DOT 5.1 brake fluid

E

emerystora

New member
Apr 6, 1999
14,608
1
1
In case that some of you have not noticed, there is a relatively new DOT brake fluid.

It is DOT 5.1. NOTE that this is NOT a silicone based fluid. It is glycol bases and compatible with DOT3 and DOT4.

DOT 4 and DOT 5.1 are both glycol-based brake fluids and are used widely in the automotive and cycle industry. They are controlled by standards set out by the Department of Transportation (DOT) - hence the name.
The main difference between these two brake fluids is in their boiling points. Part of the standards that need to be met by the manufacturers of DOT fluids are the minimum dry and wet boiling points. These are the minimum temperatures that the brake fluid must perform at before the brake fluid starts to boil, which can lead to complete brake failure

Here are the specs for the Dry Boiling Point and the Wet Boiling point

DRY WET

DOT3 401 F. 284 F.

DOT 4 446 F 311 F.

DOT 5 500 F. 356 F. (silicone)

DOT 5.1 518 F. 374 F.

Remember, these are only the minimum standards. Brake fluid manufacturers can and often do improve on these figures and it is possible to find DOT 4 brake fluid with a higher boiling point than some DOT 5.1 fluids on the market.

Since DOT 4 and 5.1 are both glycol-based brake fluids they are compatible with each other, which means they can be readily mixed without harming your brake system. It is important never to mistake DOT 5.1 (glycol-based) with DOT 5 which is silicone-based and should never be mixed with any other DOT fluid.

I recently installed Dave Lenzi’s new rear brake system and I used Wagner DOT 5.1 severe duty brake fluid.
I found it on AMAZON for $12.98 for a 32oz (1 quart) container.
This is about 1/2 the price at an auto parts store.

Emery Stora
77 Kingsley
Frederick, CO
 
How do you like Dave’s rear brake system?

Dolph

DE AD0LF

Wheeling, West Virginia

1977 26’ ex-PalmBeach
1-Ton, Sullybilt Bags, Reaction Arms, Manny Transmission, Howell EFI & EBL

“The Aluminum and Fiberglass Mistress"

>
> In case that some of you have not noticed, there is a relatively new DOT brake fluid.
>
> It is DOT 5.1. NOTE that this is NOT a silicone based fluid. It is glycol bases and compatible with DOT3 and DOT4.
>
> DOT 4 and DOT 5.1 are both glycol-based brake fluids and are used widely in the automotive and cycle industry. They are controlled by standards set out by the Department of Transportation (DOT) - hence the name.
> The main difference between these two brake fluids is in their boiling points. Part of the standards that need to be met by the manufacturers of DOT fluids are the minimum dry and wet boiling points. These are the minimum temperatures that the brake fluid must perform at before the brake fluid starts to boil, which can lead to complete brake failure
>
> Here are the specs for the Dry Boiling Point and the Wet Boiling point
>
> DRY WET
>
> DOT3 401 F. 284 F.
>
> DOT 4 446 F 311 F.
>
> DOT 5 500 F. 356 F. (silicone)
>
> DOT 5.1 518 F. 374 F.
>
> Remember, these are only the minimum standards. Brake fluid manufacturers can and often do improve on these figures and it is possible to find DOT 4 brake fluid with a higher boiling point than some DOT 5.1 fluids on the market.
>
> Since DOT 4 and 5.1 are both glycol-based brake fluids they are compatible with each other, which means they can be readily mixed without harming your brake system. It is important never to mistake DOT 5.1 (glycol-based) with DOT 5 which is silicone-based and should never be mixed with any other DOT fluid.
>
> I recently installed Dave Lenzi’s new rear brake system and I used Wagner DOT 5.1 severe duty brake fluid.
> I found it on AMAZON for $12.98 for a 32oz (1 quart) container.
> This is about 1/2 the price at an auto parts store.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Dolph
It is great. I replaced four rear 11” disc brakes with Chevy calipers with Dave’s 13” discs on the mid axle and no brakes at all on the rear. I also replaced my P30 master cylinder with the original to give higher pressure. It is now more like braking a car than a motorhome. A huge difference. I highly recommend it.

I’ve installed mine and another set for another GMCer. We left the rear drum brakes on his so he had parking brakes. I am waiting for Dave to release his hydraulic parking brake kit so I can add it to mine.

