DOT3/4 vs DOT5 - Solicone vs. Glykol based brake fluid

[frauhansen]

Moin together

Short history. My M1123 is from Barstow and was overhauled in 2009. After that it was in the desert and I got it with 2'000mi.
For the TÜV a brake force regulator had to go in. The rear axle had over braked too much.

Now the good man, who mechanically delivered a clean performance, but filled up DOT3.
In the truck itself is emblazoned inside the and front of the "Silicone only" sticker.

I wrote him that in the hope he had written DOT3 on the bill out of habit. But no, he has used DOT3, so glycol based.

But now comes what makes me either suspicious or angry.
He wants to tell me now that the vehicles are converted to glycol based, so DOT3/DOT4 at the revision in Barstow.
This can be seen on the "spindle inspected" sticker.
But this makes no sense to me! On the one hand, the spindle has nothing to do with the brake and secondly, this would be completely new to me and thirdly, there comes for me the logic ...
The truck was painted once in Barstow. And after that the military knowingly put the wrong stickers in the truck?! The "everything according to manual" military? Did the old stickers still have to be used up?

There is something wrong... can one of you say something about the situation?

Thank you & best regards,
Gerd

Quote:
"it was again not easy to obtain the appropriate information. It behaves as follows:

If one of these vehicles has been overhauled; as in your case, a conversion takes place. The brake system is converted whereby all components are exchanged in which rubber seals are installed. After the conversion. DOT 3 or 4 is prescribed. DOT 3 has a lower boiling point than DOT 4, but in all probability you will never reach it with your vehicle. Furthermore, DOT 3 is in contrast to DOT 4 chemically less aggressive, which is rather beneficial to the entire brake system.

All vehicles on which the conversion has been done can be recognized by the sticker "Spindle's inspected." This is the inspection you have described.
You can find it at the following position on your car: picture of my car from the front.
End quote

 

[Coug]

I'm pretty sure the trucks with ABS use 5.1, but unaware of the other trucks using it.

I recently did brake fluid on my 2010 Barstow rebuild, and it definitely had silicone fluid in it as there was a little water sitting in the bottom of the reservoir.

Only article I found about brake fluid is this one for the NSN for HMMWV ABS brake fluid being DOT 5.1


Also, as far as I know, the military doesn't use either DOT 3 or 4 in any tactical vehicle, but I've been out for a while and wasn't a mechanic, I just spent most my time in the motorpool.

 

[Mogman]

Sounds like BS to me.
It is going to be expensive to completely flush that system, all the stuff that comes out must be disposed of.

 

[Mogman]

I will be willing to bet any vehicle that sat for 10-20 years with DOT 3 in it needs a complete brake overhaul, that is why the military uses DOT 5
Oh yes, what moron labeled a glycol based brake fluid DOT 5.1?????

 

[MarkM]

Brake Fluid DOT Grades

DOT3

DOT3 brake fluid is the "conventional" brake fluid used in most vehicles.

Advantages:

DOT3 fluid is inexpensive, and available at most gas stations, department stores, and any auto parts store.

Disadvantages:

DOT3 fluid eats paint!

DOT3 fluid absorbs water very readily (This is often referred to as being hydroscopic). As such, once a container of DOT3 has been opened, it should not be stored for periods much longer than a week before use.

Since DOT3 fluid absorbs water, any moisture absorbed by the fluid can encourage corrosion in the brake lines and cylinders.

DOT4

DOT4 brake fluid is the brake fluid suggested for use in some late model cars.

Advantages:

DOT4 fluid is available at most auto parts stores, and at some (but not all) gas stations or department stores.

DOT4 fluid does not absorb water as readily as DOT3 fluid.

DOT4 fluid has a higher boiling point than DOT3 fluid, making it more suitable for high performance applications where the brake systems are expected to get hot.

Disadvantages:

DOT4 fluid eats paint! Small leaks around the master cylinder will eventually dissolve away the paint on your bodywork in the general vicinity of the leak, and then give rust a chance to attack the body of your car!

DOT4 fluid is generally about 50% more expensive than DOT3 fluid.

Since DOT4 fluid still absorbs some water, any moisture absorbed by the fluid can encourage corrosion in the brake lines and cylinders.

DOT5

DOT5 brake fluid is also known as "silicone" brake fluid.

