Hi all, picked up a Wilwood GP310 caliper to replace the stocker on my 98. (Wilwood says it's direct replace for 99 and down). I also purchased a brand new Magnum brake line.

Question is - the new caliper says to use DOT 3, 4, or 5.1 only, but my stock master cylinder says only use DOT 5. I know you can't mix, but if I flush out the stock master, can I use a different brake fluid? Or is the master really only designed to only use DOT 5?

 

check out on google or safari site will define uses and recommended types Wild Bill

 

Consult google...thanks for advice.

 

DOT 3, 4, 5.1 are all glycol based. Dot 5 is silicone. As you say, you should never mix them and I don't think you'd ever get the master cylinder cleaned completely of the Dot 5.

If it was me I'd contact Wilwood and ask if I could use DOT 5 - they have an email address for tech support (customerreply@wilwood.com) and a phone number (805 388-1188) on their site.

 

DOT 5 is the best there is, as long as you are not ABS. It tends to get frothy when the abs actuates, this is bad.


But has a higher boil point and does not absorb water like the glycol fluids. If you are not ABS I would change over to dot 5.

 

I know this is an older thread but I was searching the forum looking for info on if DOT 5 should be used in Wildwood GP310 calipers. This thread was the best I could find but there really wasn't an answer from the manufacturer. Here is what I found from Wildwood:

https://www.wilwood.com/PDF/NewProdu...08_Harleys.pdf

Gregg

 

I've had a Wilwood GP310 for over two years now, using DOT 5. No issues at all. I don't recall seeing anything about using 3, 4, or 5.1. I don't recall any instructions at all, just the caliper in the Wilwood box. So, I just used what I always used, DOT 5.

I would assume the Wilwood engineers are aware that most Harleys use DOT 5, at least in the 1990's.

John

 

Yep old thread, but important stuff.

Note what Wilwood says: "Harley-Davidson Motorcycles specifies use of DOT 5 silicone brake fluid because [reasons]. Wilwood disc brake calipers will work with either fluid, BUT NEVER mix DOT 5 [with any other type]."

I've been running GP310's on my 1990 for years with DOT 5. No trouble at all. And a huge performance improvements compared to the stock calipers.

With an older bike, it is best to test your fluid, rather than assume that no one put in the wrong stuff over the years. Easy to do. Take a small, clear jar (a baby food jar is perfect). Fill it half way with water. Take a syringe (any pharmacy will give you one) and pull a half a teaspoon or so of fluid out of the master cylinder. Put it in the water and shake/stir. Give it a moment. DOT 5 won't mix with water. Any other type will.

 

I agree. I was thinking about that yesterday. I have only had my bike for 2 years and I haven't opened up the master cylinder yet. I'll definitely test the fluid first. I'm hoping for a nice upgrade from stock once I install the calipers, stainless brake lines and Russell floating rotors.

Gregg

 

My experience is the difference is night and day. I'm sure you'll be delighted!