Emery Stora
77 Kingsley
Frederick, CO

>
> How do you like Dave’s rear brake system?
>
> Dolph
>
> DE AD0LF
>
> Wheeling, West Virginia
>
> 1977 26’ ex-PalmBeach
> 1-Ton, Sullybilt Bags, Reaction Arms, Manny Transmission, Howell EFI & EBL
>
> “The Aluminum and Fiberglass Mistress"
>

>>
>> In case that some of you have not noticed, there is a relatively new DOT brake fluid.
>>
>> It is DOT 5.1. NOTE that this is NOT a silicone based fluid. It is glycol bases and compatible with DOT3 and DOT4.
>>
>> DOT 4 and DOT 5.1 are both glycol-based brake fluids and are used widely in the automotive and cycle industry. They are controlled by standards set out by the Department of Transportation (DOT) - hence the name.
>> The main difference between these two brake fluids is in their boiling points. Part of the standards that need to be met by the manufacturers of DOT fluids are the minimum dry and wet boiling points. These are the minimum temperatures that the brake fluid must perform at before the brake fluid starts to boil, which can lead to complete brake failure
>>
>> Here are the specs for the Dry Boiling Point and the Wet Boiling point
>>
>> DRY WET
>>
>> DOT3 401 F. 284 F.
>>
>> DOT 4 446 F 311 F.
>>
>> DOT 5 500 F. 356 F. (silicone)
>>
>> DOT 5.1 518 F. 374 F.
>>
>> Remember, these are only the minimum standards. Brake fluid manufacturers can and often do improve on these figures and it is possible to find DOT 4 brake fluid with a higher boiling point than some DOT 5.1 fluids on the market.
>>
>> Since DOT 4 and 5.1 are both glycol-based brake fluids they are compatible with each other, which means they can be readily mixed without harming your brake system. It is important never to mistake DOT 5.1 (glycol-based) with DOT 5 which is silicone-based and should never be mixed with any other DOT fluid.
>>
>> I recently installed Dave Lenzi’s new rear brake system and I used Wagner DOT 5.1 severe duty brake fluid.
>> I found it on AMAZON for $12.98 for a 32oz (1 quart) container.
>> This is about 1/2 the price at an auto parts store.
>>
>> Emery Stora
>> 77 Kingsley
>> Frederick, CO
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
How many hours would you estimate for one person to do the install?
Thanks, scott
--
Scott Nutter
1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
installed MSD Atomic EFI
Houston, Texas
 
What about leaving the rear dumbs as they are but replacing the mid drums
with 13-inch discs? I would think the mid discs would brake harder than
rear drums while the rear drums would still brake some.

> How many hours would you estimate for one person to do the install?
> Thanks, scott
> --
> Scott Nutter
> 1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final
> drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
> installed MSD Atomic EFI
> Houston, Texas
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
John P. & Scott N.:
Yup- that’s what Dave Lenzi recommends and sells (larger calipers) on the mid rear wheels!
Mike/The Corvair a holic

Sent from my iPhone

>
> What about leaving the rear dumbs as they are but replacing the mid drums
> with 13-inch discs? I would think the mid discs would brake harder than
> rear drums while the rear drums would still brake some.
>

>>
>> How many hours would you estimate for one person to do the install?
>> Thanks, scott
>> --
>> Scott Nutter
>> 1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final
>> drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
>> installed MSD Atomic EFI
>> Houston, Texas
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
> --
>
> *John Phillips*
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
> What about leaving the rear dumbs as they are but replacing the mid drums
> with 13-inch discs? I would think the mid discs would brake harder than
> rear drums while the rear drums would still brake some.
> *John Phillips*

John,

I have done the dynamic study and with modern radial tires (not what the original designs were for), and the total effects of the system are such that
if you do not use a reaction arm or floating backplate in the system, you might just as well ignore the rear-rear as it can never provide significant
braking force. I did not do the study with limits set for higher braking on the intermediate wheels.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
John,
Rick Flanagan would like to discuss with you this issue as he and few
others have been losing at this issue and feel the same.
He is planning to test this unit and analyze what will happen in a very
hard panic test.
We know how the original Reaction Arm Sys does.