Advantages:

DOT5 doesn't eat paint.

DOT5 does not absorb water and may be useful where water absorption is a problem.

DOT5 is compatible with all rubber formulations. (See more on this under disadvantages, below.)

Disadvantages:

DOT5 does NOT mix with DOT3, DOT4 or DOT5.1. Most reported problems with DOT5 are probably due to some degree of mixing with other fluid types. The best way to convert to DOT5 is to totally rebuild the hydraulic system.

Reports of DOT5 causing premature failure of rubber brake parts were more common with early DOT5 formulations. This is thought to be due to improper addition of swelling agents and has been fixed in recent formulations.

Since DOT5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can cause localized corrosion in the hydraulics.

Careful bleeding is required to get all of the air out of the system. Small bubbles can form in the fluid that will form large bubbles over time. It may be necessary to do a series of bleeds.

DOT5 is slightly compressible (giving a very slightly soft pedal), and has a lower boiling point than DOT4.

DOT5 is about twice as expensive as DOT4 fluid. It is also difficult to find, generally only available at selected auto parts stores.

DOT5.1

DOT5.1 is a relatively new brake fluid that is causing no end of confusion amongst mechanics. The DOT could avoid a lot of confusion by giving this new fluid a different designation. The 5.1 designation could lead one to believe that it's a
modification of silicone-based DOT 5 brake fluid. Calling it 4.1 or 6 might have been more appropriate since it's a glycol-based fluid like the DOT 3 and 4 types, not silicone-based like DOT 5 fluid.

As far as the basic behavior of 5.1 fluids, they are much like "high performance" DOT4 fluids, rather than traditional DOT5 brake fluids.

Advantages:

DOT5.1 provides superior performance over the other brake fluids discussed here. It has a higher boiling point, either dry or wet, than DOT 3 or 4. In fact, its dry boiling point (about 275 degrees C) is almost as high as racing fluid (about 300 degrees C) and 5.1's wet boiling point (about 175 to 200 degrees C) is naturally much higher than racing's (about 145 C).

DOT5.1 is said to be compatible with all rubber formulations.

Disadvantages:

DOT5.1 fluids (and Spectro's Supreme DOT4) are non-silicone fluids and will absorb water.

DOT5.1 fluids, like DOT3 & DOT4 will eat paint.

DOT 5.1 fluids are difficult to find for sale, typically at very few auto parts stores, mostly limited to "speed shops."

DOT 5.1 will be more expensive than DOT3 or DOT4, and more difficult to find.

https://www.tccoa.com/posts/1043350/react?reaction_id=1

Above is an old tech article I did a long time ago for the Thunderbird & Cougar club of America. I still have my old 1993 Mercury Cougar that I purchased new.

Mark

 

[NDT]

Military uses DOT 5 only. Period.

 

[Mogman]

One error I see is DOT 4 does not have a higher boiling point than DOT 5

DOT5 is slightly compressible (giving a very slightly soft pedal), and has a lower boiling point than DOT4.

 

[87cr250r]

Anything military should still be DOT 5. There is no difference between components in a DOT 3 system and DOT 5, however I believe the combination of fluids can cause the rubber components to swell and fail. DOT 3 systems are more reliable. If it's been fully cleared out of old fluid and switched over, DOT 3 is fine. If it's mixed I would recommend blowing the contaminated fluid out and refilling with one or the other.

 

[Mogman]

Anything military should still be DOT 5. There is no difference between components in a DOT 3 system and DOT 5, however I believe the combination of fluids can cause the rubber components to swell and fail. DOT 3 systems are more reliable. If it's been fully cleared out of old fluid and switched over, DOT 3 is fine.

Reliability IS the selling point of DOT 5, DOT 3 absorbs water and becomes corrosive

 

[87cr250r]

On the other hand, DOT 5 doesn't absorb water which is corrosive. There is no chance of protecting the system from any water if the fluid can't absorb it.

M1008 caliper piston.

 

[Coug]

For those saying military only uses DOT 5, here is the PSMagazine article giving an NSN for a 1 quart bottle of DOT 5.1 as well as the NSN for the 55 gallon drum, and stating it's for the ABS equipped HMMWVs.

