C1256/1391--anyone ever try using DOT4 brake fluid?

Someday, I'll remember to proofread the thread title before posting....

Debating whether to try another experiment and curious if anyone has tried it yet.

Over the last several months, our black 2005 has had the brake accumulator cycling on 9 second intervals. 3 seconds running then 6 seconds off, trying to maintain pressure. It finally coded on Friday 2/5 and we just parked it at the house. The weekend of 1/30, I had installed new axles and front hubs on this car. The brake accumulator assembly was in the planning stage, so it didn't come as a surprise. I finally got a chance to start looking at it yesterday, screen captured all the TechStream info and cleared the codes. The car is still doing the 9 second cycle time, and the accumulator pressure sensor is staying in the same voltage range as previously. Used it as my errand car all day yesterday with no problems.

One thing in my plan was to perform a full brake fluid flush prior to digging into the accumulator replacement procedure to see if it changes the cycle time. After reading up on the accumulator job (probably way too much) and getting side tracked about brake fluids, I'm debating whether to do a DOT3 flush (OEM recommended fluid), check the results, and then flush again using DOT4. DOT3 viscosity is supposed to be <1500 and DOT4 <1800. Although there's some over lap, it would be interesting if I could find a specific brand DOT3 that is near 1500 and a specific brand DOT4 that is around 1800. Try them both to see how it affects accumulator leakage. Some references say DOT3 is recommended for ABS systems due to it being a bit thinner, allowing the ABS pulses to function better. Makes sense, but I suspect DOT4 shouldn't create any problems for an experiment.

Trying to find viscosities of specific brands has been a bit elusive for me. Anyone have any input or recommendations?

 

Sam....not all brake fluids use the same exact components. Two different manufacturers can very easily have different compositions, which can have different viscosities. The spec for DOT4 is <1800. I want one closer to 1800, not 1000. There is even DOT4 available that is 700ish.

 

Reading comprehension....check it out.

From post number 1:
Debating whether to try another experiment and curious if anyone has tried it yet.... and....
Although there's some over lap, it would be interesting if I could find a specific brand DOT3 that is near 1500 and a specific brand DOT4 that is around 1800. Try them both to see how it affects accumulator leakage.

It's not that difficult to understand that all I'm looking for is some input if anyone knows of any charts/data/research that shows different brands of brake fluid and their actual viscosities. A bit similar to the information that is out there for various engine oils and transmission fluids.

Although not interesting to you, you still feel the need to throw in your opinion, and that's fine. It's interesting to me, and that's all that matters. I know for fact the ABS pump cycles every 9 seconds in this car. What I don't know, is what the current viscosity of the brake fluid is, or if finding a DOT4 @1800ish will make it cycle every 10 seconds or 15 seconds or 20 seconds. Could flushing the system with a brake fluid that is twice the current viscosity change the leakage rate and improve that cycle time? The only way to find out for sure is to try it. I have the time, the knowledge and the equipment. All I need is viscosity information, which may not be available. If not, I'll find something else to do. I have a project list a mile long. You enjoy spending time yanking people's chains on forums. Maybe I enjoy doing things like this. To each, their own. We all have hobbies. This doesn't have to be complicated.

 

Thanks Elek! Looks like one data point on the DOT4 ESP is probably a misprint, but in the big scheme, taking normal driving weather conditions and temperatures into account, all the blend viscosities are likely to be similar or at least similar enough and low enough that my 'clock' wouldn't detect the difference on cycle time. Some you win some you don't. Guess I'll have to try some Mobil 1 20W-50, see what that does..............










wonder how many people are getting ready to furiously type on the keyboard right now

 

A bit of an update. Maybe this can help someone avoid a major repair. I decided I was going to try a few things before getting into a full actuator swap. Took the accumulator off a salvage yard actuator (I have a few) and installed it into the car.

This can be done in less than an hour, without disconnecting any brake lines. Just remove the cowl and windshield wiper assembly. Used techstream to bleed all pressure from the system and then pulled the ABS relays so the pump couldn't start. Then swapped the accumulator tank.

Removed the vast majority of the brake fluid from the reservoir using one of these:

Progressive™ Flavor Injector | Bed Bath & Beyond (bedbathandbeyond.com)

and then filled reservoir with fresh DOT3. Did not perform any additional brake bleeding.

Cycle time on the actuator went from 9 seconds ( 3 seconds run, 6 seconds off) to averaging 43 seconds. I used the stopwatch/lap function on my phone to measure countless cycles over 2 days while watching pressure sensor reading on techstream. Reset the timer every time the pump started. Sometimes the actuator wouldn't bleed off at all until I cycled the brake pedal, so those cycles weren't counted. Took the car for several drives and each time returned to the house and did more timing checks, using the lap function each time the pump started. Very consistent results.

Being curious, I re-installed the original pressure tank over the weekend. Same result. 43 second average over 30 cycles. Maybe next weekend I'll swap the brake fluid in the reservoir again and do a full bleed/flush to see what happens. Or just leave it the heck alone and call it a success. Somewhere around August will be the three year point of having purchased this car. I have no accurate idea of the age of the fluid that was in the car, but potentially, the difference between old fluid and new fluid can be enough to make a difference. If that can make a difference, then it seems likely anything with a different viscosity can make a difference. Isn't that why, for a long time, DOT3 was recommended over DOT4 for early ABS systems? The DOT4, being thicker, didn't bleed off fast enough for proper brake pulsing?

So perhaps the questions that were mentioned in post 6 have some legs to stand on. As Chef Gordon Ramsay frequently says, perhaps someone else in this thread can piss off.

As for this (from the beginning of the post):
Maybe this can help someone avoid a major repair.

Keep up with your brake fluid replacement schedule. It may (or may not) make the difference between needing an actuator replacement (or not)..one example does not make a surefire solution, but it does provide possible temporary relief ..