What brake fluid are you using for hydraulic brakes?

[US6x4]

It's time for me to replace the rubber brake lines and flush out the old fluid that might have been mixed by the PO. The TM only states "non-petroleum" product and I'm not sure what that would be called today. DOT 5?
I have read of some guys converting to DOT 3, but I don't want to mess with incompatible fluid versus rubber parts in case they don't play nice. So what is the go-to factory style brake fluid for my M813?

 

[doghead]

Dot 5

 

[porkysplace]

I use DOT 5 just like the military .
There are probably a hundred threads on this.Here is 1 changing fluids,
[h=1]Changing from DOT 3 to DOT 5[/h]

 

[Brutacus]

"Dot 5" for me. I just use what the TM says to use.

 

[gimpyrobb]

Buy in bulk or get screwed price wise.

 

[sandcobra164]

Dot 5, search online to find a vendor if you're taking on a project like you stated and need a gallon or more of fluid. Quick top off levels of Dot 5 can be found at you're local Harley Davidson shop as they use it as well but it's expensive if you break it down to dollars for ounce.

 

[US6x4]

My TMs denote nothing with "DOT 5" in their verbiage, but it was published in 1972 which may be prior to that classification name.

So 2 questions now: how much do I need for a complete flush?

And what size is the master cylinder plug threads so I can get the correct adapter for the pressure bleeder? Something like 3/4 NPT or straight thread with o-ring?

 

[162tcat]

Mine came with DOT 3 from the local government (wsdot). Flushed it again with DOT 3 after changing all soft lines and it's still happy. If you have DOT 5, I'd stick with that. If it's like mine, might as well stay with that.


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[frank8003]

My TMs denote nothing with "DOT 5" in their verbiage, but it was published in 1972 which may be prior to that classification name.

So 2 questions now: how much do I need for a complete flush?

And what size is the master cylinder plug threads so I can get the correct adapter for the pressure bleeder? Something like 3/4 NPT or straight thread with o-ring?

Put the master cylinder part number or NSN into Part Target and read everything about it?
Oops, that didn't work!
http://www.parttarget.com/2530-00-7...&searchoption=sku&originalsearchtext=12356931
...........so just guessing from here probably 1/4" NPT.?


If you are going to install/use a pressure brake bleeder than you should read this. Especially the first part of page two if this applies to your truck.
View attachment master cylinder remote roscommon nn17.pdf

 

[jbayer]

The plug in the MC cap is 1/8" NPT.

 

[US6x4]

Thanks for all of the good info! I searched the forum numerous times but must not have had the right key words. That 'part target' site is a new one for me and I'll keep an eye on that one.

 

[US6x4]

Well I drew a sample of fluid from the MC and it could be bad news...

This mixture is half water / half brake fluid from MC after an hour of sitting and there is zero separation. I have a bad feeling the PO simply added "brake fluid" from the parts store (DOT 3) into the MC. He did mention bleeding the brakes previously so who knows what is down stream.

From what I've read here I shouldn't panic until I know what type is in the wheel cylinders?

 

[162tcat]

Well I drew a sample of fluid from the MC and it could be bad news...View attachment 717642

This mixture is half water / half brake fluid from MC after an hour of sitting and there is zero separation. I have a bad feeling the PO simply added "brake fluid" from the parts store (DOT 3) into the MC. He did mention bleeding the brakes previously so who knows what is down stream.

From what I've read here I shouldn't panic until I know what type is in the wheel cylinders?

If it's been changed over DOT 3, it's plenty easy to continue flushing the system with the same DOT 3 to make sure it's fresh and clean. Mine came that way and I flushed it one more time when I got it as preventative maintenance. Lots of Miles hauling heavy without issue. Was hauling gravel and the excavator yesterday, left the scale at 49k after getting loaded up. DOT 3 stops her just fine and it's much more affordable to keep up on regular brake fluid maintenance such as flushing or wheel cylinders due to availability and cost. Just change all of the rubber lines(5 of them) before you invest in any fluid no matter what you use.

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[red]

Dot 5 will separate on top of Dot 3 and water, so if there is any 5 in the system (assuming the truck has been sitting) then it would be in the sample you pulled from the master cylinder. So the truck has most likely been supplied with dot 3 fluid.

Either fluid works fine in the regular driving world, just make sure it's clean fluid and not intermixed.

These trucks don't have a sealed brake system (master cylinder vents to outside air by design) which allows moisture into the brake fluid. More humid/wet the environment the faster this happens.

 

[162tcat]

Dot 5 will separate on top of Dot 3 and water, so if there is any 5 in the system (assuming the truck has been sitting) then it would be in the sample you pulled from the master cylinder. So the truck has most likely been supplied with dot 3 fluid.

Either fluid works fine in the regular driving world, just make sure it's clean fluid and not intermixed.

These trucks don't have a sealed brake system (master cylinder vents to outside air by design) which allows moisture into the brake fluid. More humid/wet the environment the faster this happens.

In addition to what he said, DOT 5 will also lose its purple color over time and look more gray like the sample you have. It's likely a mix of DOT 3 and 5 as stated above.

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[US6x4]

Ok, here is a sample from the right rear wheel cylinder with NO water added. Lots of tiny bubbles initially, but now the bubbles are just in the top. Do you think this is a mix of 3 & 5?
Should I add water to learn more?

 

[porkysplace]

Ok, here is a sample from the right rear wheel cylinder with NO water added. Lots of tiny bubbles initially, but now the bubbles are just in the top. Do you think this is a mix of 3 & 5?
Should I add water to learn more?View attachment 717663

This thread may help you , the last post has a picture of fresh mixed fluid.
[h=1]Brake fluid -how to tell which kind you have DOT 3 or DOT 5[/h]

 

[162tcat]

Ok, here is a sample from the right rear wheel cylinder with NO water added. Lots of tiny bubbles initially, but now the bubbles are just in the top. Do you think this is a mix of 3 & 5?
Should I add water to learn more?View attachment 717663

That sample just confirms that the system is overdue for maintenance and a flush. At this point, you'll be replacing all of the fluid so use whichever you want. Are the brakes working good currently? If so, your MC and air pack are probably fine so replace the rubber lines and flush flush flush. This is also a good time to adjust all of the shoes.

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[US6x4]

That sample just confirms that the system is overdue for maintenance and a flush. At this point, you'll be replacing all of the fluid so use whichever you want. Are the brakes working good currently? If so, your MC and air pack are probably fine so replace the rubber lines and flush flush flush. This is also a good time to adjust all of the shoes.
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162tcat - I am planning to do everything you mentioned. My 5 rubber lines should arrive this week and will get replaced. The brakes worked well enough when I last drove it although not until the last 2-3" of pedal so I plan on doing the minor adjustment to the shoes.

Now, in terms of sequence what should I do? Replace the rubber lines and then flush everything out? Remove old lines, purge all fluid, then install new lines and flush & bleed? Install new lines and then flush & bleed? I'm not sure what will work best.

 

[US6x4]

I added water to the last sample I posted and most of the fluid has moved to the top. It seems that the fluid from the wheel cylinder is mostly dot 5 with a little dot 3 in there.