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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Suspension - Brakes - Steering> Dot 5 Silicone Brake Fluid?? Yes or No ??
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Topic Review (Newest First)
04-15-2002 06:22 AM
dmorris1200 WOW!!! You said firm and hard!
04-14-2002 09:34 PM
4 Jaw Chuck I guess HD thinks the average rider needs the extra protection from possible paint damage more than stellar braking power. The Harleys I've driven all have had less than eyeball popping braking power (the newer ones are much improved). Since most are cruised not raced it might not matter anyway and having the calipers out in the air stream probably keeps them from boiling the fluid. Some people like the spongy brake feel actually and say to me that hard brakes don't have a proper feel that is easily modulated? Beats me?, I like-em firm and hard myself. This is beginning to sound like a dirty movie!
04-14-2002 05:07 PM
dmorris1200 Well 4 Jaw was right, never having owned a jap bike I decided to do a little ridin' today. It just happened to be a beautiful day here in Jersey. Of course it didn't take me long to find a few guys on some Hondas. I checked and their master cylinders were marked DOT4 only. Also found a BMW bike also marked DOT4 only. Now I know this topic has kind of gone off in an odd direction but know I really don't understand why Harley uses DOT5. From what almost everyone has said on this topic I would think DOT4 would be the way to go but they (Harley) didn't. Maybe there is no answer to why, just put whatever the stupid manufacter calls for in. <img src="confused.gif" border="0">
04-14-2002 07:37 AM
4 Jaw Chuck Only Harley Davidson uses DOT 5, all the other makes use DOT 5.1. It might say DOT 5 on the cover but remember the European MFG don't recognize silicone fluid so they mean DOT 5.1. Don't make the mistake of confusing them, it really is a stupid convention you would think they could have adopted a designation like DOT 6 ?

Wait! how stupid of me, that would be logical and make sense. I have to stop using my head for these things.
04-14-2002 06:50 AM
dmorris1200 That's an interesting qustion by Phat, I don't really know but I'll take some guesses. The first thing it says in my Harley Davidson sevice manual is never use anything but denatured alcohol to clean system components, any normal mineral based cleaners are a definate no-no. Which I think means if you're switching over a DOT4 system to a DOT5 cleaning and replacing almost everything is critical. Any old chemial or cleaning agents in that system will cause trouble. That might explain why a new system built clean that never had anything but DOT5 in it would be less trouble. My bike is 11 years old with DOT5 fluid in it, so I know Harleys been using DOT5 for at least that long. One other observation I made is the reservoir covers on my bike are both screwed and sealed tight to the reservoirs. This might allow less air to penetrate the system. I think PAULWELDIT mentioned DOT5 absorbs air. The last thing you want on a 100hp two wheeler is bad brakes and all they use is DOT5. Go figure? <img src="confused.gif" border="0">
04-14-2002 04:51 AM
Phat Now this aint a trick question.. i really dont know the answer.Why do all the new bikes use it??? I really dont know.!! Have they figured out something or????
04-13-2002 09:02 PM
PAULWELDIT In the early 80's the US Postal Service was one of the first vehicle fleets to ban use of asbestos brake linings. With the replacement brake parts manufactures, knowing that in short few years the manufacture of asbestos brake was to be ban by law,the Postal became one of the "test beds" for the soon to be required "non-abestos" linings.About the sametime it also took on the use of "DOT 5" brake fluid.Unfortuantely the brake failures & maintenance increased about 75-80%.Every thing from leaks, to loss of pedal. A carrier would call in Saying he had "no brake pedal". By the time the vehicle was towed in and the next day or so we got to check it out, the brakes would be fine.Closer investigation reveal Silicone fluid the culprit, not the originally accused "Non- asbestos" linigs.
It's a "DOUBLE DAMN"--in the case of a Postal carrier or as PHAT said a race car driver's repeated use of the brake was double trouble.Silicone fluid does not absorb water but it does absorb "air"and the brake system being vented the more the pedal was used the more the fluid became "aerated" so the pedal became "spongy" or even went away completely. After the vehicle set for awhile and all the air bubbles disappeared the brakes were fine. The "Double Damn" was that when the air got into the fliud,the tiny bubbles created were very "abrasive"which lead to failure of master & wheel cylinder rubber parts & their bores(especially aluminum M.C.'s).Silicone brake fliud is also affected by altitude and as stated by many brake part manufactures & Chysler Corp. for one: "Warranty Void if DOT 5 fliud is used". "What's" a little"bubbled" paint when DOT 3&4 fliuds are in less question and probably "Safer". Paulweldit

[ April 13, 2002: Message edited by: PAULWELDIT ]</p>
04-13-2002 04:01 AM
lakeroadster On my home built Model A I used DOT 5 silicone brake fluid from the beginning. I have not had any problems with the braking system in the five years it has been on the road.