HMMWV: NSN for ABS Brake Fluid

Warfighters, if you only need to order small amounts of DOT 5.1 brake fluid for your HMMWV’s ABS system, you’re in luck! Read on and we'll tell you what you need to know...

www.psmagazine.army.mil

 

[Mogman]

On the other hand, DOT 5 doesn't absorb water which is corrosive. There is no chance of protecting the system from any water if the fluid can't absorb it.

M1008 caliper piston.

View attachment 897325

I don't see any corrosion, just mud
Besides no brake system can go without maintenance

 

[Mogman]

Moin together

Short history. My M1123 is from Barstow and was overhauled in 2009. After that it was in the desert and I got it with 2'000mi.
For the TÜV a brake force regulator had to go in. The rear axle had over braked too much.

Now the good man, who mechanically delivered a clean performance, but filled up DOT3.
In the truck itself is emblazoned inside the and front of the "Silicone only" sticker.

I wrote him that in the hope he had written DOT3 on the bill out of habit. But no, he has used DOT3, so glycol based.

But now comes what makes me either suspicious or angry.
He wants to tell me now that the vehicles are converted to glycol based, so DOT3/DOT4 at the revision in Barstow.
This can be seen on the "spindle inspected" sticker.
But this makes no sense to me! On the one hand, the spindle has nothing to do with the brake and secondly, this would be completely new to me and thirdly, there comes for me the logic ...
The truck was painted once in Barstow. And after that the military knowingly put the wrong stickers in the truck?! The "everything according to manual" military? Did the old stickers still have to be used up?

There is something wrong... can one of you say something about the situation?

Thank you & best regards,
Gerd

Quote:
"it was again not easy to obtain the appropriate information. It behaves as follows:

If one of these vehicles has been overhauled; as in your case, a conversion takes place. The brake system is converted whereby all components are exchanged in which rubber seals are installed. After the conversion. DOT 3 or 4 is prescribed. DOT 3 has a lower boiling point than DOT 4, but in all probability you will never reach it with your vehicle. Furthermore, DOT 3 is in contrast to DOT 4 chemically less aggressive, which is rather beneficial to the entire brake system.

All vehicles on which the conversion has been done can be recognized by the sticker "Spindle's inspected." This is the inspection you have described.
You can find it at the following position on your car: picture of my car from the front.
End quote

The fact is unless your M1123 had ABS it had DOT 5 in it and was marked so, since you cannot mix the two, in fact a complete rebuild of the system is recommended when switching between the glycol based and silicone based fluids and vice versa, he screwed up big time and now your complete brake system is contaminated.

 

[Mullaney]

The fact is unless your M1123 had ABS it had DOT 5 in it and was marked so, since you cannot mix the two, in fact a complete rebuild of the system is recommended when switching between the glycol based and silicone based fluids and vice versa, he screwed up big time and now your complete brake system is contaminated.

.
It's sad @frauhansen but @Mogman is right. You won't really know until you either have the fluid tested (like you would motor oil) or you just guess. Guessing is definitely bad for YOU and your truck. The mechanic might have just typed whatever they normally type on their invoices.

If you buy a gallon of whichever brake fluid you decide to use, that should be enough to refill your brake system. I think I would open the bleeders and force our whatever is in there into an old coffee can. Wear safety glasses. Splash in the eye is bad for your eyes. Then bleed like normal...

 

[Retiredwarhorses]

DOT 5 is used because it does not absorb water….military has used DOT 5 BFS forever.
If the 2 get mixed, which they do often….just flush it out, at that time, just figure out if you want DOT3/4 or DOT 5.
this is no different than the changing over PS Fluid from ATF to a true PS fluid….is that case, it was done for commonality of P.O.L
”petroleum, oils and lubricants“

 

[frauhansen]

i will flush all the DOTx out of the System an will fill it new with DOT5.
What I must credit the mechanic but as an excuse is. On the cover of the master brake cylinder is DOT3. But I suspect that this was just grabbed 1:1 from the GM shelf.

 

[GopherHill]

i will flush all the DOTx out of the System an will fill it new with DOT5.
What I must credit the mechanic but as an excuse is. On the cover of the master brake cylinder is DOT3. But I suspect that this was just grabbed 1:1 from the GM shelf.

I thought master cylinders with DOT5 in them had yellow painted lids.

