Brake fluid change and related questions

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The only fluid I've yet to change in my LLV is the brake fluid. On the reservoir caps it says to use Dot 5. It appears that at some point after the last brake change that either the previous owner or a shop mixed Dot 3/4 in with the Dot 5.

I can understand why they spec'd Dot 5, as the LLV with fleet use do A LOT of braking. Seeing as I'm just using it with normal driving conditions, I'm debating as to whether Dot 5 is necessary or to convert to Dot 3/4.

What would be the best way to flush the contaminated system? Just turkey baster the reservoir, remove it and clean it and then flush with fresh fluid? I've read on some other sites that some folks will do flushes with denatured alcohol and then run low pressure air through to make sure everything is dry before putting in new fluid?

When my truck has sat for a week or more, the brakes are VERY touchy (when I drove it home the first time I almost got whiplash more than once from just lightly tapping on the brakes!) Now knowing the condition of the current fluid, I definitely want to get fresh in there. I'm really considering reverting to Dot 3/4.

Thoughts/Input/Suggestions?
 
Really? DOT 5? Peoblem is DOT 3 and 5 mix like oil and water, meaning they don't mix. Running fluid thru it till all the globs go away is one way to do it
 
Originally Posted By: jkhawaii
Really? DOT 5? Peoblem is DOT 3 and 5 mix like oil and water, meaning they don't mix. Running fluid thru it till all the globs go away is one way to do it


Yep, Dot 5. That's what it looks like in the reservoir, silicone at the bottom and amber liquid at the top.
 
Shouldn't be a problem to change the system to DOT 3 if you want to. If it's already mixed, then its something that should be taken care of quickly to prevent seal damage. Turkey baster the reservoir, refill with DOT3, then bleed all over 4 corners several times. Even once the fluid runs clear, I'd keep going for several more "pumps". Once you're done with all 4 corners, I'd go back around and do it again.

The touchy brake issue may not be brake fluid related. That sounds more like dirty brake shoes/pads...or contaminated shoes. I don't know the braking system on one of those vans that well, but I'm assuming rear drum. When brake fluid leaks onto the shoes, they'll be very grabby for the first couple stops.
 
Originally Posted By: jjcom
The touchy brake issue may not be brake fluid related. That sounds more like dirty brake shoes/pads...or contaminated shoes. I don't know the braking system on one of those vans that well, but I'm assuming rear drum. When brake fluid leaks onto the shoes, they'll be very grabby for the first couple stops.


That was one of my considerations, with Dot 3/4 being less expensive just flushing the [censored] out of them (figuratively and literally). They indeed are rear drums and leaks, it's interesting though as I don't have the grabby feel normally. Just when it has sat for a while.
 
Are you certain that it came with DOT-5 from the factory? That would be very unusual for an all-weather on-read vehicle. DOT-5 is only safe for racing and show car applications, where the vehicle isn't operated after being stored in below-freezing conditions. Moisture in the brake system can end up as ice pellets which have the potential to block fluid flow.
 
Originally Posted By: djb
Are you certain that it came with DOT-5 from the factory?


Just pulled out the big U.S.P.S. LLV service manual and says Dot 3. Now just pulled out my book of maintenance records I received and it looks like it was converted to Dot 5 by Midas in 2008 when they redid the brakes.

That being the case, I definitely want to go back to Dot 3/4. Should just doing a lot of bleeding and flushing with new fluid be sufficient to get all the silicone out?
 
Nice going, Midas...
They only jacked the bill up with that crud, and should be horsewhipped.

Lots of flushing should get her back to normal.
Then again after a week. Get 3 large bottles of brake fluid.
Don't waste your time with small ones - you'll NEED a lot.

In the back of my mind, I know silicates in antifreze ]plate] onto parts to protect them. I wonder if the type of silicone in that fluid does a similar thing?

Anyways, flush her out. I like vacuum bleeding for one guy - some like pressure bleeding - keep the reservoir full!
BTW, do you have ABS? Some systems need a special controller to bleed the brakes fully with them [passages in the actual unit].
 
I was definitely thinking of getting at minimum a gallon to flush (Napa Brand Dot 4). I figure I'll see how that works and in a year flush again (with another brand if I'm not satisfied with how the run on the Napa/Warren Unilube fluid went.)

No ABS, so don't have to worry about that.
 