I am using a Mustang non-power master cylinder, GM front disc calipers with a Midland booster, GM drum rear, and have an adjustable proportioning valve in the rear line.

I will admit, it doesn't have the "throw you through the front windshield" feel that you get in a new car. Mostly because the Midland booster isn't doing much, running a prety high lift cam, there isn't much vacuum available.
04-10-2002 02:33 PM
Phat I really did not mean to say pressure ...i guess i meant to say travel.If you have driven with dot 5 you will know what i mean.Your leg will get really tired quick with all the pumping your doing.You are correct it is like stepping on marshmellows. Sorry but i dont splain stuff so good.
04-10-2002 02:03 PM
4 Jaw Chuck When I used DOT 5 it did not cause higher pedal pressure only a mushy feel because it is slightly more compressible than DOT 3 or 4. With the mechanical advantage at the pedal it becomes very noticeable.

Higher pedal pressure could be caused by the coagulation of DOT 3/4 and DOT 5 if the systems were no properly diassembled and cleaned with alcohol to remove the last traces of the incompatible fluid.

Despite what they teach you in school liquids are compressible, but the amount is miniscule compared to gases.
04-10-2002 12:34 PM
hogerdoger somebody needs to explain why dot 5 requires more brake pedal force than dot 3 or 4. One would think that all hydraulic fluids would compress the same therefore reqiuring the same pedal force.
04-10-2002 06:51 AM
Phat Dot 5 should in my opinion not be used on anything(not even your john deer lawn tractor).It does not work in a race car.Just ask the guy that was in front of me all nite on the local short track(he did not have much rear bumper left )I have fixed many brake problems on rods also by simply removing the dot 5 . I have heard a few success stories using Dot 5 mostly from some of the SCCA vette boys but most of them payed to have there work done and i suspect they were getting 4 and paying for 5.. I have allways used the Castrol GTX dot 4 product and have no problems.(nope i dont work for them) If you mix dot 3 with 4 it lowers the boiling point.The boiling point on Dot 4 comes down to what Dot 3 is in a matter of months so if you dont do the bleed and flush deal every year there is probably no great gains in using Dot 4. The pedal pressure alone would stop me from every using Dot 5 again.If you ever had to drive down into a corner in the triple digits and pushed on the middle pedal with dot 5 you would never use it again. LOL Its great selling point is it does not eat paint. Well a little tip ...dont put it on the paint Now this is a real tip ...not kidding.Buy brake fluid in small containers(no swap meet crap,or gallon jugs)After you break the seal and use it toss the rest out.If its on the shelf for a few months its not worth putting in your car. I could go on and on about Dot 5 as i was sponsered by a company that makes the stuff ,but we could just not get the stuff to work.Brakes would hang up on a 50 lap race.You would have to stand on the brake pedal to get it slightly slowed down.We finally kept the stuff in the hauler but would make sure the brakes were bleed at the shop(were no one saw we were not using the product) I am no engineer but it wont get used in this shop again.

[ April 10, 2002: Message edited by: Phat ]</p>
04-10-2002 03:06 AM
dmorris1200 You know I kind of figured that, just how it was writen. I'm just a sucker for detail sometimes. I just have to assume that there are some out there reading this that have never even seen a brake pad and are just now learning. It can get confusing with the different types and like I said I've mixed DOT4 in many DOT3 systems. Oh well off to work I go!
04-09-2002 09:42 PM
4 Jaw Chuck Thats not what I meant, DOT 3 or 4 mix together just fine and are interchangeable with DOT 5.1, these are all glycol based fluids with different temperature ratings and viscosities.

You can't mix DOT 3,4,5.1 (glycol) with DOT 5 (silicone) you will get a jelly, give it a try and see for yourself.

[ April 09, 2002: Message edited by: 4 Jaw Chuck ]</p>
04-09-2002 07:49 PM
dmorris1200 This is for 4 Jaw Chuck, just wondering about you saying (never mix fluids of different DOT classifications). I know you can't put DOT3 into a DOT4 system because DOT4 is rated higher. It would be like putting type F trans fluid in a new car calling for MerconV. But I have a bottle of Castrol GTLMA brake fluid in front of me. It says right on it 'exceeds DOT3 and DOT4 specifications and mixes with both'. It's more expensive so we don't generally use it unless the system calls for DOT4 but sometimes if we're out of DOT3 at our station we'll use the DOT4 until we get more from parts dept. It says right on the bottle mixes with all conventional brake fluids (DOT3 & 4). Yes if you add DOT4 to DOT3 you are lowering the boiling point of the DOT4, but if the system only requires DOT3 you're still ahead of the game.
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