. Can I get away with just running new DOT 3 fluid through all of system until runs clear? I hate brake jobs on BN2, 1956.

Thanks, Marty

Not sure where to post this. I found problem which I should have checked first. Both back drums were warped needed to be machined. Work great now. Pedal is a little low but solid. Thanks everyone for your help!! Marty
 
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Re: Decided to replace brake fluid. Can't see bottom of reservoir with dark fluid

That darkness is from deteriorating rubber. I would replace all the seals.
 
Re: Decided to replace brake fluid. Can't see bottom of reservoir with dark fluid

Thanks John. All seals would be all four wheel cylinders and master cylinder? Plus all flex brake lines? I just replace all of that 8 years ago. Better safe than sorry but a real pain to do. These new parts seem to have a short life span. Thanks again Marty
 
Re: Decided to replace brake fluid. Can't see bottom of reservoir with dark fluid

Brake fluid gets darker over time, probably due to heat (except DoT5, which seems to go from purple, to clear, to amber/brown). Unless you've put 100K miles on the car, my opinion is your seals--unless you see any moisture around or under the dust boots--and flex lines should be OK. I'd start with a good flush--you'll probably need a whole quart--then go from there.
 
Re: Decided to replace brake fluid. Can't see bottom of reservoir with dark fluid

Bob_Spidell said:
Brake fluid gets darker over time, probably due to heat (except DoT5, which seems to go from purple, to clear, to amber/brown). Unless you've put 100K miles on the car, my opinion is your seals--unless you see any moisture around or under the dust boots--and flex lines should be OK. I'd start with a good flush--you'll probably need a whole quart--then go from there.
Click to expand...
Thanks Bob. I like doing easy first.
 
Re: Decided to replace brake fluid. Can't see bottom of reservoir with dark fluid

I'm with Bob and if it turns out that more than a flush is necessary you will only have wasted the price of the fluid versus the possibility of saving a lot of work and not-inconsiderable cost of parts.
 
It is true brake work is a pain but your life depends on them. I check the fluid color on my TR 6 brake and clutch it is a tell all ahead of trouble. I then suck out the res. and add new to top off with clear fluid and to note DOT 5 is a good call if you do a lot of say down hill driving that add a lot of heat to brakes. Madflyer
 
Re: Decided to replace brake fluid. Can't see bottom of reservoir with dark fluid

Michael Oritt said:
I'm with Bob and if it turns out that more than a flush is necessary you will only have wasted the price of the fluid versus the possibility of saving a lot of work and not-inconsiderable cost of parts.
Click to expand...

Thanks sounds like a plan.
 
Being that many brake fluids are hygroscopic, capable of sucking moisture from the air, it can be a prudent move to replace these fluids every three years or such, so as to save both time and resources on the repair or replacement of parts that might oxidize otherwise. While you are at it, I would suggest checking/changing the clutch fluid as well if applicable.
 
Is the brake fluid dark at each wheel? The braided stainless line can collapse inside and not function. That could create darker brake fluid in that wheel only. You cannot inspect the line from the outside as it is only the interior that collapses and the braided housing retains the shape. It would tend to act like a one way valve, not releasing the brake.
 
Re: Decided to replace brake fluid. Can't see bottom of reservoir with dark fluid

Bob_Spidell said:
Brake fluid gets darker over time, probably due to heat (except DoT5, which seems to go from purple, to clear, to amber/brown). Unless you've put 100K miles on the car, my opinion is your seals--unless you see any moisture around or under the dust boots--and flex lines should be OK. I'd start with a good flush--you'll probably need a whole quart--then go from there.
Click to expand...

Great idea Bob. At same time I will replace the reservoir that looks bad and left rear cylinder that is sticking (both Moss and only 6 years old) and then flush out all of old fluid. Any way to limit air in lines when doing this? Zero chance right? The trick will be how I can tell when it runs clear. Maybe buy something to suck fluid out with clear plastic line so I can see it? Thanks for help, Marty
 
I rebuilt my 4 wheel disc system in 2017 with all new rubber and DOT5 fluid. After that I had a spongy pedal but was not able to do better because of air trapped in the fluid. Last year on my return from Deadwood, my axle sprung a leak on my rear pads. Replaced everything without bleeding and the sponginess was a little worse.

A couple of days ago, bled the brakes again, adding new bleeder screws wrapped in teflon tape. Finally I have a hard pedal. Guess the air finally settled out to the tops of the calipers and was removed by the bleeding process.