Just when I thought I had it all figured out.... Was reading in my service manual and it says to use Dot 3 for the hydraulic brakes. Next section is about the Master Cylinder and that says to use Dot 5 in it.

Is it just me or does that seem conflicting?
 
Called up a USPS vehicle maintenance facility and the guy says Dot 5, unless it flush it all out (which he said is usually almost impossible to get it all out of the calipers and drums) and flush it out with alcohol.

Anyone wanna put in their 2¢ on this?
 
Originally Posted By: GoalieFergy53
Just when I thought I had it all figured out.... Was reading in my service manual and it says to use Dot 3 for the hydraulic brakes. Next section is about the Master Cylinder and that says to use Dot 5 in it.

Is it just me or does that seem conflicting?


It sure does!
Since your cap is emblazoned with 'DOT 5' on it, maybe you should continue to use it.
You have an oddball situation - practically unique.
 
Originally Posted By: mechtech2
You have an oddball situation - practically unique.


There's nothing normal about my truck, so it would figure that the problems would be as quirky as it is. lol

One other thing the mechanic said is that even though it's spec'd for Dot 5 (mainly to keep water out) that he's up in the air on how the master cylinder o-rings hold up with it.
 
that is very strange. I have never seen a factory vehicle meant for everyday use with dot 5 fluid. If possible, which seems like a PITA though, covert to dot 3/4.
 
Originally Posted By: mattd
that is very strange. I have never seen a factory vehicle meant for everyday use with dot 5 fluid. If possible, which seems like a PITA though, covert to dot 3/4.


That's USPS spec's for ya, I would think all the stop-and-go would keep the brakes pretty hot. The high boiling temperatures of Dot 5 and the fact that once Dot 5 is in there, it's pretty low maintenance would appeal to the long-term budget of the Postal Service (how's that workin' out for them these days? lol)

I'm gonna [censored]-shoot and flush the Dot 5 out and go to Dot 4. I figure I'll get as much of the silicone out as I can, run the first fill of Dot 4 for 6 months~1 year and see how it does. I'll do another flush with Dot 4 to get the old fluid with any silicone that might have gotten kicked up out.

Now I just gotta make a D.I.Y. pressure bleeder and then we'll see how it goes!
 
DOT 5 was originally developed for the military and for the USPS, because DOT 3 has such a strong affinity for moisture that it can absorb it from the air, and even through the rubber hoses. For vehicles that are supposed to last a long time, or be unused for long periods, it's great stuff. I wouldn't be surprised to see DOT 5 in a LLV.

Originally Posted By: djb
Are you certain that it came with DOT-5 from the factory? That would be very unusual for an all-weather on-read vehicle. DOT-5 is only safe for racing and show car applications, where the vehicle isn't operated after being stored in below-freezing conditions. Moisture in the brake system can end up as ice pellets which have the potential to block fluid flow.



Lots of misinformation and FUD about DOT 5, and that's one of them. It doesn't get water in it the way DOT 3 does, it repels water. About the only way it would get water in is if you pour it in there. True, it doesn't mix with water and it would be dangerous to have any water in it since the superior boiling point of DOT 5 would be lowered to that of water, but since I switched the MG's brakes over about 7 years ago, I still don't have water (or rust) in it, and it's still crystal clear.

On the other hand, it's expensive, hard to find sometimes, and shouldn't be used with antilock brake systems. Some folks don't like that the compressibility is slightly higher, especially when it gets hot, although it's not too noticeable in my MG.

To the OP, since it doesn't mix with DOT 3, switching types should really be done by clearing out all the old. I changed my MG over when I replaced the master cylinder and brake lines, and cleaned out all the wheel cylinders.
 
Last edited:
Originally Posted By: Dave Sherman
To the OP, since it doesn't mix with DOT 3, switching types should really be done by clearing out all the old. I changed my MG over when I replaced the master cylinder and brake lines, and cleaned out all the wheel cylinders.


I read a few different posts elsewhere that Dot 5 doesn't do as well braking in higher elevations. Seeing as I live in a mountainous region and I do plan to road trip in my mail truck, I wouldn't mind having to flush the brake fluid on yearly/bi-yearly basis for a firmer, more consistent pedal and braking system.

I've never been one to "half-butt" tasks so I want to do it right (not like braking systems are important right? lol) Going through my records, I don't see records of new hoses being purchased (it got a new set of calipers last year though?) Hoses are cheap, so no harm in changing them if it means I can thoroughly flush out all the Dot 5.
 
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