 

[frauhansen]

yes, but the stamped metal... the stemps in the metall are DOT 3

 

[Vapor Trail]

DOT 5 is used because it does not absorb water….military has used DOT 5 BFS forever.
If the 2 get mixed, which they do often….just flush it out, at that time, just figure out if you want DOT3/4 or DOT 5.
this is no different than the changing over PS Fluid from ATF to a true PS fluid….is that case, it was done for commonality of P.O.L
”petroleum, oils and lubricants“

If you were starting out with a completely new non ABS system which would you use. Kept inside, little offroad use

Also, how much does a complete system use?

 

[MarkM]

An old brake fluid article of mine:


Brake Fluid DOT Grades

DOT3

DOT3 brake fluid is the "conventional" brake fluid used in most vehicles.

Advantages:

DOT3 fluid is inexpensive, and available at most gas stations, department stores, and any auto parts store.

Disadvantages:

DOT3 fluid eats paint!

DOT3 fluid absorbs water very readily (This is often referred to as being hydroscopic). As such, once a container of DOT3 has been opened, it should not be stored for periods much longer than a week before use.

Since DOT3 fluid absorbs water, any moisture absorbed by the fluid can encourage corrosion in the brake lines and cylinders.

DOT4

DOT4 brake fluid is the brake fluid suggested for use in some late model cars.

Advantages:

DOT4 fluid is available at most auto parts stores, and at some (but not all) gas stations or department stores.

DOT4 fluid does not absorb water as readily as DOT3 fluid.

DOT4 fluid has a higher boiling point than DOT3 fluid, making it more suitable for high performance applications where the brake systems are expected to get hot.

Disadvantages:

DOT4 fluid eats paint! Small leaks around the master cylinder will eventually dissolve away the paint on your bodywork in the general vicinity of the leak, and then give rust a chance to attack the body of your car!

DOT4 fluid is generally about 50% more expensive than DOT3 fluid.

Since DOT4 fluid still absorbs some water, any moisture absorbed by the fluid can encourage corrosion in the brake lines and cylinders.

DOT5

DOT5 brake fluid is also known as "silicone" brake fluid.

Advantages:

DOT5 doesn't eat paint.

DOT5 does not absorb water and may be useful where water absorption is a problem.

DOT5 can handle extreme temperature variations and is the go to fluid for military applications.

DOT5 is compatible with all rubber formulations. (See more on this under disadvantages, below.)

Disadvantages:


Reports of DOT5 causing premature failure of rubber brake parts were more common with early DOT5 formulations. This is thought to be due to improper addition of swelling agents and has been fixed in recent formulations.

Since DOT5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can cause localized corrosion in the hydraulics.

Careful bleeding is required to get all of the air out of the system. Small bubbles can form in the fluid that will form large bubbles over time. It may be necessary to do a series of bleeds.

DOT5 is slightly compressible (giving a very slightly soft pedal), and has a lower boiling point than DOT4.

DOT5 is expensive. It is also difficult to find, generally only available at selected auto parts stores.

DOT5.1

DOT5.1 is a relatively new brake fluid that is causing no end of confusion amongst mechanics. The DOT could avoid a lot of confusion by giving this new fluid a different designation. The 5.1 designation could lead one to believe that it's a
modification of silicone-based DOT 5 brake fluid. Calling it 4.1 or 6 might have been more appropriate since it's a glycol-based fluid like the DOT 3 and 4 types, not silicone-based like DOT 5 fluid.

As far as the basic behavior of 5.1 fluids, they are much like "high performance" DOT4 fluids, rather than traditional DOT5 brake fluids.

Advantages:

DOT5.1 provides superior performance over the other brake fluids discussed here. It has a higher boiling point, either dry or wet, than DOT 3 or 4. In fact, its dry boiling point (about 275 degrees C) is almost as high as racing fluid (about 300 degrees C) and 5.1's wet boiling point (about 175 to 200 degrees C) is naturally much higher than racing's (about 145 C).

DOT5.1 is said to be compatible with all rubber formulations.

Disadvantages:

DOT5.1 fluids (and Spectro's Supreme DOT4) are non-silicone fluids and will absorb water.

DOT5.1 fluids, like DOT3 & DOT4 will eat paint.

DOT 5.1 fluids are difficult to find for sale, typically at very few auto parts stores, mostly limited to "speed shops."

DOT 5.1 will be more expensive than DOT3 or DOT4, and more difficult to find.