> > What about leaving the rear dumbs as they are but replacing the mid drums
> > with 13-inch discs? I would think the mid discs would brake harder than
> > rear drums while the rear drums would still brake some.
> > *John Phillips*
>
> John,
>
> I have done the dynamic study and with modern radial tires (not what the
> original designs were for), and the total effects of the system are such
> that
> if you do not use a reaction arm or floating backplate in the system, you
> might just as well ignore the rear-rear as it can never provide significant
> braking force. I did not do the study with limits set for higher braking
> on the intermediate wheels.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Emery,
I have been eyeballing Dave's rear brake system for about a year. I would like to set it up as you have yours(disc on the mid gear, and no brakes on
the aft).
How many hours would you estimate to do the job with only one person doing the work?
Thanks,
Scott.
--
Scott Nutter
1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
installed MSD Atomic EFI
Houston, Texas
 
Has anyone looked into switching wheel cylinder positions so the mids do
not lift as much leaving more weight on the third wheel?
In that configuration, the mids would be the very last to lock up in a
panic stop. I would think there would be more braking than running the back
axle brakeless unless the mids had enough pole vaulting action to unload
the back axle.

> Emery,
> I have been eyeballing Dave's rear brake system for about a year. I would
> like to set it up as you have yours(disc on the mid gear, and no brakes on
> the aft).
> How many hours would you estimate to do the job with only one person doing
> the work?
> Thanks,
> Scott.
> --
> Scott Nutter
> 1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final
> drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
> installed MSD Atomic EFI
> Houston, Texas
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
Scott,

We installed Dave system on a coach at our work Rally this past August. I think they started on friday morning and pulled it off the lift late
saturday. There was lots of show and tell, we quit working at 4 or 5 pm. And I know we were stopped when they broke off a bleeder in the rear
brake drum and had to run to town to find a wheel cylinder. There was some time spent removing rear disk and rebuilding the rear brakes back to oem,
and it also was swapping out the master cylinder, brake booster, ect.. up front as well. So in the end, this coach ended up with 80mm
front(already was in place), dave's 13" setup on the mid, and a drum on the rear. It also has a leigh harrison 4 bag system. as I understood, that
4 bag system works best with Dave's mid disk. if people are testing, they need to see how it works with the different air bag systems as well.
today, there are are 6+ different airbag systems that are out on coaches. Talking with Dave, he has his system installed on OEM airbag coaches, and
can skid the tire in a panic stop. He still feels they still have vastly superior braking even with OEM air bags, but with it on the leigh harrison 4
bag system, he says it helps keep more pressure down on the tire on the ground and the harrison 4 bag system is ideal match for his braking system.

the time it takes is subjective. What take a day on one coach, may take a week on the next. At least that is my experience the past few years.

> Emery,
> I have been eyeballing Dave's rear brake system for about a year. I would like to set it up as you have yours(disc on the mid gear, and no brakes
> on the aft).
> How many hours would you estimate to do the job with only one person doing the work?
> Thanks,
> Scott.

--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
People have, I believe the recommendation is to run 7/8" on the rear, and 1
1/8" on the middle. The problem being is that they will only be optimal for
one traction situation, either over or under braking the axles under all
other scenarios, and never matching a reaction arm system in any event (as
that keeps the weight, and thus the traction, the same on all tires).

On Wed, Oct 24, 2018 at 1:50 AM John Phillips
wrote:

> Has anyone looked into switching wheel cylinder positions so the mids do
> not lift as much leaving more weight on the third wheel?
> In that configuration, the mids would be the very last to lock up in a
> panic stop. I would think there would be more braking than running the back
> axle brakeless unless the mids had enough pole vaulting action to unload
> the back axle.
>
> On Tue, Oct 23, 2018 at 4:52 PM Scott Nutter

>
> > Emery,
> > I have been eyeballing Dave's rear brake system for about a year. I would
> > like to set it up as you have yours(disc on the mid gear, and no brakes
> on
> > the aft).
> > How many hours would you estimate to do the job with only one person
> doing
> > the work?
> > Thanks,
> > Scott.
> > --
> > Scott Nutter
> > 1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21
> final
> > drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
> > installed MSD Atomic EFI
> > Houston, Texas
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
>
>
> --
>
> *John Phillips*
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Emery,
I’m not looking to start a debate, but would know why you chose DOT 5.1 over DOT 4? Are there other advantages to doing so that we are unaware of? I have glanced at spec sheets and noticed some differences, but am curious as to your professional opinion.

I won’t be needing brake fluid for a good while since I stocked up back when ATE Super Blue became a banned substance. ATE Super Blue and ATE type 200(gold) carry the same specs, and have a fairly high temp spec, higher than the DOT 5.1 minimum. The ATE type 200 can still be purchased for under $12 per litre if you look hard enough.

