Topic: Brake Rebuild and DOT Fluids

[SD750F]

Okay, I will start by saying that I have read some insights on a couple "other" forums and web sites on the subject of DOT fluids. And I must say, from an engineering point I don't see the problem if you completely flush and remove the old DOT3 or DOT4 before using DOT5. I have received some positive and negative feedback.

Okay here is my siutaiton. I have a 1978 Honda CB750F that I am re-building this winter. One of the projects is a complete rebuild of the front and rear masters and calibers. I will be installing new seal kits and put them trough a complete cleaning to remove any slug and old DOT3 fluids. The lines, seals and bolts will be stainless steel with teflon inserts on the lines. I will make sure that there is no material conflicts with the new DOT5 I want to use. So I do not think there will be any material corrosion or galling that might happend. Some feedback was, "That is the way to do it!". And others were, "No way man! You will end up on the side of the road at best in a year or so and will have to redo your entire brakes!".

So I have opened up this topic, no for the feedback.

Thanks

[angeldeville]

I'm not an expert by any means but I have always been warned of seals swelling with dot-5.

I know that if I was putting my limited time into rebuilding my brakes, I would rather be safe than sorry. So I usually use the dot 3/4 fluid.

I I could find some definite proof that dot-5 wouldn't cause any damage I'd switch for sure.

[crazypj]

You can go from DOT3~4 to DOT 5 without too much trouble.
 You CAN'T switch back to DOT 3~4 from DOT 5 without changing all the seals and lines.
Flushing the system to change fluid doesn't work with DOT 5, you have to remove caliper piston to clean out any contamination (any water vapour condenses to lowest point which is way below the bleed nipple)
You should also dismantle master cyl  to check it.
The ONLY advantage of DOT 5 is it doesn't damage paint, it actually needs more maintenance in the long run. (as the US military have found out)
DOT 3 or 4 may absorb water vapour, but, it stays in solution/supension so when you change it  you end up with pretty much clean fluid.
PJ

[lrutt]

I have Dot 5 in my 76K model now for 10 years I bet. I also have it in my wifes Virago for at least 6 years. My 78K has it in as well.

Works great, no more sludge, even down here in humid florida. Best move to make IMO. Just clean the system well. I just flushed through with Dot 5. once I blew all the 3 out with air. I did rebuild the MC on my 76, but the others were just a straight flush.

[eldar]

I dont use dot3. I stop just fine. I suppose MAYBE it could be more work in the long run but then how long do you leave the same fluid in? I will probably flush and pull my caliper apart every couple of years. Doubt there will be an issue then.

[dusterdude]

dot 5 has been in the panhead for oh about 15 years now.its also been in the 750`s front brake for about a year and a half now too.

[kghost]

I have DOT 5 in my 750...works just fine.....

If you are using new seals none of the postulated reasons for not using DOT 5 are valid.

Silcon DOT 5 is not hydroscopic...meaning it will not absorb water. So if your starting fresh no worries. DOT 3 will and does sop up water like a sponge.

Ditto on the seals...new seals and you will not have any compatability issues.

[Bob Wessner]

A worthwhile read on the subject. I still use DOT 3/4 and change it at least every two years. It's an easy job so changing it annually is not a hassle nor would it be expensive in my opinion, but everyone has their favorite.

http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

[Jerry Rxman Griffin aka MuthaF'er]

I put DOT5 in my front brake this spring along with Speed Bleeders. Works great. No probs no complaints. When my seal went the DOT3 ate up the paint on my caliper, my disc, and the arm that holds the caliper. I decided after powder coating the lower fork legs and brake parts that I didn't want that happening again. I still have DOT3 in the rear which will get changed over to DOT5 when it's time to powder coat the rear components.