FWIW I use a 100ml plastic syringe and clear tubing to pull from each caliper.
 
Before DOT issued the requirement that all hydraulic brake fluid needs to be "Amber Clear" you could buy ATE brand in either clear or blue which made for an extremely easy two-person procedure to drain the old while adding the new, looking for the color change It's now illegal to sell the ATE Blue so you won't find it anywhere but a while back I purchased some dye specifically designed to work with DOT 3/4 and I plan to use it this spring or sooner.
 
Re: Decided to replace brake fluid. Can't see bottom of reservoir with dark fluid

Martinld123 said:
Great idea Bob. At same time I will replace the reservoir that looks bad and left rear cylinder that is sticking (both Moss and only 6 years old) and then flush out all of old fluid. Any way to limit air in lines when doing this? Zero chance right? The trick will be how I can tell when it runs clear. Maybe buy something to suck fluid out with clear plastic line so I can see it? Thanks for help, Marty
Click to expand...

I made a 'tool' for pressure bleeding from a reservoir cap for one-man bleeding. It works well but sometimes if someone's around I'll finish off with the old-fashioned 'pump-hold-bleed-repeat' method. For pressure, I turn the regulator out as far as it will go, below the gauge's range, which I think yields about 10PSI or less. One thing my dad and I learned the hard way is to not torque the bleeder screws down too hard (which is tempting); we couldn't get good pedal on his '46 Chevy 2-ton and eventually discovered that a bleeder seat had cracked. 'Snug and a tug' is about all you need.

Edit: For capture, I use clear vinyl tubing--I don't recall for sure, but it's probably 3/16" or 1/4" ID--into an old, clear mayonnaise jar with a couple holes in the lid so I can see any bubbles (you only need one hole to bleed, but when done I route the bleeder end back into the jar so the fluid doesn't end up where it shouldn't and the tube stays mostly clean). Ratcheting end wrenches--I have bleeders in 7/16" and 3/8" wrench sizes--make loosening and tightening the bleeders a lot easier.

Pressure Cap.JPG
 
Guido36 said:
Having experienced total brake failure with no warning with DOT 5 on two occasions, for anybody who is using or considering using DOT 5 here is a worthwhile read about the pros and cons....

https://techtalk.mpbrakes.com/brake-fluid/can-i-use-dot-5
Click to expand...

Couple of things:

1) What was the nature of your 'total brake failure?'
2) How did you definitively determine that DoT5 was the cause?

From the article:

"Combining even trace amounts of a glycol-based brake fluid with DOT 5 can cause the two incompatible fluids to gel, resulting in poor braking. Converting to DOT 5 also requires thorough flushing and removing ALL traces of the old fluid to avoid seal damage."

Are you saying you didn't properly prepare your system: thorough flush, preferably with denatured alcohol, and (ideally) replacement of rubber parts? I did a (proper) conversion to DoT5 on my BJ8 about 100K miles ago and have never had a problem I could attribute to DoT5.

For what it's worth, we had DoT4 'gel' in our BN2's completely rebuilt system after the car sat for a couple years (IIRC, it was Lockheed brand). When I read the linked article, an ad for Pentosin BF--recommended for BMWs I believe--appeared, which I installed after getting the gelled 'fluid' out. It has performed well.
 
Brake pedal went to floor with no warning and no brakes - luckily I was doing less than 10 mph at a show and managed to stop with the parking brake before nearly taking out the NSRA Safety Inspection tent! This was in a car I had recently purchased and hadn’t thought to check the brake fluid type. There can be incompatibility issues between certain rubber seals and DOT 5. The attached article gives more insight on seals and seal material types....

http://www.adlersantiqueautos.com/articles/brake1.html
 
Having boned up on the DOT 5 conversion issues...

I did my DOT 5 conversion the conservative way: removed all the calipers, cleaned with brake clean spray, installed new rubber kits. My Fiat dual-circuit master cylinder was new at the time. The hard lines I flushed with brake clean spray and compressed air. I used Dow Corning Silicone grease for installing the pistons and some other areas needing brake grease. Motorcyclists have been using this grease on their calipers.

Having said the above, the article is reasonable - if in doubt, stay with DOT 3,4, 5.1.

However, many folks have been running DOT 5 for 10 or 20 years.

Right now in normal non-competitive driving, I'm getting good performance from DOT 5 - without the paint issues.
 
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