Les Burt
Montreal
'75 Eleganza 26'
 
I have always been interested in newer specifications regarding brake fluid.
I appreciate the high boiling point especially the wet boiling point.
The main difference between DOT 3, 4 and 5.1 is a different ratio of glycol and borate ester and the amount of other additives.
Borate esters added raise the boiling point above that of glycol based fluids.
DOT 5.1 has a lower viscosity at lower temperatures which gives better flow in brake lines in cold weather operation. Most people won’t notice this but it is a slight advantage.
The military is especially interested in low viscosity because of the arctic use of military vehicles. They want to be able to move their vehicles around the world without having to change to brake fluids.
Anyone that is currently using DOT 4 fluids (especially those with 500 deg point points (dry) don’t have to worry about changing to DOT 5.1. I was replacing the master cylinder as well as the rear calipers so I decided that it would be an upgrade to flush and replace all of the brake fluid so I went with the latest spec.

I have been asked to give a seminar on the history and current state of brake fluids at the GMCMI convention in Tallahassee.

Emery Stora
77 Kingsley
Frederick, CO

>
> Emery,
> I’m not looking to start a debate, but would know why you chose DOT 5.1 over DOT 4? Are there other advantages to doing so that we are unaware of? I have glanced at spec sheets and noticed some differences, but am curious as to your professional opinion.
>
> I won’t be needing brake fluid for a good while since I stocked up back when ATE Super Blue became a banned substance. ATE Super Blue and ATE type 200(gold) carry the same specs, and have a fairly high temp spec, higher than the DOT 5.1 minimum. The ATE type 200 can still be purchased for under $12 per litre if you look hard enough.
>
>
> Les Burt
> Montreal
> '75 Eleganza 26'
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Thank you Emery,
I was aware of the lower viscosity, as most current abs systems require LV fluid.

Les Burt
Montreal
'75 Eleganza 26'

>
> I have always been interested in newer specifications regarding brake fluid.
> I appreciate the high boiling point especially the wet boiling point.
> The main difference between DOT 3, 4 and 5.1 is a different ratio of glycol and borate ester and the amount of other additives.
> Borate esters added raise the boiling point above that of glycol based fluids.
> DOT 5.1 has a lower viscosity at lower temperatures which gives better flow in brake lines in cold weather operation. Most people won’t notice this but it is a slight advantage.
> The military is especially interested in low viscosity because of the arctic use of military vehicles. They want to be able to move their vehicles around the world without having to change to brake fluids.
> Anyone that is currently using DOT 4 fluids (especially those with 500 deg point points (dry) don’t have to worry about changing to DOT 5.1. I was replacing the master cylinder as well as the rear calipers so I decided that it would be an upgrade to flush and replace all of the brake fluid so I went with the latest spec.
>
> I have been asked to give a seminar on the history and current state of brake fluids at the GMCMI convention in Tallahassee.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
>

>>
>> Emery,
>> I’m not looking to start a debate, but would know why you chose DOT 5.1 over DOT 4? Are there other advantages to doing so that we are unaware of? I have glanced at spec sheets and noticed some differences, but am curious as to your professional opinion.
>>
>> I won’t be needing brake fluid for a good while since I stocked up back when ATE Super Blue became a banned substance. ATE Super Blue and ATE type 200(gold) carry the same specs, and have a fairly high temp spec, higher than the DOT 5.1 minimum. The ATE type 200 can still be purchased for under $12 per litre if you look hard enough.
>>
>>
>> Les Burt
>> Montreal
>> '75 Eleganza 26'
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
I did some web crawling looking for info on Borate Esters and its use in brake fluid. I was mainly seeking info on the differences between DOT 4 & 5.1
 
