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View Full Version : DOT 5 converted to DOT4?


bigbluebowtie
18th May 2007, 17:18
Anyone done this? I just did it last night and love the feel of my brakes better. I know, I know, I can ruin my paint, whatever. Doesn't matter to me. I don't really have a paint job. Bare metal. It is cleared, but if it comes off I am just going to use WD-40 to cover it. Just want some thoughts if anyone has tried this. I completely cleaned out the system with two cans of brake parts cleaner and used the Mityvac to bleed the brakes (btw, the mityvac is awesome for this). Seems to pan out fine. Stops great from 80-0. Anyone?

thunderpaw
19th May 2007, 02:01
Yeah, I just got done doing it to my 1200R. Long overdue. DOT 5 may be fine for most folks, but I just don't like it. Don't like the way it compresses, don't like the way it captures air...and I darn sure don't like the fact that any moisture in the system-since it can't be absorbed by the fluid-tends to gravitate to the low points (calipers) in the system...where it can easily overheat and result in an unintentional 'boil' of brake fluid.
The DOT 4 is much more suited for my style of riding and level of experience.

Kim

merc
19th May 2007, 02:35
Beside the above mention air retention and water absorbtion what other advantages are there?
Is it better for a particular style of riding? And what would that be? How does it feel better?
What are the disadvantages. What other DOTS are there, and why or why not use them.

yorgo
19th May 2007, 02:48
I have no idea what the differences are but I just replaced my pads and accidentally sucked air into the rear mc. Refilled it with an old can of DOT3 I had sitting on the shelf and bled it until it was nice and tight. No problems. It works fine. Whats the advantage of DOT4 or even 5?

nallac
19th May 2007, 11:17
I'm running DOT4 at the mo in mine ,I changed it to 4 by mistake ,had just bought the bike and did full brake service fluid/pads.Didn't know that was supposed to run DOT 5 .I thought the brakes felt better (most likely the new pads) Although i hadn't done that many ks on her.

Isnt the main difference between 3/4/5 a higher boiling point.

jms969
19th May 2007, 12:55
Wow this one scary thread...

whittlebeast
19th May 2007, 13:23
As the DOT number raises the boiling point raises. To get to DOT5 requires sylicone brake fluid. The down side is that DOT5 is slightly compressable. If you don't ever boil the front brakes, it is unlikely you need a higher DOT number. Boiled brakes well feel like the brakes all of a sudden need bleeding. Spongy and don't spot. This should never be an issue in the rear of a bike. If the front brakes are correctly designed the rears should be so easy to lock up they are almost useless. This is not the case on extreamly low friction surfaces but Harleys should not be ridden on these surfaces. (oil covered water, gravel on concrete, snow...)

_________________________deg F____________
Spec________Bioling Temp__wet BT___@6 months
DOT 5 Spec _____ 500 _____ 346 _____ 423
DOT 4 Spec _____ 446 _____ 311 _____ 379
DOT 3 Spec _____ 401 _____ 284 _____ 343


AW

gusotto
19th May 2007, 13:55
Wow this one scary thread...
___________________________

Agreed!!!!

I expect some of these backyard "mechanics" to soon be either in the hospital or worse after the brake fluid becomes jello-like.

Know the differences and dangers of mixing the various DOT brake fluids and what happens when mixing them before adding fluid!
Not a pretty or cheap sight.

thunderpaw
19th May 2007, 14:20
...Know the differences and dangers of mixing the various DOT brake fluids and what happens when mixing them before adding fluid!
Not a pretty or cheap sight.
Absolutely true! Mixing DOT5 with any glycol-based brake fluid is a definite no-no! It eventually precipitates out and can clog orifices in the system seriously degrading braking performance.

In clear conscience, I cannot recommend that anyone change from the OEM fluid-unless they are starting with all virgin components.

Kim

PS...and this is a hoot...my rear brake system never had DOT5 in it...it was delivered with either DOT4 or DOT3. I just found this out when I started flushing the rear system out...and yes, I can readily tell the difference...

jms969
20th May 2007, 02:57
___________________________

Agreed!!!!

I expect some of these backyard "mechanics" to soon be either in the hospital or worse after the brake fluid becomes jello-like.

Know the differences and dangers of mixing the various DOT brake fluids and what happens when mixing them before adding fluid!
Not a pretty or cheap sight.

my point exactly, turns to jelly and no brakes!!!

cantolina
20th May 2007, 02:59
If you change to DOT 5 from anything else, please change ANY rubber in your lines...

That really goes for ANY systemic brake fluid conversion....

bigbluebowtie
25th May 2007, 20:57
I completely cleaned out my system with Brake Parts Cleaner (except the rubber parts, wiped 'em clean) and added DOT 4. Backyard mechanic, yes. Very thourough in cleaning, yes too. I am going to switch out the brake line and rebuild the calipers later this summer when the kits get here. :)

yorgo
5th June 2007, 13:31
Absolutely true! Mixing DOT5 with any glycol-based brake fluid is a definite no-no! It eventually precipitates out and can clog orifices in the system seriously degrading braking performance.

In clear conscience, I cannot recommend that anyone change from the OEM fluid-unless they are starting with all virgin components.

Kim

PS...and this is a hoot...my rear brake system never had DOT5 in it...it was delivered with either DOT4 or DOT3. I just found this out when I started flushing the rear system out...and yes, I can readily tell the difference...

Well I found out you cant mix DOT fluids of different types the hard way. Should have done a little research first. Rear brake felt strange yesterday after sitting in the garage over the weekend. Got home, opened the can and found the 2 different fluids were separating. Nice clean clear fluid seems lighter then whatever the other one which was coagulating in bubbles under it. Gotta clean the system and go with 1 or the other.

rodhotter
7th June 2007, 17:48
i changed mine last year,NEVER MIX, flushed system thoroughly,russell aka brake people said this is OK, you can get better fluid if you want even dot 5.1 compatible with dot 4 not dot 5

gbinman
8th June 2007, 00:07
As the DOT number raises the boiling point raises. To get to DOT5 requires sylicone brake fluid. The down side is that DOT5 is slightly compressable. If you don't ever boil the front brakes, it is unlikely you need a higher DOT number. Boiled brakes well feel like the brakes all of a sudden need bleeding. Spongy and don't spot. This should never be an issue in the rear of a bike. If the front brakes are correctly designed the rears should be so easy to lock up they are almost useless. This is not the case on extreamly low friction surfaces but Harleys should not be ridden on these surfaces. (oil covered water, gravel on concrete, snow...)

_________________________deg F____________
Spec________Bioling Temp__wet BT___@6 months
DOT 5 Spec _____ 500 _____ 346 _____ 423
DOT 4 Spec _____ 446 _____ 311 _____ 379
DOT 3 Spec _____ 401 _____ 284 _____ 343


AW


The boiling points are an important element. It is important to mention that DOT 3, 4 & 5.1 are glycol based and DOT 5 is silicone based. There may be issues with mixing DOT 3, 4 & 5.1 but DOT 5 is absolutely incompatible with the others.

http://en.wikipedia.org/wiki/Brake_fluid or google "brake fluid DOT" and you'll find more information that you want.