Of all the legitimate things that a person could/should concern themselves
with on a GMC motorhome, I would think straying very far from what the
engineers who designed the things recommended, wouldn't be the best course
of action.
Obviously, some things, like E.P. greases, have improved in 40+ years,
and some things, like today's gasolines, have gotten worse. But, raw rubber
parts, like in brake systems, have been upgraded to hypalon, neoprene,
teflon, etc.
It behooves us to observe things like deterioration of things like
fuel hoses, and rubber parts throughout our coaches.
Also, fluid change intervals are important. Anti-freeze, ATF, Gear
lubes, Brake fluids, etc. are important.
I would caution folks about straying too far away from DOT 3 brake
fluid, particularly where SILICONE is involved.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> I did some web crawling looking for info on Borate Esters and its use in
> brake fluid. I was mainly seeking info on the differences between DOT 4 &
> 5.1
>
> From what I read, borate ester provides the following:
> - increases boiling point
> - can bind water and still retain the boiling point
> - improves lubrication qualities
> - may cause compatibility issues with some rubber components on older
> vehicles originally designed to use DOT 3 fluid.
>
> As is typical with information found on the web, there is a fair amount of
> conflicting info. One such conflict I noticed was concerning moisture
> absorption rates.
>
> Some brake fluid manufacturers state that DOT 4 fluid will absorb moisture
> at a faster rate than DOT 3, while a few others have stated the opposite.
>
> From what I interpret, the borate ester content is the reason, yet there
> is no consensus on whether the borate ester increases or decreases the
> moisture absorption rate.
>
> Since chemistry was not my strong point in school, I have a few questions
> that someone here might be able to answer.
>
> 1) How does borate ester affect moisture absorption?
>
> 2) if DOT 4 does absorb moisture at a faster rate, should fluid changes be
> done more often? The fluid manufacturers are all over the map on this.
> Logically, more often is better.
>
> 3) Since DOT 5.1 apparently has a higher borate ester content than DOT 4,
> wouldn’t it be more susceptible to moisture absorption, requiring more
> frequent changes? Again, the fluid manufacturers recommendations are
> varied.
>
> Here are a few links for reference:
> (Chosen to show the conflicting info, and not for accuracy)
>
> https://www.lubricants.total.com/brake-fluid-types
>
>
> http://www.onshoreoils.com.au/uploads/BULLETIN/Tech%20Bulletin%20TB005%20Sept%202014.pdf
>
>
> https://penriteoil.com.au/assets/tech_pdfs/Brake%20Fluid%20Testers%20-%20June%202017.pdf
>
>
> http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid
>
>
> https://www.abs-bv.nl/tl_files/content_resources/images/content/Leaflet_Use%20the%20correct%20brake%20fluid%20-%20721611_721612.pdf
>
>
> Les Burt
> Montreal
> '75 Eleganza 26'
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
DOT 5contains silicone. DOT 5.1 does not contain silicone. I don’t know why they couldn’t have just called at DOT 6 or DOT 83 or something else to reduce confusion.
 
I was planning on doing a brake fluid flush on my GMC. I do not know what brake fluid PO used in it. The manual calls for DOT3 brake fluid, so
that's what I was planning on using. I recall seeing many times recommendation to not mix DOT3 and DOT4 fluids. Do you know if I can safely do a
"replacement" of fluid to DOT4 when I'm performing the flush, or is it best to keep it at DOT3? Does OEM master cylinder "like" DOT4 or is there some
adverse reactions in the rubber component to the different fluid?
--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA
 
Vadim,
The manual indicates the use of DOT 3 brake fluid because that was the most common in use when the coaches were build. I know that Emery sold a lot of Dow brake fluid to the Big 3. You can use any DOT 3 or DOT 4 and the new DOT 5.1 as they are glycol based fluids and there for are compatible with each other. The mixing of glycol based and silicone based fluids is NOT a good thing to do. They do not play well together. To switch to a Dot 5 silicone based fluid from a glycol based fluid requires a total brake system disassembly cleaning and flushing on all componets to remove any traces of the previous glycol based fluids.

The glycol based brake fluids are hydroscopic in nature meaning that they will absorb moisture (water) and will lower the boiling point over time. Silicone based fluid will not absorb moisture and therefore the boiling point is higher than DOT3 & 4. Notice the boiling points for the 5.1 is better than the 5. I do a brake fluid replacement about every 2 years. I use a vacuum bleeder and pull the fluid thru the system from the master cylinder. I just watch the level in the master cylinder and add when it drops. The fluid in the system will have a darker brownish color because of the water that it has picked up. I bleed until the color changes to a light amber. Some of the glycol based brake fluids are colored with the blue ford brake fluid being popular. I am also watching for air bubbles.

Emery’s previous Email has a lot of very good information and would be good to reread to see the differences.

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 30’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan

>
> I was planning on doing a brake fluid flush on my GMC. I do not know what brake fluid PO used in it. The manual calls for DOT3 brake fluid, so
> that's what I was planning on using. I recall seeing many times recommendation to not mix DOT3 and DOT4 fluids. Do you know if I can safely do a
> "replacement" of fluid to DOT4 when I'm performing the flush, or is it best to keep it at DOT3? Does OEM master cylinder "like" DOT4 or is there some
> adverse reactions in the rubber component to the different fluid?
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
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